ETC B&B

Question 1

what is the purpose of the glycerol phosphate shuttle?

Answer 1

glycerol phosphate dehydrogenase transports electrons from NADH across the mitochondrial membrane for ETC by combining NADH with dihydroxyacetone phosphate —> glycerol phosphate

mitochondrial version of glycerol phosphate dehydrogenase reverses the reaction, but generates FADH2 within the mitochondria - however FADH2 generates less ATP than NADH, so glycerol phosphate shuttle is less efficient than malate shuttle

Question 2

what occurs in Complex I of the ETC?

Answer 2

NADH dehydrogenase oxidizes NADH, transferring its electrons to coenzyme Q (ubiquinone), which carries them to Complex III

H+ pumped into intermembrane space

Question 3

what occurs in Complex II of the ETC?

Answer 3

succinate dehydrogenase (TCA cycle) converts succinate to fumarate, generating FADH2 in the process

FADH2 transfers its electrons to coenzyme Q (ubiquinone), which carries them to Complex III

Question 4

what occurs in Complex III of the ETC?

Answer 4

cytochrome bc1 complex transfers electrons carried by coenzyme Q (ubiquinone) to cytochrome c

H+ pumped into intermembrane space

[recall cytochromes are proteins with heme groups that can carry electrons via changes in oxidation state]

Question 5

what occurs in Complex IV of the ETC?

Answer 5

cytochrome C oxidase combines cytochrome c with oxygen

contains copper

pumps H+ into intermembrane space, generates water via passing electrons onto oxygen

Question 6

what enzymes dictate the functions of each of the ETC complexes?

Answer 6

Complex I: NADH dehydrogenase
Complex II: succinate dehydrogenase (TCA)
Complex III: cytochrome bc1
Complex IV: cytochrome oxidase
Complex V: ATP synthase

Question 7

to which ETC complex do the following poisons bind and how do they exert their effect?
a. rotenone
b. antimycin A
c. carbon monoxide
d. cyanide
e. oligomycin A

Answer 7

these are all complex inhibitors

a. rotenone (insecticide) - binds Complex I, preventing e- transfer to CoQ
b. antimycin A (antibiotic, not clinically used) - binds Complex III (bc1 complex)
c. carbon monoxide - competes with O2 for iron binding in Complex IV
d. cyanide - binds Complex IV
e. oligomycin A - binds ATP synthase

Question 8

what is the treatment for cyanide poisoning?

Answer 8

nitrites: convert Fe2+ —> Fe3+ in hemoglobin (methemoglobin), which binds cyanide to protect mitochondria

recall cyanide binds/inhibits Complex IV of ETC (cytochrome c oxidase)

Question 9

why does a fever occur with aspirin overdose?

Answer 9

aspirin is an uncoupling agent of ETC!

fever is due to heat produced by H+ leaking out