Cell Biology Flashcards
1
Q
What are the general properties of biological membranes?
A
- Flexible
- Self repairing
- Continuous
- Selectively permeable
2
Q
What are the role of lipids in biological membranes?
A
- Phospholipids - fatty acid tails are hydrophobic and consist of saturated or unsaturated - creates kinks in tail
- Cholesterol - poor head group, non polar hydrocarbon tail
3
Q
What are the role of proteins in biological membranes?
A
- Peripheral membrane protein - bound to lipids which insert into the membrane
- Integral membrane proteins - protein its self is in phospholipid bilayer
4
Q
What are the role of carbohydrates in biological membranes?
A
- Glycoproteins
- Glycolipids
Cell recognition
5
Q
What is the role of phospholipids in membrane structure?
A
- Provide the structure and permeability barrier of membranes
- Have important roles in cell signalling and membrane interactions
6
Q
What are integral membrane proteins?
A
- Proteins that directly insert in the membrane by a hydrophobic domain
- The transmembrane domain of proteins usually form alpha helix because there is a high conc. of hydrophobic acid
- Can also from beta barrels
7
Q
What are peripheral membrane proteins?
A
- Covalently bound lipids which insert into the membrane and associate with integral membrane proteins or directly bind lipids
- Attach to membrane via covalently bound fatty acid or phenyl group
8
Q
What are the advantages of peripheral membrane proteins?
A
Mobility at the cell surface
Rapid release into the extra cellular space
9
Q
What is the role of peripheral proteins in red blood cells?
A
Cell shape determination - cytoskeleton
10
Q
What peripheral proteins are present in red blood cells?
A
- Spectrin - forms dimers - mutation can cause certain types of haemolytic anaemia
- Actin - junctional complex with tropomyosin - Ankyrin
11
Q
What integral proteins are present in red blood cells?
A
- Glycophorin
- Band 3
- They are restrained by the cytoskeleton of red blood cells
12
Q
Where can phospholipids move?
A
Can rotate or exchange on the lateral plane but move slowly between leaflets
13
Q
Do saturated or non saturated phospholipids make the membrane more fluid?
A
Saturated as it means that the membrane is less densely packed
Cold blooded animals have more saturated phospholipids so that the membranes are fluid at lower temperatures
14
Q
What is the role of cholesterol in biological membranes?
A
- Lowers permeability - makes it less fluid in the area it is present but doesn’t affect the whole membrane
- Stops crystallisation
15
Q
Why are membranes asymmetric?
A
Proteins
- Enzymes and transport proteins take up substances from one side to the other
- Receptors are orientated so they can bind to extracellular ligands
Phospholipids
- Maintains electrochemical gradient as inner surface is negatively charged
- Can lead to different fluidity in the leaflets
- Some proteins involved in cell signalling need to interact with inner leaflets
16
Q
How is asymmetry of the membrane maintained?
A
- New phospholipids move into the membrane creating gaps which are filled by scramblase which ensures equal growth on both halves
- Flipase ensure asymmetry is maintained
17
Q
What is the function of carrier proteins?
A
- Carrier proteins undergo conformational changes to transport solute
- Carrier mediated diffusion has higher rate of transport than simple diffusion
18
Q
What are the three types of carrier mediated transport?
A
- Uniport - 1 molecule transported
- Symport - coupled transport - transport molecule and co -transported ion pass through
- Antiport - coupled transport - transport molecule and co -transported ion pass in opposite direction
19
Q
How is the blood group of an individual is determined?
A
By the structure of the oligosaccharides attached to sphingomyelin and proteins in the red blood cell membrane
20
Q
What sugars do the different blood groups have on the oligosaccharide chains?
A
O - no extra sugar
A - Has GALNAC
B - Galactose
AB - both
21
Q
What are the electrical properties of membranes?
A
- Voltage difference across cell because excess positive ions on one side and negative on the other
- Combination of membrane potential and concentration gradient gives an electrochemical gradients
- Inner surface of plasma membrane os neg and outer is pos
- Created by carriers and pumps
22
Q
How do ion channels allow transport across membranes?
A
- Form narrow hydrophobic pores through the membrane
- Specific to different ions
- Allow rapid movement of ions down conc gradient
- Regulated by binding of ions
- Often target for many toxins and medicines
23
Q
How does active transport allow transport across membranes?
A
- Coupled carriers
- ATP and light driven pumps
- Driven by Na+ gradients in mammals and by H+ gradients in bacteria
24
Q
What are the uses of liposomes?
A
- Drug delivery
- Delivery of DNA and RNA into cells
- Cosmetic industry
25
How is the cytoskeleton of RBC's purified?
- Solubise in detergent
| - proteins analysed by Gel electrophoresis
26
Why is important for phospholipids to be asymmetric?
Coagulation
- Scotts disease - lack of scramblase - stops the efficient movement of phosphatidylserine causing the inhibition of coagulation
Cell recognition and apoptosis
- Receptors on plasma membrane of macrophages recognise those on old red blood cells
- Signals phagocytosis
27
Give the structure of the nuclear envelope
- Formed from two membranes
- Membranes enclose perinuclear space
- Outer membrane is continuous with the endoplasmic reticulum
- Perinuclear space can fill with newly synthesised proteins
28
Give the structure and function of the nucleoplasm
Nuclear lamina
- Layers of filaments lying close to inner membrane of the nuclear envelope
- Polymerisation and dephospho rylation makes the lamina stronger
- Involved in regulation of genetic activity
Also contains ions, enzymes and nucleotides
29
What disease can mutations in the lamina cause?
Hutchinson - Gilford progeria syndrome which prevents cleavage and can cause premature ageing
30
Give the structure and function of the nucleolus
- Most obvious structure in the nucleus - is an organelle but is not membrane bound
- Site for processing ribosomal RNA to produce ribosomes
- Contains rRNA genes, ribosomal subunits, mRNA and tRNA
31
Give the basic structure of chromosomes
DNA wraps around histone molecules to allow effective packaging
DNA is loosely packed in non dividing cells -chromatin
In cell division packaging tightens and chromosmes become visible
32
What is the structure of the nuclear pore?
