Week 5: Glycolysis Flashcards
What is glycolysis?
The sequence of enzyme-catalyzed reactions by which glucose is converted into pyruvate
How do we extract free energy from glucose aerobically or anaerobically?
First: Activate it by phosphorylation.
Second: Collect energy from the high-energy metabolites.
What are the 2 phases of glycolysis?
- Preparatory
2. Payoff
What step reactions are within the preparatory phase?
- Phosphorylation of Glucose
- Phosphohexose Isomerization
- 2nd Priming Phosphorylation
- Aldol Cleavage of F-1,6-bP
- Triose Phosphate Interconversion
What step reactions are in the payoff phase?
- Oxidation of Glyceraldehyde 3-Phosphate
- 1st Production of ATP
- Migration of the Phosphate
- Dehydration of 2-PG to PEP
- 2nd Production of ATP
What occurs during the phosphorylation of glucose?
Glucose phosphorylated by hexokinase to G6P
What energy molecules are used during the phosphorylation of glucose?
ATP and Mg++ shields its negative charge
What is the rationale behind the phosphorylation of glucose?
- Traps glucose inside cell by giving it a negative charge
2. Lowers intracellular glucose concentration to allow further uptake
What make the phosphorylation of glucose irreversible?
- Regulated mainly by products
- Hexokinase is allostericly inhibited by glucose-6-phosphate
- Glucokinase is activated by glucose (feedforward) and inhibited by fructose 6-phosphate
What the difference between hexokinase and glucokinase?
Hex: has a high affinity for glucose
Glu: has a low affinity for glucose
What is the purpose for glucokinase?
Plays an important role in controlling blood glucose levels since it is only active when glucose is high
Stimulates insulin release
What occurs during Phosphohexose Isomerization?
G6P is isomerized by phospohexose isomerase to F6P
What is the rationale behind Phosphohexose Isomerization?
- C1 of fructose is easier to phosphorylate by PFK
2. Allows for symmetrical cleavage by aldolase
Is Phosphohexose Isomerization reversible?
Yes
Does Phosphohexose Isomerization require Mg++?
Yes
What occurs during 2nd Priming Phosphorylation?
F6P is phosphorylated by PFK-1, ATP, and Mg+++ into Fructose 1,6-bidphosphate
What is the rationale behind 2nd Priming Phosphorylation ?
- Further activation of glucose
2. allows for 1 phosphate/3-carbon sugar after step 4
Which step would be the first committed step of glycolysis?
2nd Priming Phosphorylation by Phosphofructokinase-1
Why is 2nd Priming Phosphorylation by Phosphofructokinase-1 irreversible?
Phosphofructokinase-1 is highly regulated.
Allosterically inhibited by ATP and citrate
Allosterically activated by AMP and ADP
What occurs during Aldol Cleavage of F-1,6-bP?
Fructose cleaves into GAP and Dihydroxyacetone by aldolase