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protein control in cellular regulation > OXPHOS > Flashcards

OXPHOS Flashcards

1
Q

what is the primary function of the mitochondria?

A

to convert organic materials into energy in the form of ATP via the process of oxidative phosphorylation

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2
Q

what are the major products of glycolysis and where are they oxidised?

A

pyruvate and NADH, in the mitochondria

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3
Q

what is the outer mitochondrial membrane permeable to?

A

small molecules and ions

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4
Q

what is the inner mitochondrial membrane permeable to?

A

most small molecules and ions

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5
Q

what is the function of the outer mitochondrial membrane?

A

separate mitochondria from the cytosol

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6
Q

what is contained in the inner mitochondrial membrane?

A
  • respiratory chain supercomplexes
  • ADP-ATP translocase
  • ATP synthase
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7
Q

what is contained within the mitochondrial matrix?

A

-pyruvate dehydrogenase
-citric acid cycle enzymes
-fatty acid B-oxidation enzymes
-amino acid oxidation enzymes
-DNA
-ribosomes
ATP, Pi
ions

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8
Q

what is the chemiosmotic mechanism for ATP synthesis?

A

1) reduced substrate donates e-
2) electron carriers pump H+ out as electrons flow to O2
3) energy of e- flow is stored as electrochemical potential
4) ATP synthase uses electrochemical potential to generate ATP

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9
Q

apart from ATP synthesis, what are the other roles of the mitochondria?

A
  • biosynthesis of porphyrins
  • fatty acid oxidation
  • apoptosis
  • regulation of cellular redox state
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10
Q

what is the primary function of chloroplasts?

A

capture and convert light energy into chemical energy, and store this in molecules of carbohydrates

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11
Q

what are three similarities between oxidative phosphorylation and photophosphorylation?

A

1) both processes involve electron flow through a series of membrane bound carriers
2) energy made available from downhill electron flow can be used to transport protons across proton-impermeable membrane
3) free energy for ATP synthesis via ATP synthase is generated by the flow of protons back up their carrier proteins

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12
Q

how is the mitochondrial genome structured?

A

circular molecule with no histones; encodes 2 rRNAs and 22 tRNAs. produces 13 polypeptides plus some subunits of other proteins

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13
Q

what is the endosymbiotic theory?

A

mitochondria and chloroplasts evolved from separate prokaryotes which were taken inside the cell as endosymbionts

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14
Q

what evidence is there for the endosymbiotic theory?

A
  • mitochondria and chloroplasts have their own DNA, which is circular
  • mitochondrial ribosomes resemble 70S ribosomes in bacteria
  • phylogenetic analysis: mitochondrially encoded proteins cluster as a subgroup of a-proteobacteria
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15
Q

in the equilibrium between ATP ADP + Pi, when is ATP synthesised and hydrolysed?

A

synthesised: if delta G is less than 0
hydrolysed: if delta G is greater than 0

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16
Q

what is the purpose of cristae?

A

large surface area, allows for generation of membrane potential

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17
Q

what is the deltapH for the mitochondria?

A

intermembrane space - pH 7
matrix - pH 8
deltapH - 1

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18
Q

what is the deltapH for chloroplasts?

A

intermembrane space - pH 7
thylakoid - pH 5
stroma - pH 7/8
delta pH 3

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19
Q

what does delta pH refer to?

A

the difference in pH between compartments, a larger deltapH indicates a larger driving force for reaction

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20
Q

what constitutes an electrochemical potential?

A

chemical and electrical potential of protons across the mitochondrial membrane

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21
Q

what gives rise to chemical potential?

A

delta pH

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22
Q

what gives rise to electrical potential?

A

difference in proton concentrations - cause a charge difference across the membrane

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23
Q

what is the role of NADH and FADH2 in the metabolism of glucose?

A

transient energy storage, eventually oxidation in the electron transport chain to provide energy for ATP synthesis

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24
Q

how does electron transfer occur in the ETC?

A

NADH _> ubiquitone -> cytochrome c -> oxygen

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25
Q

when does ubiquinone act as an electron carrier?

A

when bound to a protein where the semiquinone radical can be stabilised by the protein environment

26
Q

how is ubiquinone anchored to the membrane?

A

through hydrophobic isoprene tail

27
Q

when is a redox reaction energetically favourable?

A

when deltaE is positive, overall deltaG is negative. the reaction is exergonic and thermodynamically favourable

28
Q

what is the role of complex II?

A

directly links the ETC to TCA cycle. electrons from fumerate are transferred to FADH2, and accepted by ubiquinone

29
Q

how do we know the reactions which occur in complex II are not coupled to proton transport?

