Cellular Respiration Flashcards
(31 cards)
1
Q
Structure of the mitochondrion
A
- matrix: inside of the mitochondrion. Contains all of the TCA cycles enzymes (kerbs cycle).
- cristae: are not fixed so they can move and fit into areas of the cell that require ATP
- cristae junctions: allow complexes in and out
- F0F1 complexes: ATP synthesis
- inner membrane: impermeable to most small molecules and ions, including H+. Embedded in the inner membrane is the respiratory complexes.
- outer membrane: freely permeable to all small molecules and ions (less than 10-12kg).
- inter membrane space
2
Q
Size of mitochondria
A
- new cell: small and very active
- developed cells: numbers decreased and they increase in size
3
Q
Function of mitochondria
A
- ATP synthesis
- carbon skeletons for biosynthetic purposes: carbon skeletons formed within mitochondria and exported to the rest of the cell for biosynthesis of other enzymes
4
Q
ATP synthesis: Kerbs cycle (citric acid cycle)
A
- reduced carriers - basic kerbs cycle (citric cycle):
- located in mitochondrial matrix
- key function to generate ADA
5
Q
Glycolysis: summary
A
Occurs in the cytoplasm - anaerobic
Each glucose molecule used up in glycolysis produces:
- 2 pyruvate molecules (each has 3 carbons).
- 2 reduced NAD molecules (each with a hydrogen atom).
- a net of 2 ATP molecules (initially 2 ATP donated for hydrolysis, but at the end 4 ATP made).
6
Q
The link reaction
A
Aerobic respiration
- pyruvate (2 per glucose) transported into mitochondrial matrix by active transport (ATP required) with a transport protein called the pyruvate-H+ symporter (takes two things and transports them together: pyruvate and hydrogen ion)
- decarboxylation - pyruvate converted to a two-cabin acetyl group: carboxyl group and hydrogen atom removed from pyruvate by large multi-enzyme complex pyruvate dehydrogenase.
- carbon goes to CO2
- hydrogen atoms removed from pyruvate and accepted by NAD = reduced NAD
- acetyl group combines with molecule called coenzyme A (CoA) to form compound acetyl CoA (for use in Krebs cycle).
7
Q
Krebs cycle: aerobic respiration
A
Series of enzyme catalysed reactions that happen in the matrix
Purpose: oxidise the acetyl CoA produced in links reaction
- 2 carbon acetyl from links reaction + 4 carbon compound oxaloacetate = 6 carbon compound called citrate.
- citrate is dehydrogenated and decarbonated = CO2, reduced NADH and 5C compound
- 5C = CO2, reduced NADH and 4C compound.
- 4C compound combines with CoA temporarily = ATP
- 4C makes reduced FADH
- isomers enzymes turns 4C back to oxaloacetate = reduced NADH
- oxaloacetate will the combine with 2C acetyl to start the cycle again
8
Q
Components of the respiratory chain
A
NAD+ linked dehydrogenases
flavin linked dehydrogenases
iron sulphur proteins
ubiquinone
cytochromes
9
Q
Dehydrogenases
A
- electrons are collected from catabolic reactions by dehydrogenases that funnel them into universal electron acceptors:
- nicotinamide nucleotides, NAD+ or NADP+
- flavin nucleotides FMN or FAD
- NAD(P)N is water soluble but cannot cross the inner mitochondrial membrane.
- the electrons carried by NAD(P)H can be shuttled across the membrane
10
Q
NAD+ linked dehydrogenases
A
- NAD linked dehydrogenases remove two hydrogen atoms from their substrates.
- one of the hydrogen atoms is transferred as a hydride ion (H-) to NAD+
- the other hydrogen ion is released into the medium as H+
- reduction reaction not energetically favourable, reoxidises it back to NAD+ (can be monitored by light absorption, NADH (reduced) absorbed more light at higher wave length
- H+ causes acidification, can follow the rate of reaction.
- NAD is a cofactor.
11
Q
flavin linked dehydrogenases
A
- contains tightly bound flavin nucleotides, either FMN or FAD.
