Multiple choice problems on Chemical bonding.
1. The chirality of an amino acid, and hence it optical activity, results from the fact that its α carbon is bonded to four different chemical groups. Of the 20 common amino acids, which is not optically active?
a) serine.
b) tryptophane.
c) isoleucine.
d) glycine.
e) glutamic acid.
2. Identify the two amino acids shown below.
A) glycine and asparagine.
B) histidine and lysine.
C) proline and valine.
D) alanine and cysteine.
E) methonine and tryptophane.
3.For the peptide given below, what is its net charge at pH 3? (written N-termàC-term)
Glu-His-Trp-Ser-Gly-Leu-Lys-Gly
Use the following pKa values for the titratable groups:
pKa, N-terminus = 10.0
pKa, Glu, carboxyl side chain = 4.0
pKa, His, imidazole side chain = 6.0
pKa, Lys, amino side chain = 11.0
pKa, C-terminus = 2.0
A) -2
B) -1
C) 0
D) +1
E) +2
4.For the same peptide given in problem #13, what is its net charge at pH 5?
A) -2
B) -1
C) 0
D) +1
E) +2
5.For the same peptide given in problem #13, what is its isoelectric point (pI)?
A) 10
B) 8
C) 6
D) 4
E) 2
6.For the same peptide given in problem #13, what is its sequence (primary structure)?
A) GHTSGLLG
B) GLLGSTHG
C) GKLGSWHE
D) EHWSGLKG
E) GAVLIMPF
7. The absorbance measured for a protein sample at 280 nm was 5. Using an extinction coefficient of 10 cm-1M-1, and a 1 cm path length, find out the protein concentration in this sample.
A) 0.5 M
B) 3 M
C) 1.25 M
D) 5 M
E) 5 mM
8.In what order would the proteins listed below elute from an anion exchange column at pH 6?
Protein A 25 kDa pI = 8.0
Protein B 10 kDa pI = 4.0
A)first A, then B.
B) first B, then A.
C) These proteins would elute together.
9. For the same proteins shown in problem #17, in what order would these proteins elute using gel filtration chromatography?
A) first A, then B.
B) first B, then A.
C) these proteins would elute together.
Identify the type of bond linking amino acids together shown below.
A) hydrogen bond.
B) ion pair.
C) carbon-carbon bond.
D) van der Waals interaction.
E) peptide bond.