Download chem 240 practice lipid problems 1. True or false? Completely

chem 240
practice lipid problems
1. True or false? Completely hydrogenated vegetable oils are saturated fats.
Explain.
True. Based on the statement that they are completely hydrogenated, these
vegetable oils have all of their double bonds reduced with hydrogen.
2. Why do membranes tend to be permeable to small nonpolar substances but
impermeable to most ions and polar substances?
Because membranes contain large portions of nonpolar hydrocarbons that ionic and
polar substances would not be able to interact with. Nonpolar substances, once
past the relatively short polar head groups on the surfaces of membranes, would
easily travel through the nonpolar middle portion of a membrane, enabling these
compounds to pass through the membrane.
As an aside, ionic and polar substances can often be transported across membranes
through channels and pores.
3. What structural feature(s) of membranes makes the lateral movement of
membrane components possible?
Membranes are composed of many lipids with similar chemical qualities arranged in
the same orientation. Most lipids have a great degree of rotational flexibility,
based on the large number of single bonds in these molecules. As we have
discussed, an increase in the number of double bonds in the fatty acid chain in a
membrane lipid also reduces the packing, or van der Waals interactions, which
increases the fluidity of a membrane. Overall, membranes are constantly in
motion. Lipids can move laterally within this membrane as a result of a combination
of the above ideas: the similar chemical natures throughout the membrane allow
lateral diffusion without the establishment of any energetically unfavorable new
interactions, and lateral motion is increased when there are fewer chemical forces
(van der Waals interactions) holding a particular lipid in a particular location.
4. Fatty acids can be oxidized at double bonds. This oxidation leads to the
formation of shorter carboxylic acids. These short carboxylic acids have a rancid
smell. Vegetable oils tend to become rancid more rapidly that animal fats. Provide
a chemical explanation.
chem 240
practice lipid problems
Knowing this information, you could suggest that vegetable oils would become
rancid more easily than animal fats, because vegetable oils are more likely to be
unsaturated.
5. List those amino acids with side chains that can be covalently attached to a
fatty acid through an ester link.
The most common site of fatty acylation is through a thio-ester bond with Cys.
You could also imagine ester linkages with other amino acids that contain a reactive
O-.
6. What property of fat-containing cells allows them to serve as the major depots
for the storage of fat-soluble vitamins?
Simply that in these cells, drops of fat are not limited, but rather grow to fill the
majority of the cell. This must have to do with different genes being active in
these cells, and these genes somehow "allow" for this specialized storage.
8. Compare and contrast the three types of membrane proteins.
1. integral (intrinsic): tightly bound to membrane; usually cross at least a major
portion of the membrane. These can only be removed from the membrane by
disruption of the membrane by the use of a reagent such as detergent.
2. extrinsic (peripheral): not tightly bound to membrane. Usually embedded in one
surface of membrane only. Can be removed from membrane with high salt or
similar techniques that do NOT disrupt the membrane.
3. Lipid-linked proteins: are covalently attached to lipids within the membrane.
There are three types – prenylated, fatty acylated, and
glycosylphosphatidylinositol-linked proteins.