```
Consists of 50 proteins and 8 subunits
4 building blocks
- Column subunit
- Annular subunit
- Lumenal subunit
- Ring subunit
https://micro.magnet.fsu.edu/cells
/nucleus/nuclearpores.html
```
33
What is the function of the nuclear pore?
- Moving substances across the nuclear envelope
- Histone molecules pass through when new DNA is needed to be packaged
- Ribosomal subunits pass through
- weights up to 5000 are freely diffusible
- Active transport - signal can cause them to open to 26nm, signal is a peptide sequence
34
What is the basic structure of the mitochondria?
Outer membrane - encloses organelle
Inner membrane - highly folded - critsae
The inner matrix contains the enzymes responsible for energy production
35
What is the evolution of the mitochondria?
An aerobic prokaryotic cell and anaerobic pre-eukaryotic cell formed a symbiotic relationship - allowed them to survive in the environments
36
How can we track the evolution of the mitochondria?
Mitochondria have their own DNA which is passed on from the mother
- Mitochondrial DNA mutates much quicker than normal DNA so it can be tracked - out of Africa theory
37
Why do mitochondrial diseases affect so many areas?
- The area that is effete is the area with the mutant mitochondria
- They don't produce enough ATP to meet cells need
38
Name some mitochondrial disorders
```
Leber hereditary optic nerve neuropathy
- Visual loss begining in you adulthood
- Conduction problems with heart
Mitochondrial encephalomyopathy, lactic acidosis and stroke-like syndrome (MELAS)
- Cognitive impairment
- Dementia
- Strokes
```
39
What is the basic structure and function of the chloroplast?
Do not have double membrane - have thylakoids
Uses CO2 to produce O2
- ATP and NADPH produced in light reaction
- They provide energy to convert CO2 to carbohydrates
40
What is the structure of peroxisomes?
- Only have a single membrane
- Do not contain DNA or ribosomes
- Found in all eukaryotic cells
- Thought to be remnant of an organelles found in ancestors
41
What is the function of peroxisomes?
Remove hydrogen atoms from various organic compounds
RH2 + O2 --> R + H2O2
H2O2 + R'H2 --> R' + 2H2O
Used to detoxify alcohol in liver
42
What are the two phases of glycolysis?
```
Preparation phase
- consumes 2 molecules of ATP
Payoff phase
- Production of 4 ATPs
- Starts at step 7
```
43
What is required in the conversion of glucose to Glucose-6-Phosphate (reaction 1)?
Hexokinase
| ATP consumed
44
What is required in the conversion of Glucose-6-Phosphate to Fructose-6-phosphate (reaction 2)?
Phosphoglucose isomerase
It is an isomerisation reaction
Freely reversible
45
What is required in the conversion of Fructose-6-phosphate to Fructose-1,6-bisphosphate (reaction 3)?
Phosphofructokinase
| ATP consumed
46
What is required in the conversion of Fructose-1,6-bisphosphate to Glyceraldehyde-3-phosphate and dihydroxyacetone phosphate (reaction 4)?
Adolase
47
What is required in the conversion of dihydroxyacetone phosphate to Glyceraldehyde-3-phosphate (reaction 5)?
Triose phosphate isomerase
48
What is required in the conversion of Glyceraldehyde-3-phosphate to 1,3-bisphosphoglycerate (reaction 6)?
Glyceraldehyde-3-phosphate dehydrogenase
| NAD-->NADH
49
What is required in the conversion of 1,3-bisphosphoglycerate to 3-phosphoglycerate (reaction 7)?
Phosphoglycerate Kinase
| ATP formed
50
What is required in the conversion of 3-phosphoglycerate to 2-phosphoglycerate (reaction 8)?
Phosphoglycaro mutase
51
What is required in the conversion of 2-phosphoglycerate to phosphphenylpyruvate (reaction 9)?
Enolase
| Releases water
52
What is required in the conversion of phosphphenylpyruvate to pyruvate (reaction 10)?
Pyruvate Kinase
| ATP produced
53
Draw the glycolysis pathway
http://biochem.co/2010/02/glycolysis/
54
What are the end products of glycolysis?
2pyruvate, 2ATP, 2H20, 2NADH
55
What happens to pyruvate under anaerobic conditions?
Converted to lactate
Using lactate dehydrogenase
NADH to NAD
Allows glycolysis to continue with the NAD
56
Why is arsenate poisonous?
- Arsenate can substitute fro phosphate in step 6 of glycolysis producing 1-arseno,3-phosphoglycerate
- This dissociated to 3-Phosphoglycerate skipping step 7
- Means no ATP produced in that step so net production in 0 ATP molecules
57
What is Tarui disease?
Defect in muscle phosphofructokinase
- causes build up of glycogen
- Cause pain and weakness
58
What does pyruvate kinase deficiency in erythrocytes lead to?
Lack of enzyme activity
| Short half life
59
What mechanisms are involved in regulation of glycolysis?
```
Hexokinase
- Regulated by glucose-6-phosphate
Phosphofructokinase
- Inhibited by ATP
- Regulated by fructose-2,6-bisphosphate as it stimulates phosphofructokinase 1 to increase glycolysis
- Phosphofructokinase 2 increases fructose-2,6-bisphosphate
Pyruate kinase
- Inhibited by ATP and acetyl coA
- Activated by fructose-1,6-bisphosphate
```
60
What is the net link reaction?
Pyruvate + CoA + NAD+ ----> Co2 + Acetyl CoA + NADH + H+
61
What is the PDH complex?
- 20-30 copies of pyruvate dehydrogenase
- 60 copies of dihydrolipoly transaceylase
- 6 copies of dihydrolipoly dehydrogenase
Regulates the link reaction
62
How does the PDH complex regulated the link reaction?
PDH complex is activated normally and deactivated when phosphorylated
Ensures that there is not a build up of acetyl CoA
63
What stimulates and inhibits the PDH complex?