- oxidised flavin can be reduced with either one electron to give the semiquinone form or with two electrons to give FADH2 or FMNH2
- the ability of flavins to accept one or two electrons means they can act as intermediates in reactions where two electrons are donated.
- there is net acidification of medium (no loss of protons).
- energy is 0, will remain in equilibrium between the two (succinate and fumarole).
12
Q
Iron sulphur proteins: types of iron centres
A
- iron is not present as haem but in association with inorganic sulphur or with sulphur atoms of cysteine amino acids.
- the arrangement of the sulphur and the ion range from simple single Fe arrangements to more complicated multiple arrangements.
3 types of iron-sulphur centres:
- Fe-S centres: a single Fe iron is coordinated by 4 sulphur atoms from the cysteine amino acid of a protein.
- 2Fe-2S centres: two iron atoms are orientated with four sulphur atoms from the cysteine amino acids and two inorganic sulphur atoms.
- 4Fe-4S centres: four iron atoms are orientated with four sulphur atoms from the cysteine amino acids and four inorganic sulphur atoms.
13
Q
Ubiquinone: coenzyme Q
A
- lipid soluble benzoquinone.
- can accept one election to become the semiquinone radical (QH+).
- upon acceptance of another election it becomes fully reduced to ubiquinol (QH2).
- like flavoprotein carriers, Q can act as a intermediate between two-electron downer and one election acceptor.
14
Q
Importance of ubiquinone
A
- small and hydrophobic.
- freely able to diffuse in the lipid bilayer of the inner mitochondrial membrane.
- shuttles reducing equivalents between less mobile electron carriers in the membrane.
- carries both electrons and protons and therefore plays a central role in coupling electron flow to proton movement. (Iron-sulphur proteins only carry electrons).
15
Q
Cytochromes
A
- iron containing haem prosthetic group.
- strong absorption of visible light.
- mitochondria contain 3 classes: a, b and c which are distinguished by differences in their absorption of light.
- in their reduced form (Fe2+ When they take the electron) each type of cytochrome has a distinctive absorption maximum.
- type a: 660nm
- type b: 560nm
- type c: 550nm
16
Q
Cytochrome C
A
- loss of cytochrome c is one of the first events when mitochondria undergo apoptosis (going towards cell death).
- lives between the outer and inner membrane, but binds to the outer surface of the inner membrane.
- absorption spectra of a cytochrome alters in accordance with its redox status (when oxidised it doesn’t really absorb light, but when reduced there is a large absorption of light).
- only carry electrons (not protons).
17
Q
Characteristics of cytochrome prosthetic groups
A
- four five-membered nitrogen containing rings in a cyclic structure called a porphryn.
- the four nitrogen atoms are coordinated with a central Fe atom, either Fe2+ or Fe3+.
- haem cofactors of a and b cytochromes ate tightly bound to their assocated proteins.
- the haem group of type c cytochromes are covalently attached through cysteines residues.
18
Q
Arrangement of ETC (electron transport chain)
A
- based on experiments with isolated mitochondria
- the mitochondria are sub-fractionated from the cell:
- use oxygen electrode to determine what substrates are oxidised.
- using a range of inhibitors the order of electron transfer can be deduced.
- order of the components can be assessed from their redox potentials.
- arrangement of components within the respiratory chain complex.
19
Q
Examples of inhibitors
A
- rotenone: prevents NADH from being oxidised (at the beginning of the chain. Oxygen electrode - all components will be oxidised).
- antimycin A: inhibits between cytochrome b and cytochrome c1. (Spectrophotometer - all components before inhibition site are reduced, and all components after the site of inhibition are oxidised).
- CN- (cyanide) or CO (carbon monoxide): inhibits the very end of chain, where electrons are passed on to oxygen. (All components are reduced). Cyanide is a non competitive inhibitor. CO is a competitive inhibitor and competes with oxygen.
20
Q
Overall reaction catalysed by electron transport chain: redox
A
Organised based on reduction potential - from low to high potential (from most negative).
