Lecture 9 + 10

Question 1

How to tell L and D isomers apart

Answer 1

• if H to COOH counter clockwise D isomer
• if H to COOH clockwise L isomer

Question 2

Which amino acid is not chiral

Answer 2

glycine - has 2 hydrogens

Question 3

Which amino acids are hydrophobic (non polar)

Answer 3

• non polar
• Gly, Ala, Pro, Val, Leu, Ile, Met, Phe, Trp, Tyr (both hydrophobic and hydrophilic -OH)

Question 4

What is proline

Answer 4

• helix breaker
• side chain cyclizes to form a covalent bond with its backbone nitrogen
• very rigid

Question 5

Which amino acids are hydrophilic (polar)

Answer 5

• Lys, Arg, His - (+) charged
• Asp, Glu - (-) charged
• Asn, Gln, Cys, Thr, Ser - polar uncharged

Question 6

Cysteine and disulfide bonds

Answer 6

• cytoplasm is reducing environment - disulfide bonds cannot form so proteins requiring these bonds are not stable
• these bonds only form in oxidizing environments
• these bonds form after protein has folded - stabilize folded form