Electron transport chain

Question 1

Oxidative Phosphorylation

Answer 1

• Makes ATP by donating electrons to complexes in the inner mitochondrial membrane

Question 2

Sources of NADH and FADH2

Answer 2

These excellent electron donors come from Glycolysis (cytoplasm), the Citric Acid Cycle (mitochondria), or fatty acid oxidation (mitochondria)

Question 3

First point of entry for electron transport chain?

Answer 3

NADH gives its electron to Complex I which contains flavin mononucleotide and iron-sulfur centers (FeS)

Question 4

Second point of entry for the electron transport chain?

Answer 4

FADH2 gives its electron to Complex II (aka Succinate Dehydrogenase) –> Shared enzyme with TCA Cycle (activity of TCA and ETC rise and fall together)

Question 5

Third step of the ETC

Answer 5

Electrons from both Complex I and II flow to Coenzyme Q (aka Ubiquinone) which is a cholesterol derivative and the only lipid in the ETC

Question 6

Forth step of the ETC

Answer 6

Coenzyme Q passes the e- to the Cytochromes (proteins with heme groups) which easily go from Fe3+ + e- –> Fe2+ when grabbing the electron and then from Fe2+ –> Fe3+ + e- when releasing the electron

Complex III (Cytochrome b and Cytochrome c1) –> Cytochrome c –> Complex IV (Cytochrome a and Cytochrome a3, together known as Cytochrome Oxidase, and contain copper instead of iron)

Question 7

Fifth step of the ETC

Answer 7

Complex IV passes e- to oxygen which then makes water

Question 8

What happens to the ETC during hypoxia?

Answer 8

No oxygen to accept electron, thus no ATP made in the ETC

Question 9

What complexes pump H+ into the space between the inner and outer mitochondrial membrane?

Answer 9

Complexes I, III, and IV (the only complexes to span the inner mitochondrial membrane)

This creates a proton gradient

Question 10

What enzyme makes ATP in the ETC?

How is this accomplished?

Answer 10

• ATP Synthase (Sometimes called Complex V)
• H+ gradient causes H+ to move towards matrix, must pass through ATP Synthase to do this, couples this reaction with phosphorylation of ADP to make ATP

Question 11

How many ATP are made per NADH and FADH2 in the ETC?

Answer 11

1 NADH –> 2.5 ATP in the ETC

1 FADH2 –> 1.5 ATP in the ETC

Question 12

ETC is controlled by what?

Answer 12

• Controlled by energy level within the cell
• High ATP –> Slows down ETC
• High ADP –> Speeds up ETC
• Not controlled by hormones

Question 13

What is uncoupling in the ETC?

Answer 13

Uncoupling –> Ionophore protein creates channel for H+ to return to mitochondrial matrix and bypass ATP synthase –> Cell tries to promote ATP production, ETC still occurs minus final step, results in just heat production but no ATP

Uncoupling agents:

• Found in brown adipose tissue of babies, used to generate heat
• Aspirin in high doses –> High metabolic rate –> Metabolic acidosis –> and possible respiratory acidosis

Question 14

What is inhibition in the ETC?

Answer 14

Some chemicals/drugs inhibit components of ETC, stops the flow of electrons, decrease ATP production, NADH and FADH2 build up, and metabolic rate falls, can lead to death pretty quickly

ETC Inhibition chemicals/drugs:

• Carbon monoxide (Inhibit Complex 4)
• Cyanide (Inhibit Complex 4)
• Barbiturates (GABA agonists) at high doses –> Used for seizure disorders (Inhibit Complex I)
• Oligomycin (inhibits ATP Synthase)
• Statins (Can inhibit the synthesis of Coenzym Q)