Week 7 Flashcards
1
Q
What is the endomembrane system in eukaryotes composed of?
A
Nuclear membrane, endoplasmic reticulum (RE, SE), golgi and lysosomes
2
Q
What is the SER? (smooth endoplasmic reticulum)
A
Most cell types have relatively little smooth ER (SER)
Phospholipid, fat and steroid (including sex hormones) manufacturer
Carbohydrate metabolism
In hepatocytes, breaks down stored glycogen to release glucose
Detoxifies lipid-soluble drugs such as barbiturates
(Adds charged water-soluble groups such as sulphate or glycuronic acid)
3
Q
What is a specialised form of the SER? What does it do?
A
Sarcoplasmic Reticulum (Found in muscle cells)
- Network of tubular sacs
- Transmits electrical signals
- Sequesters calcium ions from the cytosol
- The level of intercellular calcium regulates muscle contraction in muscle cells.
4
Q
What do muscles consist of?
A
Myofibrils, surrounded by sarcoplasmic reticulum.
5
Q
What are myofibrils made up of?
A
Repetitive arrangement of filaments called sarcomere. (The region where myosin and actin filaments overlap)
6
Q
In summary, How do muscle contractions occur?
A
Muscle cells receive action potentials from the neuromuscular junction through T tubules in the sarcoplasmic reticulum.
The sarcoplasmic reticulum releases calcium ions.
Calcium ions bind to troponin causing a conformational change in tropomyosin.
Myosin and actin can now interact which results in muscle contraction.
7
Q
What is myosin vs actin?
A
Myosin = thick filaments
Actin = Thin filaments
8
Q
Briefly What is the sliding-filament model
A
Actin and myosin slide over each other during muscle contraction, as a result of an influx of Ca ions.
H line - shortens during contraction, only myosin
A line - region containing length of a single myosin filament
I like - contains length of single actin
Z line - Sarcomere boundary and junction of actin and myosin filaments
9
Q
What are the 4 classes of protein synthesis? Where does it begin?
A
Secreted, glycosylated, lysosomal enzymes, membrane bound proteins.
Begins in the cytosol
10
Q
What proteins attach to the RER during protein synthesis?
A
Only ribosomes synthesising proteins with a specific signal peptide sequence.
The N-terminus of these proteins contains a signal peptide usually 20-30 amino acids long
11
Q
What is glycosylation (in the RER)?
A
The addition of sugars or oligosaccharides
12
Q
Glycosylation in the RER?
A
An oligosaccharide added in the RER. Composed of N-acetylglucosamine, mannose and glucose residues containing a total of 14 sugar residues transferred to the proteins in the RER
13
Q
What is glycosylation (in the golgi)?
A
The principle modification, which occurs to the proteins as they pass through the golgi
14
Q
Glycosylation of proteins in the golgi is essential, why?
A
Essential to their function,
for example in the case of mucin produced these are glycoproteins with long highly oligosaccharide chains which are essential to produce a highly hydrated gel like material
15
Q
What are lysosomes?
A
Vesicular structures that contain hydrolytic enzymes.
When a lysosome fuses with a target, H+ pumped into secondary lysosome to bring down pH, activate enzymes
Carry out autophagy (recycling of organelles), phagocytosis, and apoptosis (cell-suicide)
16
Q
Where do primary lysosomes originate?
A
The trans face of the golgi
17
Q
What causes a lysosomal storage disease?
A
Partially degraded insoluble metabolites accumulate within lysosomes if a particular lysosomal enzymes is defective.
Resulting material results in enlarged lysosomes that compromise cell function in over 50 different lysosomal storage diseases.
18
Q
Example of a lysosomal storage disease?
A
Tay-Sachs disease
Haxosaminidase A enzyme deficiency results in the accumulation of lipid ganglioside.
Symptoms due to accumulation of ganglioside in nerve cells. Death usually occurs by 2-3 years old
19
Q
Briefly outline skeletal muscle contraction
A
Electrical impulse crosses sarcoplasmic reticulum, resulting in Ca released. They bind to troponin causing change in tropomyosin, which exposes the actin-myosin binding site so its available for myosin to bind to.
