Chapter 18: Oxidative Phosphorylation

Question 1

Coenzyme Q

Answer 1

Ubiquinone: has a long isoprenoid tail that makes it lipid soluble

Can accept 1 or 2 electrons

1. Only enzyme in ETC that is NOT a protein
2. Is individually mobile within the membrane
3. Occur as large assemblies of proteins called respiratory complexes

Question 2

ETC complex I

Answer 2

NADH-ubiquinone oxidoreductase removes two electrons from NADH and transferred them to a lipid-soluble carrier, ubiquinone (Q)

The reduced product ubiquinol (QH₂) freely diffuses within the membrane

Pumps our four H⁺

Contains a flavoprotein prosthetic group called flavin mononucleotide (FMN)

Question 3

ETC complex II

Answer 3

Succinate dehydrogenase- only membrane-bound enzyme of CAC

1. Catalyzes the oxidation of succinate to fumarate by transferring electrons from succinate to FAD⁺, forming FADH₂
2. FADH₂ then subsequently transfers its electrons to ubiquinone

Does NOT directly transfer any protons across the inner mitochondrial membrane

Question 4

ETC complex III

Answer 4

Ubiquonone-cytochrome c reductase transfers two electrons from QH₂ to cytochrome c, a water-soluble electron carrier located within the intermembrane space

Pumps out two protons per cycle for a TOTAL of four

Composed of:

• Cyt b
• Cyt c₁
• Cyt c

Question 5

ETC complex IV

Answer 5

Cytochrome c oxidase- transfers electrons from cyt c to oxygen and forms water

Pumps out two protons per cycle

Composed of cyt a & cyt a₃

• Cyt a₃ is the last cytochrome and passes its electrons to oxygen

Question 6

ATP sythase

Answer 6

ATP synthase is made up of two components:

1. The F₀ component is embedded in the inner mitochondrial membrane and contains the proton channel; pumps protons
2. The F₁ component contains the three active sites and protrudes into the mitochondrial matrix; makes ATP

Question 7

Enzyme that moves ATP across the mitochondrial membrane

Answer 7

ATP-ADP translocase enables the exchange of cytoplasmic ADP for mitochondrial ATP

ADP must enter the mitochondria for ATP to leave

Question 8

Respiratory control

Answer 8

The regulation of oxidative phosphorylation by ADP

Electrons do not flow through the electron-transport chain unless ADP is available to be converted into ATP

Question 9

Regulation of ATP synthase

Answer 9

Inhibitory factor 1 (IF1) is a conserved protein that inhibits the hydrolytic ability of ATP synthase

Dinitrophenol (DNP) is known to uncouple ATP synthesis from electron transport

• Allows protons to cross the membrane freely so that no proton gradient can be formed

Question 10

Glycerol-3-phosphate shuttle

Answer 10

Transfers the reducing power of NADH across the inner mitochondrial membrane to FADH₂ and the ETC

Primary enzymes involved are cytosolic and membrane-bound glycerol-3P dehydrogenases

Shuttle functions rapidly but converts NADH to FADH2 and therefore yields one less ATP

Question 11

Malate-aspartate shuttle

Answer 11

Transfers electrons from cytosolic NADH across the inner mitochondrial membrane to NADH molecules in the matrix

Primary enzymes involved are cytosolic and matrix malate dehydrogenases and cytosolic and matrix aspartate aminotransferases

Primary transporters are the malate-α-ketoglutarate antiporter and the glutamate-aspartate antiporter

Question 12

What is the name of the mechanism proposed by Peter Mitchell that explains how ATP synthesis and electron transport are coupled?

Answer 12

The chemiosmotic theory