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The principal site of peptide neurohormone biosynthesis is the (A) nucleus (B) rough endoplasmic reticulum (C) dendrite (D) postsynaptic density (E) synaptic vesicle
c
All amino acids used in protein synthesis contain four substituents, which are attached to the alpha carbon atom, an amino group, a carboxylic acid group, a hydrogen atom and a side chain group. Which of the following statements is true? A. Both the amino group and the carboxyl group carry a charge at physiological pH - answer B. At physiological pH the amino group is negatively charged C. Both the amino group and the carboxyl group are uncharged at physiological pH D. At physiological pH the carboxyl group is positively charged E. The pKa for the a-carboxyl group is about 9-10 and the pKa for the a-amino group is about 2 For 19 out of 20 amino acids, the alpha carbon has four different substituents, thus the a-carbon is asymmetric, and amino acids may exist in either the L or D configuration. All of the following statements are true regarding the L and D configuration of amino acids, EXCEPT A. L and D forms occur equally in living organisms B. L and D forms cannot be superimposed by rotating the molecule - answer C. L forms are the predominant form found naturally in humans D. D amino acids occur rarely in humans
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