ATP hydrolysed into ADP and Pi, allowing for the myosin head to cock and change shape, causing the filaments to slide over one another. Causes a power stroke as the actin filament releases energy, therefore myosin head recocks to original shape causing muscle contraction
20
Q
What is exocytosis?
A
Material exported out of a cell.
(important in the secretion of numerous proteins including hormones, and extracellular structural proteins such as collagen and fluids such as mucus. )
21
Q
How does exocytosis occur?
A
Involves fusion of vesicles from the interior of the cell with the plasma membrane. The vesicles contents are then expelled into the surrounding medium.
22
Q
What are the different types of endocytosis?
A
- Phagocytosis
- Pinocytosis
- Receptor-medicated endocytosis
23
Q
Briefly what is phagocytosis?(endocytosis)
A
Uptake of insoluble material in protozoa, also a form of feeding
also occurs in macrophages as defence
24
Q
Briefly outline pinocytosis (endocytosis)
A
Cells pinch their plasma membrane to take up extracellular fluid in small vesicles.
Non-specific.
25
Briefly What is receptor-mediated endocytosis?
Binding of macromolecules to specific cell surface receptors which triggers endocytosis.
26
How does SARS CoV-2 enter cells?
Via receptor-mediated endocytosis
27
Outline receptor-mediated endocytosis (the process)?
The macromolecules (such as transferrin which transports iron from the blood into cells) become concentrated in endocytic pits
The endocytic pits are coated with a bristle-like protein called clathrin
Clathrin polymerises around the vesicle forming a cage like structure
28
How does the signal recognition particle (SRP) stop and start protein translation in the RER?
A signal recognition particle (SRP) attaches to the signal peptide and stops translation in the cytosol.
The SRP docks to a SRP receptor on the ER membrane and translation starts again.
29
After the SRP restarts protein translation in the RER, what happens?
Hydrophobic signal peptide passes through the membrane and loops back through the membrane and is cleaved off. The rest of the peptide passes through the membrane and into the ER lumen
The signal sequence is cleaved off with the enzyme signal peptidase.
30
What are ribosomes (protein synthesis)?
Cell machinery for joining together amino acids which travel along the length of the mRNA during translation
31
What are polyribosomes (protein translation)?
An mRNA molecule is generally translated simultaneously by several ribosomes in clusters, these are known as polyribosomes
32
What is the role of the golgi in protein synthesis?
Proteins move from the RER to the golgi by small transport vesicles where they are modified and sorted.
It also mediates the flow of proteins from the RER to various destinations within the endomembrane system.
33
What is the default pathway after protein synthesis has occurred in the RER?
Through the golgi and then to the plasma membrane for secretion.
However some proteins are tagged in the golgi for specific destinations within the cell eg lysosomal enzymes
34
Give an example of where a protein doesn't follow the typical pathway after being synthesised in the RER?
Mannose residues of lysosome enzyme proteins are phosphorylated in the cis golgi.
A mannose 6-phosphate receptor then binds these proteins in the trans golgi reticulum and directs their transfer to lysosomes
35
Who discovered autophagy?
Japanese biologist Yoshinori Ohsumi discovered the process by which a cell breaks down and recycles content.
He won the noble prize medicine award in 2016
36
Outline the signal mechanism for targeting proteins to the ER?
- mRNA leaves nucleus by nuclear pores,
- enters cytoplasm where ribosomes attach, synthesise peptide/protein
- If peptide has signal peptide, the peptide binds to a signal recognition particle (SRP) and this stops translation.
- mRNA and ribosome attached sent to translocation complex on surface of the endoplasmic reticulum and dock.
- Ribosome eventually detaches from the mRNA which releases the SRP into the cytosol ready for the next sequence.
- The rest of the synthesis for this protein occurs within the endoplasmic reticulum.
37
Give the typical pathway the protein that takes after being synthesised in the RER?
Produced in Rough ER, delivered to the cis golgi, comes out of trans golgi, packages into vesicles which take them for exocytosis and release the protein M6P out of the cell
38
What pathway does the protein take after being synthesised if it contains the mannose 6-phosphate (M6P)?
- Mannose residue attaches to the oligosaccharide during translation and the protein is phosphorylated.
- This is recognised by M6P receptor and is targeted as a lysosomal phosphorylated enzyme, therefore coated by clathrin.
