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14 Cards in this Set
- Front
- Back
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.
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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. |
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With regards to allosteric enzymes, what are C and R units?
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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.
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How is binding of a stimulatory (positive)modulator to its specific site on the regulatory subunit communicated to the catalytic subunit?
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Through a conformational change.
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When the allosteric enzyme goes thru a conformational change because of a modulator, how does this affect the catalytic subunit?
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It renders the catalytic subunit active and capable of binding the substrate with higher affinity..
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After the modulator dissociaetes from the regulatory subunit, what happens to the enzyme?
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It reverts to its inactive or less active form.
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What is feedback inhibition?
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It is inhibition of the
regulatory enzymes specifically by the end product of the pathway. |
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Give an example of feedback inhibition.
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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.
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Modifying groups phosphoryl, adenylyl, uridylyl & methyl can modulate regulatory enzymes. Of these, which is responsible for the most common type of covalent regulatory modification?
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Phosphoryl.
1/3 to 1/2 of all proteins can be phosphorylated. |
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The attachment of phosphoryl groups to specific amino acid residues of a proteins is catalyzed by ___________ .
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Protein kinases
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The attachment of phosphoryl groups to specific amino acid residues of a proteins is catalyzed by ___________ .
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Protein kinases.
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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. |
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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?
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By the cleavage of the two serine phosphate covalent bonds: the phosphoryl groups are hydrolytically removed by phosphorylase phosphatase.
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Phosphorylase b can be be reactivated - covalently transformed back into active phosphorylase a by phosphorylase kinase. How is this done?
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Phosphorylase kinase catalyzes the transfer of phosphoryl groups from ATP to the hydroxyl groups of the two specific Ser residues.
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