Lecture 26: Glucose Catabolism (Glycolysis) Flashcards
Overview of Glycolysis
Where does glycolysis happen?
Within the cytosol of cells
Overview of Glycolysis
What is glucose converted into?
pyruvate
Overview of Glycolysis
How is energy captured? What does it synthesize?
ATP and NADH
Overview of Glycolysis
What are the two phases of glycolysis?
Preparatory phase
Payoff Phase
Overview of Glycolysis
What happens in the preparatory phase?
1 molecule of glucose is converted into 2 molecules of glyceraldehyde 3-phosphate
* 2 ATP are consumed
Overview of Glycolysis
What happens in the payoff phase?
2 molecules of glyceraldehyde 3-phosphate are converted into 2 molecules of pyruvate
* 4 ATP and 2 NADH are produced
Overview of Glycolysis
What is the net production from 1 molecule of glucose?
1 pyruvate
2 ATP
2 NADH
Overview of Glycolysis
How many steps are in gycolysis?
10
Preparatory Phase
What two products are glucose broken down into?
glyceraldehyde 3-phosphate (moves to payoff phase)
Dihydroxyacetone phosphate (must be converted)
Preparatory Phase
What is step 1?
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
Preparatory Phase
What is Step 3?
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
Preparatory Phase
What is step 2?
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
Preparatory Phase
What is step 5?
Triose Phosphate Interconversion:
enam Triose phosphate isomerase converts the DHAP to GAP to continue forward.
reversible
GAP concentration kept low to pull reaction forward
Preparatory Phase
What is step 4?
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
Payoff Phase
What is step 6?
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
Payoff Phase
What is step 7?
1st production of ATP:
high evergy phosphate donated to ADP to create ATP (substrate-level phosphorylation)
Phosphogycerate kinase catalyzes
reversible, catalyzes both directions
Payoff Phase
What is Step 8?
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
Payoff Phase
What is step 9?
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
Payoff Phase
What is step 10?
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
Fates of Pyruvate
What is pyruvate used for?
Creation of:
Ethanol (used for fermentation)
Lactate (used for fermentation)
Acetyl CoA (used for Citric Acid cycle)
Regulation of Glycolysis
What 3 enzymes catalyze and regulate the spontaneous reactions of glycolysis?
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
Summary of Glycolysis
What is the Equation for Glycolysis
Glucose + NAD + 2 ADP + 2 Pi -> 2 Pyruvate + 2 NADH + 2 H + 2 ATP
