tertiary structure 9/28

Question 1

what is a protein’s 3D structure (tertiary and quaternary) determined by

Answer 1

amino acid sequence

Question 2

what can help determine 3D structures

Answer 2

-x ray diffraction and NMR spectroscopy

Question 3

what is x ray diffraction

Answer 3

protein crystal held in beam of x rays and x ray photons deflect and pattern of dots used to calculate protein that caused diffraction (need substaintale size crystal to start)

Question 4

what is NMR spectroscopy

Answer 4

• measure of spin of protons
• shows range of motions molecules go through

Question 5

fibrous proteins have predominantly what type of structure

Answer 5

secondary

Question 6

alpha keratin

Answer 6

• intermediate filament family of cytoskeletal proteins
• primary structure (Z-X-X-Z-X-X-X)_n where X is usually cysteine (cross linking sidechain), and Z is a hydrophobic residue
• alpha helical conformation since on turn of helix is 3.6 residues helix will have a hydrophobic stripe
• 2 right handed helices twist together left handed to form coiled coil, held tightly together by hydrophobic stripes
• in each coiled coil one of polypeptides is type I (acidic) and other is type II (basic)
• coiled coils associate together with others to make larger structures such as protofilaments, protofibrils, intermediate filaments, hair cells, hair

Question 7

collagen

Answer 7

• major structural filament in animal connective tissue
• primary structure: gly-X-pro or gly-X-hydroxyproline where x is any amino acid residue
• gly and pro form left handed helix with pitch 9.4 A
• three of extended helices form right handed coiled coil
• all gly residues have side chains in spae between three helices
• only gly side chains small enough to fit into position
• mutation substituting anything but gly in this position causes severe birth defects and scury is also caused by lack of collagen
• vitamin C –> hydroxyproline –> collagen
• coiled coils cross linked together by covalent bonds involving lys and hydroxylysine residues

Question 8

fibroin

Answer 8

• main component of silk and spider webs
• primary structure consists of repeating pattern (gly-ala)_n where ser can be substituted for ala
• each polypeptide chain forms strand of beta sheet with gly side chains facing one way and ala (ser) chains facing the other
• beta sheets stack with like side chains of adjacent sheets zipping together forming very strong, non elastic fiber
• various types of silk have varying amounts of a random coil configuration included within a strand and the more of this random coil the more elastic the fibers