Cell Biology Flashcards
1
Q
Who proposed the cell theory?
A
Robert Hooke
2
Q
What 2 principles were proposed by Schleiden and Schwann?
A
- All organisms consist of one or more cells
2. Cells are the basic unit of structure of all organisms
3
Q
What are the 3 types of prokaryotes?
A
- Organotrophic
- Phototrophic
- Lithotrophic
4
Q
What are some structural differences between Prokaryotes and Eukaryotes?
A
Prokaryotes: - Non-membrane bound DNA - circular DNA - Have both cell wall and cell membrane - Some have flagellum for movement Eukaryotes: - Nucleus bound DNA - nuclear envelope - No cell wall - cytoskeleton gives tensile strength and allows transport across cell
5
Q
What are some examples of tools used to study cells?
A
- Microscopes - light and electron
- Dyes
- Antibodies
- Fluorescence
- Fractionation
6
Q
What are the 2 fundamental properties of membranes?
A
- Form flexible, continuous barriers between cell and external environment and between intracellular organelles
- Selectively permeable allowing transport of ions/molecules
7
Q
What are the main components of cell membranes?
A
- Lipids
- Proteins
- Carbohydrates
8
Q
What forces hold phospholipids together in membranes?
A
Non - covalent
9
Q
Why are phospholipids described as ampiphatic molecules?
A
They have a polar (hydrophillic) head group and non-polar (hydrophobic) tail
10
Q
What makes the fatty acid tails of phospholipids saturated or unsaturated?
A
Presence of double bonds in unsaturated
11
Q
What are the 4 major membrane phospholipids?
A
- Phosphatidyl-ethanolamine
- Phosphatidyl-choline
- Phosphatidyl-serine
- Sphingomyelin
12
Q
What’s significant about Phosphatidyl-serine molecules?
A
It carries a net negative charge
13
Q
What are the properties of the phospholipid bilayer?
A
- Form bilayers with hydrophillic head groups on the surface and hydrophobic fatty acids pointing inwards
- Loosely packed to allow movement within membrane
- Self-repairing to eliminate free edge exposed to water when there is a tear
14
Q
What is the movement of phospholipids like within the membrane?
A
- Phospholipids move and rotate readily in the later plane
- Flip-flop from one leaflet to the other is slow
15
Q
What 2 factors will increase membrane fluidity?
A
- More unsaturated chains make it difficult to pack close together
- Shorter chain lengths reduce interaction between phospholipids
16
Q
How does Cholesterol affect membrane permeability?
Does this affect membrane fluidity?
A
- Cholesterol decreases membrane permeability
- It does not decrease fluidity
17
Q
In high concentrations what does Cholesterol prevent?
A
Membrane crystallisation
18
Q
What are the 2 types of membrane proteins?
A
- Transmembrane proteins
2. Membrane Associated proteins
19
Q
What are the 2 main arrangements of membrane proteins?
A
- Alpha helix
2. Beta sheets (beta barrels)
20
Q
What can attach membrane associated proteins to the lipid bilayer?
A
- Transmembrane proteins
- Lipid anchors
21
Q
What is an example of a lipid anchor?
How does it attach the protein to the bilayer?
A
- Phosphatidylinositol
- Via fatty acids or a prenyl group
22
Q
What are 3 advantages of lipid anchoring proteins?
A
- Increased mobility at cell surface
- Rapid release of protein into extracellular space
- Regulation of binding and release of proteins to membrane
23
Q
Are membrane proteins fluid?
A
Yes, but move less rapidly than phospholipids
24
Q
What are lipid rafts?
What do they do?
A
- Areas of increased rigidity and thickness in the membrane
- Keep proteins anchored preventing movement
25
What are lipid rafts composed of?
- Cholesterol
- Sphingolipids
- Proteins
26
What filamentous protein makes up the meshwork of RBC membranes?
How are they arranged?
- Spectrin
| - 2 spectrin dimers join end to end to form tetramers
27
What link together Spectrin tetramers?
What are these composed of?
Name the proteins
- Junctional complexes
- Actin filaments and proteins
- Band 4.1, Adducin and Tropomyosin
28
What 2 transmembrane proteins attach cytoskeleton to membrane?
1. Band 3
| 2. Glycophorin
29
What causes Sickle cell-shaped RBC?
Mutation in spectrin that causes it to stiffen and prevents RBC squeezing through capillaries
30
What 2 things help to maintain membrane asymmetry?
1. Tight junctions
| 2. Lipid rafts
31
Give an example of how the lipid composition of each leaflet differs?
Phosphatidyl-serine is found in the cytosolic monolayer to help maintain negative potential across membrane
32
What is the enzyme that drives symmetry in the membrane?
Scramblase
33
What is the enzyme that drives asymmetry in the membrane?
| What is different about this enzyme to Scramblase?
- Flippase
| - It is energy dependent (requires ATP)
34
What 2 cellular processes is asymmetry of membranes used in?
1. Apoptosis
| 2. Coagulation
35
How is asymmetry of membranes used in coagulation?
Phosphatidyl-serine provides nucleation site on platelets for coagulation cascade
36
What are the 4 blood groups?
| What determines what blood type an individual is?
- O, A, B or AB
| - Structure of oligosaccharide attached to RBC membrane
37
How is the blood group of an individual clinically important?
What are O blood group individuals said to be?
What are AB blood group individuals said to be?
- In blood transfusions A group or B group can only receive blood from the same group
- O blood group can be donated to anyone (universal donor)
- AB blood group can accept blood from anyone (universal acceptor)
38
What is the Glycocalyx?
- Carbohydrate-rich zone on cell surface
39
What is the function of the Glycocalyx?
- Protects cell against mechanical and chemical damage
| - Prevents unwanted cell-cell interactions
40
How is the Glycocalyx formed?
Secreted into the extracellular space and then reabsorbed back onto cell surface
41
What are the 2 main classes of membrane transporters?
1. Carriers
| 2. Channels
42
How do carriers allow transport across membrane?
Bind specific solutes and undergo conformational changes that moves solute across membrane and releases them into cell
43
How do channels allow transport across membrane?
Form continuous pores that extend across bilayer to allow specific solutes to pass through when they're open
44
How does passive transport of solutes occur across the membrane?
The concentration gradient of solutes drives their transport and direction, they go from high to low concentrations
45
What is the usual electrochemical gradient across cell membranes?
- Negative inside
| - Positive outside
46
When is active transport used?
When solutes need to be transported against their electrochemical gradients
47
What does active transport require?
ATP
48
What are the 3 ways cells carry out active transport?
1. Coupled transporters
2. ATP driven pumps
3. Light driven pumps
49
How do coupled transporters perform active transport?
Harness energy stored in concentration gradients to couple uphill transport of one solute with downhill transport of another
50
How do ATP driven pumps perform active transport?
Couple uphill transport with hydrolysis of ATP molecules
51
How do Light driven pumps perform active transport?
Couple uphill transport with input of energy from light
52
What are the 3 types of carrier-mediated transporters?
| How do they function?
1. Uniporters - passively mediate movement of one solute from one side to the other
2. Symporters - simultaneous transport of 2 solutes in the same direction
3. Antiporters - alternating transport of 2 solutes in opposite directions
53
Give 4 properties of ion channels.
1. Form narrow hydrophillic pores through membrane
2. Specific for different ions/solutes e.g. K+ and Na+
3. Allow rapid movement of ions down electrochemical gradient
4. Open and close rapidly
54
What is the opening and closing of ion channels regulated by?
- Binding of ions
- Changes in voltage
- Binding of small molecules
55
How does a cell take up Glucose against its concentration gradient?
Downhill transport of Na+ is coupled with uphill transport of glucose against its concentration gradient
56
What is the Na+/K+-ATPase used for?
Used to generate the resting membrane potential of a cell - makes the inside more negative than the outside
57
How does the Na+/K+-ATPase work as an antiporter?
Actively pumps 3 Na+ out of the cell for every 2 K+ into the cell
58
What 3 carriers are involved in the transport of Glucose across intestinal enterocytes?
1. Glucose/Na+ symporter on apical surface
2. Na+/K+-ATPase on basal surface
3. Glucose carrier on basal surface
59
Describe the route for the transport of Glucose across intestinal enterocytes.
- Glucose is transported against its concentration gradient across the apical membrane by a Glucose/Na+ symporter (Active)
- Glucose then passes through a carrier protein down its concentration gradient (Passive)
- A Na+/K+-ATPase maintains the ionic concentrations inside the cell
60
Where is the nucleus positioned in an epithelial cell?
Towards the basolateral surface if the cell
61
What is the relation of the Endoplasmic Reticulum to the Nucleus?
The Endoplasmic Reticulum is continuous with the nuclear membrane
62
What is the name of the space between the inner and outer nuclear membranes?
Perinuclear space
63
At what structures do the inner and outer mnuclear membranes meet?
Nuclear pores
64
What is the Nuclear lamina?
What is its function?
What are the 3 types of lamina?
- A protein meshwork
- Provides structural support for nuclear envelope
- Lamina A, B and C
65
What is the composition of the Nucleoplasm?
- Ions
- Enzymes
- Nucleotides
- Small amounts of DNA and RNA
66
What is different about the Nucleolus compared to other organelles?
It is not membrane bound
67
What occurs in the Nucleolus?
Processing of RNAs and their assembly into Ribosomes
68
What macromolecules are within the Nucleolus (7 macromolecules)?
- rRNA genes
- Precursor and Mature RNA
- rRNA processing enzymes
- snoRNPs (small nucleolar RNAs)
- Assembly factors - ATPases, GTPases, RNA Helicases etc.
- Ribosomal proteins
- Partly assembled ribosomes
69
What is the significance of close association of macromolecules in the Nucleolus?
It allows rapid assembly of ribosomes
70
How does DNA form chromosomes?
- DNA wraps around histones to form nucleosomes
| - These undergo supercoiling to form chromosomes
71
In a non-dividing cell how is the DNA stored?
Loosely packed strands of Chromatin
72
How many subunits make up a Nuclear Pore Complex?
8 subunits with a central plug
73
What is the name of the proteins that make up a Nuclear Pore Complex?
Nuceloporins
74
Is transport through a Nuclear Pore Complex one directional?
No, NPCs can transport in both directions simultaneously
75
What is the cut-off size (daltons) for passive diffusion of molecules through a Nuclear Pore Complex?
How is this cut-off established?
How do molecules larger than the cut-off pass through the nuclear membrane?
- 60,000 Daltons
- Nucleoporins have unstructured regions that form a disordered tangle and prevent large molecules diffusing
- Molecules larger than 60,000D must be actively transported across the nuclear membrane
76
What are Nuclear Localisation Signals?
They are responsible for the selectivity of nuclear transport
77
What are the 4 main subunits of Nuclear Pore Complexes?
1. Column subunit
2. Annular subunit
3. Lumenal subunit
4. Ring subunit
78
How can large proteins be visualised entering Nuclear Pore Complexes?
How are they transported through the NPC?
- Coating them with gold particles
| - They bind to cytosolic fibrils then proceed through the NPC
79
Give 2 examples of why Nuclear transport via Nuclear Pore Complexes is necessary.
