A. Why do ions have a difficult time getting through an artificial phospholipid

Question

A. Why do ions have a difficult time getting through an artificial phospholipid bilayer, despite their relatively small size? 1. Ions are strongly attracted to the hydrophobic acyl tails of the membrane lipids and end up 'trapped' in the membrane.

2. Ions tend to associate with a cluster of water molecules and it is energetically prohibitive for this much larger complex to cross the membrane.

3. Ions tend to form covalent bonds with the surrounding aqueous mileou, preventing them from traveling across the membrane.

4. They don't have a relatively small size; their relatively large size prevents them from entering the membrane

B. The 'fluid mosaic' model of biological membrane structure describes phospholipids as freely moving within a single leaflet of the membrane but as
being prohibited from "flipping" from one layer of the lipid bilayer to the other layer of the lipid bilayer.
1. F (false)
2. T (true)

C. Eukaryotic copper,zinc superoxide dismutases are enzymes which catalyze the conversion of the superoxide radical to hydrogen peroxide. One of these dismutases, SOD1, is a 32 kDa homodimeric enzyme. The enzyme, found predominantly in the cytosol, is known to be relatively thermally stable (i.e., it can be exposed to higher temperatures without denaturing). SOD1 is a dimeric enzyme (i.e., the active enzyme is composed of two polypeptides which interact to form a dimer) which is stabilized by an intrasubunit disulfide bond. Each subunit contains an eight-stranded betabarrel motif (a beta-sheet structure which is folded so that it forms a barrel-like structure).
Which of the following best describes the quaternary structure of this enzyme?
1. The linear sequence of amino acid residues for the monomeric subunit, MATKAVCVLK GDGPVQGIIN FEQKESNGPV KVWGSIKGLT
EGLHGFHVHEFGDNTAGCTS AGPHFNPLSR KHGGPKDEER HVGDLGNVTA DKDGVADVSIEDSVISLSGD HCIIGRTLVV HEKADDLGKG GNEESTKTGN
AGSRLACGVI GIAQ
2. The description of the active enzyme as a homodimer stabilized by an intrasubunit disulfide bond
3. The description of the monomeric subunits as each containing an 8-stranded beta barrel
4. None of the other answers are correct.

D. Consider an individual who has a mutation in both copies of the gene which encodes the major histocompatibility complex protein. This mutation disrupts the protein so that it is no longer capable of binding and presenting polypeptide fragments to cytotoxic T lymphocytes. What is the expected phenotype of this individual?

1. The individual is likely to have brown eyes.
2. The individual is likely to have blue eyes.
3. The individual exhibits a heightened susceptibility to viral infections.
4. The individual is more likely to develop cancer.
5. The individual is less likely to develop cancer.
6. The individual exhibits a reduced susceptibility to viral infections.

E. How many covalent bonds are present in the molecule , pentanol?

Explanation / Answer

Question A:

Ans: 2. Ions tend to associate with a cluster of water molecules and it is energetically prohibitive for this much larger complex to cross the membrane.

Question B:

Ans:True

Question C:

Ans: 2. The description of the active enzyme as a homodimer stabilized by an intrasubunit disulfide bond

Question D:

Ans:3. The individual exhibits a heightened susceptibility to viral infections.

Question E:

Ans:17

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