Functions of Proteins and Enzymes

An amino acid is polar acidic when the R group is __.

A carboxylate (-COO-) group.

Primary structure of proteins can be affected by slight changes in sequence, such as __ of a single amino acid.

Substitution.

Secondary structures are maintained by numerous __ bonds.

Hydrogen.

In the alpha helix, hydrogen bonds form between the O of the C=O groups and the H of __ groups.

N-H.

The helical shape of the alpha helix resembles a __ staircase.

Spiral.

In the beta helix, hydrogen bonds form between carbonyl O atoms and H atoms in __ groups.

Amide.

Tertiary structure refers to the overall __ shape of a protein.

Three-dimensional.

Hydrophobic interactions occur between amino acids that have __ R groups.

Nonpolar.

Ionic attractions between ionized R groups of polar basic and polar acidic amino acids are called __.

Salt bridges.

Disulfide bonds form between the __ groups of cysteine residues in a polypeptide chain.

-SH.

Quaternary structure consists of biologically active proteins with __ or more polypeptide chains.

Two.

Denaturing proteins destroys the shape and renders the protein __.

Biologically inactive.

Increasing temperature can cause proteins to denature when heated above __ °C.

50.

Heavy metals can denature proteins by forming bonds with __ residues.

Ionic.

Enzymes are biological __ that accelerate the rate of reactions.

Catalysts.

Lactase is an enzyme that reacts with __.

Lactose.

The lock and key model assumes that the enzyme is __.

Rigid.

The induced fit model suggests that the enzyme is __.

Flexible.

Inhibitors that covalently bond with R groups of amino acids near the active site are called __ inhibitors.

Irreversible.

Most enzymes show little activity at low __.

Temperatures.

The optimum pH level for enzymes in the human body is approximately __.

7.4.

Apoenzyme refers to an enzyme without a __.

Cofactor.

The combination of a cofactor with an apoenzyme is called a __.

Holoenzyme.

Feedback inhibition is a regulatory process where the formation of a product __ an earlier reaction.

Inhibits.

Allosteric enzymes have a binding site other than the __ site.

Active.

Negative allosteric regulators __ enzyme activity.

Inhibit.

Positive allosteric regulators __ enzyme action.

Stimulate.

Protein modification can influence the functionality of __.

Proteins.