Stimulates
- NADH, ATP, Acetyl CoA, Ca2+, Mg2+
Inhibits
- Pyruvate, NAD+, CoASH, ADP
64
How does sodium fluoroacetate affect the Krebs cycle?
Bind to aconite enzyme causing citric build up and stops Krebs cycle, causes nausea and vomiting
No antidote
65
What is required in reaction 1 of the Krebs cycle?
Acetyl CoA is added to Oxaloacetate
Citrate synthase enzyme
Froms citrate
66
What is required to convert citrate to isoscitrate in the Krebs cycle (Reaction 2)?
Aconitase
67
What is required to convert isoscitrate to alpha-ketoglutarate in the Krebs cycle (Reaction 3)?
Isocitrate dehydrogenase
NAD+ ---> NADH
CO2 released
68
What is required to convert alpha-ketoglutarate to succinyl-CoA in the Krebs cycle (Reaction 4)?
Alpha-ketugluterate dehydrogenase
NAD+ ---> NADH
CoA-sh ---> Co2
69
What is required to convert succinyl-CoA to succinate in the Krebs cycle (Reaction 5)?
Succinate thiokinase
| GTP to GDP
70
What is required to convert succinate to fumerate in the Krebs cycle (Reaction 6)?
Succinate dehydrogenase
| FAD to FADH2
71
What is required to convert fumerate to L- Malte in the Krebs cycle (Reaction 7)?
Fumerase
| H20 released
72
What is required to convert L- Malte to oxalocetate in the Krebs cycle (Reaction 7)?
Malate dehydrogenase
| NAD+----> NADH
73
What are the end products of the Krebs cycle?
6NADH, 2FADH2, 2GTP, 4CO2
74
What electron carriers are involved in oxidative phosphorylation?
- NAD and FAD
- Ubiquinone
- Cytochrome C
- Iron - sulphur proteins
75
What is complex 1 in oxidative phosphorylation?
NADH dehydrogenase
76
What happens at complex 1 in oxidative phosphorylation?
- Transfers electrons from NADH to ubiquinone forming ubiquinol
- Complex 1 pumps out 4 protons into the inner membrane space
77
What is complex 2 on oxidative phosphorylation?
Succinate dehydrogenase
78
What happens at complex 2 in oxidative phosphorylation?
- Transferes 2 electrons from FADH2 to ubiquinone
| - No protons pumped across
79
What is complex 3 in oxidative phosphorylation?
Cytochrome bc1 complex
80
What happens at complex 3 in oxidative phosphorylation?
- Ubiquinone passes electron to cytochrome C (cytochrome C can only carry one electon)
- Other electron forms semi ubiquinone and then transferred to cytochrome C
- 2 protons released into inner membrane space
81
What is complex 4 in oxidative phosphorylation?
Cytochrome oxidase
82
What happens at complex 4 in oxidative phosphorylation?
Electrons pass from cytochrome C to oxygen (final acceptor) to form water
- 4 protons consumed in making H20 - amplifies proton gradient
- 4 Protons pumped into inner membrane space
83
What happens at ATP synthase complex in oxidative phosphorylation?
- Protons move through enzyme causing y subunit to rotate inside F1 unit
- This causes change in B subunit which has ADP and Pi
- Froms ATP molecules
84
What are the end products of aerobic respiration?
36 ATP molecules
10 NADH
2 FADH2
85
How is oxidative phosphorylation regulated?
ADP/ATP determine rate of electron transfer
- At rest - Hugh ATP levels - minimal proton flow through synthase, low transfer of electrons
- During exercise - ATP consumed, ADP high, increased proton movement, increase electron transfer
86
Name some molecules that inhibit oxidative phosphorylation
```
Cyanide
- Electron transport inhibitor
- Site of action of complex IV
Carbon Monoxide
- the same
Oligomycin
- Inhibits ATP synthase
- OSCP fraction of ATP synthase effected
```
87
What is Leigh syndrome?
A fatal neurodegenerative disorder, early onset
Results in bilateral lesions in the brainstem, basal ganglia, thalamus and spinal cord
Causes psychomotor retardation and brainstem dysfunction
Due to mutation in ATP synthase?
88
What are the differences in structure between DNA and RNA?
```
DNA
- Deoxyribonucleic acid
- Thymine as a base
- Double stranded
- H group instead of OH
RNA
- Ribonucleic acid (RNA)
- Thymine replaced with uracil
- Single stranded
- OH group
```
89
What is the structure of a tRNA molecule?
- Amino acid attached
- Has multiple anticodon loops
- Anticodon loop is complementary to the RNA coding for that amino acid
90
How do tRNA and mRNA interact in protein synthesis?
mRNA does not bind directly to an amino acid so it needs tRNA with the corresponding anticodon to attach amino acids
91
What is the structure of a ribosome?
```
Has three binding sites
- Aminoacyl - tRNA (A)
- Peptidyl - tRNA (P)
- Exit (E)
Has a large subunit and small subunit
```
92
What happens at a ribosome in protein synthesis?
- An incoming amino acid - tRNA binds to vacant A site
- The original AA-tRNA moves to the P site to allow new tRNA molecule to bind
- Large and small subunits undergo relative conformational change as a new peptide bond forms between amino acids
- mRNA moves 3 nucleotides through small subunit and the used tRNA moves to E and is ejected
93
How is correct base pairing ensured in tRNA ribosome part of protein synthesis?
- Amino acid - tRNA is associated with elongation factor EF-tu-GTP (a hydrolysing protein)
- Correct base pairing activates this protein allowing it to dissociate from the complex
- Incorrect base pairing then no GTPase
94
What promotes the movement of tRNA molecules to the next binding sites in a ribosome?
Elongation factor EF-G in GTP-bound form promotes movement of tRNA molecules to the next binding site
95
How is protein synthesis initiated?
- Translation begins with AUG
- Initiator tRNA carries methionine
- Initiator factor - eLF 2
- Meets 5' capped mRNA
- Ribosome subunits bind to capped mRNA
- eLF dissociate and large subunit associates
96
How is protein synthesis terminated?
