lecture 14 - carbohydrate metabolism Flashcards
Explain why the phosphate bonds in ATP are described as high energy?
- kinetic stability implies high activation energy
- Delta g driven by the entropic stabilisation of the phosphate anion
Give two biochemical effects of glucose phosphorylation
- negative charge prevents diffusion out of the cell
- Electron with drawing effect increases reactivity of the saccharide
What are the different physiological roles of the Hexokinase and glucokinase isoforms?
- HK1 - 3 are high affinity , reduce glucose levels
- GK with lower affinity results in equilibrium
What is the mechanism for the stage 3 glycolytic reaction?
Fructose- 6 - phosphate and ATP. PFK catalyses the nucleophilic attack of the C1 -OH group of F6P on the phosphorus atom
What is the form of PFK and what are the names of its two states?
Is a tetrameric enzyme with two conformational states, R and T
What is ATP in regards to PFK?
Substrate and an inhibitor
What is the name of the active and inactive states?
R state - active
T state - inactive
What happens to PFK at high concentrations?
ATP acts a as inhibitor of PFK by binding to the T state. Decreases the affinity of PFK for F6P
what is the Pasteur effect?
Aerating yeasted broth causes yeast cell growth to increase , but fermentation rate decreases
primary explanation of the pasteur effect
When oxygen is low: pyruvate is turned in to ethanol and CO2 (low energy production)
When oxygen is high:pyruvate goes into the CAC
Secondary explanation of the pasteur effect
In aerobic conditions, the ATP and citrate production increases and the rate of glycolysis decreases.
This is because the ATP and citrate produced act as allosteric inhibitors In glycolysis on phosphofructose kinase
what does Fructose -1,6- bisphosphate turn into In the fourth reaction of glycolysis
Dihyrdoxyacetone phosphate (DHAP) and Glyceraldehyde - 3 - phosphate
What Is the enzyme that catalyses the fourth reaction in glycolysis?
aldolase
mammalian aldolase mechanism
- key catalytic amino acid residues are lysine and tyrosine
- Tyrosine is an H plus acceptor
- Lysine stabilises intermediates
bacterial aldolase mechanism
lysine replaced for 2 magnesium ions