A

the gain in free energy from oxidising FADH2 and reducing ubiquinone is virtually zero, there is insufficient energy to couple the redox reaction to proton transport

30
Q

which processes take place in the mitochondrial matrix?

A

oxidation of pyruvate and the citric acid cycle

31
Q

what is the advantage of having downhill electron flow coupled to uphill transport of proteins across a proton impermeable membrane?

A

conserves free energy of fuel oxidation as a transmembrane electrochemical potential

32
Q

why does the inner mitochondrial membrane have no porins?

A

makes it highly impermeable, and therefore able to generate a membrane potential

33
Q

what is indicated by a larger delta pH?

A

larger driving force for a reaction

34
Q

what is complex I called?

A

NADH: ubiquinone oxidoreductase or NADH dehydrogenase

35
Q

how are electron carriers in the ETC organised?

A

the four complexes of the ETC are connected by mobile electron carriers, they also have bound electron carriers to separate reduction and oxidation in space

36
Q

what are the mobile electron sources in the respiratory chain?

A
  • Nicotinamide adenine dinucleotide (NAD+/NADH)

- Flavin adenine dinucleotide (FAD/FADH2)

37
Q

how many electrons can cytochromes carry?

A

one at a time

38
Q

name 2 cytochromes

A
  • heme

- iron-sulfur centres

39
Q

what does the difference in standard reduction potential measure?

A

standard free energy change for the transfer of an electron from one molecule to another

40
Q

what was found from structure experiments into complex I of T. thermophilus?

A
  • there are three subunits in eukaryotes that are structurally similar to sodium/proton antiporters
  • there was an unexpected long a-helix perpendicular to the membrane
41
Q

what is the proposed model for proton translocation by complex I?

A

pairs of electrons from NADH are passed along a chain of iron-sulfur clusters, eventually reaching ubiquinone

42
Q

what prosthetic groups are found in complex I?

A

non-covalently bound FMN and iron-sulfur clusters

43
Q

what type of diseases are mutations to complex I associated with?

A

neurodegenerative diseases

44
Q

what is complex I?

A

a proton pump driven by energy of electron transfer. this is vectorial

45
Q

what is the structure of complex I?

A

L shaped, with one arm in the membrane and the other extending into the matrix

46
Q

what two coupled reactions are catalysed by complexI?

A

1- exergonic transfer of a hydride ion from NADH and a proton from the matrix to ubiquinone
2- endergonic transfer of 4H+ from the matrix to inter membrane space

47
Q

what is the role of complex II?

A

provides ubiquinol to be utilised in complex III

48
Q

what is the structure of complex II?

A

contains four subunits: a, b, c and d
A - FADH2 and succinate binding site
B - 3 iron sulphur clusters
C + D - heme group and quinone binding site

49
Q

what happens in complex II?

A

succinate comes in and is reduced to fumerate, electrons are transferred to FADH2 and electron transfer occurs, ubiquinone is reduced

50
Q

what is complex III?

A

cytochrome c reductase

51
Q

which three subunits are present in all species in complex III?

A

cytochrome b, cytochrome c1 and rieske protein

52
Q

why are 2 cytochrome cs required in complex III?

A

2 electrons are needed for the fully reduced ubiquinol, each cytochrome can only carry one

53
Q

what is the structure of complex III?

A

cytochrome c is located close to c1, to allow electron hopping. cytochrome b carries 2 heme groups and Rieske protein contains an iron-sulfur cluster

54
Q

what is the role of complex III?

A

couples transfer of electrons from ubiquinol to cytochrome c with the vectorial transfer of protons from the matrix to inter membrane space

55
Q

what is the purpose of the Q cycle?

A

to accommodate the switch between the 2e- electron carrier ubiquinol and one e electron carriers heme bL and bH

56
Q

what is the net effect of the Q cycle?

A

QH2 is oxidised to Q, 2 cytochrome Cs are reduced and protons are moved from P space to N space

57
Q

what is complex IV?

A

cytochrome oxidase

58
Q

what is the role of complex IV?

A

accepts electrons from reduced cytochrome c and transports them to molecular oxygen for reduction to water

59
Q

what structures are important in complex IV?

A

cytochromes and copper centres

one cytochrome and one copper centre form a binuclear centre, the site of oxygen reduction

60
Q

why does the reduction of O2 in complex IV need to be tightly controlled?

A

to avoid the escape of intermediates and generation of ROS

protein control in cellular regulation (10 decks)

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