1. Synthesis of DNA histone molecules occurs in cytoplasm and these need to be transported into the nucleus for packaging of DNA
2. Ribosomes synthesised in the Nucleolus must be transported into the cytoplasm
80
What is the evidence that some nuclear transport is an active process?
- In the absence of ATP proteins bind to fibrils but do not proceed through NPC
- When ATP is added the proteins appear in the nucleus
81
What is the structure of a mitochondria?
- 2 membranes
- Outer membrane encloses the organelle
- Inner membrane is highly folded to increase surface area for Oxidative phosphorylation
- Space between membranes is the intermembrane space
82
What does the inner matrix of mitochondria contain?
Enzymes necessary for respiration
83
What is the theory of Mitochondrial evolution?
- Aerobic bacterium were taken up by eukaryotic cells to live symbiotically as promitochondrian
- Development of multiple mitochondria provided energy for bigger cells
84
Who is mitochondrial DNA inherited from?
It is only inherited from the mother
85
Is the rate of mutations higher or lower in Mitochondrial DNA than nuclear DNA?
Why is this?
- Rate of mutations is higher in MtDNA
| - This is due to the absence of proof-reading enzymes in MtDNA
86
What can analysis of Mitochondrial DNA reveal?
| How is this linked to the Out of Africa Theory?
- Movements and establishment of new population groups can be tracked from changes in MtDNA
- Analysis of large groups of people suggest modern humans have origins in Africa from 100,000 years ago
87
What is the function of mitochondria?
| How does it achieve this?
- Energy production
- Pyruvate from Glycolysis enters the mitochondria and is converted to Acetyl CoA before entering the Krebs cycle to generate ATP
- Hydrogen ions are used in Oxidative Phosphorylation to generate ATP
88
How are inner membranes of mitochondrial adapted to produce ATP?
They have ATP synthase enzymes which use H+ ions to drive the formation of ATP
89
What is the underlying theme in mitochondrial disorders?
The lack of ability to meet cellular energy demands
90
Why is there a wide range of mitochondrial disorders?
Due to the uneven distribution of mutant mitochondria during cellular division in development
91
What is the structure of Chloroplasts?
- Have their own DNA
- Have double membrane enclosing the stroma
- Grana - stacks of thylakoid membranes which carry out photosynthesis
92
What is contained in the stroma of Chloroplasts?
All of the enzymes and substrates for photosynthesis
93
What are the 2 phases of Photosynthesis?
- Light Dependent Reaction
| - Light Independent Reaction
94
What occurs during the Light Dependent Reaction?
Photosynthetic electron transfer reactions
| - Involves the electron transfer pathway and begins with the excitation of an electron on chlorophyll by light
95
What occurs during the Light Independent Reaction?
Carbon fixation reactions
| - ATP and NADPH provide energy source and reducing power to convert CO2 into carbohydrates
96
What are Peroxisomes?
| What is their function?
- A single membrane organelle found in all eukaryotic cells
- They carry out oxidative reactions and contain a variety of enzymes e.g. urate oxidase
- Also have a role in detoxification in the liver
97
How do Peroxisomes remove Hydrogen atoms?
RH2 + O2 --> H2O2
- Peroxide produced is toxic and used by peroxisomes
H2O2 + R1H2 --> R1 + 2H2O
98
What occurs during Glycolysis?
| What are the products?
- Glucose in degraded to Pyruvate
| - 2xPyruvate, 2xATP and 2xNADH
99
What are the 2 phases of Glycolysis?
| What occurs during each phase?
1. Preparation phase - Conversion of 1 glucose into 2 Glyceraldehyde-3-phosphate
2. Pay-off phase - Conversion of Glyceraldehyde-3-phosphate into Pyruvate
100
Glycolysis - Reaction 1:
What is Glucose converted to?
What enzyme catalyses this reaction?
What is consumed in this reaction?
- Glucose --> Glucose-6-Phosphate
- Catalysed by Hexokinase
- 1 ATP is consumed (supplied in the form of MgATP)
101
What is the significance that Glucose-6-Phosphate is a charged molecule?
It traps Glucose within the cell
102
What type of Hexokinaase is found in hepatocytes?
| What is different about this type of hexokinase?
- Type 4 Hexokinase (Glucokinase) is found in hepatocytes
- Hexokinase works at maximum rate at low glucose levels
- Glucokinase don't reach maximum rate until glucose levels increase
103
Glycolysis - Reaction 2:
What is Glucose-6-Phosphate converted to?
What enzyme catalyses this reaction?
Is this reaction reversible?
- Glucose-6-Phosphate --> Fructose-6-Phosphate
- Catalysed by Phosphoglucose Isomerase
- Yes this reaction is freely reversible, direction depends on substrate concentrations
104
Glycolysis - Reaction 3:
What is Fructose-6-Phosphate converted to?
What enzyme catalyses this reaction?
What is consumed in this reaction?
- Fructose-6-Phosphate --> Fructose-1,6-Bisphosphate
- Catalysed by Phosphofructokinase-1
- 1 ATP is consumed
105
Glycolysis - Reaction 4:
What is Fructose-1,6-Bisphosphate converted to?
What enzyme catalyses this reaction?
What happens to the 2 products of this reaction?
- Fructose-1,6-Bisphosphate --> Glyceraldehyde-3-phosphate + Dihydroxyacetone Phosphate
- Catalysed by Aldolase
- Only Glyceraldehyde-3-phosphate can proceed onto next stage of Glycolysis
- Dihydroxyacetone Phosphate must be converted to another Glyceraldehyde-3-phosphate
106
Glycolysis - Reaction 5:
What is Dihydroxyacetone Phosphate converted to?
What enzyme catalyses this reaction?
- Dihydroxyacetone Phosphate --> Glyceraldehyde-3-phosphate
| - Catalysed by Triose Phosphate Isomerase
107
Glycolysis - Reaction 6:
What is Glyceraldehyde-3-phosphate converted to?
What enzyme catalyses this reaction?
What happens to NAD+ during this reaction?
What is consumed in this reaction (difference to previous reactions)?
- Glyceraldehyde-3-phosphate --> 1,3-Bisphosphoglycerate
- Catalysed by Glyceraldehyde-3-phosphate Dehydrogenase
- During this NAD+ is reduced to NADH
- Pi group is consumed but not from ATP, instead from an inorganic Pi group
108
Is the conversion of Glyceraldehyde-3-phosphate to 1,3-Bisphosphoglycerate reversible?
Yes, the same enzyme (Glyceraldehyde-3-phosphate Dehydrogenase) catalyses the reverse reaction in gluconeogenesis
109
```
Glycolysis - Reaction 7:
What is 1,3-Bisphosphoglycerate converted to?
What enzyme catalyses this reaction?
What is produced in this reaction?
Is this reaction reversible?
```
- 1,3-Bisphosphoglycerate --> 3-Phosphoglycerate
- Catalysed by Phosphoglycerate Kinase
- 1 ATP is produced
- Yes, this is the only reaction involving ATP that is reversible
110
How does exposure to Arsenate lead to poisoning?
- Arsenate is a similar size to Phosphate
- So arsenate substitutes for phosphate and product is unstable and hydrolyses
- So conversion of 1,3-Bisphosphoglycerate to 3-Phosphoglycerate is skipped and the net production of ATP is 0
111
Glycolysis - Reaction 8:
What is 3-Phosphoglycerate converted to?
What enzyme catalyses this reaction?
- 3-Phosphoglycerate --> 2-Phosphoglycerate
| - Catalysed by Phosphoglycero Mutase
112
Glycolysis - Reaction 9:
What is 2-Phosphoglycerate converted to?
What enzyme catalyses this reaction?
What is produced in this reaction?
- 2-Phosphoglycerate --> Phosphoenolpyruvate
- Catalysed by Enolase
- 1 H2O is produced
113
Glycolysis - Reaction 10:
What is Phosphoenolpyruvate converted to?
What enzyme catalyses this reaction?
What is produced by this reaction?
- Phosphoenolpyruvate --> Pyruvate
- Catalysed by Pyruvate Kinase
- 1 ATP is produced
114
Is there a net gain or loss of ATP from Glycolysis?
- 2 ATP used
- 4 ATP produced
- Net gain of 2 ATP per molecule of Glucose
115
In aerobic conditions, what is the fate of Pyruvate?
Enters mitochondria and converted to Acetyl CoA and enters Krebs cycle
116
In anaerobic conditions , what is the fate of Pyruvate?
It is converted into Lactate
117
What enzyme catalyses the conversion of Pyruvate to Lactate in anaerobic conditions?
What is also consumed in this reaction and where does it come from?
- Lactate Dehydrogenase
- NADH is oxidised to NAD+
- NADH comes from conversion of Glycerate-3-aldehyde to 1,3-Bisphosphate
118
What is the significance of the conversion of Pyruvate to Lactate in anaerobic conditions?
It allows Glycolysis to continue under anaerobic conditions for a short period of time
119
What are the 3 points for regulation in the Glycolysis pathway?
1. Hexokinase
2. Phosphofructokinase-1
3. Pyruvate Kinase
120
How is Glycolysis regulated by Hexokinase?
- Hexokinase is regulated by the concentration of Glucose-6-Phosphate
- Not a major point of regulation
121
How is Glycolysis regulated by Phosphofructokinase-1?
- Phosphofructokinase-1 is inhibited by ATP
| - Phosphofructokinase-1 is activated by AMP
122
Explain the regulation of Glycolysis using Phosphofructokinase-2.
- Phosphofructokinase-1 catalyses conversion of Fructose-6-Phosphate to Fructose-1,6-Bisphosphate
- This reaction is reversed by enzyme Fructose-1,6-Bisphosphatase
- Phosphofructokinase-2 converts F-6-P to Fructose-2,6-Bisphosphate
- F-2,6-BP promotes the forward reaction and inhibits the reverse reaction
- F-2,6-BP can be converted back to F-6-P, catalysed by a phosphorylated Fructose-2,6-Bisphosphatase
- This is activated by Protein Kinase A
123
How is Glycolysis regulated by Pyruvate Kinase?
- Pyruvate Kinase is inhibited by ATP and Acetyl CoA
| - Pyruvate Kinase is activated by Fructose-1,6-Bisphosphate
124
What is Tauri Disease?
| What does it lead to?
- Disease that prevents the conversion of Fructose-6-Phosphate to Fructose-1,6-Bisphosphatase
- Produces muscle weakness and cramping
125
Where does the Krebs' Cycle occur?
Mitochondrial matrix
126
What are some cofactors and coenzymes involved in the conversion of Pyruvate to Acetyl CoA?
- Coenzyme A
- NAD+
- FAD+
- Lipoic Acid
- Thiamine Pyrophosphate
127
What is the net reaction for the conversion of Pyruvate to Acetyl CoA?
Pyruvate + CoA + NAD+ --> CO2 + Acetyl CoA + NADH + H+
128
What happens to Pyruvate after it has entered the mitochondria from glycolysis?
What enzyme does this involve?
- It is rapidly decarboxylated
| - The enzyme is Pyruvate Dehydrogenase Complex
129
Krebs Cycle - Reaction 1:
What is Oxaloacetate converted to?
What enzyme catalyses this reaction?
What type of reaction is this?
