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PoM > ATP and mitochondria > Flashcards

ATP and mitochondria Flashcards

1
Q

where do oxidative phosphorylation reactions take place?

A

inner membrane

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2
Q

where does the krebs cycle take place?

A

matrix

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3
Q

why are the cristae folded?

A

increase SA for oxidative phosphorylation

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4
Q

what is the equation for the reoxidation of NADH by molecular oxygen in mitochondria?

A

2NADH + 2H⁺ + O₂ —–> 2NAD⁺ + 2H₂O

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5
Q

what is the equation for the reoxidation of FADH₂ by molecular oxygen in mitochondria?

A

2FADH₂ + O₂ —–> 2FADH₂ + 2H₂O

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6
Q

what is ΔG for the reoxidation of NADH?

A

-223 kJ/mol

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7
Q

what is ΔG for the reoxidation of FADH₂?

A

-170 kJ/mol

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8
Q

what is the significance of ΔG for reoxidation of NADH and FADH₂?

A

ΔG for ATP hydrolysis is only -31 kJ/mol

energy released from reoxidation of NADH and FADH₂ enough to generate several phosphoanhydride bonds

much of this energy is recovered by components of ETC and used to synthesise ATP

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9
Q

describe mtDNA’s genome.

A

16 569 bp circular genome

encodes only 37 genes

several copies can be found in one cell

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10
Q

why is mtDNA important?

A

mutations in mtDNA is often a cause of genetic diseases

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11
Q

how is mtDNA inherited and why is this important?

A

inherited via the ovum

therefore mtDNA mutations are transmitted to all maternal offspring

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12
Q

describe the origins of the mitochondria.

A

occurred early in history of life on earth

evolutionary descendent of a prokaryote that established an endosymbiotic relationship with the ancestors of eukaryotic cells

many genes needed for mitochondrial function then translocated to the nuclear genome

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13
Q

what are the 5 pieces of evidence that support the endosymbiont theory?

A

1 - mitochondria only arise from pre existing mitochondria

2- mitochondria have their own genome which resembles prokaryote genomes (circular molecule of DNA, no associated histones)

3- mitochondria have their own protein synthesising machinery, which resembles prokaryotic machinery rather than eukaryotic

4- the first amino acid of mitochondrial transcripts is fMet (formylated methionine residue), like in bacteria, rather that Met (methionine) like in eukaryotic proteins

5- many antibiotics (e.g streptomycin) that block bacterial protein synthesis also block mitochondrial protein synthesis but do not interfere with protein synthesis in eukaryotic cytoplasm

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14
Q

what are the 3 enzymes involved in the ETC?

A

NADH dehydrogenase complex

cytochrome B-C1 complex

cytochrome oxidase complex

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15
Q

what are the 2 carriers involved in the ETC?

A

ubiquinone (co enzyme Q)

cytochrome C

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16
Q

what do the enzymes and carriers in the ETC do?

A

accept electrons and in doing so, a proton from the aqueous solution

as electrons pass through each of the complexes, a proton is pumped to the intermembrane space

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17
Q

what is succinate dehydrogenase and what does it do?

A

integral membrane protein attached to inner surface of inner mitochondrial membrane

communicates directly with ubiquinone

As such one less proton is pumped to the intermembrane space, c.f. NADH and as a consequence, less ATP is produced.

The same is true for electrons donated by other FADH2 species, e.g. those generated in the glycerol phosphate shuttle and the β-oxidation of fatty acids.

18
Q

what are redox reactions?

A

electron transfer reactions

a reduced substrate donates electrons and becomes oxidised

an oxidised substrate/oxidant accepts electrons and becomes reduced

19
Q

what is a redox couple?

A

a substrate that exists in both oxidised and reduced forms

e.g NAD⁺/NADH
Fe³⁺/Fe²⁺
½O₂/H₂O

20
Q

what is the redox potential and how is standard E’0 determined?

A

ability to accept or donate electrons

determined experimentally

21
Q

what does a negative E’0 imply?

A

redox couple has a tendency to donate electrons

more reducing power than hydrogen

22
Q

what does a positive E’0 imply?

A

redox couple has a tendency to accept electrons

more oxidising power than hydrogen

23
Q

what does the transfer of electrons from one complex to another mean, energetically speaking?

