Glycolysis Flashcards
What is the overall aim in the stage 1 of glycolysis?
Break down the 6C glucose into 2x 3C GAP fragments (Glyceraldehyde 3-Phosphate).
What are the essential and irreversible steps of stage 1 glycolysis?
- Phosphorylation of glucose via ATP hydrolysis -> glucose-6-phosphate
- Fructose-6-phosphate is made and unwound into linear chain.
- Linear chain: F6P phosphorylated (ATP hydrolysis) -> Fructose 1,6-bisphosphate.
- FBP cleaved -> GAP fragments.
What are the essential and irreversible steps of stage 2 glycolysis ?
- GAP -> converted to 1,3 BPG
- This BPG is de-phosphorylated to create molecule of ATP.
- PEP is de-phosphoarylated to form ATP and pyruvate
What is the overall aim in the stage 2 of glycolysis?
Use the 3C GAP to form pyruvate molecules + overall created net 2 ATP formed.
What cofactor does glycolysis require and when is it used?
- NAD+ is essential.
- If runs out = glycolysis stops.
- NAD+ is needed to oxidise Glyceraldehyde-3-Phosphate to form 1,3 BPG. (is reduced to NADH)
How is NAD+ regenerated?
In aerobic conditions in cells:
- Pyruvate into citric + oxidative phos.
- Pyruvate oxidised in citric.
- NADH e- transferred to oxygen = water + NAD+ regenerated.
In anaerobic conditions:
- No OP, No Citric.
- Glucose oxidised to pyruvate
- Pyruvate reduced to organic molecule + undergoes fermentation process (either to ethanol or lactate). NADH is oxidised to NAD+
What is the free energy like at irreversible control points?
Strongly delta negative
What happens to the pyruvate from glycolysis?
Goes into the citric acid cycle and oxidative phosphorylation.
When the reaction is irreversible what happens to free energy?
Strongly delta negative -> pushes glycolysis forwards.
What are the regulatory/important steps in glycolysis?
Step 1: Glucose to Glucose-6-phosphate.
Step 3: Fructose-6-phosphate to Fructose-1,6-bisphosphate. (MAIN REG POINT)
Step 10: PEP to pyruvate
Enzymes of control in glycolysis
- Hexokinase: inhibit feedback i.e. after phosphorylated glucose-6-phosphate made -cannot return to glucose, hexokinase inhibited.
- Phosphofructokinase: control energy production
- Pyruvate kinase from PEP to pyruvate: feedforward activation. The production of FBP promoted the activity of enzyme to make pyruvate.
How is glycolysis useful and stimulated in muscles?
Generates ATP for muscle use.
Depends on ATP/AMP:
High AMP => PFK activated so G-6-P used up => activated hexokinase.
High ATP => PFK inactivated so G-6-P accumulates => inactive hexokinase
How is glycolysis useful and stimulated in liver?
Generates intermediates for biosynthesis + energy as liver = regulator of blood glucose levels.
ATP/AMP again but much less important.
In liver Fructose-2,6,BP allosteric activator of PFK, increased affinity for F6P = increased rate of glycolysis.
What happens to pyruvate after glycolysis?
Main => Acetyl CoA and further oxidation.
Alternative 1 => Lactate (muscle, RBCs, cancer cells etc)
Alternative 2 => Acetaldehyde -> Ethanol (Plants, yeast etc)
(Both alt reoxidise NADH -> NAD+ = no more glycolysis)
What is glycolysis?
The oxidation of glucose to form 2 pyruvate molecules and 2 ATPs/glucose.
