Chapter 14.9-14.12

1. Chapter 14.9-14.12 Proteins: Secondary, Tertiary, Quaternary, and Denaturation

2. 14.9- What is the secondary structure of a protein? • Regular and repeating structural patterns • 2 kinds of repeating patterns proposed by Linus Pauling and Robert Corey in 1940’s: 1. α-helix 2. β-pleated sheet • Hydrogen bonds hold polypeptide chain in place • Hydrogen bond connects carbonyl oxygen with amide hydrogen atom of another(–C=O---H-N-)

3. α-helix

4. α-helix • single protein chain coiled in a spiral with a right-handed twist • held together by hydrogen bonds parallel to the axis of the coil

5. β-pleated sheet

6. β-pleated sheet • Backbone of two protein chains is held together by hydrogen bonds

7. Secondary Proteins can be classified as: • 1. Fibrous proteins • 2. Globular proteins

8. Fibrous proteins: • Tough, insoluble proteins in which chains form long fibers or sheets • Wool, hair, and fingernails made of α-keratins(fibrous protein) • α-keratins are composed of α-helixes • Natural silk and spider webs are made of fibroin, proteins mainly composed of β-pleated sheets

9. Globular proteins: • Water-proteins whose chains are folded into compact, globelike shapes • Presence of hydrophilic side chains on outer surfaces account for water solubility –allowing them to travel through blood and other body fluids to sites where activity is needed

10. 14.10- What is the tertiary structure of a protein? • Three-dimensional shape • Unlike secondary, it depends on interactions of amino acid side chains

11. Tertiary Structures are stabilized five ways: • 1. Covalent Bonds • 2. Hydrogen Bonding • 3. Salt Bridges • 4. Hydrophobic Interactions • 5. Metal Ion Coordination

16. 14.11 What is the Quaternary Structure of a protein? • The way in which 2 or more protein chains form a single three-dimensional unit

17. 2 important quaternary proteins: • 1. Hemoglobin • 2. Collagen

18. Hemoglobin: • Composed of 4 polypeptide chains • 2α chains (141 amino acids) and 2 β chains(146 amino acids) • Held together by interaction hydrophobic groups and heme groups (iron in center of heterocyclic ring) • Oxygen carrier in red blood cells

19. Collagen: • Most abundant of all proteins in mammals • Makes up 30% or more of the total • Major constituent of skin, tendons, bones, blood vessels, and other connective tissues

20. How are proteins denatured? • Denaturation- the loss of the secondary, tertiary, and quaternary structures of a protein by chemical or physical agent that leaves the primary structure intact • Enzymes lose their catalytic activity and other proteins can’t carry out their biological functions when denatured

21. Denatured by: • Heat • Denaturing chemicals • pH change • Alcohol

22. Denaturation • Does not affect primary structures • Most denaturation is irreversible

23. Dietary Protein: • Protein structure must be destroyed before it can provide the nutrition for the body • Digestion involves denaturation and hydrolysis • Stomach acids denature proteins • Proteolytic enzymes in stomach and small intestine hydrolyze proteins to smaller fragments until free amino acids are formed and can be absorbed through intestinal membranes into the blood stream