- transported through the cytoplasm by a series of endosomes (specialised vesicles) where it ends up in the lysosome.
39
When is M6P receptor disassociated from the protein as it's transported to the lysosome by endosomes?
A change in pH occurs during the transfer of the protein to endosomes where the M6P receptor disassociates from the protein so it can be recycled and used again.
40
Example of glycosylation in the golgi producing mucus?
Some proteins require a lot of sugar for example in the goblet cells that produce mucus, the glycoprotein musin is a sugar-heavy compound. Makes mucus have a unique viscous characteristic so it can complete its function: trapping cell debris and pathogens so ciliated cells can flush it away.
However, can cause the genetic disease Cystic Fibrosis if mucus is produced in too large amounts.
41
What is Histoclear?
A purified, stabilised product (C10H16, d-limonene) from oranges that is a safer alternative to xylene for clearing histological sections
42
What is the difference between a ciliated cell and a cell that has microvilli?
Ciliated cells are found in the respiratory tract and are single columnar epithelial cells with hair like projections which function to remove mucus. Microvilli are finger like projections that are found in the gastrointestinal tract and are on the surface of epithelial cells to increase surface area for absorption.
43
What is regular connective tissue and irregular connective tissue?
Dense irregular connective tissue generates a network mesh of fibers often found in joints and is impact resistant. Dense regular connective tissue is where the fibers are closely packed and arranged in a parallel fashion. This is often found in ligaments and tendons.
Loose connective tissue connect tissues together to form organs.
44
What is Endothelium?
Endothelium (endo - internal) include vessels. Epithelium (epi - outer) are boundary cells between the environment and our body including skin.
45
What is the endosymbiotic theory of mitochondrial origin?
Derive from a common ancestral organelle that originated from the integration of an endosymbiotic alphaproteobacterium into a host cell.
Transition entailed a massive number of evolutionary changes including origin of hundreds of new genes and a protein import system, insertion of membrane transporters, etc.
46
Evidence for endosymbiotic theory of mitochondrial origin?
- Double membrane
- Retain own genome
- Replicate somewhat independently
47
Where are mitochondria found within the cell?
Change their position inside the cell and are moved by microtubules of cytoskeleton
Often found in regions of high ATP consumption eg in myofibrils of muscle cells
48
What does the inner membrane of the mitochondria form?
Cristae
49
What are the two compartments in the mitochondria?
Matrix inside the inner membrane and the inter-membrane space between inner and outer membrane
50
What is the mitochondrion's protein component?
Porin
(large aqueous channels)
51
What are the three major types of membrane complexes/processes in the mitochondria?
Electron transport chain
ATP synthase
Specific transporters of metabolites which vary according to cell/tissue type
52
Characteristics of the cristae (mitochondria)
increase membrane surface area
energy transducing membrane
impermeable to most small ions
53
What does the matrix of the mitochondria contain?
enzymes which catalyse Krebs cycle and fatty acid oxidation
ribosomes
mitochondrial DNA
54
Outline the process of mitochondrial respiration
During glycolysis, each glucose molecule is broken down into two molecules of the compound pyruvate. In eukaryotic cells, as shown here, the pyruvate enters the mitochondrion. There it is oxidized to acetyl CoA, which is further oxidized to CO2 in the citric acid cycle. NADH and a similar electron carrier, a coenzyme called FADH2, transfer electrons derived from glucose to electron transport chains, which are built into the inner mitochondrial membrane. During oxidative phosphorylation, electron transport chains convert the chemical energy to a form used for ATP synthesis in the process called chemiosmosis
55
Why is cyanide one of the most dangerous, fast acting poisons? (mitochondrial poisons)
Prevents passage of electrons from one of the cytochromes therefore blocking the electron transport chain.
56
Why is 2,4-Dinitrophenol (DNA) a dangerous poison? (mitochondrial poison)
makes the inner membrane leaky to H+ so that a gradient cannot be established
electron transport chain still works but energy is released as heat so the person is "cooked inside out"
57
Give an example of a mitochondrial disease?
MERRF (Myoclonic epilepsy and ragged-red fibre disease)
58
What is MERRF (Myoclonic epilepsy and ragged-red fibre disease)?
