Fermentation and Regulation of Glycolysis

Question 1

Glycolysis sucks at producing ATP, but is necessary bc it produces

Answer 1

2NADH which is necessary further down to produce ATP

Question 2

Regeneration of NAD+

Answer 2

There are limited amounts of NAD+ in the cell which is derived from vitamin niacin
NAD+ must be regenerated for glycolysis to proceed

Question 3

The 3 possible fates for pyruvate:

Answer 3

1) Anaerobic conditions for plants = alcoholic fermentation
2) Anaerobic conditions for humans = lactic acid fermentation
3) Aerobic conditions = CAC

Question 4

Alcoholic fermentation

Answer 4

Releases CO2 going to acetaldehyde, then releases NAD+ and produces ethanol

Question 5

Lactic acid fermentation

Answer 5

Releases NAD+ and produces lactate

Question 6

Aerobic conditions for pyruvate

Answer 6

Produces Acetyl CoA, which releases a CO2

then proceeds for further oxidation

Question 7

Pyruvate from the cytosol then enters the

Answer 7

mitochondria to produce Acetyl CoA

Question 8

What steps/enzymes of glycolysis are regulated and irreversible?

Answer 8

• Hexokinase (step 1)
• PFK-1 (step 3)
• Pyruvate kinase (step 10)
  All of these points are where ATP is used/produced in irreversible rxns

Question 9

These regulatory enzymes become more or less active in response to the reversible binding of

Answer 9

allosteric effectors or covalent modification (Pi addition or removal)

Question 10

Which step of glycolysis is the most regulated, also known as the pacemaker of glycolysis?

Answer 10

PFK-1 (step 3)

Question 11

Glycolysis in the skeletal muscles provide

Answer 11

ATP to power contraction (movement)
High ATP/low AMP = glycolysis inhibited bc already have energy
High AMP/low ATP = glycolysis stimulated bc need energy

Question 12

Phosphofructokinase is the most important control site because:

Answer 12

High levels of ATP allosterically inhibit the enzyme -> lowers its affinity for f-6-p

AMP reverses the inhibitory action of ATP (binds to enzyme = change in conformation) -> AMP competes with ATP for binding site, but when bound, does not inhibit the enzyme

Question 13

PFK-1 is also inhibited by a decrease in

Answer 13

pH. The inhibition of glycolysis, and therefore lactic acid fermentation, protects the muscle from damage that would result from the accumulation of too much acid

Question 14

Why does AMP but no ADP stimulate the activity of PFK-1?

Answer 14

Because ADP is used to make ATP, AMP is produced as a result

Question 15

Hexokinase is inhibited by its product:

Answer 15

g-6-p and when PFK-1 is inhibited then f-6-p increases and g-6-p is favoured, leading to the inhibition of hexokinase

Question 16

What inhibits pyruvate kinase?

Answer 16

ATP allosterically inhibits pyruvate kinase to decrease rate of glycolysis when the energy charge of the cell is high
If glycolysis increases, f-1,6-bp activates the pyruvate kinase

Question 17

The liver maintains blood-glucose concentration:

Answer 17

stores glucose as glycogen when glucose is plentiful, and it releases glucose when supplies are low
Also uses glucose to generate reducing power (NADPH) for biosynthesis and to synthesize building blocks for other biomolecules

Question 18

In the liver, glycolysis is inhibited by:

Answer 18

Citrate, which means that biosynthetic precursors are abundant, there is no need to degrade additional glucose for this purpose

Question 19

F-1,6-BP in the liver stimulates glycolysis:

Answer 19

• increasing PFK-1’s affinity for F-6-p
• Diminishing the inhibitory effect of ATP
  = Feedforward stimulation

Question 20

Glucokinase in the liver

Answer 20

Only phosphorylates glucose when glucose is abundant
Km for glucose is ~50x more than hexokinase
It is not inhibited by g-6-p (its product)

Question 21

When there is low glucose concentration, glucokinase is

Answer 21

inhibited by the liver specific glucokinase regulatory protein (GKRP) - sequesters kinase in the nucleus

Question 22

Glucokinase is also present in the pancreas:

Answer 22

Increased formation of g-6-p when blood-glucose levels are elevated secretion of insulin signals the need to remove glucose from blood for storage as glycogen or conversion into fat

Question 23

Pyruvate kinase in the liver

Answer 23

Low blood-glucose concentration -> glucagon-trigger cyclic AMP cascade -> phosphorylation of pyruvate kinase
High blood-glucose -> dephospho pyruvate kinase more active
ATP inhibits pyruvate kinase

Question 24

GLUT2 is located where?

Answer 24

Liver and pancreatic B cells

regulation of insulin and removes excess glucose from blood

Question 25

GLUT4 is located where?

Answer 25

Muscle and fat cells