Enzymes in Metabolism Flashcards
What is covalent modification?
When covalent bonds are made or broken.
What is the effect of covalent modification?
This changes the enzymes shape so it is either made active or inactive. The concentration of active enzyme is changed, so the reaction rate is changed.
How can a Kinase enzyme activate or inactivate an enzyme?
The covalent addition of a phosphate by a condensation reaction.
What do phosphatase enzymes do?
Dephosphorlylate other enzymes causing them to be activated or deactivated.
When blood sugar concentration falls which two liver enzymes are phosphorylated?
Glycogen synthase and glycogen phosphorylase
What happens when kinase adds a phosphate group to glycogen phosphorlylase?
This activates the breakdown of glycogen to release more glucose.
What happens when kinase phosphorylates glycogen synthase?
It is inactivated and stops synthesising glycogen.
What is the name given to the inactive form of trypsin produced by the pancreas?
Tyrpsinogen
Where is the trypsinogen enzyme cut?
Small intestine by proteases
Give another example covalent modification?
When covalent bonds in the polypeptide chain are cut, so the shape of the enzyme changes
What is the effect of a protease cutting the trypsinogen enzyme.
This converts the trypsinogen into the active form of enzyme trypsin.
How can the rate of formation of products by a metabolic pathway be regulated?
By changing the affinity of the enzyme in the pathway for its substrate.
What does the enzyme catalyse?
The rate-limiting step for the whole pathway
What is the affinity changed by?
A modulator molecule that binds to the enzyme.
What happens when a modulator binds?
It changes the shape of the enzyme, the active site and therefore the affinity for the substrate.
What is the modulated enzyme called?
It is called an allosteric enzyme
How does the modulator bind to the second binding site?
Through hydrogen and ionic bonds
What is the name of the second binding site?
Allosteric site
Why does the rate of reaction change?
The effectiveness of the enzyme
Under which conditions will a positive modulator bind to the allosteric site
When a product of a metabolic pathway is in short supply.
What is the effect of a positive modulator?
It increases the affinity of the enzyme for the substrate by binding to the allosteric site. This increases the rate of formation of all subsequent products in the pathway.
When will a negative modulator bind to a different allosteric site of the enzyme?
When there is enough of the final product in the pathway.
What is the effect of the negative modulator?
Reduces the affinity the enzyme has for the substrate.
Enzyme becomes less effective - Less substrate for next enzyme.
The whole pathway slows down.
What is end product inhibition?
When the product of the final reaction accumulates and slows down the first enzyme of the pathway and so slows down its own synthesis.
What two ways can the final product limit the effectiveness of the first enzyme of the pathway.
A competitive inhibitor or a negative modulator.
What is the purpose of end product inhibition?
The cell does not waste energy synthesising more product.
