Cell Structure and Function Name: ________________________

Fall, 2001 Collaborators: __________________

Homework 2

Due: Wednesday, October 10, 2001.

As a new graduate student in a lab that studies plasma membrane proteins in giraffe erythrocytes (red blood cells), you are assigned to study a newly discovered integral membrane protein.

You run an SDS-polyacrylamide gel and determine that the molecular weight of the protein is 157,000 Daltons. The lab you are in has developed methods for producing inside out and right side out vesicles from giraffe erythrocyte membranes.

You start by preparing several batches of inside out and right side out vesicles, treat them with different enzymes, and then run SDS-polyacrylamide gels to determine the effect on the protein. Your results are shown in the following table.

Molecular weight (in Daltons) of the protein in:
Treatment	Inside out vesicles	Right side out vesicles
Sodium periodate (digests sugar residues attached to proteins, cannot penetrate membranes)	157,000	152,800
Pronase (an enzyme that breaks peptide bonds, but cannot penetrate membranes.)	113,000	61,000

Like other integral membrane proteins, this one consists of three domains (extracellular, transmembrane, and cytosplasmic). Which domain contains attach sugar residues? __________________________________ (3 points)

How much of the molecular weight of this domain is due to the attached sugars? ________________________ (3 points) What is the molecular weight of each domain? Be sure to include the molecular weight of attached sugars on the proper domain (3 points each).

Extracellular _________________________________

Transmembrane_______________________________

Cytoplasmic__________________________________

Assuming that the average molecular weight of an amino acid is ~110 Daltons, predict how many times this proteins spans the bilayer? ____________________ (3 points) Would you expect the protein to be involved in cellular communication or import/export? __________________________ (2 points)