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Flashcards in Chapter 10 Terms Deck (18):

Activity at one functional site affects the activity at others.



Catalysis by aspartate carbamoylase of the first step in pyrimidine biosynthesis is inhibited by cytidine triphosphate, the final product of that biosynthesis.

Feedback (end-product) inhibition


A site distinct from the active site at which substrate binds where a regulatory molecule may bind to.

Allosteric (regulatory) site


The effects of substrates on allosteric enzymes are referred to as _______ effects.

Homotropic effect


Where the change in the enzyme is "all or none"; the entire enzyme is converted from T into R, affecting all of the catalytic sites equally.

Concerted mechanism


Assumes that the binding of ligand to one site on the complex can affect neighboring sites without causing all subunits to undergo the T-to-R transition.

Sequential model


The effects of nonsubstrate molecules on allosteric enzymes (such as those of CTP and ATP on ATCase) are referred to as ______ effects.

Heterotrophic effect


Are enzymes that differ in amino acid sequence yet catalyze the same reaction. Usually, these enzymes display different kinetic parameters, such as Km, or respond to different regulatory molecules.

Isozyme (isoenzyme)


The covalent attachment of a molecule to an enzyme or protein that can modify its activity.

Covalent modification


The enzymes catalyzing phosphorylation reactions.

Protein kinase


A sequence pattern derived from the alignment of multiple sequences that represents the nucleotide or amino acid most likely to occur at each position in a sequence.

Consensus sequence


These enzymes reverse the effects of kinases by catalyzing the removal of phosphoryl groups attached to proteins. The enzymes hydrolyze the bond attaching the phosphoryl group.

Protein phosphatase


Is activated by cAMP; it alters the activities of target proteins by phosphorylating specific serine or threonine residues.

Protein kinase A (PKA)


A sequence that matches the consensus sequence for phosphorylation except for the presence of alanine in place of serine. This thereby prevents the entry of protein substrates.

Pseudosubstrate sequence


Inactive precursor enzymes, waiting cleavage to become activated.

Zymogen (proenzyme)


Are often employed in biochemical systems to achieve a rapid response. An initial signal institutes a series of steps, each of which is catalyzed by an enzyme. At each step, the signal is amplified.

Enzymatic cascade


This clotting pathway is activated by exposure of anion surfaces on rupture of the endothelial lining of the blood vessels.

Intrinsic pathway


This clotting pathway is activated when trauma exposes tissue factor, an integral membrane glycoprotein. Exposure generates small amounts of thrombin. This is the most crucial pathway in blood clotting.

Extrinsic pathway