Chapter 19 Amino Acids and Proteins

1. Chapter 19 Amino Acids and Proteins 19.5Protein Structure: Tertiaryand Quaternary Levels

2. Essential Amino Acids • are the ten amino acids not synthesized by the body • must be obtained from the diet • are in meat and diary products • are missing (one or more) in grains and vegetables • Vegetarians needs complementary diet: Wheat/Rice/Oats plus Means/Peas/Soy

3. Tertiary Structure The tertiary structure of a protein • gives a specific three-dimensional shape to the polypeptide chain • 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

4. Tertiary Structure (continued) • The interactions of the R groups give a protein its specific three-dimensional 3o structure.

5. Cross-Links in Tertiary Structures

6. Globular Proteins Globular proteins • have compact, spherical shapes • carry out synthesis, transport, and metabolism in the cells • Eg: Myoglobin store and transport oxygen in muscle 153 AA, 17,699 dalton Myoglobin

7. Fibrous Proteins: Structure for cells & tissues Fibrous proteins • consist of long, fiber-like shapes • α-keratins make up outer layer of skin, hair, nails, horns (outer layer) - 3 α-helices coil to form filament (held by –S-S- bonds) contains some β-pleated protein. - fibrils bundled to a hair strand • β-keratins make up feathers, beaks. scales and claws of reptiles - more β-sheets than α-helices. - harder/tougher than α-keratins.

8. Chitins : a modified polysaccharide as tough as keratins Polymer of A amino sugar N-Acetylglucosamine, (C6H13O5N)n • cell walls of fungi, exoskeletons of arthropods such as crustaceans (e.g., crabs, lobsters and shrimps) and insects, the radulas of mollusks, and the beaks and internal shells of cephalopods • Chitosan: Poly D-Glucosamine,

9. Learning Check Select the type of tertiary interaction as: 1) disulfide 2) ionic 3) H bonds 4) hydrophobic A. leucine and valine B. two cysteines C. aspartic acid and lysine D. serine and threonine

10. Solution Select the type of tertiary interaction as: 1) disulfide 2) ionic 3) H bonds 4) hydrophobic 4 A. leucine and valine 1 B. two cysteines 2 C. aspartic acid and lysine 3 D. serine and threonine

11. Quaternary Structure Thequaternary structure • is the combination of two or more tertiary units • is stabilized by the same interactions found in tertiary structures • of hemoglobin consists of two alpha chains and two beta chains with heme groups in each subunit that pick up oxygen for transport in the blood to the tissues Hemoglobin

12. Summary of Protein Structures

13. Summary of Protein Structures (cont’d)

14. Learning Check Identify the level of protein structure as: 1) primary 2) secondary 3) tertiary 4) quaternary A. beta-pleated sheet B. order of amino acids in a protein C. a protein with two or more peptide chains D. the shape of a globular protein E. disulfide bonds between R groups

15. Solution Identify the level of protein structure as: 1) primary 2) secondary 3) tertiary 4) quaternary 2 A. beta-pleated sheet 1 B. order of amino acids in a protein 4 C. a protein with two or more peptide chains 3 D. the shape of a globular protein 3 E. disulfide bonds between R groups