Biochemistry Actual Exam2 Questions and
Answers Verifies 100% Correct
Which peptide has greater absorbance at 280 nm?
a.Gln-Leu-Glu-Phe-Thr-Leu-Asp-Gly-Tyr
b.Ser-Val-Trp-Asp-Phe-Gly-Tyr-Trp-Ala
Peptide "b" because Trp and Tyr absorb at 280 nm, with Trp absorbing more intensely.
Phe absorbed the least intensely at 260 nm. These amino acids absorb UV at these
ranges due to their aromatic structures.
In what order would the amino acids Arg, His, and Leu be eluted from a carboxymethyl
(CM) column at pH 6?
Leu, His, Arg based on carboxylate affinity at pH 6.
Why does a certain protein appear to have a molecular mass at 90kD when
determined by gel filtration, and 60 kD when determined by SDS-PAGE in the presence
or absence of 2-mercaptoethanol. Which molecular mass determination is more
accurate?
The protein behaves like a larger protein during gel filtration, suggesting that it has an
elongated shape. The mass determined by SDS-PAGE is more accurate since the mobility
of a denatured SDS-coated protein depends only on size.
Determine the composition of a protein from the following information:
1.Gel filtration mass: 200 kD
2.SDS-PAGE: 100kD
3.SDS-PAGE w/ 2-mercaptoethanol: 40 kD and 60 kD.
, The protein contains two 60-kD polypeptides and two 40-kD polypeptides. Each 40-kD
chain is disulfide bonded to a 60-kD chain. The 100-kD unites associate noncovalently to
form a protein with a molecular mass of kD.
What fractionation procedure could be used to purify protein 1 from a mixture of 3
proteins whose amino acid compositions are as follows?
1.25% Ala, 20% Gly, 20% Ser, 10% Ile, 10% Val, 5% Asn, 5% Gln, 5% Pro.
2.30% Gln, 25% Glu, 20% Lys, 15% Ser, 10% Cys
3.25% Asn, 20% Gly, 20% Asp, 20% Ser, 10% Lys, 5% Tyr
All three proteins are similar in size and PI, and there is no antibody available for
protein 1.
Protein 1 has more hydrophobic residues (Ala, Ile, Pro, Val) than 2 and 3. Hydrophobic
interaction chromatography could be used.
Cleavage reactions of a polypeptide by CNBr and chymotrypsin yieldfragments with
the following amino acid sequences. What is the sequence of the intact polypeptide?
a.CNBr
i. Arg-Ala-Tyr-Gly-Asn
ii. Leu-Phe-Met
iii. Asp-Met
b.Chymotrypsin
i. Met-Arg-Ala-Tyr
ii. Asp-Met-Leu-Phe
iii. Gly-Asn
Asp-Met-Leu-Phe-Met-Arg-Ala-Tyr-Gly-Asn
17. Treatment of the intact polypeptide with trypsin yields fragments with the
following amino acid compositions:
Answers Verifies 100% Correct
Which peptide has greater absorbance at 280 nm?
a.Gln-Leu-Glu-Phe-Thr-Leu-Asp-Gly-Tyr
b.Ser-Val-Trp-Asp-Phe-Gly-Tyr-Trp-Ala
Peptide "b" because Trp and Tyr absorb at 280 nm, with Trp absorbing more intensely.
Phe absorbed the least intensely at 260 nm. These amino acids absorb UV at these
ranges due to their aromatic structures.
In what order would the amino acids Arg, His, and Leu be eluted from a carboxymethyl
(CM) column at pH 6?
Leu, His, Arg based on carboxylate affinity at pH 6.
Why does a certain protein appear to have a molecular mass at 90kD when
determined by gel filtration, and 60 kD when determined by SDS-PAGE in the presence
or absence of 2-mercaptoethanol. Which molecular mass determination is more
accurate?
The protein behaves like a larger protein during gel filtration, suggesting that it has an
elongated shape. The mass determined by SDS-PAGE is more accurate since the mobility
of a denatured SDS-coated protein depends only on size.
Determine the composition of a protein from the following information:
1.Gel filtration mass: 200 kD
2.SDS-PAGE: 100kD
3.SDS-PAGE w/ 2-mercaptoethanol: 40 kD and 60 kD.
, The protein contains two 60-kD polypeptides and two 40-kD polypeptides. Each 40-kD
chain is disulfide bonded to a 60-kD chain. The 100-kD unites associate noncovalently to
form a protein with a molecular mass of kD.
What fractionation procedure could be used to purify protein 1 from a mixture of 3
proteins whose amino acid compositions are as follows?
1.25% Ala, 20% Gly, 20% Ser, 10% Ile, 10% Val, 5% Asn, 5% Gln, 5% Pro.
2.30% Gln, 25% Glu, 20% Lys, 15% Ser, 10% Cys
3.25% Asn, 20% Gly, 20% Asp, 20% Ser, 10% Lys, 5% Tyr
All three proteins are similar in size and PI, and there is no antibody available for
protein 1.
Protein 1 has more hydrophobic residues (Ala, Ile, Pro, Val) than 2 and 3. Hydrophobic
interaction chromatography could be used.
Cleavage reactions of a polypeptide by CNBr and chymotrypsin yieldfragments with
the following amino acid sequences. What is the sequence of the intact polypeptide?
a.CNBr
i. Arg-Ala-Tyr-Gly-Asn
ii. Leu-Phe-Met
iii. Asp-Met
b.Chymotrypsin
i. Met-Arg-Ala-Tyr
ii. Asp-Met-Leu-Phe
iii. Gly-Asn
Asp-Met-Leu-Phe-Met-Arg-Ala-Tyr-Gly-Asn
17. Treatment of the intact polypeptide with trypsin yields fragments with the
following amino acid compositions:
