Download 6 Protein Hydrolysis GOB Structures

19.6 Protein Hydrolysis and Denaturation
Denaturation of a
protein occurs when the
interactions of residues
that stabilize tertiary or
quaternary structures
are disrupted, which
destroys the shape and
renders the protein
biologically inactive.
Learning Goal Describe the hydrolysis and denaturation
of proteins.
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Protein Hydrolysis
Peptide bonds are broken through hydrolysis
reactions. Hydrolysis
• occurs in the stomach when enzymes
catalyze the hydrolysis of proteins to give
amino acids.
• breaks up the primary structure by breaking
the covalent peptide bonds that link the
amino acids.
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Protein Hydrolysis
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Denaturation of Proteins
Denaturation of a protein
• occurs when a change disrupts the
interactions between residues that stabilize
the secondary, tertiary, or quaternary
structure.
• does not affect the amide bonds between
amino acids.
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Denaturation of Proteins
The loss of secondary and tertiary structures in a protein
occurs when conditions change, such as
• increasing the temperature.
• making the pH very acidic or basic.
• adding certain organic compounds or heavy metal ions.
• adding mechanical agitation.
When the interactions between the residues are disrupted,
• a globular protein unfolds.
• the tertiary structure is disrupted and the protein is no
longer biologically active.
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Denaturation of Proteins, Heat
Proteins are denatured when heated above 50 °C.
The heat
• disrupts the hydrogen bonds and hydrophobic
interactions between nonpolar residues.
• does not change the nutritional value of proteins
but makes them more digestible.
High temperatures are also used to disinfect surgical
instruments and gowns by denaturing the proteins of
any bacteria present.
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Denaturation of Proteins, Acids and Bases
Proteins can be denatured by changing the pH, which
• breaks hydrogen bonds.
• disrupts ionic bonds and salt bridges.
Tannic acid, a weak acid used in burn ointments, is
applied to the site of the burn to coagulate proteins. It
forms a protective cover and prevents further loss of
fluid from the burn.
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Denaturation of Proteins, Organic Compounds
Organic compounds such as ethanol and isopropyl
alcohol act as disinfectants by
• exchanging the bacterial protein’s hydrogen bonds to
water with their own.
• disrupting the side chain intramolecular hydrogen
bonding.
An alcohol swab is used to clean wounds or to prepare
the skin for an injection because the alcohol passes
through the cell walls and coagulates the proteins inside
the bacteria.
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Denaturation of Proteins, Heavy Metal Ions
Heavy metal ions such as Ag+, Pb2+, and Hg2+
denature proteins by forming bonds with ionic
residues or reacting with disulfide
— S — S — bonds.
Dilute (1%) solutions of AgNO3 are placed in the
eyes of newborn babies to destroy the bacteria
that cause gonorrhea.
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Denaturation of Proteins, Agitation
The whipping of cream and the beating of egg whites
are examples of using mechanical agitation to
denature proteins.
The whipping action stretches the polypeptide chains
until the stabilizing interactions are disrupted.
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Denaturation of Proteins, Summary
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Concept Map
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.