Unit 1: Enzymes in Metabolism Flashcards
what is covalent modification?
covalent binding of a variety of chemical groups to the enzyme which changes the shape of the enzyme either activating or inactivating the enzyme to change the reaction rate.
what are the two types of covalent modification?
phosphorylation and proteolytic cleavage
what is a kinase enzyme?
can phosphorylate other enzymes - addition of phosphate by condensation activates or inactivates the envyme
what is phosphatase?
dephosphorylate other enzymes - remove phosphate by hydrolysis causing them to be activated or inactivated
explain glycogen and covalent modification
when the blood glucose concentration falls, two liver enzymes are phosphorylated by different kinases. One kinase phosphate to glycogen phosphorylase activating it to break down glycogen to release more glucose. The other kinase phosphorylates glycogen synthase inactivating it and stopping it synthesising glycogen.
If blood glucose level rose, reaction is revisable
explain proteolytic cleavage
pancreas cells make an inactive form of trypsin called trypsinogen. Trypsinogen is secreted into the small intestine where it is cut by a protease, converting the inactive trypsinogen to the active form of the enzyme, trypsin.
as concentration of the active form increases, so does the reaction rate.
why do pancreas cells make trypsinogen?
if the pancreas cells made active trypsin they would digest themselves. making the inactive trypsinogen keeps the pancreas cells safe and prevents digestion of enzyme trypsin until it is in the small intestine which has a mucus coating to protect the gut form action of protease
what is a modulator?
binds to cause a conformation change, change in shape of enzyme
what is an allosteric enzyme?
when modulator had binded to an active sire and cause a conformational change in the shape
what is an allosteric site?
second binding site away from the active site
with modulators, describe what happens when product of a metabolic pathway is in short supply
a positive modulator bind to an allosteric site and increases the affinity of the active site for substrate. enzyme becomes more effective and makes more of the substrate for the next enzyme on pathway
with modulators, describe what happens when there is enough product for metabolic pathway
negative modulator binds to a different allosteric site, reducing affinity of the actie site for substrate. enzyme less effective and makes less substrate for next enzyme in pathway
what is end product inhibition?
when the product of the final reaction in a metabolic pathway accumulates, it slows down the first enzyme of the path and so slows down its own synthesis
what is the advantage of end product inhibition?
End product inhibition is energetically efficient as it avoids the excess and wasteful production of the intermediates of a pathway.
