Chapter 18: Amino Acids and Proteins

Alpha helix

________ is a secondary protein structure in which a protein chain forms a right- handed coil stabilized by hydrogen bonds between peptide groups along its backbone.

Residue

________ is an amino acid unit in a polypeptide.

Alpha amino acid

is an amino acid in which the amino group is bonded to the carbon atom next to the ¬COOH group.

Organic compounds

________: Polar solvents such as acetone and ethanol interfere with hydrogen bonding by competing for bonding sites.

insoluble collagen

Cooking meat converts some of the ________ into soluble gelatin, which can be used in glue and for thickening sauces.

Secondary protein structure

regular and repeating structural patterns created by hydrogen bonding between backbone atoms in neighbouring segments of protein chains.

Zwitterion

________ is a neutral dipolar ion that has one positive charge and one negative charge.

bacterial protein

The disinfectant action of ethanol, for example, results from its ability to denature ________.

→Agents

________ that cause denaturation include heat, mechanical agitation, detergents, organic solvents, extremely acidic or basic pH, and inorganic salts:

salt bridge

A(n) ________ is a noncovalent bond; it is an ionic bond.

Mechanical agitation

________: The most familiar example of denaturation by agitation is the foam produced by beating egg whites.

Biochemistry

________ is the study of molecules and their reactions in living organisms.

PH change

________: Excess H+ or OH- ions react with the basic or acidic side chains in amino acid residues and disrupt salt bridges.

Noncovalent forces

________ are forces of attraction other than covalent bonds that can act between molecules or within molecules.

hydrophobic substance

A(n) ________ does not dissolve in water.

Detergents

very low concentrations of detergents can cause denaturation by disrupting the association of hydrophobic side chains.

Amino acids

molecule that contains both an amino functional group and a carboxyl functional group

amino acid

The pI for each ________ is different, due to the influence of the side- chain functional groups.

Alpha

amino acid is an amino acid in which the amino group is bonded to the carbon atom next to the ¬COOH group

Carboxyl-terminal (C-terminal) amino acid is the amino acid with the free ¬COO

group at the end of a protein

Heat

The weak side-chain attractions in globular proteins are easily disrupted by heating, in many cases only to temperatures above 50 °C (323 K)

Mechanical agitation

The most familiar example of denaturation by agitation is the foam produced by beating egg whites

Detergents

Even very low concentrations of detergents can cause denaturation by disrupting the association of hydrophobic side chains

Organic compounds

Polar solvents such as acetone and ethanol interfere with hydrogen bonding by competing for bonding sites

Inorganic salts

Sufficiently high concentrations of ions can disturb salt bridges

quaternary structure

two or more protein chains assembled in a larger three-dimensional structure held together by noncovalent interactions.

denaturation

the loss of secondary, tertiary, or quaternary protein structure due to disruption of noncovalent interactions and/or disulfide bonds that leaves peptide bonds and primary structure intact.