Enzymes Lecture Notes

Flashcards on Enzymes

Enzymes

Biological catalysts that are protein molecules produced by living cells.

Ribozymes

RNA modifying catalysts that are molecules of ribonucleic acid that catalyse reactions on the phosphodiester bond of other RNAs.

Catalyst Function

Enzymes increase the rate of reaction without themselves being consumed in the reaction.

Enzyme Specificity

Enzyme catalysts are highly specific and catalyze only one or a small number of chemical reactions.

Reaction Rate

The rate of an enzyme-catalyzed reaction is usually much faster than that of the same reaction when directed by non-biological catalysts.

Nomenclature of Enzymes

Originally given non-descriptive names, later improved by adding the suffix -ase.

α-amylase

Starch to glucose + maltose + oligosaccharides

Lactase

Lactose to glucose + galactose

Lipase

Fat to fatty acids + glycerol

Glucose isomerase

Glucose  fructose

Enzyme Commission (EC numbers)

A system for classifying enzymes based on their mechanism.

Hydrolases

Enzymes that use water to break up some other molecule.

Cofactor

A non-protein component required by an enzyme to carry out its catalytic function.

Apoenzyme

An enzyme that requires a cofactor; the protein part of a holoenzyme.

Holoenzyme

An enzyme containing a non-protein group.

Enzyme Function

Enzymes increase reaction rates by lowering the activation energy.

Catalysts lower the activation energy

Binding the substrate and forming a catalyst-substrate complex.

Free energy (G)

The energy stored in the bonds of a chemical that can be harnessed to do work.

Free energy change (ΔG)

The change between the free energy in the product(s) and that in the substrate(s).

Active site

A specific region of the enzyme where substrates bind and the reaction takes place.

Active site of an enzyme

The region that binds the substrates and the cofactor, if any.

Catalytic groups

Residues that directly participate in the making and breaking of bonds.

Lock and Key Model

The enzyme has a fit shape before the substrate is bound.

Induced Fit Model

Enzymes are flexible, and the shapes of the active sites can be markedly modified by the binding of substrate.

Isozymes

Enzymes that differ in amino acid sequence but catalyse the same chemical reaction.