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14 Cards in this Set

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True/false?
Allosteric enzymes are generally larger and more complex than non-allosteric enzymes.
Allosteric enzymes are generally larger and more complex than non-allosteric enzymes. Most have two or more subunits.
True/false?
On allosteric enzymes, the active site and the site for modulator is generally the same.
False.
In addition to active sites, allosteric enzymes generally have one or more regulatory, or allosteric sites specific for binding the modulator.
With regards to allosteric enzymes, what are C and R units?
In many allosteric enzymes the substrate binding site and the modulator binding sites are on different subunits called the C (catalytic) and R (regulatory) subunit.
How is binding of a stimulatory (positive)modulator to its specific site on the regulatory subunit communicated to the catalytic subunit?
Through a conformational change.
When the allosteric enzyme goes thru a conformational change because of a modulator, how does this affect the catalytic subunit?
It renders the catalytic subunit active and capable of binding the substrate with higher affinity..
After the modulator dissociaetes from the regulatory subunit, what happens to the enzyme?
It reverts to its inactive or less active form.
What is feedback inhibition?
It is inhibition of the
regulatory enzymes specifically
by the end product of the pathway.
Give an example of feedback inhibition.
The bacterial enzyme system that catalyzes the conversion of L-threonine to L-isoleucine. The first enzyme, threoinine dehydratase, is inhibited by the end product L-isoleucine.
Modifying groups phosphoryl, adenylyl, uridylyl & methyl can modulate regulatory enzymes. Of these, which is responsible for the most common type of covalent regulatory modification?
Phosphoryl.
1/3 to 1/2 of all proteins can be phosphorylated.
The attachment of phosphoryl groups to specific amino acid residues of a proteins is catalyzed by ___________ .
Protein kinases
The attachment of phosphoryl groups to specific amino acid residues of a proteins is catalyzed by ___________ .
Protein kinases.
An example of
regulation by phosphorylation is in glycogen- phosphorylase of muscle and liver. How is this regulated?
The breakdown of glycogen in skeletal muscle and the liver is regulated by variations in the concentration of the two forms of glycogen phosphorylase (the more active phosphorylase a and the less active form b). More b -> less breakdown,
more a –> more breakdown.
Phosphorylase a has two subunits, each with a specific Ser residue that is phosphorylated at its hydroxyl group. How can it be converted to phosphorylase b?
By the cleavage of the two serine phosphate covalent bonds: the phosphoryl groups are hydrolytically removed by phosphorylase phosphatase.
Phosphorylase b can be be reactivated - covalently transformed back into active phosphorylase a by phosphorylase kinase. How is this done?
Phosphorylase kinase catalyzes the transfer of phosphoryl groups from ATP to the hydroxyl groups of the two specific Ser residues.