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. 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. 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

17. 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

18. 2 important quaternary proteins: 1. Hemoglobin 2. Collagen

19. Hemoglobin: Composed of 4 polypeptide chains 2 α 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) Conjugated proteins- contain non-amino acid portions Oxygen carrier in red blood cells

20. 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

21. 14.12 How are proteins denatured? Denaturation: ◦ Loss of secondary, tertiary, or quarternary protein structure by a chemical or physical agent ◦ Leaves peptide bonds and primary structure intact

22. Agents that cause denaturation: Heat pH change Inorganic salts Organic compounds

23. Most denaturation is: Irreversible, hard boiled eggs don’t soften much when their temperature is lowered