Which of the following amino acids would most likely be found on the surface of a protein molecule?
Explanation:
The correct answer is B. This question requires two logical steps: first, you need to appreciate that the
hydrophilic amino acids are more likely to appear on the surface of a protein molecule, while hydrophobic
amino acids are most likely be found in its interior. Next, you need to figure out which of the amino acids listed is
hydrophilic. If you recall that arginine is a basic amino acid that is positively charged at physiologic pH, you
should be able to answer this question right away.
All of the other choices have neutral side chains and are uncharged at physiologic pH. They would most likely
be found in the hydrophobic core of the protein structure. Alanine (choice A), isoleucine (choice C), and leucine
(choice D) all have aliphatic side chains; phenylalanine (choice E) and tryptophan (choice F) have aromatic
side chains
A Southeast Asian immigrant child is noted to be severely retarded. Physical examination reveals a pot-bellied,
pale child with a puffy face. The child's tongue is enlarged. Dietary deficiency of which of the following
substances can produce this pattern?
Explanation:
The correct answer is B. The disease is cretinism, characterized by a profound lack of thyroid hormone in a
developing child, leading to mental retardation and the physical findings described in the question stem.
Cretinism can be due to dietary deficiency of iodine (now rare in this country because of iodized salt), to
developmental failure of thyroid formation, or to a defect in thyroxine synthesis.
Calcium deficiency (choice A) in children can cause osteoporosis or osteopenia.
Iron deficiency (choice C) can cause a hypochromic, microcytic anemia.
Magnesium deficiency (choice D) is uncommon, but can cause decreased reflexes, and blunts the parathyroid
response to hypocalcemia.
Selenium deficiency (choice E) is rare, but may cause a reversible form of cardiomyopathy
sorry actually by mistake i've posted the questions 2 times instead of the answer ..i sincererly ask for u apology...
|
Topic Tags: 
