Glycolysis

Question 1

Ways to generate ATP

Answer 1

1. Carbohydrates undergo glycolysis, TCA and ETC
2. Lipids undergo beta-oxidation, TCA, ETC
3. Proteins undergo deamination, TCA, ETC

Question 2

Pathways in which glucose can go

Answer 2

1. Glycolysis (ATP)
2. Glycogenesis (glycogen stores)
3. Lipogenesis (fat stores)

Question 3

Normal glucose level in blood

Answer 3

~5mmol/L

Question 4

Glucose transporters (GLUT)

Answer 4

Passive transporters that allow glucose molecules to be transported from blood to tissues

Question 5

GLUT 2

Answer 5

Transports glucose into liver

insulin insensitive
bidirectional

Question 6

GLUT 4

Answer 6

Transports glucose into heart, skeletal muscle, fat

unidirectional
insulin sensitive

Question 7

SGLT

Answer 7

Transports glucose into blood capillaries

Small intestine (digestion) and kidney (filtrate reabsorption)

Question 8

Glucose Trapping

Answer 8

Glucose phosphorylation traps the molecule for glycolysis and the added charged phosphate group prevents diffusion out of the liver by the bidirectional GLUT 2.

Enzymes convert glucose into glucose-6-phosphate . (hexokinase in muscle, glucokinase in liver)

Question 9

Insulin’s role for glycolysis

Answer 9

High insulin will indicate high levels of glucose in the blood. Insulin will stimulate GLUT 4 transporter of glucose into the muscle for glycolysis, and insulin will also stimulate glucokinase activity in the liver to increase glucose trapping.

Question 10

Preparatory phase of glycolysis

Answer 10

• Spends 2 ATP
• Either hexokinase (muscle) or glucokinase (liver) will trap glucose inside
• phosphofructokinase (PFK) controls the rate of glycolysis since it is the committed step. Makes fructose 1,6-bisphosphate

Question 11

What regulates phosphofructokinase (PFK)?

Answer 11

Allosterically regulated by ATP. When ATP is high, this enzyme will inhibit glycolysis. When AMP high, this will be reversed.

Question 12

Payoff phase of glycolysis

Answer 12

• Produces 4 ATP molecules (net=2ATP), 2NADH, 2 pyruvate

-anaerobic

Question 13

Fate of pyruvate

Answer 13

Under aerobic conditions, pyruvate will enter TCA cycle as acetyl-CoA.

Under anaerobic conditions, will be converted by lactate dehydrogenase to lactic acid. Lactic acid is a weak acid so dissociates into H+, lactate, and NAD+. NAD+ recycled back to be used in payoff phase of glycolysis to make 4ATP, 2NADH, 2 pyruvate again.

Question 14

What can prolonged anaerobic glycolysis cause?

Answer 14

Metabolic Acidosis. Increase in H+ from lactic acid breakdown, causes a decrease in pH and a decrease in HCO3- (increases anion gap).

Question 15

Glycolysis in RBCs

Answer 15

Can only use anaerobic glycolysis because RBCs don’t have mitochondria.

-Special shunt: 1,3-bisphosphoglycerate –> 2,3-bisphosphoglycerate (2,3-BPG) –> 3-phosphoglycerate

2,3-BPG binds to hemoglobin which allows for release of O2 to needy tissues.