Oxidative Phosphorylation and mitochondrial function

Question 1

Describe the outer membrane of the mitochondria.

Answer 1

highly porous, permeable to most ions and small molecules. can be solubilized by detergent, digitonin

Question 2

Describe the intermembrane space.

Answer 2

enzymes involved in energy transfer reactions between adenylate nucleotides: adenylate kinase, creatine kinase

Question 3

Describe the inner membrane

Answer 3

arranged in cristae -> large surface area
impermeable to most molecules
transport across uses transport protein or shuttle system
enzymes: succinate DH, alpha-glyceral-P DH, respiratory chain proteins, F1 ATPase, adenosine nucleotide translocase, Pi transporter, carnitine acyl transferase

Question 4

Describe mitochondrial matrix

Answer 4

enclosed in inner membrane

enzymes: TCA enzymes, beta-oxidation of fatty acids, PDC, branched chain amino acid dehydrogenase complex, glutamate DH

Question 5

cytochrome

Answer 5

contain heme and iron atom. heme undergoes cyclic oxidation and reduction reactions

Question 6

Describe the ETC pathway

Answer 6

complex 1 accepts electrons from NADH and passes to CoQ. Intermediate carriers are FMN and iron-sulfer centers. Complex II passes electrons from FADH2 and iron sulfur centers to CoQ (mobile). CoQ passes to cytochrom III which is made of cyt b and cyt c1. Electrons then passed to cytochrome c, which is mobile. Then electrons go to complex 4, which is made of cyt a and cyt a3, both contain Cu2++. Complex 4 then passes the electrons to O2 which reduces it to water.

Complexes 1,3, and 4 pump protons

Question 7

What drugs act on the ETC and where?

Answer 7

Complex 1 - rotenon and amytal
Complex 3- antimycin A
Complex 4 - axide, cyanide, CO

Question 8

Describe ATP Synthase, Complex 5

Answer 8

The F1 domain projects into matrix and contains ATP synthase activity. The F1 cannot synthesize ATP, but catalyzes reverse reaction (hydrolysis of ATP to ADP and Pi)l The F0 domain extends through membrane and creates channel for H+. The stalk proteins connect F0 to F1. The flow ot protons through F0 releases energy from the gradient. The energy is used to synthesize ATP.

Question 9

What is the evidence that supports the chemiosmotic theory.

Answer 9

pH gradient measurable across membrane
addition of protons to isolated mitochondria stimulates ATP synthesis
Ionophores abolish pH gradient -> inhibit ATP synthesis
compounds that block H+ through F0 channel inhibits ATP synthesis

Question 10

what does reduced ascorbate do?

Answer 10

it reduces cytochrome c, bypassing complex 1 and 3, so it has a P/O ration of 1

Question 11

What percent of energy from glucose is captured as ATP?

Answer 11

30 to 40%, rest supports mitochondrial functions or dissipated as heat

Question 12

Describe the oxidative phosphorylation in mitochondria of brown fat.

Answer 12

it dissipates a lot of heat, because of the presences of thermogenin, an uncoupling protein that uncouples oxidation and phosphorylation. this is important in warming blood of newborns and the large arteries leaving the heart are surrounded by layer of brown fat.

Question 13

Describe the relationship of respiration and oxidative phosphorylation

Answer 13

the rate of oxygen uptake parallels the need for ATP. Therefore, oxidation and phsophorylation are tighly coupled processes. As the need for ATP increases, oxygen uptake increases. The factors that influence oxygen uptake are: availability of oxidizable sustrate, adp and O2.

Question 14

What are the inhibitors of complex v?

Answer 14

oligomycin, prevents return flow of protons through F0, will also inhibit electron transport

Question 15

What are the uncouplers?

Answer 15

ionophores, uncoupling proteins, dinitrophenol, very high thyroid hormone.

Question 16

Describe the glycerol phosphate shuttle.

Answer 16

cystolic form of alpha-glycerol phosphate dehydrogenase reduces dihydroxyacetone phosphate to alpha glycerol phosphate. Reduced via NADH. alpha-glycerol phosphate crosses imm and is oxidized back to dihydroxyacetone phosphate by and enzyme that uses FAD generating FADH2. Net: cystolic NADH -> mitochondrial FADH2. Shuttle enriched in brain and fast-contracting skeletal muscle.

Question 17

Describe hte malate shuttle

Answer 17

enzymes: malate DH isozymes
On cystolic side, oxaloacetate reduced to malate by NADH, malate transported across inner mitochondrial membrane where it is reoxidized to oxaloacetate with concomitant formation of mitochondrial NADH. Shuttle enriched in liver and cardiac muscle
Net: cystolic NADH -> mitochondrial NADH

Question 18

What is the ATP-ADP exchange protein?

Answer 18

An antiporter that exchanges mitochondrial ATP for cystolic ADP. Because antiporter swaps ATP with a charge of -4 for ADP with a charge of -3, the proton motice orce is sufficient to drive exchange. It’s inhibited by atractyloside ( from plants like thistle)

Question 19

What is the phosphate transport protein?

Answer 19

antiporter - mitochondrial OH- for cystolic HsPO4-
symporter - cystolic H2PO4- and H+ into mitochondrial matrix.
electrical neutrality maintained and Pi imported

Question 20

What is the pyruvate transporter?

Answer 20

antiporter: cystolic pyruvate for mitochondrial OH-

Question 21

Describe the carnitine shuttle.

Answer 21

transport fatty acids from cytosol to mitochondrial matrix for beta-oxidation

Question 22

Describe citrate shuttle

Answer 22

tranport acetate out of mitochondria into cytosol for several reasons including fatty acid synthesis.

Question 23

Describe mitochondrial genetics

Answer 23

proteins encoded by both nuclear and mitochondrial
mitochondrial genome encodes 13 proteins that are subunits of Complex 1, 3, 4, and ATP synthase complex. It also encodes tRNAs and ribosomal RNAs for mitochondrial protein synethsis. Everything else is mitochondrial
mutations for the various components of oxyphos pathway can be in either genomes
mutations in mitochondrial genome are not inherited in the mendelian way -> variability and heterogeneity even within families