- Oxaloacetate --> Citrate
- Catalysed by Citrate Synthase
- Condensing reaction
130
Krebs Cycle - Reaction 2:
What is Citrate converted to?
What enzyme catalyses this reaction?
What is produced but then consumed in this 2-step reaction?
- Citrate --> Isocitrate
- Catalysed by Aconitase
- H2O is first removed but then added back to move hydroxyl group
131
Krebs Cycle - Reaction 3:
What is Isocitrate converted to?
What enzyme catalyses this reaction?
What is produced in this reaction?
- Isocitrate --> Alpha-Ketoglutarate
- Catalysed by Isocitrate Dehydrogenase
- CO2 is produced and NAD+ is reduced to NADH
132
Krebs Cycle - Reaction 4:
What is Alpha-Ketoglutarate converted to?
What enzyme catalyses this reaction?
What is produced in this reaction?
- Alpha-Ketoglutarate --> Succinyl-CoA
- Catalysed by Alpha-Ketoglutarate Dehydrogenase
- CO2 is produced and NAD+ is reduced to NADH
133
Krebs Cycle - Reaction 5:
What is Succinyl-CoA converted to?
What enzyme catalyses this reaction?
What is produced in this reaction?
- Succinyl-CoA --> Succinate
- Catalysed by Succinate Thiokinase
- GDP is converted to GTP
134
Krebs Cycle - Reaction 6:
What is Succinate converted to?
What enzyme catalyses this reaction?
What is produced in this reaction?
- Succinate --> Fumarate
- Catalysed by Succinate Dehydrogenase
- FAD is reduced to FADH2
135
Krebs Cycle - Reaction 7:
What is Fumarate converted to?
What enzyme catalyses this reaction?
What is consumed in this reaction?
- Fumarate --> Malate
- Catalysed by Fumerase
- H2O is consumed in this reaction
136
Krebs Cycle - Reaction 8:
What is Malate converted to?
What enzyme catalyses this reaction?
What is produced in this reaction?
- Malate --> Oxaloacetate
- Catalysed by Malate Dehydrogenase
- NAD+ is reduced to NADH
137
For each turn of the Krebs Cycle, what are the net products?
- 2 CO2
- 3 NADH
- 1 FADH2
- 1 GTP
138
For 1 molecule of Glucose what are the net products of Glycolysis, Pyruvate Dehydrogenase and Krebs cycle?
- Glycolysis - 2 Pyruvate, 2 ATP and 2 NADH
- PDH - 2 AcetylCoA, 2 CO2 and 2 NADH
- Krebs Cycle - 4 CO2, 6 NADH, 2 FADH2 and 2GTP
139
What are the 2 enzymes that regulate the activity of Pyruvate Dehydrogenase complex?
What is their effect on PDH complex?
1. PDH Kinase - inhibits PDH complex
| 2. PDH Phosphatase - activates PDH complex
140
What are some examples of allosteric regulators that increase the activity of PDH Kinase?
- NADH
- ATP
- Acetyl-CoA
141
What are some examples of allosteric regulators that decrease the activity of PDH Kinase?
- Pyruvate
- NAD+
- CoA
- ADP
- Ca2+
142
What are some examples of allosteric regulators that increase the activity of PDH Phosphatase?
- Ca2+
| - Mg2+
143
What are the 3 points of regulation in the Krebs Cycle?
| What is the regulation linked to?
1. Citrate Synthase
2. Isocitrate Dehydrogenase
3. Alpha-Ketoglutarate Dehydrogenase
- Regulation linked to the levels of substrates and products
144
What effect will an increase in the products of the Krebs cycle have on its rate?
Increase in products (e.g. NADH and ATP) will inhibit the Krebs cycle and slow it down
145
What effect will an increase in the substrates of the Krebs cycle have on its rate?
Increase in substrates (e.g NAD+ and ADP) will stimulate the Krebs cycle and speed it up
146
How does exposure to Sodium Fluoroacetate result in poisoning? (Krebs Cycle)
It inhibits Aconitase so Citrate cannot be converted to Isocitrate and the increased Citrate leads to an accumulation of Citric Acid
147
What vitamin is there a deficiency of in Beriberi disease?
How does this effect the Krebs cycle?
What symptoms does this cause in the individual?
- Vitamin B1 (Thiamine)
- Thiamine Pyrophosphate is required as part of the PDH complex and Alpha-Ketoglutarate Dehydrogenase
- Deficiency leads to high levels of Pyruvate and Alpha-Ketoglutarate in the blood
- Produces symptoms such as neurological and cardiac impairment
148
Can Fatty Acids and Amino Acids be used in the Krebs Cycle?
Yes, both can be degraded and used as substrates in the Krebs cycle
149
How can Fatty Acids be used in the Krebs Cycle?
They are broken down by 4 enzymes into 2 carbon molecules to produce Acetyl-CoA which can then enter the Krebs cycle
150
How can Amino Acids be used in the Krebs Cycle?
Amino Acids don't have to be converted they can enter the Krebs cycle directly at various points
151
What happens during Oxidative Phosphorylation? (Overview)
- Electrons are transferred from NADH and FADH2 to O2 to form H2O
- This is achieved by means of 4 membrane protein complexes
- Process generates a proton gradient across the inner mitochondrial membrane which is then used to drive an ATP synthase to produce ATP
152
What are 4 examples of electron carriers in Oxidative Phosphorylation?
1. NAD and FAD
2. Ubiquinone (Coenzyme Q)
3. Cytochromes
4. Iron-Sulfur Proteins
153
What are the 3 types of cytochromes involved in Oxidative Phosphorylation?
Are they membrane bound or soluble?
1. A - membrane bound
2. B - membrane bound
3. C - soluble
154
What is the basic formation of Iron-Sulfur proteins used in Oxidative Phosphorylation?
Iron and Sulfur molecules form complexes which then coordinate with Cysteine residues on a protein
155
Oxidative Phosphorylation - Complex I:
What are the electrons from NADH transferred to?
What enzyme catalyses this reaction?
What does this reaction produce and what happens to this?
How many protons are pumped into the inner mitochondrial space?
- NADH --> Ubiquinone
- Catalysed by NADH:Ubiquinone Oxidoreductase
- Ubiquinol is produced by this reaction and this diffuses to complex II
- 4 protons are pumped into the inner mitochondrial space
156
```
Oxidative Phosphorylation - Complex II:
What are the electrons from Succinate transferred to?
What enzyme catalyses this reaction?
What does this reaction produce?
What electron carrier is involved?
```
- Succinate --> Ubiquinone
- Catalysed by Succinate Dehydrogenase
- Ubiquinol is produced by this reaction
- Succinate transfers electrons to FAD which then transfers electrons to Ubiquinone
157
Oxidative Phosphorylation - Complex III:
What are the electrons from Ubiquinone transferred to?
What enzyme catalyses this reaction?
What is the problem with this reaction and how is it overcome?
- Ubiquinone --> Cytochrome C
- Catalysed by Cytochrome bc1 Complex or Ubiquinone:Cytochrome C Oxidoreductase
- Cytochrome C can only accept 1 electron, but Ubiquinone donates 2 electrons
- 1 electron is transferred to Cytochrome C and the other electron is recycled through the complex forming semi-ubiquinone
158
Oxidative Phosphorylation - Complex IV:
What are the electrons from Cytochrome C transferred to?
What enzyme catalyses this reaction?
What does this reaction produce?
How many protons are pumped into the inner mitochondrial space?
- Cytochrome C --> O2
- Cytochrome Oxidase
- H2O is produced by this reaction
- 4 protons are pumped into the inner mitochondrial space
159
During the formation of H2O in Complex IV of Oxidative Phosphorylation what is consumed?
What is the significance of this?
- 4 protons are consumed from inside the mitochondria
| - This helps to amplify the proton gradient across the inner mitochondrial membrane
160
What are the 2 subunits of ATP Synthase?
| What are their functions?
1. F1 - ATPase for formation of ATP
| 2. F0 - membrane embedded portion which acts as a pore for Protons to pass through to drive ATPase
161
What are the 3 states of Beta subunit of F1 ATPase?
| What is bound at each state?
1. Beta-Empty - nothing bound
2. Beta-ADP - ADP and Pi bound
3. Beta-ATP - ATP bound
162
How does the movement of Protons through ATP Synthase drive ATP formation?
- As the protons pass through the F0 complex they cause the subunits to rotate by 1/3
- Each 1/3 turn causes a conformational change in the Beta subunit of F1 ATPase
163
What is the total yield of ATP from respiration?
| Given 10 NADH and 2 FADH2 from Glycolysis, PDH complex and Krebs cycle.
- 10 NADH and 2 FADH2 give a yield of 34 ATP molecules
- Addition of 2 ATP molecules produced in Glycolysis
- Total yield = 36 ATP molecules
164
How is Oxidative Phosphorylation regulated?
- At rest, the proton motor force is high, but due to high ATP levels the flow of protons is slow
- During exercise when ATP is used up, ADP levels rise and the flow of protons through ATP Synthase is increased
165
What are the 2 types of inhibitors of Oxidative Phosphorylation?
Give an example for each type
1. Electron Transport Inhibitors - prevents carriers receiving electrons - E.g. Cyanide
2. Uncoupling Agent - dissipate the proton gradient so harder to make ATP - E.g. 2,4-Dinitrophenol
166
What is the codon for Methionine?
AUG
167
What are the 3 stop codons?
1. UAG
2. UGA
3. UAA
168
What is attached to a tRNA molecule to from Amino-acylt tRNA?
Amino acids
169
What do all of the ribosomes in a cell form?
Nissl substance
170
What are the 3 binding sites on a ribosome?
1. A - Amino-Acyl tRNA site
2. P - Peptidyl tRNA site
3. E - Exit
171
Describe the events that take place during the translation cycle.
- Incoming aa-tRNA binds to vacant A site on ribosome
- Small and large subunits of ribosome undergo conformational change, so that aa-tRNA now occupies P site
- Enzyme Peptidyl Transferase forms new peptide bonds between amino acids in ribosome
- mRNA moves 3 nucleotides through the small subunit and the tRNA is ejected from the E site
172
What enzyme forms the peptide bond between incoming amino acids in the Translation cycle?
Peptidyl Transferase
173
What elongation factor are incoming Amino-Acyl tRNAs associated with?
What type of protein is this?
- EF-Tu-GTP
| - GTP Hydrolysing protein
174
How does base pairing effect the activity of EF-Tu-GTP?
- Correct base pairing between tRNA and mRNA stimulates EF-Tu-GTP activity
- Incorrect base pairing between tRNA and mRNA inhibits the activity and the tRNA dissociates
175
If base pairing between tRNA and mRNA is correct, what happens to the EF-Tu-GTP?
What does this mean for the Amino-Acyl tRNA
- GTP is converted to GDP and the EF-Tu dissociates from the complex
- The aa-tRNA is now captured in the ribosome
176
After EF-Tu-GDP dissociates from the complex, what elongation factor binds to the A site on the ribosome?
What does this binding promote?
- EF-G-GTP
| - Binding of this promotes movements of tRNA into hybrid state (A to P and P to E)
177
What causes movement of tRNAs into P and E sites?