- Stop codons not recognised by tRNAs
- Release factors bind to A site on ribosome with stop codon in
- Pepitdyl transferase catalyses transfer of water to C terminus - causes dissociation from ribosome
97
What immediate modifications occur to proteins after they have been synthesised?
- Removal of targeting signal sequences
- Folding e.g.. to hide hydrophobic regions
- Modifications can completely change the function of the protein (e.g. different hormones often have the same precursor
98
Name some consequences of protein misfolding
- Can lead to aggregation
- Abnormal folding can lead to plaques causing alzhiemers
- Can lead to perversion - e.g.. abnormal cellular prion proteins resist protease action - recruits normal prion proteins and proliferates and infects the organism
99
What are chaperones?
They assist on folding
100
Give some examples of chaperones
- Heat shock proteins - help HSP70' and HSP60's hide hydrophobic regions
-
101
What happens to incorrectly assembled proteins?
Destroyed
- Tagged for destruction by ubiquitin - it is attached to degradation signal e.g. exposed inner region of proteins
- Destroyed by the proteasome
102
What is the role of address sequences in targeting nascent proteins?
- Adress sequence is short sequence of amino acids
- Translocation proteins recognise the adress information
- The protein and translocator bind with proteins on the membrane of the target organelle
- tans locator protein may also act as a chaperone
103
What are the important features of protein targeting to the nucleus?
- Tagged with signal peptides
- Protein has nuclear localisation signal which interest with a nuclear import receptor
- Complex interacts with fibril
- Requires energy
- Passes through nuclear pore
104
What are the important features of protein targeting to the mitochondria?
- The double membrane is crossed by unfolded protein
| - Uses two translator proteins - one on each membrane
105
What are the important features of protein targeting to the RER?
- Proteins destined for ER, Golgi, plasma membrane and secretory vesicles must be inserted into the ER membrane first
- Contain a signal sequence that mediates their attachment to ER membrane
- The sequence causes SRP (signal recognising protein) to bind causing a pause in translation
- Ribosome attaches to SRP receptor in the ER membrane
- Translation continues
- SRP dissociates an is recycled
106
What type of proteins do not have an address sequence?
Cytoplasmic proteins
107
What proteins are responsible for recognition of the address sequence?
Translocation proteins
108
What are the functions of the smooth ER?
- Phospholipid and cholesterol synthesis
- Steroid hormone production
- Synthesis and storage of glycerides
- Synthesis and storage of glycogen
- Important role as calcium store
109
What are the functions of the Golgi apparatus?
- Modification and packaging secretions
- Renewal and modification of the plasma membrane
- Delivery of material to other organelles especially the endocytic pathway
110
What is the structure of the SER?
- Connected to the nuclear envelope
- Forms hollow tubes and flattened sacs
- Chambers are cisternae (flattened membrane disks)
- No ribosomes
- Sarcoplasmic reticulum (muscle) - depolarisation passes along plasma membrane allowing release of Ca2+
111
What is the structure of the Golgi apparatus?
- Composed of cisternae
- A typical Golgi apparatus will normally consist of 5-6 cisternae
- Lies near the nucleus
- Communicates with ER by use of vesicles
112
What are vesicles coming from the ER to Golgi coated in?
- Clathrin
- COPI
- COPII
The cost is discarded before vesicles can fuse with the target compartment
113
How does the Golgi ensure the vesicles reach the correct target?
SNARES - soluble N-ethylmaleimide - sensitive factor adaptor protein receptor
- v-SNARE (Vesicle)
- t-SNARE (target)
Used to dock correct vesicle to correct target cell
114
What are the cisternae in the Golgi?
```
Cis Golgi Network
Cis Cisternae
Medial Cisternae
Trans Cisternae
Trans Golgi Network
```
115
What are the two models for travel of vesicles through the Golgi?
Vesicular transport model
- Golgi is a static structure
- Proteins progress from one cisternae to the next by a series of vesicle transports
Cisternal maturation model
- Golgi is a dynamic structure
- Cisternae progress through the apparatus from a cis to a trans cisternae
116
How are proteins moved from the Golgi to the cell membrane?
- Membrane proteins are delivered to the cell surface by the constitutive secretory pathway in non-polarised cells
- Tubules also act as transport carriers
- Microtubule act as tracks for the tubules
117
What are the different fates of endocytose material?
Degradation
Storage
Transcytosis
118
What is the difference between phagocytosis and pinocytosis?
```
Phagocytosis
- Eating of particles
- greater than 0.5micrometers
- Into a vacuole
Pinocytosis
- Drinking of particles
- Less then 0.5micrometers
- Into a vesicle
```
119
How are red blood cells phagocytosed?
Engulfed by macrophages, the membrane extends around R.B.C - specific to one cell type
120
What is the evidence for membrane recycling?
- Macrophages phagocytosed 1.1micrometers latex beads and by counting brads you can work how much of the membrane was internalised
- 30% of membrane internalised but no change in cell size - must be internalised
121
Give the role of clatharin in endocytosis?
- Clathrin coats vesicles - major route of entry
| - Forms hexagonal structured lattices, say to purify, formed of heavy and light chains
122
How is an early endosome formed?
- Cholesterol is transported by binding with LDL's
- When the cell needs cholesterol it synthesises LDL receptor membrane proteins
- When LDL binds with receptor, it causes calthrin coat to associate with membrane
- This causes invagination - forming coated vesicle containing LDL and receptor
- Vesicle becomes uncoated and becomes fused with an early endosome
- In the endoscope, PH causes ligand and receptor to break down
- Receptor buds and moves back to membrane - recycled
- Early endosome (lysosome with hydrolytic enzymes)
123
What are the elements of the cytoskeleton?
- Microtubules
- Microfilaments
- Intermediate filaments
- Associated proteins
124
What are the roles of microtubules?
Cells shape
Movement
Divison
125
What is the structure of microtubules?
- 24nm diameter hollow tubes
- Varied length
- Proliferation within microtubule made of beta-tubulin and alpha-tubulin
126
How are microtubules assembled?
