PROTEIN DENATURATION

PROTEIN DENATURATION

Protein denaturation is the partial or complete disorganization of a protein’s characteristic three-dimensional shape

Result of disruption of its secondary, tertiary, and quaternary structural interactions.

does not affect the primary structure of a protein

biochemical activity

Because the biochemical function of a protein depends on its three-dimensional shape, the result of denaturation is loss of ..

Some proteins lose all of their three-dimensional structural characteristics upon denaturation, most proteins maintain some 3D structure

Renaturation

limited denaturation changes conditions can be reversed, in which the protein is “refolded,”

IRREVERSIBLE

For extensive denaturation changes, the process is usually ….

Loss of water solubility

is a frequent physical consequence of protein denaturation.

Coagulation or precipitation

precipitation out of biochemical solution of denatured protein

Protein denaturation

involves loss of the protein’s three-dimensional structure. Complete loss of such structure produces an “unstructured” protein strand.

HEAT

disrupts hydrogen bonds by making molecules vibrate too violently; produces coagulation, as in the frying of an egg

violent whipping or shaking (mech.agitation),microwave and UV, vibration

causes molecules in globular shapes to extend to longer lengths, which then entangle (e.g., beating egg white until thickens)

H-Bond

organic solvents (e.g., ethanol, 2-propanol, acetone)

interferes with R-group interactions because these solvents also can form hydrogen bonds; quickly denatures proteins in bacteria, killing them (e.g., the disinfectant action of 70% ethanol)

strong acids and bases

disrupts hydrogen bonds and salt bridges; prolonged action leads to actual hydrolysis of peptide bonds

salts of heavy metals (Hg2+ Ag+, Pb2+)

metal ions combine with -SH groups and form poisonous salts

Effect of Heat

disrupt hydrogen bonds and non-polar hydrophobic interactions

increases the kinetic energy and causes the molecules to vibrate so rapidly and violently that the bonds are disrupted

proteins in eggs denature and coagulate during cooking. foods are cooked to denature the proteins to make it easier for enzymes to digest them

heating

Medical supplies and instruments are sterilized by … to denature proteins in bacteria and thus destroy the bacteria

High levels of thermal energy

energy may disrupt the hydrogen bonds that hold the protein together

As these bonds are broken, the protein will begin to unfold and lose its capacity to function as intended

body temperature (37 degree centigrade)

Temperatures at which proteins denature may vary, but most human proteins function optimally at ….

Effect of Alcohol

amide groups in the secondary protein structure

Hydrogen bonding occurs between ——

Hydrogen bonding between "side chains" occurs in tertiary protein structure in a variety of amino acid combinations

Alcohol

denatures proteins by disrupting the side chain intramolecular hydrogen bonding

70% alcohol

is able to penetrate the bacterial cell wall and denature the proteins and enzymes inside of the cell.

95% alcohol solution

merely coagulates the protein on the outside of the cell wall and prevents any alcohol from entering the cell.

Ions

form strong bonds with the carboxylate anions of the acidic amino acids or -SH groups of cysteine, disrupting ionic and disulfide linkages

Disulfide Bonds

Heavy Metal Salts Disrupt ???

Heavy metals

also disrupt disulfide bonds because of their high affinity and attraction for sulfur and which lead to the denaturation of proteins

can disrupt bonds in the protein, causing it to lose its structure.

mercury and lead

Salts of heavy metals such as … may be used to denature can interact with a protein's functional side chain groups to form complexes.

Protonation

of the amino acid residues changes whether or not they participate in hydrogen bonding, so a change in the pH can denature a protein.