Hydrolysis of GTP by EF-G
178
What codon does translation always begin with?
| What amino acid does this code for?
- AUG
| - Methionine
179
How is protein synthesis initiated using the initiator tRNA?
| What initiation factor does this involve?
- Initiator tRNA is loaded into the small ribosomal subunit
| - Eukaryotic Initiation Factor eIF-2
180
Which end of mRNA does the ribosome bind to initiate protein synthesis?
5' end of mRNA
181
Once small ribosomal subunit binds to mRNA what occurs?
Small ribosomal subunit initiates scanning for AUG codon (Methionine)
182
Once an AUG codon has been found on mRNA what occurs?
Initiation factors dissociate and the large ribosomal subunit associates to form the full ribosome on mRNA to begin translation
183
How is protein synthesis terminated?
- Stop codons (UAA, UAG and UGA) not recognised by tRNAs
- Release factors bind to A site on ribosome with stop codon in
- Peptidyl transferase catalyses transfer of H2O to C-terminus of protein
- Addition of water results in dissociation of protein from ribosome
184
How is the ribosome disassembled after termination of protein synthesis?
Release factor in P site causes ribosome disassembly
185
How do antibiotics work?
They can selectively inhibit the protein synthesising machinery of Bacteria
186
Why can side effects of Antibiotics arise?
Similarity between mitochondrial and bacterial protein synthesis
187
What are 2 examples of immediate modifications of proteins?
1. Removal of targeting signal sequence
| 2. Folding
188
How is the targeting signal sequence removed from a protein?
| What enzyme does this involve?
- Protein enters translocator in the ER membrane
- As it is thread through the protein is cleaved at target signal sequence
- Signal peptidase cleaves the sequence and mature protein released into ER lumen
189
When can folding of a protein occur?
- During translation (co-translational)
| - During other modifications (post-translational)
190
What forces promote the folding of a protein (4 forces)?
- Disulphide bonds
- Ionic bonds
- Hydrogen bonds
- van der Waals forces
191
What does misfolding of proteins lead to?
| Give an example of when misfiling of a protein can be detrimental.
- Misfolding of proteins leads to aggregation
| - Beta amyloid misfiling leads to aggregation forming amyloid plaques in Alzheimer's disease
192
What is perversion of a protein?
| How can it lead to disease?
- Misfolding of proteins can lead to perversion
- Abnormal prion proteins resists protease action
- Then recruits normal prion proteins and proliferates infecting the individual
193
What is the function of protein chaperones?
- To assist in protein folding
194
How do HSP70s assist protein folding?
Heat shock proteins help folding (HSP70s) using ATP
195
How do HSP60s assist protein folding?
HSP60s help later on to hide hydrophobic regions
196
How are incorrectly assembled proteins tagged for destruction?
Ubiquitin attaches to the degradation signal of a protein in hydrophobic regions
197
What are ubiquinated proteins destroyed by?
Proteosome
198
What does lipidation modifications of proteins allow?
Lipid anchoring of protein in the cell membrane
199
What does glycosylation modifications of proteins allow?
Provides protection for membrane-bound and secreted proteins
200
What is the protein modification of phosphorylation used for?
Regulation of protein interactions
201
How can phosphorylation affect proteins? (3 ways)
- Causes a major conformational change with the addition of 2 negatively charged phosphate groups
- Phosphate groups can form part of binding sites for protein-protein interactions
- Phosphate groups can mask binding sites preventing protein-protein interactions
202
How are the destinations of proteins coded?
A short sequence of amino acids acts as a patch which can be recognised and so protein is sent to destination
203
Where are signal sequences found in a protein?
N terminus
204
Do cytoplasmic proteins have signal sequences?
No the do not have signal sequences so aren't relocated an remain in the cytoplasm
205
Once a protein has been transported to its target how does it cross the membrane of the target organelle?
What happens to the signal sequence?
- Protein docks in translocator complex via signal sequence
- Protein is fed through pore and enters organelle
- Signal sequence is then cleaved by Signal peptidase
206
What are signal sequences made of in proteins destined for the Endoplasmic Reticulum?
Hydrophobic amino acids
207
What are signal sequences made of in proteins destined for the Mitochondria?
Alternating positively charged and hydrophobic amino acids
208
Outline the process of Nuclear Import.
- Nuclear Localisation Signals (NLS) in protein are recognised by Nuclear Import Receptors (NIR) causing them to bind
- Interaction between Protein-NIR complex and fibrils of Nuclear Pore Complex (NPC) allow passage into nucleus
- Unstructured regions of NPCs are pushed aside to allow protein to pass through (requires ATP)
209
What are the 2 translocators involved in Mitochondrial import?
State where they are located.
1. TOM Complex - outer membrane
| 2. TIM 23 Complex - inner membrane
210
Outline the process of Mitochondrial Import.
- Signal sequence is recognised by TOM complex causing them to bind
- TOM complex lines up with TIM 23 complex to form a single continuous pore through the mitochondrial membrane
- Protein is fed through the pore as an unfolded polypeptide chain
- Signal sequence is cleaved once protein has passed through to form the mature protein
211
What is the function of SAM Complexes?
They help transmembrane proteins in mitochondria fold correctly
212
What 2 components guide ER signal to the ER membrane?
| How do they do this?
1. Signal Recognition Particle (SRP) - binds to ER signal sequence on protein
2. Signal Recognition Protein Receptor - located in ER membrane allows binding of protein to ER membrane
213
How does the Signal Recognition Particle bind to a protein destined for the Endoplasmic Reticulum?
Both ends.
- One end binds to ER signal sequence as it emerges from ribosome
- Other end blocks elongation factor binding site to allow time for ribosome to bind to ER membrane
214
Outline the process of Endoplasmic Reticulum import.
- Signal Recognition Particle binds to signal sequence on protein and exposes a binding site for the Signal Recognition Protein Receptor
- Binding of SRP to its receptor brings Ribosome to an unoccupied translocator.
- SRP and receptor then released and translocator transfers growing polypeptide chain across ER membrane
- Signal sequence is cleaved by Signal peptidase and mature protein released into ER lumen
215
What do stop-transfer signals in polypeptide chains allow for?
Where are these found within the polypeptide chain?
- Allow integration of polypeptide into the membrane
| - Stop-transfer signals found in hydrophobic regions of polypeptide chain
216
What do combinations of start-transfer and stop-transfer signals create?
How does this happen?
- Multipass membrane proteins
- Start-transfer signals initiate translocation of polypeptide chain until a stop-transfer signal is reached
- Then a 2nd start-transfer signal reinitiates translocation until another stop-transfer signal is reached
217
What are ER Retention signals?
These are found in proteins that are resident ER proteins and cause them to remain inside the ER
218
Give an example of an ER resident protein.
Protein Disulphide Isomerase - catalyses oxidation of free SH groups on cysteine to form disulphide bonds
219
What occurs during Exocytosis?
- Vesicle to be secreted is transported to membrane
- Signals allow docking of vesicle to membrane
- Regulated release to ensure all contents of vesicle is secreted
220
Where in the cell is the Endoplasmic Reticulum generally found?
Surrounding the nucleus
221
What is the name given to the chambers in the Endoplasmic Reticulum?
Cisternae
222
What are the functions of Smooth Endoplasmic Reticulum (SER)?
(5 functions)
1. Detoxification
2. Phospholipid and Cholesterol synthesis
3. Steroid hormone synthesis
4. Glyceride and Glycogen synthesis and storage
5. Calcium storage
223
How is the Calcium stored in Smooth Endoplasmic Reticulum involved in muscle contraction?
- In the Sarcoplasmic reticulum, action potentials causes Calcium release which travel down t-tubules
- This interacts with troponin and reveals the binding site for the myosin head, promoting cross-bridging
224
What is the structure of the Golgi Apparatus?
It is made of flattened discs called cisternae
225
What are the 3 regions of the Golgi Apparatus?
1. Cis network
2. Medial network
3. Trans network
226
What are the 3 functions of the Golgi Apparatus?
1. Modification and packaging secretions for release through exocytosis
2. Renewal and modification of plasma membrane
3. Delivery of material to other organelles
227
What is material transported from the Endoplasmic Reticulum to the Golgi in?
Vesicles or Tubules
228
During transport from the the Endoplasmic Reticulum to the Golgi is any of the material lost?
No, the transport process is non-leaky and anything in the lumen of the vesicle will be delivered to the Golgi
229
What are the 2 pathways of transport within a cell?
1. Secretory pathway
| 2. Endocytic pathway
230
What covers the outside of transport vesicles?
A protein coat
231
What are the 2 layers of the protein coat on vesicles?
| What does each layer do?
- Inner coat - concentrates specific membrane proteins in a specialised patch, which gives rise to vesicle membrane
- Outer coat - assembles into a curved lattice that deforms the membrane patch and shapes vesicle
232
What are the 3 types of vesicle coats?
| What are each of their specific functions?
1. Clathrin - formation of vesicles from cell surface and golgi
2. COP I - movement through golgi complex
3. COP II - formation of vesicles from ER to golgi
233
What are the 2 directions of movement throughout the golgi called?
- Anterograde - forward transport in the Golgi
| - Retrograde - backward transport in the Golgi
234
What are the 2 types of SNARE receptors?
Where are they found?
How many polypeptides make up each receptor?
1. v-SNAREs - found in the vesicle membrane
- Usually 1 polypeptide chain
2. t-SNAREs - found in the membrane of target
- Usually 3 polypeptide chains
235
During fusion what happens to the SNARE receptors?
The v-SNAREs and t-SNAREs wrap around each other to form a stable 4 polypeptide complex to dock the vesicle
236
In which direction to proteins being processed by the Golgi move?
They bind to the Cis face and pass through the Golgi to leave by the Trans face
237
What processing of proteins occurs in the Golgi?
Sugars are added and modified on the protein
238
What are the 2 models of Golgi transport?
1. Vesicular Transport model
| 2. Cisternal Maturation model
239
What does the Vesicular transport model propose about Golgi transport?
The Golgi is a static structure and proteins progress through the Golgi by a series of vesicles
240
What does the Cisternal maturation model propose about Golgi transport?
The Golgi is a dynamic structure and cisternae progress through the Golgi from Cis cisternae to Trans cisternae
241
What 3 pathways control the movement of vesicles?
1. Signal mediated diversion to Lysosomes
2. Constitutive secretory pathway
3. Signal mediated diversion to secretory vesicles
242
What are the 3 fates of endocytosed material?
1. Degradation
2. Storage
3. Transcytosis
243
What is phagocytosis?
Extension of membrane around material to engulf foreign particles
244
What is the name given to parts of membrane that extend around material during phagocytosis?
In what manner do these form?
- Pseudopods
| - Form in an actin dependent manner
245
What is frustrated phagocytosis?
When 2 macrophages attempt to phagocytose the same material
246
What evidence is there to suggest cell membrane recycling occurs?
- Macrophages phagocytosed latex beads
- By counting the beads it was possible to estimate how much membrane had been internalised
- Showed that some membrane had been internalised but the cell size remained the same
247
What is Pinocytosis?
A continuous process that allows cells to take up small molecules like "drinking"
248
Give an example of receptor-mediated endocytosis.
