4 Metabolic Pathways And ATP Production II

Question 1

Q: How many reactions are in the krebs/ TCA cycle?

Answer 1

A: 8

Question 2

Q: Where is acetyl CoA produced and by which enzyme?

Answer 2

A: mitochondria, pyruvate dehydrogenase complex

Question 3

Q: What are the first 4 steps of the Krebs cycle?

Answer 3

A: Oxaloacetate (4C) -> citrate (6C)
E: citrate synthase
Acetyl-CoA in and HS-CoA + H+ out
(Addition of acetyl group)

Citrate (6C) -> isocitrate (6C)
(((E: aconitase
(Isomerisation where hydroxyl group is moved))))

Isocitrate (6C) -> alpha-ketoglutarate (5C)
E: isocitrate dehydrogenase
NAD+ in and CO2 + H+ + NADH out

alpha-ketoglutarate (5C) -> succinyl-CoA (4C)
E: alpha-ketoglutarate dehydrogenase complex
NAD+ and HS-CoA in and CO2 + H+ + NADH out

Question 4

Q: What are the last 4 steps of the Krebs cycle?

Answer 4

A: Succinyl-CoA (4C) -> succinate (4C)
E: succinyl CoA synthetase
GDP and Pi and H2O in and HS-CoA + GTP

succinate (4C) -> fumarate (4C)
E: succinate dehydrogenase
FAD in and FADH2 out

Fumarate (4C) -> malate (4C)
(((E: fumerase
Water in
Double bond is broken)))

Malate (4C) -> oxaloacetate (4C)
E: malate dehydrogenase
NAD+ in and H+ + NADH out

Question 5

Q: What catalyses the reaction between ADP and GTP (reversible)?

Answer 5

A: nucleoside diphosphokinase

Question 6

Q: What does one turn of the TCA cycle produce?

Answer 6

A: 3 NADH, 1 GTP, 1 FADH2, 2 CO2

Question 7

Q: Why is the Krebs cycle aerobic?

Answer 7

A: NAD+ and FAD needed are only regenerated via the transfer of electrons to oxygen during oxidative phosphorylation

Question 8

Q: Where do the TCA cycle enzymes reside?

Answer 8

A: mitochondrial matrix space since all proteins involved are soluble except succinate dehydrogenase- inner mito membrane

Question 9

Q: During oxidative phosphorylation, how many ATP do reducer cofactors yield?

NADH

FADH2

Answer 9

A: 3, 2

Question 10

Q: How many ATP does the oxidation of 1 acetyl CoA produce?

Answer 10

A: 12

Question 11

Q: What is the theoretical maximum yield of ATP from the aerobic oxidation of 1 glucose?

Answer 11

A: 38

Question 12

Q: What is the high energy linkage between acetate and CoA?

Answer 12

A: thioester

Question 13

Q: Draw the Krebs cycle diagram.

Answer 13

A: Diagram

Question 14

Q: In terms of protein metabolism, how is the amino acid alanine converted into acetyl CoA?

Answer 14

A: transamination of alanine by alanine aminotransferase to alpha-ketoglutarate

Results in pyruvate and glutamate. Pyruvate can enter TCA cycle.

Amine group transferred from amino acid to keto acid

Question 15

Q: What is the general degradation of amino acids?

Answer 15

A: aa group is removed and eventually excreted as urea

Carbon skeleton either goes into glucose production or def into Krebs cycle

Question 16

Q: What is the use of glycerol-phosphate and malate-asparate shuttles?

Answer 16

A: transfer NADH (more accurately, high energy electrons of NADH) across the cytosol into matrix of mitochondria

Question 17

Q: Which shuttles allow the transport of NADH (electrons of) across the cytosol into the mitochondrial matrix?

Answer 17

A: malate-aspartate

Glycerol phosphate

Question 18

Q: Which cells have the glycerol phosphate shuttle?

Answer 18

A: skeletal muscle and brain

Question 19

Q: Which cells have the malate-aspartate shuttle?

Answer 19

A: liver, kidney, heart

Question 20

Q: Draw a diagram and explain the glycerol phosphate shuttle?

Answer 20

A: (Electrons are transferred rather than NADH itself)

1. Cytosolic glycerol-3-phosphate dehydrogenase transfers electrons to dihydroxyacetone phosphate to form glycerol 3-phosphate

dihydroxyacetone phosphate -> glycerol 3-phosphate
E: (cytosolic) glycerol-3-phosphate dehydrogenase
NADH + H+ in and NAD+ out

2. Membrane form of same enzyme transfers electrons to FAD where then transferred to coE Q (part of electron transport chain)

Glycerol-3-phosphate -> dihydroxyacetone phosphate
E: (membrane bound) glycerol-3-phosphate dehydrogenase
E-FAD in and E-FADH2 out

E-FADH2 -> E-FAD
Q in and QH2 out

Question 21

Q: Draw a diagram and explain the malate-aspartate shuttle. Transamination involved?

Answer 21

A: Regeneration of cytosolic NAD+ = glycolysis: glucose -> pyruvate
NAD+ in and NADH + H+ out

1. hydride ion (H-) is transferred from cytoplasmic NADH to oxaloacetate to give malate, catalysed by cytosolic malate dehydrogenase MDH

oxaloacetate -> malate
E: (cytosolic) malate dehydrogenase MDH
NADH (cytoplasmic) + H+ in and NAD+ out

2. Malate is transported into mitochondria where it is rapidly re oxidised by NAD+ to give oxaloacetate and NADH, catalysed by mitochondrial MDH

malate -> oxaloacetate
E: (mitochondrial) malate dehydrogenase
NAD+ in and NADH + H+ out

A: malate into mito and alpha-ketoglutarate into cyto
B: glutamate into mito and aspartate into cyto

A: Transamination involved:
Glutamate + oxaloacetate-> alpha-ketoglutarate +aspartate

Transamination allows different compounds to pass through transporters

Question 22

Q: Catabolic or anabolic reactions?

NADPH
NADH

Answer 22

A: anabolic (building), catabolic (breakdown)

Question 23

Q: What is the collective of a H+ (proton) and 2 electrons known as?

Answer 23

A: H-

Question 24

Q: What is reductive biosynthesis?

Answer 24

A: anabolic pathways that require hydride ions (H-)

Question 25

Q: What are two examples of the use of NADPH in reductive biosynthesis?

Answer 25

A: cofactor involved in thymidine synthesis

Cofactor involved in biosynthesis of cholesterol

Question 26

Q: How does NADH assist as a cofactor in th biosynthesis of cholesterol?

Answer 26

A: catalyses the final reaction

C=C bond is reduced by transfer of a hydride ion (H-)