1. Which is a correct description of the use of separation techniques to separate a dipeptide from a pentapeptide?
a. the dipeptide emerges faster than the pentapeptide from a gel filtration column
b. the dipeptide migrates faster towards the cathode than the pentapeptide on SDS-PAGE
c. the dipeptide migrates to a more anodal position than the pentapeptide on electrofocusing
d. the dipeptide sediments faster than the pentapeptide in an ultracentrifugal field
e. none of these methods would separate the dipeptide from the pentapeptide
2. The gel in SDS PAGE creates a network of crosslinks that proteins must pass through. In order for this to work ALL of the protein molecules must be positively charged so that they will be attracted to the cathode at the top of the gel.
True or false?
3. You carry out an isoelectric focusing experiment in a pH gradient that runs from low pH on the left to high pH on the right. Your protein stops moving in the pH gradient at a position corresponding to pH 7.5. Which of the following statements about your protein is FALSE?
a. The pI of the protein is equal to the pH at which the overall charge on the protein molecule is neutral
b. Mutating all of the glutamic acid residues in your protein to glutamines would result in the protein focusing to a position in the gradient to the left of pH 7.5
c. The difference between the observed pI and the theoretical pI may be a result of changes in the pK of ionizable side chains due to the proximity of other charged groups
d. Mutating all of the asparagine residues to glutamines would not significantly change the position of your protein in the pH gradient.
e. None of the above statements are FALSE.
Answer 1: a) The dipeptide emerges faster than the pentapeptide from a gel filtration column
Comments: Gel filtration chromatography separate the molecules based on their size, the smaller molecules (in this case dipeptide) elute first/faster than the larger molecule (in this case pentapeptide). So both the peptides are separated. SDS-PAGE used for separation of molecules based on charge, in this case, we do not know the charge of di or pentapeptide.
Answer 2: a) False
Comments: The proteins should be negatively charged so that the proteins will move from cathode to anode
Answer 3: b) Mutating all of the glutamic acid residues in your protein to glutamines would result in the protein focusing on a position in the gradient to the left of pH 7.5
Comments: The mutating glutamic acid to glutamines the overall charge changed that influence in PI of the newly formed protein
1. Which is a correct description of the use of separation techniques to separate a dipeptide...