- Low density Lipoproteins transport Cholesterol around the body in the blood
- When a cell needs cholesterol they synthesise LDL receptors and place them in their membrane
- LDL binds to receptor and is endocytosed
- Vesicle fuses with endosome which then fuses with lysosomes to convert LDLs to Cholesterol for cell to use
249
What is framed when 3 molecules of Clathrin link?
| What can these structures form?
- Clathrin Triskelia
| - These can link up to form pentagonal or hexagonal lattices
250
What happens to Clathrin coats at the endosome?
Clathrin coat dissociates and degrades due to low pH
251
Once a endocytsoed vesicle has fused with the early endosome, what are the 2 possible fates of the ligand?
1. Recycled to cell surface by vesicles budding off from Endosome
2. Sent to Lysosome for hydrolisation
252
What causes ligands to dissociate from their receptors once they have been endocytosed and fused with the endosome?
What happens to the receptor after this?
- The low pH of endosome causes ligand to dissociate from receptor
- The receptor can be recycled back the cell membrane via vesicles that bud off from endosome
253
What are Clathrin-coated pits?
Areas of membrane that are endocytosed to from cathrin coated vesicle
254
What is the cytoskeleton?
A dynamic, complex, intracellular network of tubules, filaments and fibres found in all eukaryotes
255
What are the 3 protein filaments that make up the cytoskeleton?
1. Actin filaments
2. Microtubules
3. Intermediate filaments
256
What are the functions of Actin filaments?
| 3 functions
- Determine shape of cell's surface
- Necessary for whole cell locomotion
- Drive cytokinesis
257
What are the functions of Microtubules?
| 3 functions
- Determine position of membrane enclosed organelles
- Direct intracellular transport
- Form mitotic spindle that segregates chromosomes
258
What is the function of Intermediate filaments?
Provide mechanical strength
259
What is the function of Accessory proteins in the cytoskeleton?
What are they essential for?
- Regulate and link filaments to other filaments and cell components
- Essential for controlled assembly of cytoskeletal filaments
260
What are motor proteins in the cytoskeleton?
Motor proteins convert energy of ATP hydrolysis into mechanical force that can move organelles along filaments or move filaments themselves
261
What subunits make up actin filaments?
| What type of proteins are these?
- Actin subunits
| - Globular proteins
262
What subunits make up microtubules?
| What type of proteins are these?
- Tubulin subunits
| - Globular proteins
263
What are intermediate filaments made from?
Made from elongated and fibrous subunits
264
What 2 contacts do all 3 cytoskeletal filament use to assemble?
What structure do they form?
1. End-to-end contacts
2. Side-to-side contacts
- Helical structures
265
What produces differences in the stability and mechanical properties of the 3 cytoskeletal filaments?
Differences in structures of subunits and strength of attractive forces between subunits
266
What forces hold subunits of cytoskeletal filaments together?
What does this allow for?
- Non-covalent forces
| - Rapid assembly and disassembly
267
How do the subunits of actin filaments assemble?
| What is the name of the structure formed?
- Head-to-tail forming a tight, right-handed helix
| - Form F-actin
268
Actin filament are polar, what are the 2 structurally different ends?
What is the speed of growth at these ends?
- Minus end - slow growing
| - Plus end - fast growing
269
Describe the rate of assembly of actin filaments when polymerisation is activated.
- Instability of smaller actin aggregates creates a barrier resulting in a lag phase
- During this some aggregates transition to become more stable filaments, leading to rapid filament elongation
- As the conc. of actin monomers decline the system approaches steady state at which the rate of addition of new actin monomers = the rate of disassembly
270
What 2 types of filament can Actin exist as?
What is bound to each of these types of filaments?
Do these types of filament grow or shrink?
1. D form - ADP bound - polymers shrink
| 2. T form - ATP bound - polymers grow
271
What determines whether the subunits at the end of actin filaments are in D form or T form?
The rate of hydrolysis of ATP compared to the rate of new subunit addition
272
What form are the subunits of actin filaments in at the plus end?
Why is this?
- T form
| - Rate of new addition is greater than the rate of hydrolysis
273
What form are the subunits of actin filaments in at the minus end?
Why is this?
- D form
| - Rate of new addition is less than the rate of hydrolysis
274
What is 'treadmilling' of actin filaments?
Filaments have addition at plus end (T form) and and disassembly at minus end (D form)
275
What is the function of the actin filament association protein Profilin?
Recruits actin monomers for polymerisation at plus end
276
What is the function of the actin filament association protein Thymosin?
Binds actin monomers and prevents them from adding to plus end
277
What is the function of the actin filament association protein Gelosin?
Involved in severing of actin filament
278
What is the function of the actin filament association protein Fimbrin?
Responsible for close packing of actin filaments
279
What are the 2 globular proteins that form Tubulin?
1. Alpha tubulin
| 2. Beta tubulin
280
What is significant about the binding sites for GTP on Alpha and Beta tubulin?
- GTP bound to Alpha tubulin is physically trapped and cannot be hydrolysed
- GTP bound to Beta tubulin can be hydrolyse to GDP
281
What is the structure of a microtubule?
| How many protofilaments make up a microtubule?
- Hollow, cylindrical structure
| - 13 parallel protofilaments
282
Microtubules have polarity, what are the 2 structurally different ends?
What is exposed at each of these ends?
1. Plus end - Beta tubulin exposed
| 2. Minus end - Alpha tubulin exposed
283
What 2 types of filament can Tubulin exist as?
What is bound to each of these types of filaments?
Do these types of filament grow or shrink?
1. D form - GDP bound - polymers shrink
| 2. T form - GTP bound - polymers grow
284
How is a "GTP cap" on microtubules created?
When subunit addition is high and the protofilament is growing rapidly, it is likely that new subunit will be added before GTP hydrolysis of the previous subunit - creates the GTP cap
285
How can the tip of a protofilament be in the D form?
When subunit addition is low and protofilament is growing slowly, it is likely that GTP hydrolysis of the previous subunit will occur before the addition of a new subunit
286
What is Dynamic Instability of microtubules?
Rapid interconversion between growing and shrinking state at a held monomer concentration
287
How does Dynamic Instability occur in microtubules?
The end of a microtubule that was growing in the T form for some time can suddenly change to the D form and begin to shrink rapidly. It may then regain a T form and begin to grow again
288
What is a catastrophe in dynamic instability of microtubules?
Change from growth to shrinking
289
What is a rescue in dynamic instability of microtubules?
Change from shrinking to growth
290
Where are microtubules nucleated from?
Microtubule Organising Centre (MTOC)
291
What is the y-tubulin ring complex?
Accessory proteins help create a ring of y-tubulin which serves as a template for microtubule assembly
292
At which end are microtubules attached to the centrosome?
Attached at the minus end with plus ends pointing out
293
What is found embedded within the centrosome?
| What occurs here?
- Pair of Centrioles
| - Microtubule assembly
294
As well as microtubule assembly, what other structures can Centrioles produce?
Centrioles can function as basal bodies for formation of ciliary axoneme
295
What 2 effects can Microtubule Associated Proteins (MAPs) have?
1. Stabilise microtubule against disassembly
| 2. Mediate interaction of microtubules with other cell components
296
What is the fucnction of MAP-2 in microtubules?
Cross-links microtubules for filament bundling
297
What is the structure of an Intermediate filament?
- 2 monomers form a coiled coil structure
- The dimers then associate in an antiparallel fashion to form a staggered tetramer
- These tetramers then pack together laterally to form the filament
298
What is the difference in structure between actin filaments/microtubules and intermediate filaments?
Both ends of intermediate filaments are the same and therefore they lack structural polarity
299
What are some examples of different cell types that express different intermediate filaments?
- Epithelial - type 1 and 2 keratins
- Nuclear - Lamins A, B and C
- Axonal - Neurofilament proteins
300
What is an example of clinical condition that is associated with disturbances in cytoskeletal function?
ALS - associated with accumulation of and abnormal assembly of neurofilaments in motor neurones
301
What are the 2 major classes of Microtubule-based motor proteins?
1. Kinesins
| 2. Dyneins
302
What direction to Kinesins move in?
| What function do kinesins serve?
- Plus end directed (move towards plus end)
| - Involved in mitotic spindle formation and chromosome segregation
303
What direction to dyneins move in?
| What function do dyneins serve?
- Minus end directed (move towards minus end)
| - Involved in construction of microtubule spindle and positioning of centrosome and nucleus in cell migration
304
Is Kinesin responsible for anterograde or retrograde transport?
In what direction is this transport?
- Anterograde
| - Towards the periphery of the cell
305
Is Dynein responsible for anterograde or retrograde transport?
In what direction is this transport?
- Retrograde
| - Towards the centre of the cell
306
How does Kinesin bind to organelles in order to transport them?
Kinesin binds to the organelle directly
307
How does Dynein bind to organelles in order to transport them?
Dynein binds to the organelle indirectly via another protein - Dynactin
308
What is the Mitotic Spindle?
| What process depends on the Mitotic Spindle?
- A bipolar array of Microtubules that pull sister chromatids apart in anaphase
- Chromosome segregation
309
What is the spindle pole?
Focused at the centrosome and is what minus ends of microtubules associate with, whilst the plus ends radiate outwards
310
What are the 3 type of Microtubules involved in the mitotic spindle?
1. Interpolar MTs
2. Kinetochore MTs
3. Astral MTs
311
What do Interpolar microtubules attach to?
| What do they do?
- The plus ends extend across the equator and interdigitate with other interpolar MTs from the opposite spindle pole
- They help to stabilise the bipolar spindle
312
What do Kinetochore microtubules attach to?
| What do they do?
- The plus ends attach to sister chromatid pairs at the protein structures called Kinetochores
- They help separate the sister chromatid pairs
313
What do Astral microtubules attach to?
| What do they do?
- The plus ends attach to cell membrane
| - They help to position the spindle correctly
314
How is the nuclear membrane broken down prior to mitosis?
- Phosphorylation of subunits of Nuclear Pore Complexes causes them to disassembly
- Phosphorylation of Nuclear Lamina causes them to disassembly and nuclear membrane breaks down
315
What occurs during Anaphase A?
Poleward movement of the chromosomes
316
What occurs during Anaphase B?
Separation of spindle poles themselves
317
What 2 poleward forces does Anaphase A depend on?
1. Force generated by Microtubule depolymerisation at plus end, this acts to pull the kinetochore towards the pole
2. Microtubule flux - minus end depolymerisation causes poleward movement of microtubule
318
What 2 motor proteins does Anaphase B depend on?
| What do they each do?
1. Kinesin - push the poles apart via Interpolar MTs
| 2. Dynein - pull the poles apart via Astral MTs
319
What is Cytokinesis?
Division of cytoplasm into 2 daughter cells
320
What structure underlies the process of Cytokinesis?
| What is this structure made of?
- Contractile ring
| - Composed of actin filaments, myosin II filaments and regulatory proteins
321
When and where does the contractile ring assemble?
During anaphase, the contractile ring assembles beneath the plasma membrane
322
How does the contractile ring initiate Cytokinesis?
After anaphase, the actin and myosin II filaments contract to divide the cytoplasm into 2
323
What is the midbody formed during Cytokinesis?
| What is contained in the midbody?
