14.9-14.10

1. 14.9-14.10 By Kaitlin Kodack

2. 14.9- What is the secondary structure of a protein? • Three kinds of secondary structure: α-helix, β-pleated sheet & random coil • Repeating patterns in a protein backbone • Most common are α-helix and β-pleated sheet • Don’t have a repeating pattern, they are called random coils. • Helix is a protein chain that is twisted into a right handed coiled spring. • Shape of the helix is maintained by many intramolecular hydrogen bonds between the backbone.

5. β- sheet structures can occur between molecules when polypeptide chains run parallel or antiparallel. • Hydrogen bonding occurs between –C=O and H-N- groups & between R groups on side chains. • Most proteins, like globular ones, consist of certain portions of their molecules. The rest have a random coil. • Globular proteins contain all three secondary structures in different parts of their molecules.

6. Keratin is a fibrous protein found in hair, nails, horns and wool. Is the one protein that has mainly an α-helix structure. • Silk is made from fibroin, another fibrous protein. • Repeating pattern classified as a secondary structure is the extended helix of collagen. • Collagen is the structural protein of connective tissue in which it provides support and elasticity • Bone, cartilage, tendon, blood vessel, skin

7. The collagen is the most abundant protein in humans. • Makes up about 30% by weight of all the body’s protein. • Primary structure of collagen helped make the extended helix possible. • Each strand repeats the pattern, Gly-X-Y; every third amino acid in the chain is glycine. • Glycine has the shortest side chain of all amino acids. • 1/3 of the X amino acid is proline and Y is often hydroxyproline.

8. 14.10- What is the tertiary structure of a protein? • Three-dimensional arrangement of atoms in a protein. • Includes interactions of the side chains. • Tertiary structures are stabilized in 5 ways • Covalent bonds • Hydrogen bonding • Salt bridges • Hydrophobic Interactions • Metal Ion Coordination

9. Covalent Bonding • Most often used is the disulfide bond. • Amino acid cysteine is converted to dimer cystine. • When cysteine residue is in one chain and another cysteine residue is in another chain, disulfide bond makes a covalent bond and binds the chains together.

11. Hydrogen Bonding • Between backbone -C=O and -N-H groups. • Between polar groups on or between side chains and peptide backbone.

13. Salt Bridges • Also called electrostatic attractions. • Occurs between two amino acids with ionized side chains- between a acidic amino acid and a basic amino acid chain. • Held together by simple ion-ion attraction

14. Hydrophobic Interactions • Polar groups turn outward (toward aqueous solution) and nonpolar turns inward ( away from water molecules) • Nonpolar interact with each other, not in water regions. • Weaker than hydrogen bonding or salt bridges. • Acts over large surface areas and can stabilize a loop or some other tertiary structure.

15. Metal Ion Coordination • Two chains with same charge can repel each other, but they can also be linked by a via metal ion. • Ex: two glutamic acid side chains would attract magnesium ion forming a bridge. • Human body requires certain trace minerals- necessary component of proteins.

16. Side chains of some proteins can fold one way. • Long polypeptides can fold numerous ways. • Chaperone is a protein that helps other proteins to fold in to biologically active conformation and enables partially denatured proteins to regain their biologically active conformation.

17. The End 