- Polymerisation occurs and then hydrolysis
The minus end addition is slow and hydrolysis catches up and plus end addition is fast and hydrolysis lags behind - dynamic instability
- They grow from centrioles (basal bodies) which anchor them down - organising centres
127
What is the structure of microfilaments?
- 5-8nm fibres
- Globular and filamentous
- 375 amino acids
- 42kD
128
What are the cell type specific actins?
- Striated muscle (alphaSK and alpha C)
- Smooth muscle (alphaSM and gammaSM)
- Non muscle (beta and gamma)
129
How are microfilaments assembled?
Actin subunits bunch in oligomers
- Lag phase - trimer nucleation
- Steady state - addition of monomer is equal to loss of monomers
- More stable and less variable than microtubules
- Rapid remodelling e.g. Actin pushes acrosome in sperm into the egg cell wall
Critical concentration. of actin in cell to make polymerisation
130
Name some acting binding proteins
- Gelsolin
- Thymosin
- Profilin
- Fimbrin
131
What is the structure of intermediate filaments?
```
10nm filaments
Most eukaryotic cells
5 subunits
- 1 and 2 epithelial keratins
- Destine in muscle
- Make neurofilaments
- Nuclear laminas
- Coiled coil structure
```
132
What is the function of intermediate filaments?
- Structural support
| - Special structures - nuclear lamina, muscle, horn
133
How are intermediate filaments assembled?
- Dimers from tetrameters, which associate with each other to form protofilaments
- Antiparallel - no polarity
- Tetrameters form tubes
134
What accessory proteins are used in microtubules?
- alpha and beta tubulin dimers
- Assembly promoting proteins - MAP2
- Motor proteins - dynein and kinesin
135
What is dynein?
A cytoskeleton motor protein that moves along microtubules and uses ATP
It transports things and is responsible for the beat of cilia and flagella
- Ciliary and cytoplasmic types
- Minus end directed
136
What is kenesin?
A cytoskeleton motor protein that binds directly organelles and uses ATP
- Cytoplasmic only
- Plus end directed
137
What is retrograde and anterograde transport?
Plus and minus end directed gives a direction to organelle movement
- Dynein and kenesin cause organelles to move in opposite directions
138
What parts of the cytoskeleton are involved in mitosis?
All contribute
- Intermediate filaments - Nuclear membrane
- Microtubules - chromosomes
- Microfilaments - cytokinesis
139
What is the role of microtubules in mitosis?
- Cytoplasmic microtubules are disassembled
| - Spindle poles extend using different types of microtubules
140
What is the role of kinetochore microtubules in mitosis?
- They attach at the centromeres and exert force on chromosomes on metaphase plate
- Moved to poles as the microtubules shorten
- Microtubules from opposite poles overlap to pull poles apart
141
What is the role of acid filaments in cytokinesis?
Contractile ring made of Actin/myosin interaction restricts the cell so much that it pinches off
142
How is actin involved in muscle contraction?
- Ca2+ is a regulator in power stroke
- Myosin binding to actin
- Actin slides over myosin bringing z discs closer together
143
Give some characteristics of the myosin family?
- Many types
- Ubiquitous
- Always have a motor domain
144
How does actin allow cel motility in non muscle cells?
- Filopodia - polymerisation of actin which pushes forward the cell
- Lemellipodia - filaments at the end polymerising forming a meshwork of filaments extending out the end
- Like it is reaching forward - adhesion to the surface
- Back contacts to move the whole cell forward
145
What sizes are the cilia and flagella?
Cilia : 2-10 x 0.5 micrometers
| Flagella: 100-200 x 0.5micromters
146
What is the major structure cilia and flagella?
The axoneme
147
What is the axoneme?
- Has 9 microtubules outside and 1 pair in the middle referred to as 9+2 assembly
- One fibre is complete and other is not - polarity
- Contains radial spokes which bind 9+2 together
- When microtubules enter cell body inner pair disappear
148
What is the structure of a basal body?
Have a similar structure to centrioles
- 9x3 array - 9 pairs of triplets
- 0.2x0.4micrometers
149
How dynein involved in producing cell movements?
Dynein causes microtubules to bend by anchoring them together, generating a force, hydrolysis of ATP
- Anchored together by basal bodies
- Inner dynein arm - closest to the centre affects wave shape
- Outer dynein arm - affects power to move
150
What are the major structures of the extra cellular matrix?
```
Fibrous proteins
- collagens
- Elastin
Adhesion proteins
- Fibronectin
- Laminin
Hydrated macromolecules
- Glycosaminoglycans (GAGs)
- Proteoglycans
```
151
What is the structure of collagen in the extracellular matrix?
- 20-40 variants
- Triple helix
- Some look long and some look like dots under an electron microscope
- 3 alpha chains
- Fibroblast family and epithelial cells
152
What can a defect in collagen lead to?
Ethlers-Danlos syndrome
- Vascular form
- Arterial rupture
153
How is collagen synthesised?
Hydroxylation of selected prolines and lysines
- Defects lead to scurvy
Glycosylation of collagen chain
Auto assemble into fibrils which aggregate into fibres
154
What is the role of elastic fibres in the ECM?
Elastin - cross links between individual monomers. It is disordered as its not being stretched. It bends normally makes it very stretchy
155
What can defects in elastic fibres lead to?
Marfans syndrome
| - Elongated limbs (FBM1 gene mutations)
156
What sugars are involved in the ECM?
```
GAGs
- Disaccharide chains
- 70-200 units long
- Good for making a hydrated structure - polar
Hyaluronic acid
- Non sulphated
- Secreted across plasma membrane
- Can be 300nm - length of a cell
Proteogylcans
- Long sugar chain - very flexible
- Structure well conserved
```
157
What are the roles of sugar in ECM?
```
Bind water and expand
Cartilage and tendon
Packing
- Empty spaces in embryogenesis
- Hyalurondase
Filter
Signal binding
- Cell surface
- Extracellular matrixing
- Small molecules such as growth factor - bind and keep by membrane-more chance of finding a receptor
Adhesion glycoproteins: Fibronectin
- Bind cells
- Binds collagen
- RGD sequence
- Laminin
- Basal laminae - allows cells to know whats in and out of the cell
- essential in axon promoting
```
158
What is the structure and function of integrins in the ECM?
