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MCAT Bio. Chem Ch. 2
Question | Answer |
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Enzymes | Biological catalysts that are unchanged by the reactions they catalyze and are reusable. |
Note About Enzymes And Their Reactions | Each enzyme catalyzes a single reaction or type of reaction with high specificity. |
Oxidoreductases | Catalyze oxidations-reduction reactions that involve the transfer of electrons. |
Transferases | Move a functional group from one molecule to another molecule. |
Hydrolases | Catalyze cleavage with the addition of water. |
Lyases | Catalyze cleavage without the addition of water and without the transfer of electrons. The reverse reaction (synthesis) is more important biologically. |
Isomerases | Catalyze the interconversion of isomers, which include constitutional isomers and stereoisomers. |
Ligases | Join two large biomolecules, often of the same type. |
Exergonic Reactions | Release energy, Delta G is negative |
What Enzymes Do In Biological Reactions | They lower the activation energy required for the reactions |
Note About Enzymes and Delta G and Delta H | They do not alter free energy (Delta G) or enthalpy (Delta H), they change the rate at which equilibrium is reached (kinetics). |
How Enzymes Act | They stabilize the transition state to provide a favorable micro environment or bond with substrate molecules. |
Active Site | Site of catalysis. |
Lock And Key Theory / Induced Fit Model | Hypothesizes that the enzyme and substrate are exactly complementary. |
Induced Fit Model | Hypothesizes that the enzyme and substrate undergo conformational changes to interact fully. |
Cofactors | Metal cations that are required by some enzymes |
Coenzymes | Small organic molecules that are required by some enzymes. |
Saturation Kinetics | As substrate conc. increases, the reaction rate does as well until a max. value is reached |
Michaelis-Menten Plot | Represents saturation kinetics as a hyperbola |
Lineweaver-Burk | Represents saturation kinetics as a line |
Note On How Enzymes Can Be Compared | by their Km and vmax values |
Km | Michaelis-Menten Constant, which is the substrate conc. at which the enzyme is functioning at half of its max. velocity. |
Cooperative Enzymes | Display a sigmoidal curve because of the change in activity with substrate binding. |
Temp and pH Effects On Enzyme Activity | Changes in temp and pH result in denaturing an enzyme and loss of activity due to loss of secondary, tertiary, or quaternary structure |
Note About Salinity's Impact On Enzymes | Salinity can impact the action of enzymes. |
Feedback Inhibition | Regulatory mechanism in which the catalytic activity of an enzyme is inhibited by the presence of high levels of a product later in the same pathway. |
Reversible Inhibition | The ability to replace the inhibitor with a compound of greater affinity or to remove it using mild laboratory treatment |
Competitive Inhibition | Results when the inhibitor is similar to substrate and binds at the active site. This can be overcome by adding substrate. vmax is unchanged, Km increases. |
Noncompetitive Inhibition | Results when the inhibitor binds with equal affinity to the enzyme and the enzyme-substrate complex. vmax is decreased, Km is unchanged. |
Mixed Inhibition | Results when the inhibitor binds with unequal affinity to the enzyme and the enzyme-substrate complex. vmax is decreased, Km is increased or decreased depending on if the inhibitor has higher affinity for the enzyme or enzyme-substrate complex. |
Uncompetitive Inhibition | Results when the inhibitor binds only with the enzyme-substrate complex. Km and vmax both decrease. |
Irreversible Inhibition | Alters the enzyme in such a way that the active site is unavailable for a prolonged duration or permanently. New enzyme molecules must be synthesized for the reaction to occur again. |
Allosteric Sites | Sites of an enzyme that can be occupied by activators which increase either affinity or enzymatic turnover. |
Phosphorylation | Covalent modification with phosphate that can alter the activity or selectivity of enzymes. |
Glycosylation | Covalent modification with carbohydrate that can alter the activity or selectivity of enzymes. |
Zymogens | Secreted in an inactive form and are activated by cleavage. |