PROTEIN FUNCTIONS

PROTEIN FUNCTIONS (continued)

PROTEIN FUNCTIONS (continued)• Catalytic proteins function as enzymes.• Structural proteins in animals form the structural materials

other than the inorganic components of the skeleton.• Storage proteins can store small molecules or ions.• Protective proteins are antibodies, a substance that helps

protect the body from invasion by viruses, bacteria, and other foreign substances, as well as blood clotting.

• Regulatory proteins are responsible for hormone regulation of body processes.

• Nerve impulse transmission proteins are receptors of small molecules that pass between gaps separating nerve cells.

• Movement proteins are muscle proteins.• Transport proteins are proteins that bind and transport

numerous small molecules and ions through the body.

PROTEIN SHAPES• Fibrous proteins are long rod-shaped or stringlike molecules

that intertwine to form fibers (examples: collagen, elastin, & keratin).

• Globular proteins are spherical-shaped proteins that form stable suspensions in water, or is water soluble (examples: hemoglobin & enzymes).

PROTEIN COMPOSITION• Simple proteins contain only amino acid residues.• Conjugated proteins contain amino acid residues and other

organic or inorganic components (prosthetic groups).

PROTEIN COMPOSITION (continued)

PRIMARY PROTEIN STRUCTURE• Primary protein structure: • is the linear sequence of amino acids in a

protein chain.• determines secondary and tertiary

structures.• is important for the functioning of proteins;

small variations in the primary structure can cause profound differences in the functioning of proteins.

PRIMARY PROTEIN STRUCTURE (continued)

SECONDARY PROTEIN STRUCTURE• Secondary protein structure:• is determined by hydrogen bonding between amide

groups of amino acid residues in the chain.

• An -helix occurs when a single protein chain twists so it resembles a coiled helical spring; hydrogen bonding occurs between carbonyl and amide every 4 residues.

• A -pleated sheet occurs when several protein chains lie side by side and are held in position by hydrogen bonds between the amide carbonyl oxygen atoms of one chain and the amide hydrogen atoms of an adjacent chain.

SECONDARY PROTEIN STRUCTURE (continued)• An -helix is found in:• keratin,• myosin,• epidermin, and• fibrin.

SECONDARY PROTEIN STRUCTURE (continued)• -pleated sheets are found extensively only in silk protein.

SECONDARY PROTEIN STRUCTURE (continued)• Random coil molecular structure:

TERTIARY PROTEIN STRUCTURE• Tertiary protein structure:• is the specific 3-D shape of a protein resulting from

interactions between “R” groups of amino acid residues.• has “R” group interactions that include:• disulfide bridges, which form between cysteine

residues.• salt bridges, which are ionic bonds that form between

acidic and basic residues.• hydrogen bonds, which form between polar residues.• hydrophobic interactions, which form between nonpolar

residues.

TERTIARY PROTEIN STRUCTURE (continued)

TERTIARY PROTEIN STRUCTURE (continued)

• In an aqueous environment, the interaction of hydrophilic and hydrophobic side chains with water also determines shape.

QUATERNARY PROTEIN STRUCTURE

• All proteins have primary, secondary, and tertiary structure, but not all proteins have quaternary structure.

• Quaternary structure is the arrangement of subunits that form a larger protein.

• Subunits are polypeptides that have primary, secondary, and tertiary structure.

• Conjugated proteins with quaternary structure contain subunits as well as prosthetic groups, which may be organic or inorganic components.

• Heme is an example of aprosthetic group:

QUATERNARY PROTEIN STRUCTURE (continued)• Hemoglobin has:• four chains (subunits), which are two identical alpha

chains and two identical beta chains.

• four heme groups.

• hydrophobic forces that hold the subunits together.

PROTEIN HYDROLYSIS• Heat and acid or base can completely hydrolyze proteins.

• This is an important process in protein digestion (uses enzymes).

PROTEIN DENATURATION• Protein denaturation:• is the process by which a protein loses its

native state (characteristic quaternary, tertiary, and secondary structure).

• leads to a loss of biological activity (function).

PROTEIN DENATURATION (continued)