- Mitochondrial genetic disease
- Mutation in mitochondrially encoded tRNA Lys gene
- Abnormal mitochondrial morphology
- No cure
59
What does MERRF primarily affect, causing what??
A multisystem disease affecting muscles and nerves - causing epilepsy and general muscle weakness
60
What are the components of a chloroplast?
Outer membrane,
Inner membrane,
Stroma,
Grana (stack of thylakoid membrane)
61
What are the two stages of photosynthesis?
Light dependent reactions and Calvin cycle (light independent)
62
Where does the light dependent reaction take place?
Thylakoid membrane
63
Where does the calvin cycle take place?
Stroma
64
Briefly outline the light reaction (photosynthesis)?
The light reaction converts solar energy to chemical energy
Light energy absorbed by chlorophyll in the thylakoid membranes is used to transfer electrons and hydrogen to the electron carrier NADP+ so that it becomes NADPH.
Water is split during this process and oxygen given off as a by product.
ATP is also generated from ADP and inorganic phosphate
The thylakoid membranes of the chloroplast are the site of the light reactions
65
What wavelengths work best for photosynthesis?
Red and blue light wavelengths work best for photosynthesis
66
What is the porphyrin ring in Chlorophyll a and b?
Light-absorbing "head" of the molecule
67
What are the two separate photosystems in the light reaction?
Photosystem II absorbs light energy, best at 680nm, reaction centre is P680
Photosystem I absorbs light energy best at 700nm, so reaction centre is P700
68
Briefly outline the calvin cycle?
takes place in the stroma. Carbon enters the cycle in the form of carbon dioxide and leaves in the form of sugar.
The cycle requires ATP as an energy source and consumes NADPH as a source of high energy electrons.
Generates hexose phosphates for starch (storage), cellulose (cell walls) and sucrose (translocation), lipids (membranes) and amino acids (protein synthesis)
69
At least three steps in the light reactions contribute to the H+ gradient by increasing H+ concentration in the thylakoid space. What is step one?
Water is split by photosystem II on the side of the membrane facing the thylakoid space;
70
At least three steps in the light reactions contribute to the H+ gradient by increasing H+ concentration in the thylakoid space. What is step two?
As plastoquinone (Pq) transfers electrons to the cytochrome complex, four protons are translocated across the membrane into the thylakoid space;
71
At least three steps in the light reactions contribute to the H+ gradient by increasing H+ concentration in the thylakoid space. What is step three?
a hydrogen ion is removed from the stroma when it is taken up by NADP+
72
What powers ATP synthase in the light reaction and chemiosmosis during photosynthesis?
The diffusion of H+ from the thylakoid space back to the stroma (along the H+ concentration gradient) powers the ATP synthase
73
What molecules produced in the light dependent reaction duel the calvin cycle?
NADPH and ATP
74
How is light energy absorbed by the chlorophyll for photosynthesis?
(Pigments absorb light energy as photons, an electron is elevated to an orbital of higher energy)
Generally when pigments absorb light, electrons quickly drop down to their original energy losing their excess energy as head. In the thylakoid membrane a primary electron acceptor traps a high-energy electron that has absorbed the photon before it can drop back down
75
What are the different pigments in the thylakoid membrane?
(how light energy absorbed by chlorophyll)
Chlorophyll a, chlorophyll b and carotenoids.
Only chlorophyll a can participate directly in the light reaction but other pigments absorb light energy at different wavelengths and transfer it to chlorophyll a.
76
What pair of localised chlorophyll pigment can donate their excited electron the the primary electron acceptor?
(how is light energy absorbed by chlorophyll)
Chlorophyll A can only donate their excited electrons to the primary electron acceptor. This is known as the reaction centre.
The other pigments function as light-gathering antennae, collecting energy from the photons and pass it inwards to the reaction centre.
(Reaction centre and the primary electron acceptor are together termed a Photosystem)
77
How do photosystems absorb photons?
They have antennae pigment molecules which absorb photons. Energy transferred between pigments to the central pair chlorophyll. Electrons elevated to higher energy state and taken by primary electron acceptor
78
Photosystem I and Photosystem II co-operate together to produce what?
