Lecture 8A

Question 1

Fibrous Protein Structure

Answer 1

• Long extended structures, many polypeptides
• usually water insoluble
• often have structural function

Question 2

Globular Protein Structure

Answer 2

• Roughly spherical in shape
• Polypeptide folds back upon itself, water soluble, enzymes are globular

Question 3

Important Structural Proteins: a-keratin

Answer 3

• Mechanically durable and chemically unreactive
• a-keratin in mammals and b-keratin in brids/reptiles

Question 4

Cysteine Residues

Answer 4

• Can form disulphide bonds that crosslink between chains
• Can be cleaved by B-mercaptoethanol,
• This reoxidizes it into a new form which creates hair curl

Question 5

2-Silk Fibroin

Answer 5

• Spider silk
• Ordered B-sheets surrounded by disordered a-helices and B-turns
• Silk has regions of antiparallel B-sheet structure with alternating Gly and Ala residues, which hold the sheets together

Question 6

3-Collagen

Answer 6

• Found in tendons and connective tissue
• Highly repeating structure
• Hydroxyproline and hydroxylysine residues necessary for proper collagen structure
• Several posttranslaationally modified amino acids occur in collagen
• Scurvy was a collagen tissue degradation
• left-handed helix

Question 7

Tropocollagen

Answer 7

• 3 left handed helices form a right handed cable
• Small Gly residues are small enough to fit inside the helix
• H-bonding with Gly amide N-H helps hold it together
• Many tropocollagen helices make a collagen fiber

Question 8

Fibrous Proteins: Keratins

Answer 8

• Right handed a-helices form a left-handed “coiled coil”
• a-keratin sequences show a pseudo-repeat of 7 residues
• a-keratins are elastic, have many disulphide bonds