Module 6: V7 - V11

Question 1

What is the importance of the PDH complex?

Answer 1

can be considered as the 1st control point of the Krebs cycle

Question 2

Why are B group vitamins important?

Answer 2

used extensively in metabolism

Question 3

What is the first reaction of the Krebs cycle? Is this reaction exergonic or endergonic?

Answer 3

the formation of citrate from oxaloacetate and acetyl-CoA

the reaction is highly exergonic because it involves the hydrolysis of a thioester

Question 4

What is the second reaction of the Krebs cycle? Is this reaction exergonic or endergonic?

Answer 4

citrate is converted to isocitrate in two-steps (via a cis-aconitate intermediate) catalyzed by aconitase
unfavourable yet driven to the right by the rapid consumption of isocitrate in the cycle

Question 5

What is the third reaction of the Krebs cycle? Is this reaction exergonic or endergonic?

Answer 5

isocitrate is then converted to a-ketoglutarate by isocitrate dehydrogenase producing CO2 + NADH
exergonic + irreversible

Question 6

What is the fourth reaction of the Krebs cycle? Is this reaction exergonic or endergonic?

Answer 6

a-ketoglutarate is converted to succinyl-CoA by the a-ketoglutarate dehydrogenase complex
exergonic + irreversible

Question 7

What is the fifth reaction of the Krebs cycle? Is this reaction exergonic or endergonic?

Answer 7

succinyl-CoA is then converted to succinate by succinyl CoA synthetase
exergonic

Question 8

What is the sixth reaction of the Krebs cycle? Is this reaction exergonic or endergonic?

Answer 8

succinate is converted to fumarate by succinate dehydrogenase which produces FADH2
not exergonic or endergonic, instead = 0

Question 9

What is the seventh reaction of the Krebs cycle? Is this reaction exergonic or endergonic?

Answer 9

fumarate is converted to L-malate via a carbanion intermediate by the enzyme fumarase
exergonic

Question 10

What is the eighth reaction of the Krebs cycle? Is this reaction exergonic or endergonic?

Answer 10

conversion of malate to oxaloacetate by malate dehydrogenase which produces another NADH

Question 11

How much energy is produced per glucose?

Answer 11

2 ATP, 10 NADH (2 cytosolic, 8 mitochondrial), 2 FADH2 and 2 GTP ~ 30-32 ATP in total

Question 12

Where and how is redox energy (NADH + FADH2) utilised?

Answer 12

mitochondria are the sites of oxidative phosphorylation in eukaryotes

Question 13

What is oxidative phosphorylation?

Answer 13

defined as the process of transforming redox energy formed under aerobic conditions during glycolysis and the citric acid cycle into chemical energy in the form of ATP

Question 14

How does oxidative phosphorylation drive the unfavourable formation of ATP?

Answer 14

redox energy is converted to an electrochemical gradient which drives the unfavourable formation of ATP

Question 15

What is the first step of phosphorylation?

Answer 15

1. transfer of electrons from NADH to complex I and/or from FADH2 to complex II

Question 16

What is the second step of phosphorylation?

Answer 16

2. flow of electrons through large multi-component inner mitochondrial membrane complexes and mobile electron transporters of the electron transport chain

Question 17

What is the third step of phosphorylation?

Answer 17

3. pumping of protons (H+) from the matrix to the intermembrane space (IMS) using the proton pumps of complex I, III, and IV as electrons flow through these complexes

Question 18

What is the fourth step of phosphorylation?

Answer 18

4. flow of protons (H+) from the IMS through the Fo component of ATP Synthase back into the matrix resulting in the rotation of the Fo component and the ɣ subunit of F1 and the synthesis of ATP from ADP and Pi by the F1 component

Question 19

What creates the proton gradient that is used to drive ATP synthesis?

Answer 19

flow of electron through complexes in the inner mitochondrial membrane and the subsequent pumping of protons from the matrix into the intermembrane space (IMS)

Question 20

How many H+ ions are pumped across complex I? How does this occur?

Answer 20

4 H+ ions
NADH + H+ donate 2 electrons which results in a series of events that end in the reduction of coenzyme Q (movement of electrons)

Question 21

What is Coenzyme Q?

Answer 21

a lipophilic IMS dwelling mobile electron carrier that transfers electrons from complex I and II to complex III

Question 22

What is complex II known as? Is it a H+ pump?

Answer 22

also known as succinate dehydrogenase from the TCA cycle

complex II is not a H+ pump (generates ubiquinol)

Question 23

How many H+ ions are pumped across complex III? How does this occur?

Answer 23

4 H+ ions
receives ubiquinol from complex I and II
uses the electrons from ubiquinol for proton pump action

Question 24

What is Cytochrome c?

Answer 24

a small soluble protein the resides in the IMS that accepts electrons from complex III and donates them to complex IV

Question 25

How many H+ ions are pumped across complex III? How does this occur?

Answer 25

4 H+ ions | electrons on cytochrome c generates proton pump action

Question 26

What is the electron transport chain?

Answer 26

flow of electrons through complexes in the inner mitochondrial membrane and the subsequent pumping of protons from the matrix into the IMS creates a proton gradient that is used to drive ATP synthesis

Question 27

How does mitochondrial ATP synthase use the H+ gradient?

Answer 27

uses H+ gradient to drive the unfavourable synthesis of ATP from ADP + Pi -> ATP synthesis results from the rotational catalysis mechanism

Question 28

What is the structure of ATP synthase?

Answer 28

comprised of a Fo (stalk) and F1 (head) component Fo spans the inner mitochondrial membrane and is comprised of the a, b and c subunit, subunits in mammals F1 is located on the matrix side of the inner membrane and is comprised of α, β, ɣ, σ, ε subunits

Question 29

How many binding sites does the F1 component have?

Answer 29

three nonequivalent adenine nucleotide binding sites, one for each a/B pair one site is in the B-ATP conformation, which binds ATP tightly, a second is in the B-ADP conformation which binds ADP + Pi and a third is in the B-empty conformation the proton motive force causes rotation of the γ subunit (green) as H+ is pumped through the Fo component.

Question 30

How many protons are required per ATP?

Answer 30

in mammals 8 protons are required to turn the ATP synthase through one complete cycle (only 8c subunits) so, estimated ≈4 protons are required synthesize 1 ATP

Question 31

Why much ATP is yielded per NADH and FADH2?

Answer 31

2. 5 ATP per NADH | 1. 5 ATP per FADH2

Question 32

Why does FADH2 produce less ATP than NADH?

Answer 32

because FADH2 does not pass through complex I

Question 33

Can oxidative phosphorylation occur without the Krebs cycle and vice versa?

Answer 33

no, these processes are not able to occur without each other

Question 34

Oxidative phosphorylation seems a lot of effort. Why don't we just use glycolysis? What is the advantage?

Answer 34

oxidative phosphorylation produces a lot more ATP