Chapter 16: Glycolysis

Glycolysis

metabolic process that breaks down glucose into pyruvate (6C —> 3C)

occurs in cytoplasm of all cells

anerobic and aerobic

evolutionarily conserved with all forms of life (just needs cytoplasm)

Starting materials

1 Glucose

2 NAD+

2 ADP

2 Pi

Products

2 pyruvate

2 NADH

2 ATP

Glycolysis net gain

2 ATP

2 NADH

Phase 1

energy investment; 2 ATP

hexokinase & PFK1

Phase 2

Energy Payoff;

4 ATP (2 from each GAP); Phosphoglycerate Kinase (7), Pyruvate Kinase (9)

2 NADH (1 from each GAP); Glyceraldehyde-3-phosphate dehydrogenase (6)

Irreversible Reactions

1 (G—> G6P) hexokinase

3 (F6P —>F16B) PFK1

10 (PEP —> Pyruvate) pyruvate kinase

Step 1

irreversible rxn

hexokinase

glucose —> glucose-6-phosphate

1 atp consumed

glucose gains phosphate group

glucose + ATP → glucose-6-phosphate + ADP

phosphorylation traps glucose in cell (G6P cannot escape cell)

hexokinase —> induced fit model

Step 1

Hexokinase

glucose —> glucose-6-phosphate

Step 2

glucose-6-phosphate (G6P) → fructose-6-phosphate (F6P)

Phosphoglucose isomerase

Changes constitutional isomeric form of G6P

Step 2

Phosphoglucose Isomerase

Glucose-6-phosphate (G6P) → Fructose-6-phosphate (F6P)

Step 3

irreversible reaction

fructose-6-phosphate —> fructose 1,6- biphosphate

Phosphofructokinase-1 (second phosphate group added)

rate-limiting and committing step —> point of glycolysis control

ATP consumed (second)

Step 3

PFK1

fructose-6-phosphate —> fructose 1,6- biphosphate

Step 4

Fructose-1,6-bisphosphate —> DHAP + GAP

Aldolase

6 carbon F16B gets split into two 3 carbon molecules

from here all reactions occur twice (per 3 carbon molecule)

Step 4

Aldolase

Fructose-1,6-bisphosphate —> DHAP + GAP

Step 5

DHAP —> GAP/ G3P

triose phosphate isomerase

DHAP gets converted into 2 GAP

Step 5

Triose phosphate isomerase

DHAP —> 2 GAP

Step 6

GAP —> 1,3 Biphosphoglycerate

Glyceraldehyde-3-phosphate dehydrogenase (produces the NADH)

Produces NADH (GAP loses e- and makes NAD —> NADH)

phosphate group added w/o ATP

Step 6

GAP —> 1,3 Biphosphoglycerate + NADH

Glyceraldehyde-3-phosphate dehydrogenase

Step 7

1,3-bisphosphoglycerate (1,3-BPG) → 3-phosphoglycerate (3-PG)

Phosphoglycerate kinase

ATP produces from kinase (2)

Step 7

Phosphoglycerate kinase

1,3-bisphosphoglycerate (1,3-BPG) → 3-phosphoglycerate (3-PG) + 2 ATP

Step 8

3-phosphoglycerate (3-PG) → 2-phosphoglycerate (2-PG)

Phosphoglycerate mutase

phosphate group gets moved from C3 —> C2

Step 8

Phosphoglycerate mutase

3-phosphoglycerate (3-PG) → 2-phosphoglycerate (2-PG)

Step 9

2-phosphoglycerate (2-PG) → phosphoenolpyruvate (PEP)

Enolase

h20 removed —> PEP (high energy molecule)

Step 9

Enolase

2-phosphoglycerate (2-PG) → phosphoenolpyruvate (PEP)

Step 10

irreversible

PEP —> Pyruvate

pyruvate kinase

high energy PEP gets transferred to ADP —> ATP

Step 10

Pyruvate Kinase

PEP —> pyruvate

Acronym

Good Girls Find Friends Doing Biology Practice Problems

Glucose —> G6P —> F6P —>F16B —> DHAP —> 13BG —> 3PG —> 2PG —> PEP —> Pyruvate

Glycolysis Inhibition

at rest

HIGH atp levels bc its not being used

1) first enzyme (hexokinase) is inhibited, G6P builds up —> glucose cannot enter pathway (negative feedback)

2) PFK inhibited —> ATP = allosteric inhibitor —> glycolysis slowed (rate limiting step!)

3) pyruvate kinase inhibited (backup/ secondary response)

Glycolysis Stimulation

Low ATP

PKF activated —> AMP = allosteric activator —> F16B directly activates pyruvate kinase

products: CO2 + H2O (with O2), Lactate (without O2)