Overall steps of glycolysis Flashcards
How many molecules of glucose are used and pyruvate produced during glycolysis?
One molecule of glucose is oxidised to 2 molecules of pyruvate
How many molecules of NAD+ are reduced to NADH?
2 molecules of NAD+ are reduced to 2 molecules of NADH
How many molecules of ATP are used and produced?
2 molecules are USED in production of fructose 1,6-bisphosphate
4 molecules of ATP are produced
= Net gain of 2 molecules of ATP
What is the overall equation for glycolysis?
Glucose + 2Pi + 2ADP + 2NAD+ —-> 2Pyruvate + 2ATP + 2NADH + 2H+
BUT redox part of equation is not balanced!
What happens to the pyruvate produced by the glycolytic pathway- Aerobic conditions and anaerobic?
Subject to further metabolism
Aerobic conditions: Oxidise pyruvate further to carbon dioxide and water= More energy is generated in form of ATP
Pyruvate becomes decarboxylated by Acetyl CoA
Anaerobic conditions: Reduce pyruvate to lactate or ethanol while oxidising NADH to NAD+ to balance redox process
Pyruvate —> Acetaldehyde + CO2 —–> Ethanol + NAD+
ALL PROCESSES REGENERATES NAD+ TO ALLOW GLYCOLYSIS TO CONTINUE= Needed for glyceraldehyde 3-phosphate dehydrogenase activity
Where does conversion of pyruvate to lactate occur?
What is it catalysed by? What is the overall equation for the conversion of glucose to lactate?
Why is the accumulation of lactic acid bad?
Anaerobic muscle (and sour milk)
Catalysed by: Lactate dehydrogenase Glucose + 2Pi + 2ADP —-> 2Lactate + 2ATP
Build up in muscle= Causes cramp due to H+ build up
Which cycle converts lactate back to pyruvate?
In mammals: Lactate is transported to the liver where the Cori Cycle converts it back to pyruvate by Lactate dehydrogenase
Can then convert into glucose by gluconeogenesis
Cycle needs ATP!
To produce 1 molecule of glucose from 2 molecules of pyruvate= Need to hydrolyse 6 molecules of ATP
Where does the conversion of pyruvate to ethanol take place?
What are the two enzymes which carry out this process?
Carried out by a variety of microorganisms
Carried out by yeasts used in brewing and baking= carbon dioxide= Dough rises
1) Loses CO2= Pyruvate decarboxylase
2) Oxidises NADH to NAD+= Alcohol dehydrogenase
Which is more efficient at generating ATP- Aerobic or anaerobic conditions?
Aerobic: Complete oxidation of glucose to carbon dioxide and water= Many more ATP per molecules of glucose
Aerobic organisms can out-compete anaerobic organisms
What are the main control points of the glycolytic pathway?
1) First irreversible step= Phosphorylation of fructose 6-phosphate to fructose 1,6-biphosphate
2) Formation of glucose 1-phosphate from starch by phosphorylase
3) Formation of glucose 6-phosphate from glucose by hexokinase
PFK Regulation: How does allosteric inhibition by ATP regulate PFK activity?
Allosteric inhibition= Conformational changes shape of enzyme by binding to a site other than its active site
1) AMP and ADP= Activates the enzyme
High levels happen when there is not enough ATP= enzyme will be more active= More F 1,6-BP will be produced= Glycolysis continues
2) ATP= Deactivates
High level accumulates when ATP is not used= Not needed= Enzyme is inactivated therefore less F 1,6-BP will be produced and therefore less glycolysis will happen
PFK regulation: How does citrate regulate its activity?
Citrate= Inhibits
Citrate is the first product of the citric acid cycle
High levels= Plentiful supply of citric acid cycle intermediates= No additional break down of glucose necessary= Inhibits
PFK regulation: How is PFK regulated fructose 2,6-biphosphate synthesis and degradation?
Bifunctional enzyme: Phosphofructokinase 2 and Fructose biphosphatase 2
F 2,6-BP= Strongly activates PFK= Stimulates glycolysis
Fructose 6-phosphate —-> F 2,6-BP by PFK2 (synthesis)
F 2,6-BP —–> Fructose 6-phoshate by FBPase 2 (hydrolysis)
When there high levels of PFK2= High levels of F 2,6-BP= PFK is stimulated= Glycolysis increases
Phosphorylation of the enzyme= FBPase is ACTIVATED while PFK2 is INHIBITED= Less F 2,6-BP as they are converted to Fructose 6-phosphate
Low levels of blood glucose, the hormone glucagon is released into the bloodstream= cAMP cascade is caused causing phosphorylation of the enzyme= Glycolysis is slow= More glucose is conserved
PFK regulation: How does levels of H+ regulate its activity?
H+ levels= Inhibits= Rate of glycolysis decrease when pH falls significantly
Prevents excessive formation of lactate under anaerobic conditions= Prevents Acidosis e.g. in muscles during sprints
