Freshman Biology- 5.12 to 5.15
If the cofactor is an organic molecule, it is called a ______.
coenzyme
Explain how an enzyme speeds up a specific reaction.
An enzyme lowers the activation energy needed for a reaction when its specific substrate enters its active site. With an induced fit, the enzyme strains bonds the need to break or positions substrates in an orientation that aids the conversion of reactants to products.
coenzyme
An organic molecule serving as a cofactor. Most vitamins function as coenzymes in important metabolic reactions.
Explain how ATP transfers energy from exergonic to endergonic processes in the cell.
Exergonic processes phosphorylate ADP to form ATP. ATP transfers energy to endergonic processes by phosphorylating other molecules.
active site
The part of an enzyme where a substrate molecule attaches; typically, a pocket or groove on the enzyme's surface.
phosphorylation
The transfer of a phosphate group, usually from ATP to a molecule. Nearly all cellular work depends on ATP energizing other molecules by phosphorylation.
Many enzymes require nonprotein helpers called _____, which bind to the active site an function in catalysis.
cofactors
enzymes
A macromolecule, usually a protein, thta serves as a biological catalyst, changing the rate of a chemical reaction without being consumed by the reaction.
feedback inhibition
A method of metabolic control in which a product of a metabolic pathway acts as an inhibitor of an enzyme within that pathway.
cofactors
A nonprotein molecule or ion that is required for the proper functioning of an enzyme.
substrate
A specific substance (reactant) on which an enzyme acts. Each enzyme recognizes only the specific substrate or substrates of the reaction it catalyzes.
competitive inhibitor
A substance that reduces the activity of an enzyme by entering the active site in place of the substrate. A competitive inhibitor's structure mimics that of the enzyme's substrate.
noncompetitive inhibitor
A substance that reduces the activity of an enzyme without entering an active site. By binding elsewhere on the enzyme, a noncompetitive inhibitor changes the shape of the enzyme so that the active site no longer effectively catalyzes the conversion of substrate to product.
Explain an advantage of feedback inhibition to a cell.
It prevents the cell from wasting valuable resources by synthesizing more of a particular product than is needed.
activation energy
The amount of energy that reactants must absorb before a chemical reaction will start.
induced fit
The change in shape of the active site of an enzyme, caused by entry of the substrate so that it binds the substrate snugly.
The graph below illustrates the course of a reaction with and without an enzyme. Which curve represents the enzyme-catalyzed reaction? What energy changes are represented by the lines labeled a (leftmost vertical line), b (middle verticle line), and c (bottom right line)?
The lower curve. Line a is the activation energy without the enzyme; b is the activation energy with the enzyme; c is the change in energy between reactants and products, which is the same for both the catalyzed and uncatalyzed reactions.
We can think of ___________ as the amount of energy neede for reactant molecules to move "uphill" to a higher-energy, unstable state so that the "downhill" part of a reaction can begin.
activation energy
A substrate fits into a region called the _______ - typically a pocket or groove on the surface of the enzyme.
active site
A ___________ reduces an enzyme's productivity by blocking substrate molecules from entering the active site.
competitive inhibitor
A(n) _____ speeds up a reaction by lowering the activation energy needed for a reaction to being.
enzyme
If a cell is producing more of that product than it needs, the product may act as an inhibitor of one of the enzymes early in the pathway, which is . . .
feedback inhibition (reversible)
A ___________ does not enter the active site; it binds to a site elsewhere on the enzyme and its binding changes the enzyme's shape so that the active site no longer fits the substrate.
noncompetitive inhibitor
A cell couples the exergonic reaction of hydrolysis of ATP to an endergonic reaction by transferring a phosphate group from ATP to another molecule. This phosphate transfer is called _____, and most cellular work depends on ATP.
phosphorylation
The specific reactant that an enzyme acts on is called the enzyme's ______.
substrate
