Question

5. A stu dent isolated a protein and assumed it was made up of a single polypeptide. However, after treating it with excess dithiothreitol (DTT; see structure below), two polypeptides were obtained. One of the polypeptides contained 78 amino acids and the other contained 125 amino acids. Both polypeptides contained 1 Qys and 1 Met. A. Using the structure of DIT below, sketch what the protein likely looked like before treatment with DTT (label/name any key amino acids and the ends of your polypeptide). (2pts) B. Now, draw/sketch ALL of the likely products of the reaction labeling/naming any key amino acids. (3pts) Protein?? Products?? HO DTT

Answer 1

5.
DTT = C4H10O2S2 = Clealands reagent.
It serves as a strong reducing agent.
See image for the structures of protein before and after the DTT treatment.
Before the DTT treatment, the protein exists as a heterodimer joined together by a disulfide bond.
DTT reduces disulfide bonds.

HN O C HC-CHyS-S- CH2 CH Disulfide bond (cysteine) o C HN CH,SH CHOH CHOH CH2SH DTT Reduction by DTT HN 0 HC-CH2-SH HS-CH)-CH о-с о O HN

9.

A = Phospholipid (A phosphate group and two fatty acids attached to glycerol moiety)
B = Triacylglycerol (Three fatty acids are linked to glycerol moiety by ester bonds)

Phospholipids are the major components of biological membranes due to their amphibolic nature.
They contain a polar head and a non-polar tail.
Polar tails face the hydrophilic environment while the non-polar tails cluster together to form a hydrophobic core.

Non-polar tail Polar head