Links the extracellular matrix and the cytoskeleton
- alpha and beta subunits with a matrix binding site between them
- Coils through cell membrane and actin binds to COOH end in the cytosol
159
What is an integrin related disease?
Glanzmann's thrombasthenia
- Caused by abnormal integrity receptors on platelets meaning that the extra cellular matrix cannot bind to the cytoskeleton
- Stops bloods ability to clot
160
What are the three types of junctions?
Tight junctions
Gap junctions
Adherens junctions
161
What are the roles of tight junctions?
- To prevent fluid, ion and membrane flow
- Variable extent
- Paracelullar transport - passive but selective
- Transcellular transport - diffuse into one side and endocytose out the other - active
162
Where are tight junctions found?
- Epithelia
| - Gut
163
What proteins are used in tight junctions?
- Claudin
- Occludin
- Proteins are linked to actin in the cytoskeleton
164
in tight junctions, lids are segregated, which are on what membrane?
```
Apical
- Glycolipid
- Cholesterol
Basolateral
- Phosphatidylcholine
```
165
What is the function of gap junctions?
- Close apposition of membranes- avoid travelling long distances
- Form low resistance channels/pore
- Allow regulation of transport - controls the opening and closing of pores
- Found a lot in the heart and smooth muscle
166
What is the structure of gap junctions?
- Two connections in register forming open channels; - composed of 6 subunits
- Large molecules cannot be transported
- Allow ions such as Ca2+ and amino acid, ATP and CAMP
- mRNA, proteins cannot pass through - communications only
167
How are gap junctions regulated?
- PH, Ca2+ and cell signals control channels and if they're open or closed
- Ca2+ - damage
168
Where are adherens junctions found?
- Cadherins junction e.g.. epithelial cells
| - Calcium dependant homophilic interaction
169
What is the structure of adherens junctions?
- Calcium dependant homophilic interaction
- Cadherins only attach the cadherins - between cells
- Catherine dimers attach to actin in the cytoskeleton
- Forms belt like structure in cells
170
What is are belt desomosomes? (adherens junctions)
- Actin - associated
- Contractile - if contact actin ring then invagination occurs (epithelia cells) will eventually pinch off to form an epithelial tube - essential in development processes
171
What is the difference between desmosomes and hemidesmosomes?
```
Desmosomes
- Cell-cell junctions
- Cadherins and intermediate filaments
Hemidesmosomes
- Attach cells to basal lamina
- Integrins and intermediate filaments
```
172
Give an example of a condition related to a dysfunction in cell junctions?
Pemphigus
- Autoimmune skin blistering
- Autoimmune response against cadherin which stops integrity of skin
- Doesn't bind to actin but to intermediate filaments
173
Where does fertilisation occur?
In the ampulla of the uterine tube about 12 hours after ovulation
174
How is a blastocyst formed?
Cleavage occurs a few hours after zygote implants on uterus wall
Gives 2 blastomeres
If 2 blastomeres split then twins
4-5 days after ovulation. the morula enters the uterine cavity and becomes blastocyst
175
What germ layer does the nervous system develop from?
Ectoderm
176
What germ layer does muscle and the vascular region develop from?
Mesoderm
177
What germ layer does the gut, lungs and liver develop from?
Endoderm
178
What germ layer does epithelial tissue develop from?
All of them
179
Define differentiation
Unequal but controlled change in structure resulting in a functionally different area
180
What is hyperplasia?
Increasing number of cells
181
What is hypertrophy
Increasing volume of cells
182
What are adult stem cells?
Most tissues contain cells that are both differentiated and cells waiting to differentiate
They are determined so are committed to s particular developmental pathway
183
What is the structure of skeletal muscle?
- Multinucleated (always on edge of the cell)
- Long, unbranched
- Transverse tubules - dips in membrane (sarcolema) allows contraction into depth of cell
- Sarcoplasmic reticulum (Ca2+ storage)
184
What is the function of skeletal muscle?
Voluntary contraction
185
What is the structure of smooth muscle?
- Uninucleated
- Unbranched fibres
- Unstriated
186
What is the function of smooth muscle?
Involuntary contraction
187
What is the structure of cardiac muscle?
- Branched fibres
- Intercalated discs
- Purkinjie fibres (glycogen)
- Faintly striated
188
What is the function of cardiac muscle
Heart rhythm
189
What are the properties of myosin?
- Made of two similar molecules
- Heavy chain molecular domain - globular protein
- alpha helix - strength
- Light chains
- A band
- 1.6micrometer
- 300 myosin molecules per filament
- Polarised
- 6x10^10 filaments per cm2 of muscle
- Properties - spontaneously assembles into filaments, ATPase, binds polymerised actin
190
What are the properties of actin?
- Made up of globular proteins called g.actin
- Tropomysoin spirals around actin - its over receptors which are revealed when tropomyosin unravelled. The receptors allow myosin head head to bund to actin
- I band
- 1.0micrometer long
- 8nm diameters
- 380nactin molecules per filaments
- 6x10^10 filaments
191
What are the properties of tropomyosin?
- Double alpha helix
- Every 38.5nm lies troponin complex
- Three troponin - Tn1 (binds actin) and TnT - Binds tropomyosin
- When myosin head binds to actin, ATPase breaks down ATP which causes mysoin head to bind which moves the actin slightly
192
Outline muscle contraction?
- Cytosolic calcium levels start very low and cross bridge formation is blocked by tropomyosin
- Actin potential releases Ca2+ sarcoplasmic reticulum which binds to Tnc, releasing the block and cross bridges form = contraction
- I band gets smaller and A ban stays the same
193
What are the functions of epithelial cells overall?
- Protection
- Absorption
- For secretion
- Rest o basement membrane
- Avascular
- Non innervated
- Specialised on apical, lateral ans basal surfaces
194
What is raw structure of simple squamous epithelium and where is it found?
