MODULE 12: Chapter 11.3

Question 1

What was the original name of the ATP synthase complex?

Answer 1

Complex V

It was considered part of the electron transport system.

Question 2

What are the two large structural components of the mitochondrial ATP synthase complex?

Answer 2

F1 and Fo

F1 encodes catalytic activity, and Fo functions as a proton channel.

Question 3

What does the subscript letter ‘o’ in Fo refer to?

Answer 3

Oligomycin inhibition

The antibiotic oligomycin inhibits the activity of the Fo proton channel.

Question 4

How many polypeptide chains do most ATP synthase complexes contain?

Answer 4

At least 20 polypeptide chains

Question 5

What subunits make up the yeast mitochondrial F1 component?

Answer 5

Three α subunits, three β subunits, one γ subunit, one δ subunit, one ε subunit

The β subunits contain the three catalytic sites.

Question 6

What is the function of the rotor in the ATP synthase complex?

Answer 6

It rotates as protons enter and exit the c-subunit ring.

Question 7

What are the three functional units of the yeast ATP synthase complex?

Answer 7

Rotor, catalytic headpiece, stator

The rotor consists of γ, δ, ε subunits, and the c-subunit ring.

Question 8

What is the role of the stator in the ATP synthase complex?

Answer 8

Holds the headpiece in place so it does not turn with the rotor.

Question 9

What is the binding change mechanism of ATP synthesis?

Answer 9

It explains how conformational changes in β subunits control ATP production.

Question 10

What are the three conformations of the β subunits in the binding change mechanism?

Answer 10

L (loose), T (tight), O (open)

Question 11

How many protons are required for each ATP synthesized in the yeast mitochondrial ATP synthase complex?

Answer 11

Approximately 3 protons

Question 12

What does the γ subunit do during ATP synthesis?

Answer 12

Rotates counterclockwise with each ∼120° rotation

Question 13

What happens to the β subunits during the ATP synthesis process?

Answer 13

They undergo conformational changes from L to T to O and back to L.

Question 14

What is the significance of the Kd value for the F1 headpiece for ATP?

Answer 14

It increases from about 10−12 M to 10−6 M in the presence of proton-motive force.

Question 15

True or False: The ATP synthase complex functions as an ATP hydrolyzing enzyme in the absence of Fo.

Answer 15

True

Question 16

What stabilizes the enzyme in a single conformation at the catalytic site?

Answer 16

Phosphoaminophosphonic acid–adenylate ester (ANP)

Question 17

What is the role of the β subunit in the ATP synthase complex?

Answer 17

Contains the catalytic sites for ATP synthesis.

Question 18

What is the function of the c ring in the ATP synthase complex?

Answer 18

Part of the rotor that rotates during proton flow.

Question 19

What discovery did Walker make regarding β-subunit conformations?

Answer 19

Differences in conformations are associated with differential affinities for ATP.

Question 20

What two components are the yeast δ subunit and bacterial ε subunit equivalent to?

Answer 20

Yeast δ subunit is equivalent to bacterial ε subunit

This should not be confused with the bacterial stator component.

Question 21

What is the primary enzyme function of the F1 headpiece?

Answer 21

ATP hydrolyzing enzyme (ATPase)

Question 22

What is the main finding regarding proton flow through Fo?

Answer 22

It is not directly involved in the catalytic mechanism.

Question 23

What is the role of H⁺ flow through Fo in ATP synthesis?

Answer 23

H⁺ flow through Fo is not directly involved in the catalytic mechanism.

Question 24

What does Boyer’s model predict about ATP hydrolysis by the F1 headpiece?

Answer 24

ATP hydrolysis should reverse the direction of the γ subunit rotor.

Question 25

What is the conformational change sequence at a β subunit during ATP hydrolysis according to Boyer's model?

Answer 25

O T L O

Question 26

Who conducted the experiment to build a synthetic molecular motor using Escherichia coli F1 component?

Answer 26

Masasuke Yoshida and Kazuhiko Kinosita, Jr.

Question 27

What modifications were made to the α, β, and γ subunits in the synthetic molecular motor experiment?

Answer 27

A short peptide was added to immobilize the β subunit and a cysteine codon was inserted in the γ subunit.

Question 28

What was the purpose of the fluorescent actin filament in Yoshida and Kinosita's experiment?

Answer 28

To monitor rotation of the γ subunit using fluorescence microscopy.

Question 29

What happens to the actin propeller when reaction buffer containing Mg²⁺ and ATP is added?

Answer 29

It rotates in the clockwise direction, opposite to that predicted for ATP synthesis.

Question 30

What type of motion was observed in the γ-subunit rotation during the experiment?

Answer 30

Stepwise ratchet motion.

Question 31

What was the maximum speed of the actin propeller observed in the experiments?

Answer 31

130 revolutions per second.

Question 32

How was ATP synthesized in the follow-up experiments by Yoshida and Kinosita?

Answer 32

By forcing the γ subunit to turn in the counterclockwise direction using a magnetic bead and electromagnets.

Question 33

What does the two-channel model propose regarding proton movement in ATP synthase?

Answer 33

Protons enter and exit the c-subunit ring through two half-channels in the a subunit.

Question 34

What happens when a proton enters the half-channel in the a subunit?

Answer 34

It comes in contact with a negatively charged Asp59 residue in the c subunit.

Question 35

What effect does protonation of Asp59 have on the c-subunit ring?

Answer 35

It allows the c-subunit ring to rotate counterclockwise.

Question 36

What is the stoichiometry problem associated with proton movement in the c-subunit?

Answer 36

It implies a nonstoichiometric number of 3.3 H⁺ crosses the membrane for each 120° rotation of the γ subunit.

Question 37

What is the typical number of H⁺ that need to cross the membrane for a full 360° rotation of the γ-subunit rotor?

Answer 37

10 H⁺

Question 38

What does the binding change mechanism describe?

Answer 38

How the ATP synthase complex converts conformational changes into the production of ATP.

Question 39

What are the three functional units of the bacterial ATP synthase complex?

Answer 39

* Rotor (c-subunit ring and γ subunit) * Catalytic headpiece (β subunits) * Stator (a subunit and stabilizing arm)

Question 40

What conformations do the β subunits cycle through during ATP synthesis?

Answer 40

* Loose (L) * Tight (T) * Open (O)

Question 41

How many ATP are produced for every complete 360° turn of the rotor?

Answer 41

3 ATP

Question 42

True or False: ATP synthesis is dependent on an electrochemical proton gradient.

Answer 42

False

Question 43

Fill in the blank: The binding change mechanism was proposed by _______.

Answer 43

Paul Boyer