Glycolysis and Krebs Cycle

Question 1

What is the hydride ion (H-)?

Answer 1

• hydrogen atom with an extra electron
• breakdown of carbohydrates can supply protons and electrons for chemical energy provision
• when a substrate is oxidised it gives up 2 hydrogen atoms, passing one as a hydride ion (H-) to NAD+ (to make NADH) or FADH (to make FADH2) and the other is released as a proton (H+) to the aqueous environment

Question 2

What is glycolysis?

Answer 2

• an anaerobic metabolic pathway with a low energy yield taking place in the cytosol
• reactant: glucose
• products: pyruvate x2 and NADH

Question 3

What is the investment phase?

Answer 3

2 ATP molecules used to phosphorylate glucose (thermodynamically favours catabolism)

Question 4

What is the pay off phase?

Answer 4

• x4 ATP molecules
• x2 NADH
• x2 high energy triose sugars
• 2H+

Question 5

How does exercise speed up glycolysis?

Answer 5

• exercise can augment the glycolytic rate by 100 fold
  
  • substrate availability: increased glycogenolysis favours glycolysis to proceed
  • physiological factors: greater blood flow with exercise increases flow of glucose molecules towards the active muscle
  • cellular factors: increased glucose uptake by glucose transporters, such as GLUT4
  • molecular factors: allosteric activation of pyruvate kinase and phosphofructokinase involved with glycolysis

Question 6

What is the krebs cycle?

Answer 6

• an aerobic metabolic pathway with a low energy yield taking place in the mitochondrial matrix
• reactant: Acetyl CoA
• products: ATP, NADH, FADH2

Question 7

What is pyruvate oxidation?

Answer 7

• shutting of pyruvate to the mitchondria can yield large amounts of ATP
• mitochondria are the site of multiple oxidation reactions
• pyruvate can be oxidised to acetyl coA via pyruvate dehydrogenase, in turn generating NADH

Question 8

What happens in the krebs cycle?

Answer 8

• a series of 9 reactions that oxidise acetyl coA into carbon dioxide via a series of metabolites that produce electron carriers in the mitochondria - NADH and FADH2
• a small amount of ATP is produced, but 6 NADH and 2 FADH2 can be utilised for a high energy yield in the mitochondria
  
  • note that 1 glucose produces 2 pyruvate and then 2 acetyl coA molecules
• the metabolites are completely recycled
• similar to glycolysis, the krebs cycle can be upregulated 100 fold during exercise by changed in key metabolites that modulate key enzymatic steps:
  
  • decrease in ATP/ADP and increase in Ca2+

Question 9

What are some regulatory enzymes?

Answer 9

• pyruvate dehydrogenase
  
  • citrate synthase
  • aconitase
  • aconitase
  • isocitrate dehydrogenase
  • a-ketoglutarate dehydrogenase
  • succinyl-coA synthetase
  • succinate dehydrogenase
  • funarase
  • malare dehydrogenase