Biochemistry Chapter 10: Carbohydrate Metabolism II

Question 1

Acetyl-CoA

Answer 1

Contains a high energy thioester bond that can be used to drive other reactions when hydrolysis occurs

Question 2

What can acetyl-CoA be formed from?

Answer 2

pyruvate via pyruvate dehydrogenase complex (a 5-enzyme complex in the mitochondrial matrix that forms and is also inhibited by - acetyl-CoA and NADH)

Question 3

Pyruvate dehydrogenase

Answer 3

oxidizes pyruvate, creating CO2; it requires thiamine pyrophosphate (vitamin B1, TPP) and Mg2+

Question 4

Dihydroprpyl transacetylase

Answer 4

oxidizes the remaining two carbon molecule using lipoic acid, and transfers the resulting acetyl group to CoA, forming acetyl-CoA.

Question 5

Dihydrolipoyl dehydrogenase

Answer 5

uses FAD to reoxidize lipoic acid, forming FADH2. This FADH2 can later transfer electrons to NAD+, forming NADH that can feed into the electron transport chain

Question 6

Pyruvate dehydrogenase kinase

Answer 6

phosphorylates PDH when ATP or acetyl-CoA levels are high, turning it off

Question 7

Pyruvate dehydrogenase phosphatase

Answer 7

dephosphorylates PDH when ADP levels are high, turning it on

Question 8

Acetyl-CoA can be formed from…

Answer 8

fatty acids, which enter the mitochondria using carriers

Question 9

How does fatty acid and CoA move into the intermembrane space?

Answer 9

Couples with fatty acid in the cytosol to form fatty acyl-CoA, which moves to the intermembrane space.

Question 10

How does fatty acid acetyl-CoA cross the inner membrane

Answer 10

acyl is transferred to carnitine to form acyl-carnitine

Question 11

What is the final step to make acetyl-CoA?

Answer 11

acyl group is transferred to a mitochondrial CoA to re-form fatty acyl-CoA, which can undergo Beta-oxidation to form acetyl-CoA

Question 12

What can acetyl-CoA be formed from?

Answer 12

the carbon skeletons of ketogenic amino acids, ketone bodies and alcohol.

Question 13

Where does the citric acid cycle take place?

Answer 13

The mitochondrial matrix

Question 14

What is the main purpose of the citric acid cycle?

Answer 14

main purpose is to oxidize acetyl-CoA to CO2 and generate high-energy electron carriers (NADH and FADH2) and GTP

Question 15

Citrate synthase

Answer 15

couples acetyl-CoA to oxaloacetate and then hydrolyzes the resulting product, forming citrate and CoA-SH.
(-) ATP, NADH, succinyl-CoA and citrate

Question 16

aconitase

Answer 16

isomerizes citrate to isocitrate

Question 17

isocitrate dehydrogenase

Answer 17

oxidizes and decarboxylates isocitrate to form alpha-ketoglutarate. This enzyme generates the first CO2 and first NADH of the cycle. As the rate limiting step of the citric acid cycle, it is heavily regulated:
(-) ATP and NADH
(+) ADP and NAD+ are activators

Question 18

A-ketoglutarate dehydrogenase complex

Answer 18

acts similarly to PDH complex metabolizing a-ketoglutarate to form succinyl-CoA. This enzyme generates the second CO2 and second NADH of the cycle. It is inhibited by ATP, NADH and succinyl-CoA;
(+) ADP and Ca2+

Question 19

Succinyl-CoA synthetase

Answer 19

hydrolyzes the thioester bond in succinyl-CoA to form succinate and CoA-SH. This enzyme generates the one GTP generated in the cycle

Question 20

Succinate dehydrogenase

Answer 20

oxidizes succinate to form fumarate. This flavoprotein is anchored to the inner mitochondrial membrane because it requires FAD, which is reduced to form the one FADH2 generated in the cycle.

Question 21

Fumarase

Answer 21

hydrolyzes the alkene bond of fumarate, forming malate

Question 22

Malate dehydrogenase

Answer 22

oxidizes malate to oxaloacetate. This enzyme generates the third and final NADH of the cycle

Question 23

Electron transport chain

Answer 23

takes place on the matrix-facing surface of the inner mitochondrial membrane

Question 24

What donates electrons to the electron transport chain?

Answer 24

NADH

Question 25

What is the progression of electrons in the ETC?

Answer 25

• Complex I
• Complex II
• Complex III
• Complex IV

Question 26

Complex I

Answer 26

uses an iron-sulfer cluster to transfer electrons from NADH to flavin mononucleotide (FMN), and then to coenzyme Q, forming CoQH2. Four protons are translocated by complex I.

Question 27

Complex II

Answer 27

Uses an iron-sulfer cluser to transfer electrons from succinate to FAD, and then to CoQ, forming CoQH2. No proton pumping occurs at Complex II

Question 28

Complex III

Answer 28

uses an iron-sulfer cluster to transfer electrons from CoQH2 to heme, forming cytochrome c as part of the Q cycle. Four protons are translocated by complex III

Question 29

Complex IV

Answer 29

uses cytochromes and Cu2+ to transfer electrons in the form of hydride ions (H-) from cytochrome c to oxygen, forming water. Two protons are translocated by complex IV.

Question 30

glycerol 3-phosphate shuttle

Answer 30

electrons are transferred from NADH to dihydroxyacetone phosphate (DHAP), forming glycerol 3-phosphate. these electrons can then be transferred to mitochondrial FAD, forming FADH2

Question 31

Malate-Apartate shuttle

Answer 31

electrons are transferred from NADH to oxaloacetate, forming malate. Malate can then cross the inner mitochondrial membrane and transfer the electrons to mitochondrial NAD+, forming NADH.

Question 32

Proton-motive force

Answer 32

the electrochemical gradient generated by the ETC across the inner mitochondrial membrane.

Question 33

Chemiosmotic coupling

Answer 33

The utilization of the proton-motive force generated by the electron transport chain to drive ATP synthesis in oxidative phosphorylation.

Question 34

ATP synthase

Answer 34

the enzyme responsible for generating ATP from ADP and an inorganic phosphate.

Question 35

F0 portion

Answer 35

ion channel allowing protons to flow down the gradient from the intermembrane space to the matrix

Question 36

F1 portion

Answer 36

uses the energy released by the gradient to phosphorylate ADP into ATP.

Question 37

Energy yield of glycolysis

Answer 37

2 NADH and 2 ATP

Question 38

Energy yield of pyruvate dehydrogenase

Answer 38

1 NADH per molecule of pyruvate. (each glucose has 2 pyruvate molecules)

Question 39

Energy yield of citric acid cycle

Answer 39

3 NADH, 1 FADH2, and 1 GTP (2 times per glucose)

Question 40

Energy yield of NADH

Answer 40

2.5 ATP,

Question 41

Energy yield of FADH2

Answer 41

1.5 ATP

Question 42

Energy yield of GTP

Answer 42

converted to ATP

Question 43

How many ATP per glucose molecule total?

Answer 43

25