Glycolysis

Question 1

Preparatory Phase

Answer 1

2 ATP spent to activate glucose yield 2 glyceraldehyde 3-phosphate

Question 2

Payoff Phase

Answer 2

yield 4 ATP, net gain 2 ATP, 2 NADH result in 2 pyruvate

Question 3

Pyruvate fates

Answer 3

TCA cycle (aerobic) LDH (muscle) Fermentation (yeast) BIosynthesis (alanine, PEP)

Question 4

Glucose fates

Answer 4

Structural polymer synthesis Storage (glycogen, starch, sucrose) Oxidation via PPP (ribose 5-phosphate Oxidation via glycolysis (pyruvate)

Question 5

Step 1

Answer 5

Phosphorylation Glucose–>glucose 6-phosphate enzyme=hexokinase dG=-16.7 ATP is phosphoryl group donor KEY REGULATORY POINT

Question 6

Step 2

Answer 6

Isomerization glucose 6-phosphate–>fructose 6-phosphate enzyme=phosphoglucose isomerase dG=+1

Question 7

Step 3

Answer 7

Phosphorylation fructose 6-phosphate–>fructose 1,6 bisphosphate enzyme: phosphofructokinase-1 (PFK-1) PFK-1 catalyzes transfer of phosphoryl group from ATP to fructose 6-phosphate KEY REGULATORY POINT

Question 8

Step 4

Answer 8

Cleavage fructose 1,6 bisphosphate–>dihydroxyacetone phosphate (DHAP) and glyceraldehyde 3-phosphate enzyme: aldolase readily reversible reaction

Question 9

Step 5

Answer 9

Isomerization DHAP–>glyceraldehyde 3-phosphate enzyme: triose phosphate isomerase

Question 10

Step 6

Answer 10

Oxidation/Phosphorylation glyceraldehyde 3-phosphate–>1,3 bisphosphoglycerate enzyme: glyceraldehyde 3-phosphate dehydrogenase (GAPDH) First of 2 energy conserving reactions of glycolysis that eventually lead to formation of ATP NAD+ oxidizes enzyme substrate intermediate endergonic

Question 11

Step 7

Answer 11

Phosphorylation 1,3 bisphosphoglycerate–>3-phosphoglycerate enzyme: phosphoglycerate kinase Transfer of phosphoryl group from 1,3 bisphosphoglycerate to ADP Second of 2 energy conserving reactions very exergonic

Question 12

Step 8

Answer 12

Isomerization 3 phosphoglycerate–>2 phosphoglycerate enzyme: phosphoglycerate mutase

Question 13

Step 9

Answer 13

Dehydration 2-phosphoglycerate–>phosphoenolpyruvate (PEP) enzyme: enolase

Question 14

Step 10

Answer 14

Phosphorylation phosphoenolpyruvate–>pyruvate enzyme: pyruvate kinase KEY REGULATORY POINT

Question 15

glucose

Answer 15

Question 16

glucose 6-phosphate

Answer 16

Question 17

fructose 6 phosphate

Answer 17

Question 18

fructose 1,6 bisphosphate

Answer 18

Question 19

dihydroxyacetone phosphate

Answer 19

Question 20

glyceraldehyde 3 phosphate

Answer 20

Question 21

1,3 bisphosphoglycerate

Answer 21

Question 22

3 phosphoglycerate

Answer 22

Question 23

2 phosphoglycerate

Answer 23

Question 24

phosphoenolpyruvate

Answer 24

Question 25

pyruvate

Answer 25

Question 26

substrate channeling

Answer 26

GAPDH and phosphoglycerate

No intermediate between gly3P and 3-PG (coupled reaction) so conversion is faster than predicted rates

Helps drive substrate level phosphorylation

Question 27

substrate level phosphorylation

Answer 27

Seen in coupled reaction between G3P and 3PG

Formation of ATP from substrate (1,3BPG)

Driven by substrate channeling

Question 28

phosphoglycerate mutase

Answer 28

3PG—>2PG isomerization

2 active site histidines

Phosphoryl transfer from one His that contains a P to C2, other acts as general base catalyst to remove H

Phosphoryl transfer from C3 to first active site His, second His is general acid catalyst and donates H

2,3 bisphosphoglycerate intermediate

Question 29

pyruvate kinase deficiency

Answer 29

ADP+PEP–>pyruvate+ATP

Deficiency leads to decrease in ATP produced through glycolysis, which causes shortage of normal RBC

Question 30

pyruvate kinase regulation

Answer 30

PEP+ADP—>pyruvate+ATP

Activated by AMP (when ATP is used in muscles, etc it becomes AMP) and F-1,6BP

Inhibited by ATP, alanine (can be synthesized from pyruvate in one step), and acetyl CoA (synthesized from pyruvate to kickstart citric acid cycle; slowing of acetyl CoA then kickstarts gluconeogenesis via oxaloacetate)

Question 31

hexokinase regulation

Answer 31

glucose–>G6P

Inhibited by G6P

Question 32

phosphofructokinase regulation

Answer 32

F6P–>F1,6BP

Activated by AMP and F2,6BP (insulin causes increase in cellular levels, activating glycolysis)

Inhibited by ATP and citrate

Question 33

fructose 2,6 bisphosphate

Answer 33

Insulin causes increase in intracellular levels by activating PFK-2, thus increasing glycolysis and decreasing gluconeogenesis

Glucagon causes decrease in intracellular levels by activating FBPase-2 (and inhibiting PFK-2), inhibiting glycolysis and stimulating gluconeogenesis

Question 34

Fate of Pyruvate

Answer 34

Hypoxic/Anaerobic conditions:

2 Pyruvate–>2 Lactate

2 Pyruvate–>2 EtOH + 2 CO₂

Aerobic conditions

2 Pyruvate–>2 Acetyl Co-A–(citric acid cycle)–>4CO₂ + 4 H₂0

Question 36

Fermentation

Answer 36

Anaerobic Glycolysis

Generate ATP without NAD⁺ or O₂

Reduce pyruvate to another product

Regenerate NAD⁺ for further glycolysis under anaerobic conditions

Electron transfer from NADH to O₂ in the mitochondria provides energy for synthesis of ATP

Question 37

Overall Glycolytic Process

Answer 37

Carbon: Glycose–> 2 Pyruvate

Phosphoryl Groups: 2 ADP + 1 P_i–> 2 ATP

Electrons: 2 H+ (via G3P) + 2 NAD⁺—> 2 NADH

Question 38

Fermentation

Answer 38

Anaerobic Glycolysis

Generate ATP without NAD⁺ or O₂

Reduce pyruvate to another product

Regenerate NAD⁺ for further glycolysis under anaerobic conditions

Electron transfer from NADH to O₂ in the mitochondria provides energy for synthesis of ATP