1 20.6 protein structure: tertiary and quaternary structure 20.7 protein hydrolysis and denaturation...
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20.6 Protein Structure: Tertiary and Quaternary Structure
20.7 Protein Hydrolysis and Denaturation
Chapter 20 Amino Acids and Proteins
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The tertiary structure: Gives a specific overall shape to a protein. Involves interactions and cross links between
different parts of the peptide chain. Is stabilized by
Hydrophobic and hydrophilic interactions Salt bridges
Hydrogen bondsDisulfide bonds
Tertiary Structure
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Tertiary Structure
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Tertiary Structure
The interactions of the R groups give a protein its specific three-dimensional tertiary structure.
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Globular Proteins
Globular proteins: Have compact,
spherical shapes. Carry out synthesis,
transport, and metabolism in the cells.
Such as myoglobin store and transport oxygen in muscle.
Myoglobin
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Fibrous Proteins
Fibrous proteins: Consist of long, fiber-like shapes. Such as alpha keratins make up hair, wool,
skin, and nails. Such as feathers contain beta keratins with
large amounts of beta-pleated sheet structures.
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Quaternary Structure The quaternary structure
contains two or more tertiary subunits.
Hemoglobin contains two alpha chains and two beta chains.
The heme group in each subunit picks up oxygen for transport in the blood to the tissues.
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Summary of Structural Levels
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Protein hydrolysis: Splits the peptide bonds to give smaller
peptides and amino acids. Occurs in the digestion of proteins. Occurs in cells when amino acids are needed
to synthesize new proteins and repair tissues.
Protein Hydrolysis
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Hydrolysis of a Dipeptide
In the lab, the hydrolysis of a peptide requires acid or base, water and heat.
In the body, enzymes catalyze the hydrolysis of proteins.
+
H3N CH COH
OCH3
+
H2O, H+
++
heat,
CH2
OH
H3N CH C
O
N
H
CH C
O
OH
CH3
CH2
OH
CH C
O
OHH3N
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Denaturation involves the disruption of bonds in the secondary, tertiary and quaternary protein structures.
Heat and organic compounds break apart H bonds and disrupt hydrophobic interactions.
Acids and bases break H bonds between polar R groups and disrupt ionic bonds.
Heavy metal ions react with S-S bonds to form solids.
Agitation such as whipping stretches chains until bonds break.
Denaturation
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Denaturation of protein occurs when:
An egg is cooked. The skin is wiped with
alcohol. Heat is used to cauterize
blood vessels. Instruments are sterilized in
autoclaves.
Applications of Denaturation