Choose the correct answer from the list. Not all the answers will be used. A) un
ID: 566651 • Letter: C
Question
Choose the correct answer from the list. Not all the answers will be used. A) uncharged B) deprotonated C) three D) -amino group E) two F) C-terminus G) lysine H) racemic mixture I) zero J) protonated K) isoleucine L) tryptophan M) phenylalanine 1, when a peptide bond is formed, an reacts with a carboxylate group. 2. In the peptide Trp-Ser-Val, valine is at the 3. At a pH below its pK, the -amino group of lysine is . 4. At a pH above its pK, the -carboxylate group of Asp is . 5. Biological systems usually produce a single enantiomer, whereas chemical synthesis produces a 6. In the tripeptide Trp-Val-Phe, the N-terminal residue isExplanation / Answer
1.
When a peptide bond is formed, an alpha amino group reacts with a carboxylate group.
Explanation:
Peptide bond is the linkage between two amino acids in peptide chain. It has a structure –CO-NH-. CO part of the peptide linkage comes from carboxylate group of one amino acid and NH part comes from alpha amino group of another amino acid.
Thus, correct option is D) alpha amino group.
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2.
In the peptide Trp-Ser-Val, valine is at the C-terminus.
Explanation:
Peptide sequence is written using short forms of amino acids connected to each other. By convention amino acid at left end has free amino group(N-terminum) and amino acid at right end has free carboxylate group (C-terminum).
In the given sequence of peptide amino acid at right end is valine. Therefore, it is at the C-terminus.
Therefore, correct option is F) C-terminus.
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3.
At a pH below its pK, the E-amino group of lysine is protonated.
Explanation:
Amino acid contains two ionisable groups, namely amino and caboxylate group. At a pH below pK value, these ionisable groups are in protonated stage.
Therefore, correct option is J) protonated.
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4.
At a pH value above its pK, the beta carboxylate group of Asp is deprotonated.
Explanation:
Amino acid contains two ionisable groups, namely amino and caboxylate group. At a pH above its pK value, ionisable groups are in deprotonated form.
Therfore, correct option is B) deprotonated.
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5.
Biological system usually produces a single enantiomer, whereas chemical synthesis produces a racemic mixture.
Explanation:
Biological system uses chiral environment for synthesis, hence it produces single enantiomer. Whereas, in simple chemical synthesis, there is no chiral differentiation, resulting in formation of racemic mixtures.
Therefore, correct option is H) racemic mixture
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6.
In a tripeptide Trp-Val-Phe, the N-terminal residue is tryptophan.
Explanation:
By convention, amino acid on left side has free amino group or N-terminal. Thus, in given peptide sequence, amino acid on left side is Trp. Trp is the code for tryptophan.
Therefore, correct option is L) tryptophan.