A non-cyclic electron flow to generate NADH, ATP and to split water
Light excited electrons from P700 which pass to the electron acceptor, but are then passed to NADP+ to produce NADPH
P700 is now in an oxidised state
79
What wavelength is most efficient?
Red and blue are more efficient than green
80
Non-cyclic electron flow, what happens in photosystem II?
P680 also becomes excited and donates an electron to its primary acceptor. The electron passes down an ETC until its accepted by the oxidised P700. Energy generated by this is used to pump H+ out of the thylakoid membrane and generate a H gradient, used to ATP synthase to produce ATP
P680 is now an oxidised state and P680 gets its electrons from a water molecule, therefore splitting it and generating O2
81
First step of non-cyclic electron flow, using PSI and PSII?
PSII splits water
Electrons replace those lost by P680
Generates O2 and H+
82
Second step of non-cyclic electron flow, using PSI and PSII?
Favourable movement of electrons down electron transport chain
via plastoquinone and plastocyanin
Energy derived generates ATP
83
Second step of non-cyclic electron flow, using PSI and PSII?
No splitting of water by PSI
Electrons originally from water replace those lost at P700
Linear movement of electrons
84
Third step of non-cyclic electron flow, using PSI and PSII?
NADPH is electron carrier required for Calvin Cycle, passes through electron transporter ferrodoxin
85
What photosystem is used during cyclic electron flow (photosynthesis)?
PSI can operate alone to produce ATP.
Electrons are passed from the primary electron acceptor through a chai, including ferredoxin, the cytochromes and plastocyanin. Then the electron is passed back to P700
86
At each step of the cyclic electron flow, the electron looses energy to do what?
Energy lost is used to pump hydrogen ions across the thylakoid membrane. Generating a H gradient across the membrane, used to drive ATP synthase which generates ATP.
87
What does the cyclic electron flow use?
A single photosystem to make ATP and doesn't produce NADPH or oxygen
88
How is ATP produced during non-cyclic electron flow?
H+ gradient established across thylakoid membrane as water is split in thylakoid space and due to electron transport chain activity
ATP synthase uses H+ gradient to generate ATP
89
Summary of Cyclic electron flow?
Electrons can be passed to Ferredoxin --> cytochrome complex of electron transport chain
Replace those lost by P700
No water splitting and no NADPH is generated
90
What is phase one of the calvin cycle?
Carbon fixation:
RuBP combines with CO2 catalysed by rubisco to form 3-Phosphoglycerate
91
What is phase 2 calvin cycle?
3-phosphoglycerate is reduced by 6ATP forming 1,3-bisphosphoglycerate.
Reduced again 6NADP+ to form 3 carbon compound glyceraldehyde-3-phosphate (G3P).
1 G3P is used to form 1 hexose sugar (glucose and other organic compounds
92
What is phase 3 of calvin cycle?
Regeneration of CO2 acceptor (RuBP)
Remaining 5 G3P are regenerated by 3ATP to form Ribulose bisphosphate which can be use again in phase 1
93
How many rounds of calvin cycle must occur to produce 1 hexose sugar
6 cycles of the cycle must occur to form 1 glucose molecule
94
Chemiosmosis in chloroplasts and mitochondria?
Both use same basic mechanism to generate ATP.
an ETC located in a membrane pumps H+ across membrane. Energy for this generated by passing e- through a series of progressively more electronegative carriers
Membrane contains an ATP synthase complex that uses gradient of H+ for phosphorylation of ADP to ATP
Some e- carriers are very similar in mitochondria ad chloroplasts including quinones and cytochromes
95
Differences in mitochondria and chloroplast chemiosmosis?
Mito: ETC pumps H+ out of matrix.
Chloro: ETC pumps H+ into the thylakoid compartment
Mito: High energy e- fed into ETC come from oxidisation of food molecules
Chloro: High energy e- are generated in photosystems by absorption of photons
96
Describe methane combustion as an energy-yielding redox reaction?
Mitochondria are able to use high energy electrons derived from organic molecules
Electrons in C-H bonds are higher energy than those in C-O or H-O bonds
The reaction releases energy to the surroundings because the electrons lose potential energy when they end up being shared unequally, spending more time near electronegative atoms such as oxygen
97
What is the equation for oxidisation and reduction of methane, as an energy yielding redox reaction
CH4 + 2O2 --> CO2 + ATP + 2H2O
CH4 to CO2 is oxidisation.
