Lecture 8: Glycolysis

Question 1

What are the 10 steps of glycolysis

Answer 1

1. Glucose is phosphorylated to glucose-6-phosphate (uses 1 ATP)
2. Glucose-6-phosphate is isomerised to fructose-6-phosphate
3. Fructose-6-phosphate is phosphorylated to fructose-1,6- bi phosphate (uses one ATP)
4. Fructose-1,6-bi phosphate is cleaved into dihydroxyacetone phosphate and glyceraldehyde-3-phosphate (G3P)
5. Dihydroxyacetone is isomerised to glyceraldehyde-3-phosphate
6. Glyceraldehyde-3-phosphate is oxidised to 1,3- bisphosphoglycerate (required 1 NAD and Pi)
7. 1,3-bisphosphoglycerate is dephosphorylated to 3-bisphosphoglycerate (produces one ATP)
8. The remaining phosphate group is transferred to a different carbon so 3-bisphosphoglycerate is transferred to 2-phosphoglycerate
9. Water is removed from 2-phosphoglycerate to form phosphoenolpyruvate
10. One phosphate group is transferred to ADP Forming ATP
    Phosphoenolpyruvate is dephosphorylated to pyruvate (generation of 1 ATP)
    Remember 6-10 occurs twice for each one glucose molecule

Question 2

What is the overall equation for glycolysis?

Answer 2

Glucose-> pyruvate
Glucose + 2ADP + 2 Pi + 2NAD
2 pyruvate + 2 ATP + 2 NADH + 2H + 2H2O

Input = 2 ATP 
Output = 4 ATP 
Overall = 2 ATP per glucose

Question 3

What are the 3 fates of pyruvate

Answer 3

1. Aerobic respiration
2. Ethanol fermentation
3. Lactic acid fermentation

Question 4

1. Aerobic respiration

We’re does it happen, and what are we left with?

Answer 4

In the mitochondrion

Pyruvate is completely metabolised to CO2 and H2O

Question 5

2. Ethanol fermentation
   We’re does it occur and what to
   What is its overall equation

Answer 5

In the cytoplasm
In yeast in the absence of O2
-it’s a 2 step reaction
-overall equation for ethanol fermentation
Glucose-> ethanol
Glucose + 2ADP + 2 Pi -> 2 ethanol + 2CO2 + 2 ATP + 2H2O

Question 6

3. Lactic acid fermentation

Answer 6

In the cytoplasm
-in muscles and many microbes
-a single step reaction
Overall equation for lactic acid fermentation:
Glucose -> lactate
Glucose + 2 ADP + 2Pi -> 2 lactate + 2 ATP + 2 h2O

Question 7

What are the energetics of lactic acid fermentation?

Answer 7

Energetics of lactic acid fermentation 
We have 2 half reactions 
1.glucose -> 2 lactate
2. 2 ADP + 2 Pi -> 2 ATP + 2H2O
Energy is released by reaction one and trapped by reaction 2

Question 8

Why do cells convert pyruvate to ethanol or lactate when O2 is not available?

Answer 8

Because NADH is re-oxidised to NAD+ for reuse

Energy generation with no net loss of resources