Glycolysis and the Krebs cycle

Question 1

What are the products of the Krebs cycle?

Answer 1

2 CO2
1 ATP
3 NADH
1 FADH2

Question 2

What are the products of glycolysis?

Answer 2

4 molecules of ATP produced but net gain of 2 by substrate-level phosphorylation
2 NADH and 2 water molecules produced
2 pyruvate produced from 1 glucose

Question 3

Describe the process of glycolysis :

Answer 3

Glycolysis harvests chemical energy by oxidising glucose to pyruvate
Occurs regardless if oxygen is present in the cytoplasm
2 major phases - energy investment phase and the energy payoff phase
10 steps make up the glycolytic pathway

Question 4

What is a high electron carrier?

Answer 4

NAD+ is a high energy electron carrier

Question 5

What is a co-enzyme?

Answer 5

Coenzyme - non protein compound that an enzyme requires to function
Easily cycled between oxidised and reduced states
Works with dehydrogenase enzymes to catalyse the removal of hydrogen atoms

Question 6

Describe the energy investment phase:

Answer 6

Enzyme Hexokinase transfers a phosphate group from ATP to glucose
Enzyme Phosphorglucoisomerase converts glucose 6-phosphate into fructose 6-phosphate
Enzyme Phosphofructokinase transfers a phosphate group from ATP to opposite end of the sugar
Enzyme Aldolase splits sugar molecule into 2 different 3-carbon sugars - G3P and DHAP
Enzyme Isomerase facilitates rapid conversion between G3P and DHAP

Question 7

Describe the energy payoff phase:

Answer 7

G3P is oxidised. Phosphate group attached to oxidised sugar forming 1,3-bisphosphogylcerate
Phosphoglycerokinase transfers phosphate group to ADP. 3-phosphoglycerate formed
Phosphoglyceromutase relocates phosphate group forming 2-phosphoglycerate
Enolase extracts water molecule forming phosphoenolpyruvate
Phosphoenolpyruvate converted to pyruvate by pyruvate kinase transferring a phosphate group to ADP

Question 8

What happens post glycolysis?

Answer 8

Before citric acid cycle pyruvate must be converted to Acetyl coenzyme A
Pyruvate carboxyl group is removed producing CO2
2-carbon fragment is oxidised forming acetate, extracted electrons are transferred to NAD+ forming NADH
Acetate combines with coenzyme A forming acetyl Co.A
1 glucose molecule produces 2 CO2, 2 acetyl Co.A and 2 NADH molecules

Question 9

Describe the process of the Krebs cycle:

Answer 9

Acetyl CoA adds 2-carbon acetyl group to oxaloacetate forming citrate
Aconitase converts citrate into isocitrate
Isocitrate oxidised by isocitrate dehydrogenase forming ⍺-ketoglutarate, CO2 and NADH are produced
⍺-ketoglutarate dehydrogenase + coenzyme A form succinyl CoA, CO2 and NADH are produced
Phosphate group transferred to GDP forming GTP by enzyme succinyl CoA synthetase
Enzyme succinate dehydrogenase oxidises succinate by transferring to hydrogens to FAD forming FADH2 and fumarate
Fumarase facilitates addition of water molecule to fumarate forming malate
Malate dehydrogenase oxidises malate to reduce NAD+ to NADH thus regenerating oxaloacetate