Lecture 26: Glucose Catabolism (Glycolysis)

Question 1

Overview of Glycolysis

Where does glycolysis happen?

Answer 1

Within the cytosol of cells

Question 2

Overview of Glycolysis

What is glucose converted into?

Answer 2

pyruvate

Question 3

Overview of Glycolysis

How is energy captured? What does it synthesize?

Answer 3

ATP and NADH

Question 4

Overview of Glycolysis

What are the two phases of glycolysis?

Answer 4

Preparatory phase
Payoff Phase

Question 5

Overview of Glycolysis

What happens in the preparatory phase?

Answer 5

1 molecule of glucose is converted into 2 molecules of glyceraldehyde 3-phosphate
* 2 ATP are consumed

Question 6

Overview of Glycolysis

What happens in the payoff phase?

Answer 6

2 molecules of glyceraldehyde 3-phosphate are converted into 2 molecules of pyruvate
* 4 ATP and 2 NADH are produced

Question 7

Overview of Glycolysis

What is the net production from 1 molecule of glucose?

Answer 7

1 pyruvate
2 ATP
2 NADH

Question 8

Overview of Glycolysis

How many steps are in gycolysis?

Answer 8

10

Question 9

Preparatory Phase

What two products are glucose broken down into?

Answer 9

glyceraldehyde 3-phosphate (moves to payoff phase)
Dihydroxyacetone phosphate (must be converted)

Question 10

Preparatory Phase

What is step 1?

Answer 10

Phosphorylation of Glucose:
Glucose enters into glycolysis by conversion to glucose 6-phosphate using enam hexokinase (prevents glucose from exiting the cytosol, makes the reaction irreversible and spontaneous), regulated by product inhibition

uses 1 ATP

there are regulation sites at irreversible site

Question 11

Preparatory Phase

What is Step 3?

Answer 11

2nd Priming Phosphorylation:
addition of phosphate onto the C1 position using phosphofructokinase (PFK) to activate, used to further activate the 6-carbon unit
spontaneous, irreversible

Uses 1 ATP

Phosphofructokinase is key enzyme that regulates the pace of glycolysis

Question 11

Preparatory Phase

What is step 2?

Answer 11

Phosphohexose Isomerization:
catalized by phosphohexose isomerase
converts glucose into fructose (from aldose to ketose) as it is easier to add phosphates to the C1 position and allows for symetrical cleave
reversible

product concentration kept low to drive forward

Question 11

Preparatory Phase

What is step 5?

Answer 11

Triose Phosphate Interconversion:
enam Triose phosphate isomerase converts the DHAP to GAP to continue forward.
reversible

GAP concentration kept low to pull reaction forward

Question 11

Preparatory Phase

What is step 4?

Answer 11

Aldol cleavage of F-1,6-bP:
Using the enam Aldolase, it cuts the carbon into Glyceraldehyse 3-phospahte (GAP) and dihydroxyacetone (DHAP)
reversible

GAP concentration kept low to pull reaction forward

Question 12

Payoff Phase

What is step 6?

Answer 12

Oxidation of GAP:
enam Glyceraldehyde 3-phosphate dehydrogenase is used to oxydize aldehyde group into a carboxyl group.
produced energy and stores in carboxyl group
NAD+ is a cofactor and is reduced to NADH
reversible

coupled to next reaction to pull forward

Question 13

Payoff Phase

What is step 7?

Answer 13

1st production of ATP:
high evergy phosphate donated to ADP to create ATP (substrate-level phosphorylation)
Phosphogycerate kinase catalyzes
reversible, catalyzes both directions

Question 14

Payoff Phase

What is Step 8?

Answer 14

Migration of the Phosphate:
Phosphoglycerate Mutase catalyzes the migration of the functional group (phosphate shifts from C3 to C2)
reversible

reactact concentration kept high by PGK to push forward

Question 15

Payoff Phase

What is step 9?

Answer 15

Dehydration of 2-PG to PEP:
enolase dehydrates 2-phosphoglycerate (2-PG) to form Phosphoenolpyruvate (PEP), high evergy phosphate
slightly reverisble

product concentration kept low to pull reaction forward

Question 16

Payoff Phase

What is step 10?

Answer 16

2nd Production of ATP:
substrate-level phosphorylation
pyruvate kinase transfer the phosphate to ADP and leaves pyruvate
the enam requires a cofactor of divalent metals (Mg++ or Mn++)
irreversible/spontaneos

Question 17

Fates of Pyruvate

What is pyruvate used for?

Answer 17

Creation of:
Ethanol (used for fermentation)
Lactate (used for fermentation)
Acetyl CoA (used for Citric Acid cycle)

Question 18

Regulation of Glycolysis

What 3 enzymes catalyze and regulate the spontaneous reactions of glycolysis?

Answer 18

Hexokinase: inhibited by product glucose-6-phosphate
Phosphofructokinase: rate limiting step, more ATP and pH decrease limits PFK activity
Pyruvate kinase: last step in glycolysis, ATP allosterically inhibits pyruvate kinase, fructose 1,6 biphosphate activates it

Question 19

Summary of Glycolysis

What is the Equation for Glycolysis

Answer 19

Glucose + NAD + 2 ADP + 2 Pi -> 2 Pyruvate + 2 NADH + 2 H + 2 ATP