9.3 Glycolysis

Question 1

When is glycolysis the primary pathway for ATP synthesis?

Answer 1

in anaerobic conditions and in cells lacking a mitochondria

Question 2

How many steps, enzymes, and intermediates are there?

Answer 2

10 steps, 10 enzymes, 9 intermediates

Question 3

Where does glycolysis take place?

Answer 3

cytosol

Question 4

What does glycolysis use?

Answer 4

1 glucose, 2 NAD+, 2 ADP, 2 Pi

Question 5

What does glycolysis generate?

Answer 5

2 pyruvates 2 NADH, 2 H+, 2 ATP, 2 H2O

Question 6

What is the net reaction?

Answer 6

Glucose + 2 NAD+ + 2 ADP + 2Pi <–> 2 Pyruvate + 2 NADH + 2 H+ + 2ATP + 2 H2O

Question 7

Why so many steps?

Answer 7

Too much energy with one step, too much energy wasted, efficient energy usage through smaller steps

Question 8

Why 10 steps for 2 ATP?

Answer 8

Pyruvate production is important for later energy generation, NADH electron carrier, 32 ATP made from 1 glucose

Question 9

Kinase

Answer 9

Transfers a phosphate group between ATP and another substrate. Used to make or consume ATP.

Question 10

Isomerase

Answer 10

Changes structure of substrate; molecular formula remains the same, creates isomers, reversible

Question 11

Phosphatase

Answer 11

Removes phosphate group from a substrate, ATP not involved, release Pi

Question 12

Other Enzymes involved:

Answer 12

adolase, mutase, enolase

Question 13

What are the major events of stage 1?

Answer 13

2 ATP consumed, creates negatively charged molecules that can’t diffuse out of cell, Produces 2 G3P for stage 2.

Question 14

Which steps are most important in stage 1?

Answer 14

Steps 1 and 3

Question 15

Reaction 1

Answer 15

Substrates: glucose, ATP
Products: glucose-6-phosphate, ADP
Enzyme: hexokinase or glucokinase (pancreas and liver)

IRREVERSIBLE
ATP consumption
Phosphorylation prevents glucose from leaving cell

Question 16

What inhibits hexokinase?

Answer 16

Glucose 6-P inhibits hexokinase. Feedback inhibition - products inhibit; Glucose-6-P binds to hexokinase and inhibits ATP binding by allosteric regulation

Question 17

Reaction 2

Answer 17

Substrate: glucose-6-phosphate
Product: fructose-6-phosphate
Enzyme: phosphoglucose isomerase

Carbonyl moved from C1 to C2 (necessary for next step)
Concentration driven

Question 18

Reaction 3

Answer 18

Substrates: fructose-6-phosphate, ATP
Products: fructose-1,6-bisphosphate, ADP
Enzyme: phosphofructokinase-1 (PFK-1)

IRREVERSIBLE
ATP consumption
Allosterically regulated by energy charge
Rate-limiting step for the entire glycolysis pathway

Question 19

Regulation of PFK-1

Answer 19

Controlled by energy charge (ATP availability)
Activators: AMP, ADP, fructose-2,6-bisphosphate
Inhibitors: phosphoenolpyruvate, ATP

EC low - activate glycolysis
Active (R) state when ADP bound
Inactive (T) state when ATP bound

Question 20

Reaction 4

Answer 20

Substrate: fructose-1,6-bisphosphate
Products: dihydroxyacetone phosphate and glyceraldehyde-3-phosphate
Enzyme: aldolase

Reverse aldol concentration; create ketone and aldehyde
Cellular metabolite concentrations favor forward reactions

Question 21

Reaction 5

Answer 21

Substrate: dihydroxyacetone-P
Product: glyceraldehyde-3-P
Enzyme: triose phosphate isomerase

Enediol intermediate
Both products from reaction 4 -> single pathway

Question 22

What are the major events in stage 2?

Answer 22

2 Glyceraldehyde-3-P enter, 4 ATP produced (net gain 2), 2 NADH produced, 2 H+ produced

Question 23

Reaction 6

Answer 23

2x substrates: G-3-P, NAD+, Pi
2x products: 1,3-bisphosphoglycerate, NADH, H+
Enzyme: glyceraldehyde-3-phosphate dehydrogenase

NADH production
Oxidation of C1
Product quickly consumed, coupled with step 7

Question 24

Reaction 7

Answer 24

2x Substrates: 1,3-bisphosphoglycerate, ADP
2x Products: 3-phosphoglycerate, ATP
Enzyme: phosphoglycerate kinase

ATP production (2)
Intermediate 2,3-BPG
Coupled with step 6

Question 25

Reaction 8

Answer 25

2x Substrate: 3-phosphoglycerate
2x Product: 2-phosphoglycerate
Enzyme: phosphoglycerate mutase

Shift phosphate C3 to C2

Question 26

Reaction 9

Answer 26

2x Substrate: 2-phosphoglycerate
2x Product: phosphoenolpyruvate (PEP), H2O

Dehydration reaction

Question 27

Reaction 10

Answer 27

2x Substrate: PEP, ADP
2x Product: pyruvate, ATP
Enzyme: pyruvate kinase

IRREVERSIBLE
2 ATP
Actually 2 coupled reaction

Question 28

Which steps are irreversible?

Answer 28

1,3,10 are irreversible steps - highly exergonic

Question 29

Energy molecules produced?

Answer 29

Net gain 2 ATP, 2 NADH

Question 30

What is NADH used for?

Answer 30

To make ATP in oxidative phosphorylation