Glycolysis and Krebs Cycle Review

Question 1

Preparatory Phase function
Pay-off Phase function

Answer 1

Carbon is activated via 2 phosphorylation events, expending ATP.
The ring is cleaved to form 2 trioses

Trioses are oxidized
Phosphoryl groups used to produce ATP via substrate level phosphorylation of ADP
4 ATP (2 net) produced and 2 pyruvate

Question 2

Preparatory Phase of Glycolysis steps

Answer 2

1) Glucose —> Glucose-6-phosphate catalyzed by hexokinase (all cells) or glucokinase (liver)
- ATP consumed

2) Glucose-6-phosphate —> Fructose-6-phosphate catalyzed by phosphoglucose isomerase

3) Fructose-6-phosphate —> Fructose-1,6-bisphosphate catalyzed by phosphofructokinase-1
- ATP consumed

4) Fructose-1,6,-bisphosphate —> Glyceraldehyde-3-phosphate + Dihydroxyacetone phosphate catalyzed by aldolase

5) Dihydroxyacetone phosphate —> glyceraldehyde-3-phosphate catalyzed by triose phosphate isomerase

Question 3

Pay-off phase of glycolysis steps (2x)

Answer 3

1) Glyceraldehyde-3-phosphate+ Pi —> 1,3-bisphosphoglycerate catalyzed by glyceraldehyde-3-phosphate dehydrogenase
- NADH + H+ produced

2) 1,3-bisphosphoglycerate —> 3-phosphoglycerate catalyzed by phosphoglycerate kinase
- ATP produced

3) 3-phosphoglycerate —> 2-phosphoglycerate catalyzed by phosphoglycerate mutase
- H2O produced

4) 2-phosphoglycerate + H2O —> phosphoenolpyruvate catalyzed by enolase

5) Phosphoenolpyruvate —> pyruvate catalyzed by pyruvate kinase
- ATP produced

Anaerobic conditions:
6) Pyruvate —> lactate catalyzed by lactate dehydrogenase
- NAD+ produced

Question 4

Krebs Cycle

Answer 4

1) Acetyl coA + oxaloacetate –> Citrate + coA
Citrate synthase

2) Citrate –> Isocitrate
Aconitase

3) Isocitrate + NAD+ –> a-ketoglutarate + NADH + H+ + CO2
Isocitrate dehydrogenase

4) a-ketoglutarate + NAD+ + CoA –> succinyl coA + NADH + H+ + CO2
A-ketoglutarate dehydrogenase

5) succinyl-coA + GDP + Pi –> succinate + coA + GTP
succinate thiokinase

6) succinate + FAD –> fumarate + FADH2
succinate dehydrogenase

7) fumarate –> malate
fumarase

8) malate + NAD+ –> oxaloacetate + NADH + H+
malate dehydrogenase

Question 5

Krebs cycle products per pyruvate

Answer 5

2 CO2
1 FADH2
1 GTP
3 NADH
3 H+

Oxidative decarboxylation of intermediates

Question 6

Arsenic inhibits which enzymes?

Malonate?

Fluorocitrate?

Antimyacin?

Oligomyacin?

Answer 6

These inhibitors can be used in the lab to test efficacy of Krebs cycle efficiency
Arsenic inhibits: PDH and KGDH (a-ketglut)
Malonate: succinate dehydrogenase
Fluorocitrate: aconitase

These inhibitors can be used to measure mitochondrial respiration:
Antimyacin: inhibts complex III
Oligomyacin: inhibits complex V

Question 7

Irreversible reactions in Krebs cycle

Answer 7

1, 3 and 4 are one way
Citrate synthase, isocitrate dehydrogenase and a-ketoglutarate dehydrogenase
Also pyruvate dehydrogenase

Question 8

What is a keto acid dehydrogenase?
Example?

Answer 8

any enzyme using coA
ex. a-ketoglutarate dehydrogenase catalyzing a-ketoglutarate –> succinyl-coA

Question 9

Nutrients required for cellular respiration

Answer 9

Minerals: Mn, Fe (Ca and Mg as activators)
Cofactors: Niacin (B3, NADH), Thiamine (B1, TPP), Pantothenic acid (B5), Biotin (B7), (ribo)Flavin (B2, FMN)
Glucose for adenosine production and AA for protein synthesis

Question 10

Intermediates from Krebs cycle can be used to build:

Answer 10

• amino acids
• porphyrin rings/heme (succinyl coA)
• nucleotides (ribose-5-phosphate PPP)
• fatty acids (citrate)
• urea cycle (fumarate)
• glucose via gluconeogenesis

Question 11

NADH inhibits which steps of the Krebs cycle?

Answer 11

PDH, citrate synthase, isocitrate dehydrogenase, a-ketoglutarate dehydrogenase, malate dehydrogenase

Question 12

ATP inhibits which steps of Krebs cycle?

GTP?

Answer 12

ATP inhibits: PDH, citrate synthase, isocitrate dehydrogenase, a-ketoglutarate dehydrogenase

GTP inhibits: a-ketoglutarate dehydrogenase

Question 13

Succinyl coA is an allosteric regulator for which enzyme(s) in Krebs cycle?

Answer 13

Succinyl-coA inhibits: Citrate synthase and a-ketoglutarate dehydrogenase

Question 14

Ca2+ is an allosteric regulator for which enzyme(s) in Krebs cycle?

Mg2+?

Answer 14

Ca2+ activates: PDH, isocitrate dehydrogenase, a-ketoglutarate dehydrogenase

Mg2+ activates: PDH

Question 15

Acetyl coA is an allosteric regulator for which enzyme(s) in Krebs cycle?

Answer 15

Acetyl CoA inhibits: PDH
Acetyl coA activates: citrate synthase

Question 16

Citrate is an allosteric regulator for which enzyme(s) in Krebs cycle?

Answer 16

Citrate as a product inhibits citrate synthase