2O2 to 2HO2 is reduction.
98
NAD as an electron carrier in respiration?
- NAD+ accepts high energy electrons from organic molecules
- Donates them to the electron transport chain
- Cannot be transported into/out of the mitochondria directly so much be regenerated
99
Where does glycolysis take place in the mitochondria?
Within the cytosol and only releases a small amount of energy stores in glucose (by substrate level phosphorylation), most of the energy remains in two molecules of pyruvate
100
Where does the Krebs Cycle take place in respiration?
Pyruvate then enters the mitochondria and the Krebs cycle occurs in the matrix.
101
Where does the ETC take place in respiration?
Electron carriers NAD and FAD collect electrons from the Krebs cycle and transfer them to the ETC. This is located on the inner membrane of the mitochondria.
The ETC pumps H+ across the inner membrane to generate an ion gradient. This is used by ATP synthase to generate ATP
102
What does glycolysis use to generate ATP?
Substrate level phosphorylation
(Substrate with ‘’high energy’’ phosphate bond
Transferred directly to ADP to generate ATP)
103
Why does glycolysis yield limited ATP?
Breakdown of glucose (6C) to generate pyruvate (2x 3C)
ATP produced by two steps but also used up at two steps
High energy electrons passed onto electron carrier NAD+ to generate NADH
104
What is the first step of glycolysis?
Hexokinase transfers a phosphate group from ATP to glucose, making it more chemically reactive. The charge on the phosphate also traps the sugar in the cell. Glucose 6- phosphate is converted to fructose 6-phosphate.
105
What is the second step of glycolysis?
Phosphofructokinase transfers a phosphate group from ATP to the opposite end of the sugar, investing a second molecule of ATP.
106
What is the third step of glycolysis?
Aldolase cleaves the sugar molecule into two different three-carbon sugars. Conversion between DHAP (dihydroxyacetone phosphate) and G3P: This reaction never reaches equilibrium; G3P is used in the next step as fast as it forms
107
What is the fourth step of glycolysis?
Two sequential reactions: (1) The sugar is oxidized by the transfer of electrons to NAD+, forming NADH. (2) Using energy from this exergonic redox reaction, a phosphate group is attached to the oxidized substrate, making a high-energy product.
108
What is the fifth step of glycolysis?
The phosphate group is transferred to ADP (substrate-level phosphorylation) in an exergonic reaction. The carbonyl group of G3P has been oxidized to the carboxyl group (—COO–) of an organic acid (3-phosphoglycerate). This enzyme relocates the remaining phosphate group.
109
What is the sixth step of glycolysis?
Enolase causes a double bond to form in the substrate by extracting a water molecule, yielding phosphoenolpyruvate (PEP), a compound with a very high potential energy. The phosphate group is transferred from PEP to ADP (a second example of substrate-level phosphorylation), forming pyruvate.
110
How is pyruvate transported into the mitochondrial matrix?
Pyruvate is a charged molecule, so enters mitochondrion via active transport, with the help of a transport protein.
Pyruvate dehydrogenase complex catalyses decarboxylation, oxidisation of NAD and association of CoA with Pyruvate forming Acetyl CoA. The acetyl group of acetyl CoA will enter the citric acid cycle
111
Briefly outline the links reaction?
Pyruvate (3C) is converted to acetyl CoA (2C) with the loss of carbon dioxide (1C)
112
What does the Krebs cycle use to generate ATP?
Substrate level phosphorylation
113
What is the krebs cycle also known as?
Citric acid cycle or Tricarboxylic acid (TCA) cycle
114
Give an overview of the krebs cycle?
High energy electrons from acetyl group (2C) passed onto electron carriers NAD+ or FAD
FAD accepts electrons of slightly lower energy than NAD+
Only a small amount of ATP is produced
115
Briefly outline ETC in respiration?
High energy electrons passed into electron transport chain
Stepwise extraction of energy from high energy electrons
Each component of the chain is slightly more electronegative than the previous
Passed onto oxygen to generate H2O
FADH2 passes on electrons at slightly lower stage than NADH
No ATP is made directly
Energy used to produce a H+ gradient across the inner mitochondrial membrane
116
What does the ETC in respiration consist of?
