Enzymes: Basic Properties

35 QA flashcards covering key concepts from the lecture notes on enzymes, cofactors, coenzymes, and vitamin-derived coenzymes.

What is an enzyme?

A biological catalyst that speeds a biochemical reaction by lowering the activation energy.

What are ribozymes?

RNA molecules that act as enzymes.

Define activation energy.

The minimum energy required to activate reactants to a state in which they can convert to products.

What is the reaction rate?

The speed at which a chemical reaction proceeds.

How are most enzymes named?

They typically end with the suffix -ase, named after the substrate or the enzyme’s role.

Are enzymes consumed in a chemical reaction?

No; they are not consumed.

What is enzyme specificity?

Enzymes can distinguish and bind to a specific substrate from similar compounds.

What is the role of the active site binding?

The 3D arrangement of the active site allows the substrate to approach and bind at the appropriate angles.

Describe the Lock and Key model.

A model where the substrate fits the active site like a key fits a lock without altering the enzyme.

Describe the Induced-fit model.

A model in which the enzyme’s active site changes shape to fit the substrate.

How much faster are enzyme-catalyzed reactions than uncatalyzed ones?

Typically 10^3 to 10^8 times faster.

What is enzyme regulation?

Enzymatic activity is regulated by molecules/pathways to meet cellular needs; drugs can activate or inhibit.

Why are enzymes localized within cells?

To isolate substrates/products and organize enzyme pathways.

What is an apoenzyme?

The inactive enzyme form without its nonprotein cofactor.

What is a holoenzyme?

The active enzyme form with its nonprotein cofactor.

What is a cofactor?

A nonprotein moiety that is a metal ion (e.g., Zn^2+, Fe^2+).

What is a coenzyme?

A nonprotein organic moiety that can be a cosubstrate or a prosthetic group.

What is a cosubstrate?

A small organic molecule that transiently associates with the enzyme and dissociates after the altered state.

What is a prosthetic group?

A small organic molecule permanently associated with the enzyme.

How do cofactors and coenzymes participate in catalysis?

They provide a functional group with the right size, shape, and properties to participate in catalysis.

What are the two strategies cofactors/coenzymes use to assist catalysis?

(1) Active-site residues provide proximity/orientation; (2) Cofactors/coenzymes provide a functional group to participate in catalysis.

What are cofactors?

Metal ions that can bind to enzymes and substrates, acting as electrophiles or stabilizers of developing negative charges.

Are cofactors derived from vitamins?

Coenzymes are usually derived from vitamins; cofactors are metal ions.

What is an activation-transfer coenzyme?

A coenzyme that directly binds to the substrate covalently and activates the bound moiety for catalysis.

Name two key features of activation-transfer coenzymes.

(1) A group that binds to the enzyme; (2) A separate functional group that covalently binds to the substrate; they depend on the enzyme for activity.

Function of tetrahydrofolic acid (THF)?

Transfers one-carbon units; involved in synthesis of methionine, purines, and thymidine monophosphate.

what are ligases

catalyze formation of bonds between carbon and O, S, N coupled to hydrolysis of high-energy phosphate bonds.

What is an oxidoreductase?

catalyze oxidation-reduction reactions

what is a transferase?

catalyze transfer of C-,N-, or P- containing groups

what is a hydrolase?

catalyze cleavage of bonds by addition of water

what is a lyase?

catalyze cleavage of C-C, C-S, and certain C-N bonds

what is an isomerase?

catalyze racemization of optical or geometric isomers