- Single layer of flattened cells with parallel oval nucleus
- Found in alveoli, intestine
195
What is raw structure of simple cuboidal epithelium and where is it found?
- Single layer of cells, roughly square in profile with a round nucleus
- Found in kidney tubules and in ducts of glands
196
What is raw structure of simple columnar epithelium and where is it found?
- Single layer of cells taller than with oval, perpendicular nucleus
- Present in small intestine - microvilli
- Gall bladder
- Bronchus - with cilia
- Goblet cells - mucus in centres
197
What is raw structure of stratified epithelium (non-keratinised) and where is it found?
- Non-karatinsed
- Found in mouth oesophagus/ vagina - glycogen present energy source for sperm
- Bottom layer on basement membrane
198
What is raw structure of stratified epithelium (keratinised) and where is it found?
- Keratinised
- Found on outside of body as hairy or non hairy skin
- Prevention of damage - thick layers on bottom of the feet
- Keratin is much thicker in the thick sin
199
What is raw structure of stratified cuboidal epithelium and where is it found?
- Rare
| - Found in some large ducts e.g. mammarily glands
200
What is the structure of pseudo - stratified epithelia and where is it found?
- Does not fit in category as all cells rest on basement membrane - so simple but looks stratified
- Found in trachea as it stretches easily
- Found in urinary bladder - stretches and is fine proof
201
What is the role of basement membrane in epithelium?
- Vital complainant of all epithelia
- Composed of several extracellular proteins including collagen and fibronectin
- Separates epithelium from underlying connective tissue
- Essential for proper functioning and survival of the epithelium
202
What are the characteristics of glands?
- Secrete through ducts (exocrine)
- Secrete without ducts (endocrine)
- Multicellular glands can have a complex duct system
- Can secrete many things e.g.. mucus or protein (serous)
203
What do unicellular goblet cells secrete?
Secrete mucus
- Pale
- Washed out
Round nuclei
204
What do multicellular ascinus glands secrete?
```
Parotid gland serous
- Proteins
- Darker
- Flat nuclei
Mandibular gland
- Mixed
```
205
What are the characteristics of connective tissue?
- CT connects, supports and acts in around organs
- Also involved in storage, repair, transport and protection
- formed from mesoderm
- Consists of varying proportions of fibres, cells, matrix
- Can range from blood to bone
206
What are the characteristics of collagen?
- White
- Thick
- Generally unbranched
- Strength and support
- Tendons are dense and regular but dermis is dense and irregular
- Collagen is produced by fibroblasts
- 3 chains of alpha helices
- Rich in glycine and proline
- Typically 34 genes and vitamin C requires
207
What are the types of collagen?
```
Type 1
- Large branched fibres e.g.. bone tendon, skin
Type 2
- Sheets
- e.g. basement membrane
Type 3
- Short fibrils
- e.g. Anchoring fibrils in BM of skin
```
208
What are the characteristics of elastic fibres?
- Made by fibroblasts
- Contain hydrophobic protein - elastin
- Often bound with fibrilln
- Highly cross kinked allowing stretch and recoil, causing elasticity wherever they occur
- Only seen using special stains
209
What are fibroblasts?
- Round euchromatic nucleus
- Abundant cytoplasm
- Lots of RER
- e.g. Umbilical cord
210
What are fibrocytes?
- Flat heterochromatic nucleus
- Scant cytoplasm
- Little RER
- e.g. tendon
211
What are adipocytes?
- Fat cells
- Brown fat (unilocular) has many mitochondria
- White fat (multilocular) most common
- Begin as spindle shaped and mature into FAT cells
- lost of SER
- Receptors for insulin, thyroid, hormones
- Good blood and autonomic nerve supply
212
Give the characteristics of the matrix in connective tissue?
- Produced by fibroblasts
- Mainly GAGs (large, unbranched polysaccharide chains, repeating disaccharide unit
- High negative charge
- Strong hydrophilic
- Retains sodium - turgid
- Can from proteoglycans - huge molecules with large hydration spaces allowing selective diffusion e.g.. EMC gel
213
What are the types of GAGs
- Hyalalronic acid - cartilage synovial fluid
- Chondroitin sulphate - cartilage bone, blood vessels
- Heperan sulphate
- Keratan sulphate - cartilage, intervertebral discs
214
What are the role of axons and dendrites?
The axon - long and unbranched until it meets its target
| Dendrites - multiple short branches extending from the cell body
215
What are myasthenia gravis?
- Autoimmune disease when antibodies attack ACh receptors at neuromuscular junction
- Leads to muscle weakness
- eye, face pharynx and larynx are the worst affected
- Leads to trouble with eye movements and speaking
216
How much blood is present in males and females?
Males: 13.5 - 18 g/dL Hb
Females: 12-16g/dL Hb
217
How are erythrocytes formed?
Erythropoesis
| - Haematocytoblasts ---> reticulocytes (lots of RER) ---> RBC
218
What are leukocytes?
White blood cells
- Leukorytosis - increased wbc probably due to infection
- Leukopenia - decreased wbc
- Formed by leukopoesis
219
What are the two main types of leukopenia?
```
Granulocytes
- Neutrophils
- Eosinophils
- Basophils
Agranulocytes
- Lymphocytes
- Monocytes
```
220
What are sinusoids?
Blood vessels - larger than capillaries
- Little basement membrane
- Specialised vascular channels linked by endothelium
- e.g.. liver, bone
221
What factors are involved in homeostasis?
- The cessation of blood loss from damaged vessels
- Requires cell-cell communication
- Vascular phase
- Coagulation phase
- Tissue repair and clot breakdown - fibrinolysis
222
What happens in the vascular phase?
. Vasoconstriction
- Vascular muscle spasm
- 30 mins
. Endothelium cells contract which exposes basal lamina underneath to blood
. Endothelium cells contract which exposes basal lamina underneath to blood
. Endothelial cells release factors
- ADP - platelet aggregation
- Tissue factor - extrinsic pathway
- Prostacyclin - reduces the spread of platelet aggregation
. Endothelins (peptide hormones, stimulate contraction of smooth muscle, promotes divison cells)
- Endothelial adhesion increases - cell either side of tear may stick together in small capillaries
223
How are platelets formed?
