Glycolysis

Question 1

Describe the two types of transporters for glucose into or out of a cell.

Answer 1

1. GLUTs transport with concentration gradient.
2. SGLT are symporters, glucose goes against its conc. gradient attached to a sodium, which is going with its conc. gradient.

Question 2

What are the key substrates and products of glycolysis?

Answer 2

Substrates: 1 glucose, 2 NAD+, 2 ADP + Pi
Products: 2 Pyruvates, 2 NADH, 2 ATP

Question 3

What is the first reaction in glycolysis catalyzed by?

Answer 3

Hexokinase in most tissues, and by glucokinase in the liver . Glucokinase has higher Km for glucose. Hexokinase is inhibited by its product.

Question 4

What cycle takes lactate into the liver to produce glucose?

Answer 4

The Cori Cycle.

Question 5

How much ATP can FAD2H produce? NADH? Acetyl CoA?

Answer 5

FAD2H: 1.5 ATP
NADH: 2.5 ATP
Acetyl CoA: 10 ATP (generates FAD2H and NADH)

Question 6

In order for the reducing power of NADH (prod. in cytosol) to be used to generate ATP, it must be in mitochondria. Cannot cross inner membrane. How is this done in the various tissues of the body?

Answer 6

In heart, liver, and kidneys, malate aspartate shuttle is pulled forward by NADH oxidation on electron transport chain in mitochondria.

In skeletal muscle and brain, glycerol 3-phosphate shuttle is used by FAD(2H) oxidation. Not as efficient.

Question 7

What are the 3 key regulatory steps in glycolysis?

Answer 7

1. Phosphorylation of glucose by glucokinase (liver) or hexokinase (everywhere else).
2. Phosphorylation of fructose 6-phosphate by PFK-1.
3. Transfer of phosphate from phosphoenolpyruvate to ADP by pyruvate kinase (PK).

Question 8

What are the 4 allosteric binding sites on PFK-1? What is their effect on glycolysis?

Answer 8

Activating:
-AMP (most sensitive indicator of energy balance)
-Fructose 2,6-bisphosphate
Inhibitory:
-ATP (unless at real low concentrations, than it’s an activator)
-Citrate

Question 9

Describe the diversion of substrates from glycolysis.

Answer 9

1. Glucose-6- Phosphate leaves to pentose phosphate pathway to produce NADPH and ribose
2. Glucose-6-phosphate goes to glycogen synthesis, the storage form of glucose.
3. Dihydroxyacetone phosphate goes glycerol 3-phosphate (NADH shuttle; triglyceride synthesis)
4. 2,3-BPG shunt
5. Serine