lecture 20 - carbohydrates 2 - PoNF

What is glycolysis?

the breakdown of glucose by enzymes, releasing energy and pyruvic acid.

Where does glycolysis occur?

cytosol

2 phases of glycolysis

1. energy investment phase 2 ATP used

2. energy payoff phase - Net 2 ATP gain (4 gained altogether)

Step 1: Glycolysis

what is formed?

Enzyme used?

ATP used?

irreversible or reversible

Glucose --> Glucose 6-phosphate (phosphorylation)

hexokinase enzyme

ATP used

IRREVERISBLE

step 2 of glycolysis

what is formed

enzyme used

ATP used?

irreversible or reversible

glucose-6-phosphate --> fructose-6-phosphate (conversion)

phosphohexase isomerase

ATP and ADP used as it is REVERSIBLE due to free energy

step 3 of glycolysis

what is formed

enzyme used

ATP used?

irreversible or reversible

fructose-6-phosphate --> fructose-1,6-biphosphate (phosphorylation)

phosphofructokinase-1 (PFK-1)

IRREVERSIBLE - first committed step of glycolysis - cannot go back after this

step 4 of glycolysis

what is formed

enzyme used

ATP used?

irreversible or reversible

cleavage of fructose-1,6-biphosphate (splitting part of glycolysis - 1 Glc into 2 triose sugars)

fructose-1,6-biphosphate aldoase (aldoase for short)

REVERSIBLE

step 5 of glycolysis

what is formed

enzyme used

ATP used?

irreversible or reversible

interconversion of triose sugars

triose phosphate isomerase

REVERSIBLE

yields 2 G-3-P per glucose

what triose can only participate in glycolysis

glyceraldehyde-3-phosphate

step 6 of glycolysis

what is formed

enzyme used

ATP used?

irreversible or reversible

oxidation of G-3-P to 1,3-biphosphate

dehydrogenase

2 NADH produced

REVERSIBLE

first energy payoff phase

step 7 of glycolysis

what is formed

enzyme used

ATP used?

irreversible or reversible

transfer from 1,3-BiPG to ADP

enzyme - phosphoglycerate kinase

2 ATP produced

spontaneous

substrate level phosphorylation

REVERSIBLE

step 8 of glycolysis

what is formed

enzyme used

ATP used?

irreversible or reversible

conversion of 3-PG to 2-PG

enzyme - phosphoglycerate mutase

REVERSIBLE

step 9 of glycolysis

what is formed

enzyme used

ATP used?

irreversible or reversible

dehydration of 2-PG to PEP

enzyme - enolase

REVERISBLE

step 10 of glycolysis

what is formed

enzyme used

ATP used?

irreversible or reversible

transfer of PEP to ADP

enzyme - pyruvate kinase

2 ATP produced

final step - produces pyruvate

IRREVERSIBLE

No NAD+ has what effect on glycolysis?

Inhibits it, NAD+ is required for glycolysis.

Fate of Pyruvate

Depends on oxygen availability.

- oxygen is present, pyruvate oxidised to acetyl-CoA, enters the citric acid cycle

- Without oxygen, pyruvate reduced in order to oxidise NADH back to NAD+ (2 lactate or 2 ethanol + CO2)

function of pyruvate dehydrogenase

converts pyruvate to acetyl-CoA so it can enter citric acid cycle

Function of lactate dehydrogenase

changes lactate to pyruvate to enter citric acid cycle

Fate of blood lactate

cori cycle

- ATP made via substrate level phosphorylation producing lactate - converted to glucose in liver via gluconeogenesis

- liver repays O2 debt

What is gluconeogenesis?

production of glucose from amino acids

is glucose irreversible or reversible

irreversible

reactions A + B of gluconeogenesis

pyruvate --> oxaloacetate --> maltate --> outside mitochondria --> maltate --> PEP

substrates - pyruvate carboxylase

maltate dehydrogenase

PEP carboxykinase

reaction C of gluconeogenesis

checkpoint

irreversible

enzyme - fructose-1,6-phosphatase

F-1,6-BiP + H2O --> fructose-6-phosphate + Pi

reaction D of gluconeogenesis

3rd bypass

glucose-6-phosphatase

dephosphorylation

PEP --> pyruvate generates how many ATP

10

where is fructose metabolised

liver