Glycolysis

Question 1

What are the three stages of catabolism?

Answer 1

• Hydrolysis of complex molecules into constituent monomers
• Conversion to acetyl CoA
• Oxidation of acetyl CoA - produces ATP and NADH

Question 2

Describe anabolism.

Answer 2

• Endergonic
• Requires reducing coenzymes - NADH

Question 3

Define cellular respiration

Answer 3

• Set of metabolic reactions - CATABOLIC
• Convert chemical energy from oxygen to cellular energy, ATP and CO2

Question 4

Describe glycolysis.

Answer 4

• Occurs in cytoplasm
• Can occur aerobically or anaerobically depending on oxygen availability
• Allows production of ATP even in anaerobic conditions

Question 4

Describe the energy investment phase.

Answer 4

• Phosphate group from ATP transferred to glucose by glucokinase/hexokinase, forming G6P
• Isomerisation - converted to F6P
• Phosphorylation of F6P by PFK to form F 1,6-Bisphosphate.
• PFK allosterically inhibited by high ATP

Question 5

Describe the cleavage phase.

Answer 5

• F1,6-Bisphosphate cleaved. by aldolase to form G3P and DHAP
• DHAP converted to G3P

Question 6

What is the rate-limiting step in glycolysis?

Answer 6

• PHOSPHORYLATION by PFK (during energy investment phase)

Question 7

Describe the generation phase in glycolysis. PART 1

Answer 7

• G3P oxidised and phosphorylated to 1,3-BPG. NAD+ reduced to NADH
• Phosphate transfer from 1,3-BGP to ADP. Forms 3-phosphoglycerate and ATP

Question 8

Describe the generation phase in glycolysis. PART 2

Answer 8

• 3-PG isomerised to 2-PG - dehydrates to form PEP
• Pyruvate kinase transfers phosphate group from PEP and ADP produciong pyruvate and ATP

Question 9

What occurs following aerobic glycolysis?

Answer 9

• Pyruvate enters mitochondria, oxidised to acetyl CoA and enters TCA cycle
• Reduction of NAD+ and FAD to NADH and FADH2
• Carry electrons to ETC - oxidative phosphorylation occurs

Question 9

Why are the following steps irreversible?
-G6P production
- F-1,6 BP production
- Phosphoenol pyruvate to pyruvate

Answer 9

• Highly negative ΔG values

Question 10

Describe anaerobic glycolysis. PART 1

Answer 10

• Aerobic metbaolism no longer keeps up with energy demands
• Lactic acid formation
• Less efficient method of ATP production
• Lactate converted to glucose in liver - carried to muscles

Question 11

Describe anaerobic glycolysis PART 2

Answer 11

• Pyruvate reduced to lactate by LDH
• Reduction allows NADH oxidisation to NAD+
• NAD+ re-enters glycolysis to synthesise ATP
• Takes place in areas without oxygen - eye, cornea and RBCs

Question 12

Describe hexokinase

Answer 12

• Found in blood, tissues.
• Low Km and Vmax.
• Inhibited by G6P - efficient at low glucose

Question 13

Describe glucokinase

Answer 13

• Found in liver, pancreas.
• High Km, Vmax.
• Regulated by insulin. High insulin = high GK activity

Question 14

What inhibits and activates PFK?

Answer 14

• Inhibited by citrate, ATP and H+
• Activated by AMP and Fructose 1,6-bisphosphate

Question 15

Describe pyruvate kinase regulation.

Answer 15

• ALLOSTERIC - Activated by high Fructose 1,6-BP. Inhibited by high ATP
• HORMONAL - INSULIN AT HIGH GLUCOSE activates PK. Glucagon at LOW GLUCOSE increases AMP, inhibit PK

Question 16

How does insulin regulate glycolysis?

Answer 16

• Stimulate uptake of glucose from blood at high glucose
• Activates GK, PFK and PK

Question 17

How does glucagon regulate glycolysis?

Answer 17

• At low glucose, stimulates conversion of glycogen from liver into glucose
• Inhibits GK, PFK and PK

Question 18

Give an example of hemolytic anaemia.

Answer 18

• Pyruvate kinase deficiency e.g G6PD deficiency
• Autosomal recessive
• Reduced glycolysis and ATP production.
• Premature RBC lysis (no ATP to maintain sodium-potassium ATPase to maintain cell shape)