- As the cleavage furrow narrows due to contraction of contractile ring the midbody forms
- This contains remainder of the central spindle which is derived from the overlapping Interpolar MTs
324
What are cilia and flagella built from?
- Mticrotubules
| - Dynein
325
Name an example of a cell that flagella are found on.
| What does the flagella allow?
- Sperm
| - Wave-like movement enables sperm to swim
326
Name an example of where cilia can be found.
| What do they do here?
- Lining respiratory tract
| - Cilia beat to waft the mucus that traps bacteria etc. up the tract to be swallowed
327
The bending of what structure in cilia and flagella results in their movement?
Axoneme
328
What is the structure of an axoneme?
- 9 doublet microtubules (each composed of a complete MT and an incomplete MT fused together) are arranged in a ring
- These surround a pair of single MTs
- At regular positions along the length of the MTs accessory proteins cross-link MTs together
- Dynein motors form bridges between neighbouring MTs
329
How does the activity of Dynein produce movement of cilia and flagella?
How do the cross-linking accessory proteins effect this movement?
- When activated Dynein tries to walk up neighbouring Ts causing them to slide relative to one another
- Cross-linking accessory proteins prevents sliding and instead force generates a bending movement
330
What is the structure of a Basal Body?
| And what do they do?
- Core of basal bodies is a centriole with 9 groups of fused triplet microtubules arranged in a ring
- Basal bodies act to firmly root cilia at cell surface
331
What are the 2 types of actin-based movement?
1. Muscle movement - moves whole organism
| 2. Non-muscle movement - moves individual cells
332
What is the contractile unit of muscles?
| How do they influence the appearance of skeletal muscle?
- Sarcomere
| - Give skeletal muscles their striated appearance
333
What are the 2 components of the sarcomere?
| What protein filaments make up these components?
- Thick filaments - Myosin
| - Thin filaments - Actin
334
Describe the process of how myosin filaments slide over actin filaments to cause muscle contraction.
- At start of cycle, myosin head is bound tightly to an actin filament
- ATP molecule binds to back of myosin head and causes a conformational change in the actin binding site that reduces the affinity of the myosin head for the actin filament allowing it to move along the actin filament
- Movement in lever arm causes head to be displaced along actin filament and hydrolysis of ATP molecule occurs
- Weak binding of myosin head to actin results in release of Pi group from ATP hydrolysis and the myosin head binds tightly to actin filament
- Triggers power stroke - the force generating change in shape of myosin head causes it to regain its original conformation
335
What is the sliding filament theory?
During muscle contraction, myosin filaments slide over the actin filaments which results in shortening of the sarcomere and the muscle contracts
336
What initiates muscle contraction?
| What causes this change?
- Sudden rise in cytosolic Ca2+
| - Caused by action potential opening voltage gated Ca2+ channels in T tubules of sarcoplasmic reticulum
337
What are the 4 accessory proteins involved in regulating myosin head binding to actin filaments?
What do each of these bind to?
1. Tropomyosin - binds along groove of actin filament
2. Troponin I - binds to tropomyosin
3. Troponin T - binds to actin
4. Troponin C - binds Ca2+ ions
338
How does Troponin I-T complex effect myosin head binding to actin filament?
How does binding of Ca2+ to Troponin C initiate muscle contraction?
- At rest, Troponin I-T complex pulls tropomyosin out of actin groove which prevents myosin head binding to actin filament
- Ca2+ binding to Troponin C causes Troponin I to release actin and tropomyosin moves back into actin groove allowing myosin head to bind to actin filament t and initiate contraction
339
What are the 3 distinct activities involved in cell migration using actin-rich cortex beneath the cell membrane?
What happens during each of these activities?
1. Protrusion - plasma membrane is pushed out in front of cell by actin polymerisation
2. Attachment - Actin cytoskeleton connects across cell membrane to sub-stratum
3. Traction - Bulk of trailing cytoplasm is pulled forward
340
What are filopodia?
One-dimensional extensions containing a core of long. bundled actin filaments
341
What are lamellipodia?
Two-dimensional extensions contain cross-linked mesh of actin filaments
342
How do filopodia and lamellipodia allow cell motility?
They extend forward and attach to sub-stratum and then contraction at the bar of the cell propels rest of cell forward
343
What is 'Gel-sol transition' in the movement of Amoeboid?
| How does this allow movement?
- Transition from gel-like cytoplasm (outer region) to liquid-like cytoplasm (inner region)
- Actin underlying cell membrane has weak point allowing membrane protrusion an extension
344
What are the 6 main cell junctions?
1. Tight junction
2. Adherins junction
3. Desmosomes
4. Gap junction
5. Hemidesmosomes
6. Focal adhesions
345
What is the function of tight junctions? (2 functions)
1. Seals gap between epithelial cells to prevent passing of molecules between cells
2. Define different areas of cell membranes e.g. confine transmembrane proteins to specific membrane surfaces
346
What is the major protein vital for formation of tight junctions?
Claudins
347
What are 2 proteins, other than claudins, involved in tight junctions?
What do they both do?
1. Occludin - limits junctional permeability
| 2. Tricellulin - seals cell membranes together
348
Where are tight junctions distributed?
Found in all epithelial tissues e.g. epithelia lining the gut
349
What is a clinical condition linked with the dysfunction of tight junctions?
- Mutation in claudin that allows reabsorption of Mg2+ from urine prevents reuptake and causes Mg2+ loss in the urine
350
What is the function of adherins junctions?
Connects actin filaments in one cell with that of another to join cytoskeletons of adjacent cells
351
What is the transmembrane adhesion protein used in adherins junctions?
How do these proteins join together?
- Cadherins
| - Join in a homophillic manner i.e. the same 2 cadherin protein join together
352
What ion are Cadherins dependent upon for formation of adherins junctions?
Ca2+
353
Where are adherins junctions distributed?
- Epithelial tissues
| - Heart where they anchor actin bundles on the contractile apparatus and link contractile cells end-to-end
354
What structure do asherins junctions produce in epithelial cells?
What does this structure allow for?
- Adhesion belt, a continuous connection of actin filaments beneath apical surface of epithelia
- Co-ordinated contraction of this belt allows for processes such as invagination and formation of tubes in morphogenesis
355
What is the function of desmosomes?
Connect intermediate filaments in one cell to those in the adjacent cell to provide mechanical strength
356
What is the transmembrane adhesion protein used in desmosomes?
Non-classical Cadherins
357
Where are desmosomes distributed?
- Epithelial tissues
| - Tissues subject to high levels of mechanical stress e.g. heart and epidermis
358
What is a clinical condition caused by the dysfunction of desmosomes?
How does it cause its symptoms?
- Pemphigus
| - Produce antibodies against desmosomal cadherins that disrupts desmosomes in the skin and causes severe blistering
359
What is the function of gap junctions?
Creates direct channels between adjacent cells to allow passage of small, water-soluble molecules from cell to cell
360
What is the transmembrane adhesion protein that create gap junctions?
How do they combine to produce the channel?
- Connexins
| - 6 connexins join to form a connexon (channel)
361
Where are gap junctions distributed?
- Connective tissues
- Epithelial tissues
- Heart muscle - allows electrical coupling of contractile cells for synchronous contraction
362
What factors regulate whether gap junctions are open or closed? (4 factors)
- Voltage difference between 2 cells
- Membrane potential of 2 cells
- pH
- Conc. of Ca2+
363
What is the function of hemidesmosomes?
Anchor intermediate filaments in a cell to the extracellular matrix
364
What is the transmembrane adhesion protein in both hemisdesmosomes and Focal adhesions?
Integrin
365
What is the function of focal adhesions?
Anchor actin filaments in a cell to the extracellular matrix
366
What are the 3 major macromolecules that make up the Extracellular Matrix (ECM)?
1. Glycosaminoglycans (GAGs)
2. Fibrous Proteins
3. Glycoproteins
367
How can GAGs associate with proteins?
The can combine with proteins to form Proteoglycans
368
What is the structure of GAGs?
- Unbranched polysaccharide chains composed of repeating disaccharide units
- Repeating units consist of an amino sugar and ironic acid
369
What does the negative charge on GAGs result in?
Attracts cations (e.g. Na+) so they are osmotically active and water is sucked in to form a gel-like layer
370
What force do GAGs protect against?
Compressive forces in tissues and joints
371
What is the structure of a collagen molecule?
| What amino acids are they rich in?
- Long, stiff, triple stranded helical structures in which 3 alpha-chains are wound around each other
- Proline and Glycine
372
What type of collagen is the most common?
| Where is it most commonly found?
- Type I Collagen
| - Skin and bones
373
How do fibroblasts form collagen fibres?
- Synthesise and secret collagen fibrils in correct orientation
- They crawl over and tug on collagen to create tendons and ligaments and layers of connective tissue
374
What forces do collagen fibres provide resistance to?
Tensile forces
375
What do elastic fibres in ECM allow?
Recoil of tissues after stretch
376
What is the main protein in Elastic tissue?
Elastin
377
How is elastin formed?
Tropoelastin secreted into EC space and assembled into elastic fibres (elastin)
378
Give an example of where elastic tissue is found in large quantities.
Elastic arteries e.g. Aorta
379
What function do glycoproteins play in the ECM?
Contribute to organising matrix and attaching cells to it
380
What is an example of a glycoprotein in the ECM?
Fibronectin
381
What does fibronectin bind to? (3 things)
- Collagen
- Proteoglycans
- Integrins on surface of cells
382
What are the functions of the Basal lamina? (4 functions)
- Support epithelial cells
- Filter fluids e.g. in kidney tubules
- Determine cell polarity
- Influence cell metabolism
383
What is the main protein in the basal lamina?
Laminin
384
What is the function of integrins?
- Allow cells to bind to the ECM
| - Involved in actin-based movement
385
What is an example of a disease that affects integrins?
| What are the symptoms?
- Glanzmann's disease
- Individuals don't express integrins to bind clotting factors e.g. fibrinogen
- Results in defective clotting and excessive bleeding
386
Where does fertilisation of an egg by a sperm occur?
What is the term that refers to the fusion of sperm and egg?
What structure does this produce?
- The ampulla of the uterine tube
- Syngomy
- Zygote
387
State the steps of blastocyst formation.
| Where does the embryo implant itself?
1. Cleavage of zygote to form 2 Blastomeres
2. Cell division produces ball of cells - Morula
3. Cavity forms in the Morula to form the Blastocyst
- Embryo implants onto the back of the uterine wall
388
What are the 3 parts of a Blastocyst?
| What do these produce?
1. Trophoblast - produces the placenta
2. Embryoblast - produces the offspring
3. Blastocoel - cavity in embryo
389
How many days does the average pregnancy last?
266 days from fertilisation
390
What are the 3 germ layers?
1. Ectoderm
2. Mesoderm
3. Endoderm
391
What are the 4 basic tissues?
| From which germ layer do these tissues form from?
1. Nervous - Ectoderm
2. Muscle - Mesoderm
3. Connective - Mesoderm
4. Epithelial - All 3 layers
392
What 2 types of growth increase tissue volume in the developing embryo?
What do each of them involve?
1. Hyperplasia - increasing the number of cells
| 2. Hypertrophy - increasing the volume of cells
393
What is differentiation in embryo development?
