Molcell Homework #2

HOMEWORK  2

DUE ON WEDNESDAY,  September 14, 2016

1. If the gene encoding the enzyme, glycerophosphate acyl tranferase is mutated, how does this affect phospholipid metabolism? (3 points)

This enzyme is responsible for adding a fatty acid chain to a glycerophosphate. If this enzyme is mutated, then the substrate for the subsequent reaction in the pathway is not made, potentially halting the entire pathway.

1. A mutation in the gene encoding HMG-CoA reductase has been identified in the regions binding the proteins - Insig-1 and Insig-2. This affects the binding of the enzyme to the two proteins (3 points)

1. When cholesterol levels are in excess, how does this mutation affect regulation of cholesterol metabolism?

When levels of cholesterol are in excess, you want to get rid of HMG-CoA Reductase; however, if Insig-1 and Insig-2 fail to bind, then you are without a mechanism that degrades HMG CoA Reductase, meaning that you will continue to make too much cholesterol. An inevitably fatal defect. If this causes constitutive binding, it may be a good thing because your body is not functioning the way it should in terms of processing cholesterol. If this is the case, then you do not want to make any more cholesterol and may want HMG-CoA Reductase degraded.

1. When cholesterol levels are low, how does this mutation affect regulation of cholesterol metabolism?

This has no effect on regulation because you simply need functional HMG-CoA Reductase (which you do not want degraded). If it is constitutive binding and your body wants more cholesterol, so degrading the enzyme that is instrumental to cholesterol synthesis. This would be a negative defect.

1. If the amount of cholesterol is increased in a region of the phospholipid bilayer and then a FRAP experiment is conducted in the same region of the bilayer, what do you think would be the result of the FRAP experiment? Explain in terms of fluorescence arbitrary units. (2 points)

 Cholesterol decreases membrane fluidity. This means that if a FRAP was done on a region of high cholesterol concentration, then it would take longer than usual to recover the fluorescence arbitrary units back to normal.