A

transfer is energetically favourable

as electrons progress along the chain electrons lose energy

24
Q

what is ATP synthase?

A

multimeric enzyme

depending on proton flow direction, the complex either synthesises (protons move from intermembrane space to matrix) or hydrolyses (protons move from matrix to intermembrane space) ATP

25
Q

describe the structure of ATP synthase.

A

membrane bound part (F₀)

part projects into the matrix (F₁)

26
Q

how does ATP synthase synthesise ATP?

A

rotation of the enzyme drives transition states, with altering affinities for ATP and ADP

consequently, conformational energy flows from the catalytic subunit into the bound ADP and Pᵢ to promote the formation of ATP (chemical energy)

27
Q

describe the setup of an oxygen electrode.

A

small chamber within which the solution is housed

base formed by oxygen-permeable teflon membrane

under the membrane, a compartment contains the Pt cathode and the Ag anode

28
Q

what does an oxygen electrode do?

A

measures oxygen concentration in a solution

29
Q

how does an oxygen electrode work?

A

~0.6V applied between anode (+) and cathode (-)

oxygen diffuses through the teflon membrane and is reduced to water at the Pt cathode
O₂ + 4H⁺ + 4e⁻ —-> 2H₂O

the circuit is completed at the Ag anode (oxidised to AgCl by the KCl electrolyte)
4Ag⁺ + 4Cl⁻ —-> AgCl + 4e⁻

the resulting current is proportional to the oxygen concentration in the sample

30
Q

how can the oxygen electrode by used to investigate the ETC?

A

suspension of mitochondria from a tissue placed into the oxygen electrode

oxygen consumption of suspension monitored for set time period
1- baseline respiration measured
2- ADP added, causing rapid increase in oxygen consumption
3- if the quantity of ADP added is known then the ratio of the amount of ADP phosphorylated to the oxygen consumed can be calculated (ADP:oxygen index - measures efficiency of mitochondrial phosphorylation system)
4- ADP all consumed, system returns to basal respiration rate

therefore, effects of various substrates and inhibitors on ETC can be determined

31
Q

why is any interruption to oxidative phosphorylation/ATP synthesis likely to cause cell death?

A

only a limited amount of ATP is available at any time

each ATP molecule has a short lifespan (1-5 mins)

therefore any interruptions causes rapid depletion and probably death, depending on cell type and metabolic requirements (only a few minutes for neurones, a few hours for muscle)

32
Q

what is the most common cause of a failure of oxidative phosphorylation?

A

lack of oxygen

hypoxia/anoxia

33
Q

what is uptake of oxygen by mitochondria controlled by and why is it important?

A

controlled by components of ATP production (ADP and Pᵢ)

respiratory control - allows body to adapt oxygen consumption to actual energy requirements

34
Q

what are metabolic poisons?

A

molecules that interfere with either the flow of electrons along the ETC or the flow of protons through ATP synthase, interrupting ATP synthesis

highly toxic

35
Q

how do cyanide and azide act as metabolic poisons?

A

bind with high affinity to the ferric form (³⁺) of the haem group in the cytochrome oxidase complex

blocks final step of ETC

36
Q

how does malonate act as a metabolic poison?

A

resembles succinate

competitive inhibition of succinate dehydrogenase

slows electron flow from succinate to ubiquinone by inhibiting oxidation of succinate to fumarate

37
Q

how does rotenone (isoflavone found in some roots and seeds) act as a metabolic poison?

A

inhibits transfer of electrons from complex I to ubiquinone

38
Q

how does oligomycin (antibiotic produced by Streptomyces) act as a metabolic poison?

A

inhibits oxidative phosphorylation

binds to ‘stalk’ of ATP synthase

blocks flow of protons through the enzyme

39
Q

how does dinitrophenol (DNP) act as a metabolic poison

A

proton ionophone

shuttles protons across inner mitochondrial membrane

40
Q

how can DNP induce weight loss?

A

transports protons across the mitochondrial membrane

this uncouples oxidative phosphorylation from ATP production

leads to an increase in metabolic rate and body temperature

41
Q

why was DNP abandoned as a weight loss drug?

A

margin between effective and lethal doses is very slight

many deaths and permanent injuries as a result

now illegal to sell for human consumption, although people still buy and use it with painful consequences

42
Q

where is DNP still used?

A

pesticides

food dye

PoM (42 decks)

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