1. Proteins: Secondary, Tertiary, Quaternary, and Denaturation
Chapter
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