Unequal but controlled change in structure resulting in a functionally different area
394
What is meant if a cell is totipotent?
It can differentiate to form any type of cell in the body
395
What is the basis of differentiation in a developing embryo?
All cells contain ALL genes but will only express specific genes resulting in differentiation
396
Is differentiation reversible?
No, each 'choice' is unidirectional and irreversible
397
Stem cells in adults are Determined, what does this mean?
They are committed to a particular developmental pathway
398
What is meant if a cell is unipotent?
It can only differentiate into 1 type of cell
399
What is meant if a cell is pluripotent?
It can differentiate into several types of cells
400
Other than selective gene activation, what other factors can influence gene activity?
Epigenetic influences - secretions in the embryo (morphogens) can result in gene activation in cells
401
How does the position of a cell effect Epigenetic influences on gene activity?
Cells in different positions will be subject to different concentrations of morphogens which will result in different differentiation pathways
402
What are morphogens?
Signal molecules that cause commitment of cells by activating specific genes in the cell
403
What is the process induction in the developing embryo?
| Give an example of when this occurs?
- The presence of one tissue influences the development of other tissues
- The notochord induces neural tube formation then disappears
404
What process produces the 3 layered structure of a developing embryo?
Gastrulation
405
What is terminal differentiation?
When a cell fully differentiates into one of the highly specialised cell types in the body
406
What occurs during gastrulation?
- Invagination of cells from external blastula forms the Endoderm
- Some cells then move into the space between the Ectoderm and Endoderm to form the Mesoderm
407
What can abnormalities in growth and differentiation cause in individuals?
- Cancer
| - Deformties
408
What are the 3 types of muscle?
| Are these voluntary or involuntary?
1. Skeletal - voluntary
2. Smooth - involuntary
3. Cardiac - involuntary
409
What are the 2 functional classifications of muscle?
| Give an example for each.
1. Fast twitch - Biceps Brachii
| 2. Slow twitch - Intestinal tract muscles
410
What are the 2 biochemical classifications of muscle?
| What is the difference between the 2 types?
1. Red - have lots of mitochondria so very oxidative
| 2. White
411
What are the 3 layers covering muscles?
| What do they each cover?
1. Endomysium - surrounds muscle cells
2. Perimysium - surrounds bundles (fascicles) of muscle cells
3. Epimysium - surrounds the whole muscle
412
What is the structure of skeletal muscle?
- Multinucleated - peripherally located nuclei
- Long, unbranched fibres
- Striated
413
What do T-tubules in sarcolemma of skeletal muscles allow?
Co-ordinated contraction of muscle cell
414
What does the sarcoplasmic reticulum store?
Ca2+ ions
415
What is the structure of smooth muscle?
- Uninucleate
- Unbranched fibres
- Unstriated
416
What is the structure of cardiac muscle?
- Uninucleate
- Branched fibres
- Muscle cells connected by intercalated discs
417
Cardiac muscle cells have an inherent rhythm, what does this mean?
Cells initiate contraction without external stimuli
418
What are the purkunje fibres in the heart?
| What molecule are the cells rich in?
- The internal conduction system of the heart
| - Glycogen
419
How many molecules of Myosin per filament are there in muscle?
What is the structure of a myosin filament?
- 300 myosin molecules
| - Coiled coil filaments with motor head domains on one end
420
How many molecules of Actin per filament are there in muscle?
What is the structure of an actin filament?
What polypeptide wraps around actin filaments?
- 380 actin molecules
- G-actin molecules join to form thin filaments of F-actin
- Tropomyosin
421
```
In a sarcomere, what are the:
- Z lines
- M line
- I band
- A band
- H zone
What happens to these during contraction?
```
- Z lines - attaches actin filaments and marks boundaries between sarcomeres
- M line - middle of a sarcomere
- I band (isotropic) - zone of thin filaments (actin) not superimposed by thick filaments (myosin)
- A band (anisotropic) - entire length of a single thick filament
- H zone - zone of thick filaments (myosin) not superimposed by thin filaments (actin)
- During contraction, I bands and H zone shortens to bring the Z lines closer together, whilst A bands do not change their length
422
What are the 3 biological activities that Myosin performs?
1. Spontaneously assembles into filaments
2. Enzyme (ATPase)
3. Binds actin filaments
423
What is the structure of Tropomyosin?
What complex attaches to tropoymyosin?
What 3 parts make up this complex?
What do these 3 parts each bind?
- Double alpha helix
- Troponin complex
1. Troponin I - binds actin
2. Troponin T - binds tropomyosin
3. Troponin C - binds Ca2+
424
What structure do epithelial cells rest on?
Basement membrane
425
Are epithelia innervated?
| Do they have a blood supply?
- No they are not innervated
| - No they are avascular
426
What is the function of epithelia?
| What 3 things are epithelia involved in?
- They form barriers for:
1. Protection - e.g. skin
2. Absorption - e.g. lining of gut
3. Secretion - e.g. glands
427
What are the 4 main types of epithelia?
| Give an example of where each can be found.
1. Simple - single layer of cells all in contact with BM (lung)
2. Stratified - many layers of cells, only bottom layer in contact with BM (skin)
3. Pseudo-stratified - appear stratified but all cells are in contact with BM (trachea)
4. Transitional - when released only bottom cells in contact with BM, when stretched all cells flatten (bladder)
428
What type of epithelia lines the alveoli of the lung?
What is the arrangement of cells in this epithelia?
What is the shape and orientation of the cells nucleus?
How does its structure relate to its function?
- Simple squamous epithelia
- Single layer of flattened cells
- Parallel, oval nucleus
- Provides a thin barrier for gas exchange to allow rapid diffusion of gases into/out of blood
429
What type of epithelia lines the kidney tubules?
What is the arrangement of cells in this epithelia?
What is the shape and orientation of the cells nucleus?
How does its structure relate to its function?
- Simple cuboidal epithelia
- Single layer of cuboidal cells
- Central, round nucleus
- Provides a large surface area for absorption of substances from the urine back into the blood
430
What type of epithelia lines the respiratory airways?
What is the arrangement of cells in this epithelia?
What is the shape and orientation of the cells nucleus?
How does its structure relate to its function?
- Simple columnar epithelia
- Single layer of columnar cells
- Perpendicular, oval nucleus
- Cells have cilia on apical surface to waft mucus up to throat to be swallowed
431
What are microvilli?
Where are they found?
How does their structure relate to their function?
- Regular, finger-like projections on the apical surface of absorptive cells
- Found on cells lining the intestinal tract
- They greatly increase the surface area through which absorption can occur
432
What are cilia?
Where are they found?
How does their structure relate to their function?
- Regular, motile appendages on apical surface of cells in respiratory tract or female uterine tubes
- Found on cells in respiratory tract and female uterine tubes
- They have filaments that actively beat to waft mucus or egg along the tract
433
In what type of areas are stratified epithelia found in?
Areas where there is constant abrasion
434
How are cells replaced in stratified epithelia?
Worn away cells are replaced from below
435
What type of epithelia lines the oesophagus/vagina?
What is the arrangement of cells in this epithelia?
How does its structure relate to its function?
- Stratified squamous non-keratinised epithelia
- Many layers of flattened cells
- Many layers of cells help to protect against damage from constant abrasion the tissue is subject to
436
What type of epithelia lines the skin?
What is the arrangement of cells in this epithelia?
How does its structure relate to its function?
- Stratified squamous keratinised epithelia
- Many layers of flattened cells
- Outer cells are no longer alive and are packed full of the protein Keratin which makes our skin waterproof
437
What type of epithelia lines the trachea/bladder?
What is the arrangement of cells in this epithelia?
How does its structure relate to its function?
- Pseudo-stratified epithelia
- Single layer of cells that are piled on top of a BM that appear to form multiple layers
- The piled structure allows the epithelia to stretch during inspiration and urine storage
438
What are 2 examples of extracellular proteins composing the basement membrane?
- Collagen Type 4
| - Fibronectin
439
What type of glands secrete through ducts?
Exocrine
440
What type of glands secrete without ducts?
Endocrine
441
What is an example of a single cell gland?
| What is its function?
- Goblet cell
| - Secretes mucus in respiratory tract to trap bacteria, which his then wafted up to the throat by cilia and swallowed
442
What is an example of multicellular gland?
Pancreas
443
What are the 3 types of glands?
What do they each secrete?
Give an example for each type.
1. Mucous gland - secretes mucous - Sublingual gland
2. Serous gland - secretes proteins e.g. enzymes - Parotid gland
3. Mixed gland - secretes both mucous and proteins - Mandibular gland
444
What are the functions of connective tissue?
- Protection
- Storage
- Repair
- Transport
- Supports organs
445
What 3 components make up connective tissue?
1. Fibres
2. Cells
3. Matrix
446
What are the 2 main types of connective tissue?
1. Collagen
| 2. Elastic
447
What is the appearance of collagen?
- White
- Thick
- Unbranched
448
What is the appearance of elastic tissue?
- Yellow
- Thin
- Branched
449
What cell produces collagen fibres?
| How do they do this?
- Fibroblasts
| - Pro-collagen is converted to Tropocollagen which is then converted to Collagen
450
What is an example of a dense and regular collagen connective tissue?
Tendons
451
What is an example of a dense and irregular collagen connective tissue?
Dermis (skin)
452
What is the structure of Collagen?
- 3 chains of alpha helices coiled around each other
| - Rich in Glycine and Proline
453
What type of Collagen is the major component of bone, tendons and skin?
What is the arrangement of these fibres like?
- Type 1
| - Large branched fibres
454
What type of Collagen is the major component of basement membranes?
What is the arrangement of these fibres like?
- Type 5
| - Sheet-like fibres
455
What cells produce elastic fibres?
| What hydrophobic protein is a major component?
- Fibroblasts
| - Elastin
456
What protein is elastin often bound with?
Fibrillin
457
Elastic tissue is highly cross-linked, what does this allow for?
Where can elastic tissue be found?
- It allows the tissue to stretch and recoil allowing elasticity
- Skin, arteries and epiglottis
458
Are fibroblasts active?
What is the appearance of their nucleus?
What is the contents of their cytoplasm?
Where is an example they are found?
- Yes
- Large, round, euchroamtic nucleus
- Lots of Rough Endoplasmic Reticulum
- Umbilical cord
459
Are fibrocytes active?
What is the appearance of their nucleus?
What is the contents of their cytoplasm?
Where is an example they are found?
- No
- Small, flat, heterochromatic nucleus
- Little of Rough Endoplasmic Reticulum
- Tendons
460
What cells make up fat tissue?
Adipocytes
461
What are the 2 types of fat?
| What is the structure of each type?
1. Brown fat - lots of small vesicles storing triglycerides
| 2. White fat - one big vesicle storing triglycerides
462
Are adipocytes active?
| Give some examples of molecules adipocytes have receptors for.
- Yes
| - Insulin, Thyroid hormones, Gluco-corticoids
463
What organelle do adipocytes have in large proportions?
| Why is this?
- Smooth Endoplasmic Reticulum
| - To produce lipids that fill the cytoplasm
464
What cells produce the matrix of connective tissue?
| What is the main component of this matrix?
