I need help with these. 5 points for answers with explanations. 1) Which of the
ID: 708597 • Letter: I
Question
I need help with these. 5 points for answers with explanations.
1) Which of the following amino acids is not chiral?
a) Alanine, B) leucine, C) serine, D) glycine
2) Which of the following amino acids has a basic side chain?
a) Leucine, B) Tyrosine, C) Serine, D) Lysine
3) Which of the following amino acids is a secondary amine?
A) Proline, B) Leucine, C) Glutamine, D) Aspargine
4) What is the approximate value of the pka of the alpha-COOH group of alpha-amino acids?
A) 5, B) 9, C)2, D) 12
5) Which of the following is a definition of the isoelectric point, pI, of an amino acid?
A) the melting point of an amino acid
B) the pH at which an amino acid has no net charge
C) the conductivity of a 1 M solution of an amino acid in water
D) the pH at which the alpha-NH2 group is completely protonated
6) What is the isoelectric point, pI, of serine (pKa of alpha-COOH, 2.21; pKa of alpha-NH3+, 9.15)?
a) 11.36, b) 20.22, c) 9.94, d) 5.68
7) What is the isoelectric point of glutamic acid (pKa of alpha-CO2H, 2.19; pKa of the side chain -COOH, 4.25, pKa of alpha-NH3+, 9.67)?
a) 4.33, b) 3.22, c) 12.88, d) 6.44
8) Which of the following statements is not true?
a) Amide bonds are planar (the alpha-carbon, the carbonyl carbon, oxygen, nitrogen, hydrogen on the nitrogen, and alpha-carbon of the next amina acid unit are all in the same place).
b) There is a higher barrier to rotation around the cabonyl carbon-nitrogen bond of an amide than there is for rotation around the carbon-nitrogen bond of amines.
9) Which of the following tripeptides is not hydrolyzed by trypsin?
a) Lys-Ser-Arg
b) Arg-Glu-Thr
c) Glu-Ser-Arg
d) Glu-Arg-Set
10) Which of the following tripeptides is not hydrolyzed by chymotrypsin?
a) Phe-Lys-Glu
b) Gln-Ser-Phe
c) Gln-Tyr-Ser
d) Lys-Tyr-Phe
11) Which of the following is not a polypeptide?
a) alpha-keratin
b) myoglobin
c) fibroin
d) heme
Explanation / Answer
1) D glycine is achiral here C is surrounded by 2 H,1NH2 and 1COOH.
2) D lysine has side chain with NH2 group,
3) A , proline is cyclic amino acid i.e its N group is secondary
4) C , they have roughly value of 2.3 ,
5) B , at isolectric point charge due to NH3+ cancells by COO- ,
6) D
7) B,
8) B , Carbon and Nitrogen forms partial double bond in amide bond in amino acids which restricts rotation
9) C , Trypsin cleaves when Lysine or Arginine iis present in peptide bonds at left side but not at extreme right as in C/
10) B , Chymotrypsin cleaves when Phe,Tyr present in left side but not on right as in B.
11) D , heme is prosthetic group but not polypeptide of hemoglobin