Bone marrow produced
- Formed from polyploid megakaryocyte precursors
- Pocket of cytoplasm surrounded by membrane pinch off
- Anucleate platelets fragment
- 10 day life span
224
What is the platelet phase?
Starts 15 seconds after injury
| Temperature dependant >35 c
225
What happens in platelet adhesion?
Rapid
To the endothelium and basal lamina (exposed collagen)
Adhesion leads to activation of platelets
Adhesion leads to aggregation of platelets
Involves von Willebrand factor, this promotes platelet aggregation and activation
226
What happens in platelet activation?
```
Shape change
Swelling and spike extension
Granulolysis releases ADP (aggregation)
Serotonin (spasm)
Thromboxane A2 (spasm)
Clotting Factors (e.g. PF3)
Platelet derived growth factor (vessel repair)
Ca2+ (aggregation & clotting)
```
227
What happens in platelet aggregation?
Stimulated by soluble factors ADP, thromboxane A2, Ca2+
positive feedback
Inhibited by Prostacyclin and NO from intact endothelium
Variety other compounds
Aspirin
228
What happens in coagulation phase?
T +30 sec
Cascade of enzyme reactions
- Recurring principle
Intrinsic pathway
- Collagen triggered activation proenzymes
Extrinsic pathway
- Starts tissue factor (factor III) damaged tissue
Vitamin K essential for the production of clotting factors in the liver
229
How are blood clots restricted?
```
Prevention of thrombus formation
Thrombin inhibition – anti-thrombin III
Natural anticoagulants
-Heparin, thrombomodulin, prostacyclin
-Thombolytics
aspirin, warfarin,
```
230
Name some genetic abnormalities related to abnormal heamostasis?
```
Haemophillia
- An x linked disease
- Royal disease
Deep vein thrombosis
- Clotting factor accumulation
- Liver function
- (hepatitis, Vitamin K deficiency)
```
231
What is a receptor?
Receptors are macromolecular protein complexes that serve as recognition sites for neurotransmitter and hormones
232
Give an example of signalling molecules?
- NO and CO (diffuse from endothelial cells where they bind directly to the target enzyme
- Amino acids - glutamate, glycine
- small peptides
- Proteins - insulin and glucagon
- Steriods - testosterone
233
What is contact-dependant signalling?
- Ligand is not secreted as both ligand and receptors are membrane proteins
- Used in communication in neighbouring cells or extracellular matrix
234
What is autocrine signalling?
- Very short distance - a cell signals to self or identical neighbouring cells
- Signalling cell secretes a ligand which binds to own receptors - reinforces
- Cancer cells use this to stimulate proliferation
235
What is paracrine signalling?
- Short distance - signals to neighbouring cells
| - Signalling molecule doesn't diffuse far or its destroyed by ECM
236
What is endocrine signalling?
- Long distance - cels signal for distributed in body
| - Signalling molecule are secreted into bloodstream e.g.. hormone
237
What is synaptic signalling?
- Used by neurones to communicate with neurones or other cell types
- Ligand is called neurotransmitter
- Long or short distance, axons can be 1mm to 1m
- Neurotransmitter moves through synaptic cleft
238
What are the steps in the intracellular signalling cascades?
```
Relay proteins
- Pass the massage
Adapter proteins
- Link signalling proteins
- Do not participate
Bifurcation proteins
- Take the message to another signalling pathway
Transducer proteins
- Converts the signal to another form
Integrator proteins
- Integrates signals from different signalling pathways before relaying a signal
Latemt gene regulatory proteins
- Migrate to nucleus when activated
```
239
What is the function of signalling cascade?
- The steps give opputunit for signal modulation
- Amplifies signal strength
- Integrate signalling pathways
- Postive feedback loop amplifies
- Negative feedback loop terminates
240
Give the properties of intracellular receptors
- Ligand gated gene regulatory proteins
- In absence of ligand, receptor is bound to an inhibitory protein
- dissociates when ligand binds
- Binding of Ligand target gene expression
241
Give the properties if ion channel linked receptors
```
Gated by
- Intra/extracellular ligands
- Change in membrane voltage
- Mechanical stretch
Channels are normally closed, ligand binding opens the channel pore ions pass through
Involved in synaptic signalling
```
242
Give the properties of G-protein linked proteins (GPCR)
- Single polypeptide chain
- 7 transmembrane domains
- No ion pore or enzymatic activity
- Most common type
- Involved in regulation of sleep, blood pressure, mood, food, pain, immune response, caner growth
- Most drugs target GPCRs
- Ligand binding --> conformational change
- Starts cascade
- Cause alpha subunit to dissociate
- GTP ---> GDP leads to inactivation of alpha subunit
243
Name some types of G-proteins
Gs - Stimulates adenylyll cyclase and guanylyl
G1 - Inhibits adenylyll cyclase and guanylyl
Gq - Stimulates phospholipase
244
What is the role of cyclic AMP in signalling cascade?
- cAMP is rapidly destroyed by cAMP phosphodiesterase
- Activates protein kinase A (PKA)
- PKA can mediate a change quickly
245
What is the role of phospholipase C-B in signalling cascades?
- G proteins with Gq alpha subunits activates phospholipase c-B
- Phosphorylation;ipase hydrolyses phophatidylinsitol 4, 5 bisphosphate
- PIP2 is hydrolysed to DAG and IP3
- IP3 diffuses to ER, releases Ca2+ stored in ER to cytosol, Ca2+ triggers signals
- DAG activates protein kinase C, Ca2+ causes protein kinase C tp eve to plasma membrane
- PKC is activated which targets proteins
246
What is the role of enzyme -linked receptors in signalling cascades?
- Single polypeptide chain
- Ligand causes dimerisation of receptor
- Leads to activation of enzymatic activity
247
What is the difference between kinase and phosphatases?
Kinase
- Transfers phosphate group from ATP
Phosphatase
- Enzyme that removes phosphatase group