Energy liberated in three smaller steps instead of one (NADH to oxygen).
A negative redox carrier will reduce one that is more electro positive then it.
From low to high reduction potential:
- NADH and succinate are the primary electron donors.
- flavoproteins
- ubiquinone
- iron sulphur protein
- cytochromes
21
Q
The protein complexes of electron transport chain
A
Complex 1: NADA dehydrogenase - prosthetic groups FMN, Fe-S
Complex 2: succinate dehydrogenase - prosthetic groups FAD, Fe-S
Complex 3: cytochrome bc1 complex (ubiquinone) - prosthetic groups Hemes, Fe-S
Complex 4: cytochrome aa3 oxidase - prosthetic groups hemes, CuA, Cug
Complex 5: ATP synthesis - not par of the respiratory chain as it can stand alone.
22
Q
Electrons travel along the respiratory chain
A
As 2 electrons travel along the respiratory chain, 10 protons are pumped across the membrane
23
Q
Other substrates pass electrons to ubiquinone
A
- cytosolic glycerol-3-phosphate pass electrons to glycerol 3-phosphate dehydrogenase on the outer surface of the inner membrane
- this pathway is important in shuffling reducing equivalent from the cytosolic NADH into the mitochondrial matrix
- fatty acrylic-CoA passes electrons to ubiquinone by a series of proteins
24
Q
Why these different pathways?
A
Each pathway contributes electrons to keep the pool of ubiquinone (QH2) reduced
This ensures that complex 3 is fully reduced
25
Are all complexes fixed in the membrane?
No - all complexes, cytochrome c and UQ are mobile
But cyt c and UQ move 10 times faster than other complexes
26
Stoichiometry of the complexes: are all complexes in equal amounts?
No - for every complex 1 there are:
- 2 complex 2
- 3 complex 3
- 7 complex 4
- 14 cyt c
- 63 UQ
Because complexes are mobile and not in equal amounts, electrons are transported across by collisional interactions
- UQ acts ac electrons carriers between complex 1 and 2
- cyt c between 2 and 3
27
Chemiosmotic hypothesis
- depends on the translocation of protons across the inner membrane
- this generates a ‘protonmotive force’ (pms)
- this established proton circuit couples electron transport tonATP synthesis
- ATP synthesised as a result of the proton gradient generated by electron transport
- hypothesis based on 4 tenets:
1. An ion impermeable inner membrane
2. H+ translocating respiratory chain
3. H+ or OH- linked exchange diffusion system
4. Reversible H+ translocating ATP synthesis
28
Proton motive force
Formed of a electrical components and a chemical component and both of them are a force to drive ATP synthesis
29
The ATP synthase (complex 5)
- located on the inner mitochondrial membrane
- large complex composed of two distinct components
- F1
- F0
- the F1 complex is a peripheral membrane protein - synthesis of ATP from ADP and Pi catalysed by F1
- the F0 complex is an integral membrane protein - protons flow through the F0 channel to the matrix
- this protein can carry out two functions, the synthesis (ATP synthesis) and breakdown (ATPase) of ATP.
30
How does ATP synthase work?
- rotational catalysis is key to the binding change mechanism for ATP synthesis
- proposed by Paul Boyer after detailed kinetic and binding studies of F1F0 complex
- the 3 binding sites of F1 take turns in catalysing ATP synthesis
- a give beta subunit alters it conformation
31
ATP head piece from the top
Each bets (1, 2 and 3) have a active site with a different conformation, but are interchangeable.
- in the ‘open site’ conformation ADP and inorganic phosphate (Pi) have easy entry
Rotating 1 of gamma subunit:
- causes a conformational change and changes the active sites of every one.
- beta two goes from tightly bound ATP to an ‘open site’ and releases it.
Next: no rotation, but ADP and Pi in beta two ‘tight site’ bind together to form ATP
As the spindle turns 360 degrees it does this in 3 stages. Each time it has a rotation it releases ATP and forms ATP, so 3 ATP molecules are formed each complete turn of the head.
