Explain why the steroid hormone estradiol (MW 272) readily crosses membranes by simple diffusion but the much smaller H+ requires transport proteins
What will be an ideal response?
Answer: The nonpolar molecule estradiol has a higher partition coefficient, because it can much more readily dissolve in and diffuse across the hydrophobic phase of a membrane. Any charged molecule, even one as small as H+, forms a shell of hydration, which would require an input of energy to dissolve in the lipid bilayer. A H+ protein transporter circumvents this problem by screening the H+ from the hydrophobic phase of the membrane during transport.
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rRNA is (select all that apply):
A. associated with ribosomes. B. the least abundant RNA in the cell. C. the most abundant RNA in the cell. D. relatively consistent in sequence between organisms. E. considerably variable in sequence between organisms.
Answer the question using the accompanying figure.Which number identifies the tympanic membrane?
a. 4 b. 5 c. 6 d. 8 e. 10
The most effective portion(s) of the visible spectrum in driving photosynthesis is (are):
a) the violet-blue portion. b) the yellow-green portion. c) the red-green portion. d) Both a) and b) are correct. e) Both a) and c) are correct.
Why should antibiotics not be given to a patient with Escherichia coli O157:H7?
A) Antibiotics tend to act as a hapten with this infection and are likely to cause an allergic response. B) This pathotype is part of the normal digestive tract of humans. C) This is not a bacterium, and therefore antibiotics would be ineffective. D) Antibiotics do not reduce disease and may precipitate HUS. E) This pathotype is only found in cattle and does not infect humans.