Consists of a collection of multiprotein complexes embedded in the inner membrane of the mitochondria. Most components are attached to prosthetic groups (non-protein components essential for catalytic functions)
117
How does the ETC generate energy?
Via redox reactions, which occur when there is a transfer of one or more e- from one reactant to another. The reactant which loses an electron is oxidised while the reactant receiving the electron is reduced. This process associated with energy release
118
How does the ETC become reduced?
Each member of the ETC becomes reduced when it accepts an electron. It passes on the e- to its downhill neighbour (always has slightly higher affinity for the electron) and so returns to an oxidised state
119
What is the first molecule an electron is passed to in the ETC?
Flavoprotein.
So called as its prosthetic group is flavin mononucleotide
120
After passing to flavoprotein e- carrier, where does it go?
Onto an iron-sulphur protein and then to ubiquinone and then to a seies of electron carriers called cytochromes. Cytochromes have four organic rings surrounding an iron atom, however it cannot carry oxygen.
121
Where does the last cytochrome in the ETC pass the e- to?
Onto oxygen, which picks up a pair of H+ to form water.
122
What is FADH2 role in the ETC?
Transfers e- into the ETC but adds its electrons at a lower energy than that of NADH. It adds its e- directly to ubiquinone.
At the bottom of the chain O2 is very electronegative.
123
What is the overall energy drop from NADH to oxygen in the electron transport chain?
53kcal/mol, but this is broken up into many small steps by the ETC
124
Describe the process of chemiosmosis in respiration?
Inner membrane of mitochondria has many copies of ATP synthase. This enzyme makes ATP from ADP and Pi and uses a H+ gradient as its energy source.
125
What is ATP synthase?
A large multiprotein complex which can be seen under the electron microscope in the inner membrane of the mitochondria, and has a large mushroom-like appearance
126
During chemiosmosis, where does the H+ gradient that drives ATP synthesis exist?
What maintains this gradient?
Between the opposite sides of the inner membrane.
It is the ETC that generates and maintains this gradient. ETC uses energy from exergenic flow of e- to pmp H+ from mitochondrial matrix to intermembrane space. H+ pass back through ATP synthase and the exothermic process is used to attach inorganic phosphate to ADP, producing ATP.
127
What couples the electron transport chain?
Chemiosmosis to ATP synthesis.
128
What does the ATP synthase protein complex function as?
A mill powered by the flow of H+.
Multiple ATP synthase reside in mitochondrial and chloroplast membranes, each part of the complex consists of a number of polypeptide subunits. ATP synthase is the smallest molecular rotary motor known.
129
How does ATP synthase work?
Fo portion is a H+ channel
F1 head is site of ATP synthesis
Movement of H+ through Fo:
causes rotation of the rotor and central stalk, while the stator keeps the enzymatic F1 stationary
forces sequential conformational changes in the central stalk and F1
provides the energy for ATP synthesis
10H+ moving back into matrix generates ~3 ATP molecules
130
What is mitochondria brown fat?
Brown fat is a specialised type of adipose tissue. Found in large amounts in neonates.
131
What is the function of mitochondria in brown fat?
To produce heat.
Thermogenin is a H+ channel in inner membrane in brown fat mitochondria. H+ leak back without passing through ATP synthase --> now ATP produced.
Energy produced by the electron transport chain is released as heat.
132
What does MERRF stand for?
Myoclonic epilepsy and ragged-red fibre disease
133
Mitochondrial defects have been implicated in a wide variety of degenerative diseases, why is treatment limited?
- New and emerging area of medicine
- Mitochondria inherited only from the mother
- Ethical issues
134
What has been developed to reduce mitochondrial diseases being inherited?
A new IVF technique has been developed which avoids passing on defective mitochondria --> the embryo has 3 genetic parents.
However, there are ethical issues with this treatment.
135
What is the z-line in muscles
Sarcomere boundary and junction of actin and myosin filaments
136
What is H line in muscles
Shortens during contractions and contains myosin only
137
What is the A line in muscles
Region containing length of a single myosin filament
138
What is the I line in muscles
Region containing length of a single actin filament
