2)Order the molecules on the following list according to their ability to diffus

ID: 34095 • Letter: 2

Question

2)Order the molecules on the following list according to their ability to diffuse through a lipid bilayer, beginning with the one that coresses the bilayer the most readily.

Cl-,O2,ribose, tRNA,H2O

3)Hydrophobicity can be measured as the free energy change (Delta G') for the transfer of a given amino acid form water to n-octanol, in units of kcal/mole.

A)Listed below are four amino acids and four hydrophobicity values determined using the above scale. Match the hydrophibicity values with the correct amino acids.

Amino acids: Phenylalanine, arginine, isoleucine, serine.

Hydrophobicity(kcal/mol): -1.71,1.81,-1.12,0.46

B) Notably, the hydrophobicity values(as determined above) for aspartic acid changes from 0.43 kcal/mole to 3.64 kcal/mol when the pH is changed from 2 to 7. Explain this observation.

Explanation / Answer

2. O2, H2O, Cl-, ribose, tRNA

3. A

Amino acid

Hydrophobicity (KCal/mol)

Phenylalanine

-1.71

Arginine

1.81

Isoleucine

-1.12

Serine

0.46

B. When pH of the medium increased from 2 to 7 H+ ion would be removed from aspartic acid and a negative charge will be induced. At this high pH the presence of high concentration ionic molecules alters the hydrophobicity of the amino acid.