Exam 3: Amino Acids and the Primary Structures of Proteins

The liquid that emerges from the bottom of a chromatographic column is called the supernatant.

Which technique is most sensitive and accurate for the determination of a proteinʹs molecular weight?

How do the pK_a values of an ionizable side chain compare when the amino acid is free versus when it is in a polypeptide chain?

During the fractionation process which of the following remain in the supernatant?

Affinity chromatography can be used to save many purification steps compared to other techniques due to its high specificity for the target protein.

Ultraviolet UV) light can be used to estimate protein solution concentrations because

In a biochemistry laboratory a student added ammonium sulfate to a tube containing a buffered protein solution. The student then centrifuged the solution. What was the student probably trying to do?

Cation-exchange resins have negatively charged groups covalently attached to the column matrix.

An octapeptide was determined to have the following amino acid composition: Lys 2), Phe 2), Gly 1), His 1), Leu 1), Met 1). The native peptide was run through one cycle of the Edman degradation and the PTH-leucine derivative was identified by HPLC. When the native peptide was exposed to cyanogen bromide CNBr), a heptapeptide and free glycine were recovered. Incubation of the native protein with trypsin gave a tetrapeptide, a tripeptide, and free lysine. The peptides were separated and each run through one cycle of the Edman degradation. The tetrapeptide yielded the PTH-leucine derivative, and the tripeptide yielded the PTH-phenylalanine derivative. Incubation of the native protein with pepsin produced a dipeptide and two tripeptides. The amino acid composition of the tripeptides not the order) were determined to be Phe, Gly, Met) and Phe, Lys, Lys). What is the sequence of the octapeptide? Specificities of Proteases BrCN cuts at the C-terminal side of Met Trypsin cuts at the C-terminal side of Lys or Arg Pepsin cuts at the N-terminal side of Phe, Trp or Tyr

Which amino acid is ideal for the transfer of protons within the catalytic site of enzymes due to the presence of significant amounts of both the protonated and deprotonated forms of its side chain at biological pH?

Proline is distinct among the 20 commonly found amino acids because

Tyrosine and tryptophan are less hydrophobic than phenylalanine because

The primary structure of a protein describes the .

The pH inside cells is normally near pH 7. At pH 7 which statement is true about the charges ionization state of the α-Carboxyland α-Amino groups of an amino acid?

If the R group of an amino acid is -CH₃, then the name of this compound is

Most purification procedures for proteins are carried out at room temperature.

In which technique is a protein solution a pumped through a metal needle at high voltage to create tiny droplets that are analyzed for their mass/charge ratio?

The distribution of amino acids in a protein often cannot be determined precisely by acid hydrolysis. Why?

Proteins are treated with substances such as 2-mercaptoethanol to remove disulfide bonds before being sequenced because the disulfide bonds will interfere with the sequencing procedure.

The pK_aʹs of arginineʹs α-Carboxyl group, α-Amino group and side chain are 1.8, 9.0 and 12.5, respectively. Calculate the isoelectric point.