Lec 7: Glycolysis I (Roseman)

Question 0

In the muscle, what activates PFK1?

Answer 0

AMP (high during exercise, while ATP is low)

Question 1

Describe the Km for glucose of hexokinase vs. glucokinase. What is the implication?

Answer 1

Hexokinase has a low Km (high affinity). Glucokinase has a high Km (low affinity). Hexokinase is working even when glucose levels are low. Glucokinase only works after a meal when glucose levels are high.

Question 2

In the muscle what inhibits PFK1?

Answer 2

ATP and citrate. High ATP–you don’t need glycolysis. High citrate–intramitochondrial levels of NADH and ATP are high so the TCA cycle is saturated.

Question 3

What does insulin stimulate in glycolysis?

Answer 3

Glucokinase is induced when insulin levels are high. Insulin also stimulates phosphatases that dephosphorylate and activate pyruvate kinase.

Question 4

In the conversion of pyruvate to lactate, what is being oxidized and what is being reduced?

Answer 4

Pyruvate reduced to lactate. NADH oxidized to NAD+. Regenerated NAD+ can now continue glycolysis.

Question 5

What is the rate limiting step?

Answer 5

Phosphofructokinase step (F-6-P to F-1,6-bisphosphate)

Question 6

What are the four fates of pyruvate?

Answer 6

1. Converted to lactate (used by liver for gluconeogenesis or by heart and kidney which convert it to pyruvate and oxidize for energy)
2. Converted to acetyl CoA (enters TCA)
3. Converted to oxaloacetate (replenishes intermediates of TCA)
4. Transaminated to alanine

Question 8

What can not go across the mitochondrial membrane?
A. Oxaloacetate
B. malate
C. Aspartate
D. Glutamate 
E. Alpha-ketoglutarate

Answer 8

A. Oxaloacetate

Question 9

How many moles of ATP does one mole of NADH produce in the electron transfer chain? How many does one mole of FADH2 produce?

Answer 9

NADH–2.5 moles

FADH2–1.5 moles

Question 10

What does hexokinase do in glycolysis?

Answer 10

adds phosphate to glucose trapping it in the cytoplasm secondary to it being an irreversible reaction

Question 11

Which steps in glycolysis are irreversible?

Answer 11

(step 1)
Glucose:
Step 1: Hexokinase (kinase added to glucose in the 6 position)
glucose-6 phosphate

(step 3)
Fructose-6-phosphate
Step 3: Phosphofructokinase (phospate added to fructose in the 1 position)
Fructose 1,6-biphosphate

(step 10)
Phosphoenol pyruvate
Step 10: Pyruvate Kinase (creates pyruvate by removing phosphate)
Pyruvate

Question 12

What is the rate limiting step of glycolysis?

Answer 12

(step 3)
Fructose-6-phosphate
Step 3: Phosphofructokinase (phospate added to fructose in the 1 position)
Fructose 1,6-biphosphate

Question 13

Describe the first four steps of glycolysis (glucose breakdown):

Answer 13

Stage 1: Glucose Breakdown
Glucose:
Step 1: Hexokinase (kinase added to glucose in the 6 position)
glucose-6 phosphate
Step 2: Phosphoglucose Isomerase (carbonyl switched from 1 to the 2 carbon with hydroxide group)
Fructose-6-phosphate
Step 3: Phosphofructokinase (phospate added to fructose in the 1 position)
Fructose 1,6-biphosphate
Step 4: Aldolase (splits into to two molecules, creating a new aldehyde)
Dihydroaxyactone phosphate

Question 14

Describe steps 5-10 of glycolysis:

Answer 14

Stage 2: Conversion to Pyruvate

Step 5: triphosphate isomerase (shifts the carbonyl from the 2 to 3 position = ketone to an aldehyde)
Glyceraldehyde-3-phosphate

Step 6:Glyceraldehyde-3-phosphate Dehydrogenase (GENERATES high energy P bond; oxidizes trioses, using NAD+)
Glycerate 1,3-biphosphate

Step 7: Phosphoglycerate Kinase (TRANSFERS ~P TO ADP)
Glycerate 3-phosphate

Step 8: Phosphoglycerate Mutase (phosphate shifts to the 2 position)
Glycerate-2-phosphate

Step 9: Enolase (hydroxl group removed)
Phosphoenol pyruvate

Step 10: Pyruvate Kinase (creates pyruvate by removing phosphate)
Pyruvate