- Fibroblasts
| - Glycosaminoglycans (GAGs)
465
What main structural feature of GAGs allows them to support connective tissue?
- They are highly negatively charged
- Causes attraction of Sodium (and other +ve ions)
- Draws water in to make matrix turgid and gel-like
466
In what 3 important ways do neurones differ from standard cells?
1. Specialised metabolism
2. Cell membranes contain selective ion channels
3. Neurons have long cell processes radiating from the cell body
467
What 3 types of transport proteins are found in neurones?
1. Sodium/Potassium pump
2. Ligand-gated ion channels
3. Voltage-gated ion channels
468
What are the supporting cells surrounding neurones called?
| What is their function?
- Glial cells
| - Maintenance and nutrition of neurones
469
What is a synapse?
A junction between 2 neurones or between a neurone and its target organ
470
What are the 3 types of synapses (types of connection)?
1. Axosomatic - axon to cell body
2. Axodendritic - axon to dendrites
3. Axoaxonic - axon to axon
471
How do synapses ensure one way communication from presynaptic axon to postsynaptic dendrite?
- Only the presynaptic axon contains vesicles storing neurotransmitters
- Only the postsynaptic dendrite have the receptors for the neurotransmitters
472
What is the neurotransmitter at neuromuscular junctions?
Acetyl-Choline
473
What is the neurotransmitter at a synapse in ganglia of the autonomic nervous system?
Acetyl-Choline
474
What are the 2 main excitatory neurotransmitters of the central nervous system?
1. Glycine
| 2. Glutamate
475
What is the main inhibitory neurotransmitter of the central nervous system?
Gamma Amino Butyric Acid (GABA)
476
What is the neurotransmitter used between postsynaptic neurones and target tissues in the sympathetic nervous system?
Noradrenaline
477
What is the neurotransmitter used between postsynaptic neurones and target tissues in the parasympathetic nervous system?
Acetyl-Choline
478
What are the 2 methods of neurotransmitter inactivation?
1. Re-uptake into presynaptic neurone
| 2. Metabolised by enzymes in synaptic cleft
479
A deficiency of which neurotransmitter is involved in some types of depression?
What type of drugs can be used for treatment in some types of depression?
- Serotonin
| - Selective Serotonin Reuptake Inhibitors (SSRIs)
480
What is the appearance of Astrocytes?
| What is their function?
- Star-shaped with many branches
| - Branches contact blood vessels and neurones carrying nutrients between the 2
481
What cells myelinate axons in the Central Nervous System?
Oligodendrocytes
482
What cells myelinate axons in the Peripheral Nervous System?
Schwann cells
483
What is the function of Microglia?
They engulf and destroy harmful or damaged material
484
What are groups of neuronal cell bodies in the central nervous system called?
Nuclei
485
What are groups of neuronal cell bodies in the peripheral nervous system called?
Ganglia
486
How many cells per mm3 of peripheral blood do Erythrocytes make up?
5 million cells per mm3
487
How many cells per mm3 of peripheral blood do Leukocytes make up?
4000-11000 cells per mm3
488
What is the lifespan of an erythrocyte?
| What is the significance that they are anucleate when they are damaged?
- 100-120 days
| - They cannot repair themselves as they have no nucleus for transcription
489
How is the surface area of Eryhtrocytes increased for O2/CO2 transport?
- Biconcave disc shape increases SA
| - Cells are anucleate, which increases Hb capacity
490
What process produces Erythrocytes?
| What is the pathway of Erythrocyte production?
- Erythropoesis
| - Haematocytoblasts --> Reticulocytes --> Eryhtrocytes
491
What does increased circulating reticulocytes in the blood indicate?
Pathology e.g. Leukaemia
492
What organelle do reticulocytes have in large quantities?
| Why is this?
- Rough Endoplasmic Reticulum
| - To synthesise Hb for mature erythrocytes
493
What is erythrocyte production controlled by?
Erythropoetin
494
What process produces Leukocytes?
Leukopoesis
495
What are the 2 main categories of leukocytes?
1. Granulocytes
| 2. Agranulocytes
496
Are Neutrophils a granulocyte or agranulocyte?
How common are they?
What is the shape of their nucleus?
What is their function?
- Granulocyte
- Most common granulocyte
- Irregular nucleus shape
- Phagocytose and destroy microorganisms
497
Are Eosinophils a granulocyte or agranulocyte?
| What is their function?
- Granulocyte
| - Help to destroy parasites and modulate allergic inflammatory responses
498
Are Basophils a granulocyte or agranulocyte?
| What is their function?
- Granulocyte
| - Secrete histamine to help mediate inflammatory responses
499
Are Monocytes a granulocyte or agranulocyte?
What cells do they mature into?
What is their function?
- Agranulocyte
- Once they leave the blood they mature into Macrophages
- Phagocytose and destroy microorganisms, dead cells and damaged cells
500
Are Lymphocytes a granulocyte or agranulocyte?
What are the 2 types of Lymphocytes?
What are their functions?
- Agranulocyte
1. B Lymphocytes - produce antibodies
2. T Lymphocytes - kill virus infected cells
501
What cells do platelets originate from?
| What is the function of platelets?
- Megakaryocytes
- Platelets adhere specifically to endothelial lining of damaged blood vessels to help repair breaches and aid in blood clotting
502
What are the 3 layers in arteries and veins?
| innermost to outermost
1. Tunica Initima
2. Tunica Media
3. Tunica Adventitia
503
What is the structure of the tunica intima?
Thin, simple squamous endothelial cells
504
What is the structure of the tunica media in elastic arteries?
Large amounts of elastic tissue to allow arteries to stretch and recoil during contraction of heart
505
What is the structure of the tunica media in muscular arteries?
Large amounts of smooth muscle to allow contraction to regulate blood pressure
506
What is the structure of the tunica adventitia?
- Connective tissue with some elastic tissue
| - Vasa vasorum - blood vessels own blood supply in thick vessels
507
What is the structure of capillaries?
Single layer of Endothelial cells on basement membrane
508
What are the 2 types of capillaries?
1. Continuous
| 2. Fenestrated
509
What pathology can high pressure in elastic and proximal muscular arteries lead to?
What does this result in?
- Damage to tunica intima can lead to deposition of collagen and fatty compounds causing Atheromatous Plaques
- Can impair blood flow and result in clot formation
510
How do aneurysms form?
- If atheroma extends into tunica media, smooth muscle is replaced by non-contractile tissue
- This bulges and can eventually burst
511
What is haemostasis?
| What does this require?
- The mechanism for cessation of blood loss from damaged vessels
- Cell-cell communication
512
What are the 3 phases of haemostasis?
1. Vascular phase
2. Platelet phase
3. Coagulation phase
513
What is the 1st stage of the Vascular phase of Haemostasis?
| What does this prevent?
- Cutting of capillary leads to vascular spasm by contraction of smooth muscle to vasoconstrict the vessel
- This reduces blood flow and so reduces blood loss
514
During the vascular phase of Haemostasis what does contraction of the endothelial cells result in?
Why is this important?
- Contraction of endothelial cells exposes layer underneath basement membrane
- This exposes collagen which is important for coagulation
515
During the vascular phase of Haemostasis, what are 4 examples of factors that endothelial cells release?
What do each of these factors contribute to?
1. ADP - platelet aggregation
2. Prostacyclin - reduces spread of platelet aggregation
3. Tissue Factor - involved in extrinsic pathway of coagulation
4. Endothelins - stimulate contraction of smooth muscle
516
As well as stimulating contraction of smooth muscle in damaged vessels, what is another function of Endothelins?
They promote division of cells to repair damaged tissue in vessels
517
In smaller vessels how can endothelial adhesion help haemostasis?
- Endothelial cells can stick together to cover damaged vessels
- Can also provide attachments for platelets
518
How are platelets formed?
| How long is the life span of a platelet?
- Megakaryocytes have structures that project into marrow sinuses in the bone marrow
- These pockets of cytoplasm them pinch off to form platelets
- Life span of a platelet is 10 days
519
What is the 1st stage of the Platelet phase of haemostasis?
| What does this then promote?
- Platelet adhesion attaches platelets to site of damage
| - This then promotes platelet activation and aggregation
520
During Platelet adhesion, what do the platelets adhere to?
| What factor is important for this?
- Platelets adhere to exposed colagen in basement membrane and endothelial cells
- von Willebrand Factor is involved in adhesion and promotes activation and aggregation of platelets
521
During platelet activation, how does their shape change?
They swell and form spike extensions
522
During platelet activation, what are 6 examples of substances released by granulolysis?
What do they each do?
1. ADP - platelet aggregation
2. Serotonin - stimulates smooth muscle contraction
3. Thrombaxane A2 - stimulates smooth muscle contraction
4. Clotting factors - promote clot formation
5. Platelet derived growth factor - repair vessels
6. Ca2+ - platelet aggregation and coagulation
523
What are 3 examples of substances that stimulate platelet activation?
1. ADP
2. Thromboxane A2
3. Ca2+
524
What are 3 examples of substances that inhibit platelet activation?
1. Prostacyclin
2. Nitrous Oxide (produced by intact endothelial cells)
3. Aspirin
525
What are the 2 pathways involved in the coagulation phase of haemostasis?
What pathway do these both feed into?
1. Intrinsic Pathway
2. Extrinsic Pathway
- Common pathway
526
Which vitamin is essential for formation of clotting factors in the liver?
Vitamin K
527
Describe the extrinsic pathway of the coagulation phase of Haemostasis.
- Tissue factor is released by damaged endothelial cells
- This combines with Ca2+ and clotting factor VII
- This forms factor VII-tissue factor complex
- This activates Factor X to start the common pathway
528
Describe the intrinsic pathway of the coagulation phase of Haemostasis.
- Proenzymes are activated by clotting factor XII and Collagen
- Proenzymes combine with Ca2+ and clotting factor VIII or IX
- This forms Factor X activator complex
- This activates Factor X to start the common pathway
529
Describe the common pathway of the coagulation phase of Haemostasis.
- Factor X activates Prothrombinase
- This catalyses the conversion of Prothrombin into Thrombin
- Thrombin catalyses the conversion of Fibrinogen into Fibrin
- Fibrin fibres form the clot
530
As well as catalysing the conversion of Fibrinogen into Fibrin, what is another function of Thrombin?
It causes release of more tissue factor and clotting factors
531
Why is clot restriction important?
- It prevents the formation of a thrombus which could cause a stroke/MI
532
What are 3 substances that inhibit coagulation?
1. Thrombin stimulates anti-thrombin 3 to slow down coagulation
2. Natural anticoagulants e.g. heparin and prostacyclin
3. Thrombolytics e.g. warfarin and aspirin
533
Describe the pathway for fibrinolysis of a clot.
- Tissue plasminogen activator (t-PA) and thrombin activates Plasminogen
- Plasminogen is converted to Plasmin which digests fibrin fibres
534
What are 2 genetic abnormalities related to abnormal haemostasis?
1. Haemophilia
| 2. von Willebrands Disease
535
What are the 3 types of haemophilia?
| What clotting factors are absent in each type?
1. Haemophilia A - Factor VIII
2. Haemophilia B - Factor IX
3. Haemophilia C - Factor XI
