Protein Structure: Tertiary and Quaternary Structure 20.7 Protein Hydrolysis and Denaturation Chapter 20 Amino Acids and Proteins

2 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 bonds Disulfide bonds Tertiary Structure

3

4 The interactions of the R groups give a protein its specific three- dimensional tertiary structure.

5 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

6 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.

7 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.

8 Summary of Structural Levels

9

10 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

11 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.

12 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

13 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