MCAT KAPLAN BIOCHM CH 9 (Glycolysis)

glycolysis is converted into...

by...

2 pyruvate;

2 phosphorylated oxidations + 1 oxidation reaction

In the liver excess glucose in glycolysis is converted into

fatty acids for storage (glycogen)

what are the 5 enzymes that serve importance during glycolysis

1. hexokinase + glucokinase

2. phosphofructokinase (PFK-1 and PFK-2)

3. G3P (glyceraldehyde 3-phosphate dehydrogenase

4. 3PG (3-phosphoglycerate Kinase)

5. pyruvate kinase

hexokinase vs glucokinase

kinases: attach phosphate group from ATP--> substrates

both convert glucose--> glucose 6 phosphate

hexokinase: found in tissue and inhibited by Glucose 6P

glucokinase: found in liver and pancreatic beta-islet cells; induced by insulin

Km in hexokinase vs glucokinase

hexokinase: low Km (reach max velocity at low glucose concentration)

glucokinase: high Km (acts on glucose proportionately to its concentration

glucose 6 phosphate is turned into______ by ________

fructose 6 phosphate; isomerases

PFK1

what is it inhibited by? activated by?

Fructose-6-phosphate is phosphorylated to fructose-1,6-bisphosphate;

Inhibited by ATP and citrate (makes sense since glycolysis should be turned off when there is too much energy aka ATP)

activated by AMP (makes sense since glycolysis should be turned on when it needs energy)

what activates PFK2?

what happens

Insulin; PFK2 converts some F6P to Fructose 2,6 Biphosphate, which activates PFK1

what deactivates PFK2?

what happens?

glucagon; lowering Fructose 2,6 Biphosphate, which inhibits PFK1

G3P dehydrogenase

G3P to 1,3-bisphosphoglycerate while adding inorganic phosphate and reducing NAD+ to NADH

3-phosphoglycerate kinase

transfers phosphate group from 1,3 biphosphoglycerate to ADP to form:

1. ATP (via sub level phosphorylation)

2. 3-phosphoglycerate

substrate-level phosphorylation

ADP is directly phosphorylated to ATP (in contrast to oxidative phosphorylation which is ATP--> ADP)

pyruvate kinase

PEP to pyruvate via sub level phosphorylation (ADP--> ATP)

what is pyruvate kinase activated by? what is it known as and what does it mean?

fructose 1,6-bisphosphate from the PFK-1 reaction;

feed-forward activation meaning that product of earlier rxn of glycolysis prepares a later rxn in glycolysis

what is fermentation? what is the key enzyme? what does it do?

occurs in the absence of Oxygen;

lactate dehydrogenase

oxidizes NADH to NAD+

what happens without mitochondria and oxygen? what prevents this problem and what does it do?

glycolysis stops and available NAD+ is reduced to NADH;

lactate dehydrogenase prevents this by reducing lactate (3C) to pyruvate (3C) and oxidizing NADH to NAD+

yeast cell fermentation

- conversion of pyruvate to ethanol and CO2

- replenishes NAD+

3 important glycolysis intermediates

1. dihydroxyacetone phosphate (DHAP)

2. 1,3 Biphosphoglycerate (1,3-BPG)

3. PEP

DHAP

formed from F 1,6-BP and can be isomerize to G3P, which can be converted into glycerol

1,3-BPG and PEP

high energy intermediates used to generate ATP by substrate level phosphorylation

Irreverisble Enzymes of Glycolysis

1. glucokinase or hexokinase

2. PFK1

3. Pyruvate Kinase

glycolysis in erythrocytes yields

yields 2 ATP (anaerobic)

RBCs have biphosphoglycerate mutase which...

produces 2,3-BPG from 1,3 BPG.

mutase: moves functional group (in this case Phosphate) from one molecule to another

2,3-BPG binds allosterically to..

what does it not bind well with? why?

Hemoglobin A, which decreases affinity for oxygen;

Fetal Hemoglobin (HbF); since HbF has higher affinity for oxygen