Exam 3: Amino Acids, Peptides, and Proteins

As a protein is purified, both the amount of total protein and the activity of the purified protein decrease. Why, then, does the specific activity of the purified protein increase?

According to the table, ion-exchange chromatography would be the LEAST effective method to separate which protein mixture? Protein MW PI A 12,500 3)2 B 13,200 5)7 C 13,500 10)5 D 25,200 6)3 E 36,900 5)8 F 78,400 6)1

The term "proteome" has been used to describe:

Which statement about cystine is CORRECT?

Compare the following sequences taken from four different proteins, and select the answer that BEST characterizes their relationships. A B C 1 DVEKGKKIDIMKCS HTVEKGGKHKTGPNLH GLFGRKTGQAPGYSYT 2 DVQRALKIDNNLGQ HTVEKGAKHKTAPNVH GLADRIAYQAKATNEE 3 LVTRPLYIFPNEGQ HTLEKAAKHKTGPNLH ALKSSKDLMFTVINDD 4 FFMNEDALVARSSN HQFAASSIHKNAPQFH NLKDSKTYLKPVISET

To determine the isoelectric point of a protein, first establish that a gel:

A major advance in the application of mass spectrometry to macromolecules came with the development of techniques to overcome which problem?

Why do amino acids, when dissolved in water, become zwitterions?

Even when a gene is available and its sequence of nucleotides is known, chemical studies of the protein are still required to determine:

Only one of the common amino acids has no free $\alpha$ -amino group. Name this amino acid.

What is the approximate charge difference between glutamic acid and $\alpha$ -ketoglutarate at pH 9.5?

How are "signature sequences" useful in analyzing groups of functionally related proteins?

If protein A has a pI of 3.1, protein B has a pI of 6.8, and protein C has a pI of 8.9, which protein would elute FIRST from a cation exchange column at pH 7?

As more OH^- equivalents (base) are added to an amino acid solution, what titration reaction will occur around pH = 9.5?

What is the uniquely important acid-base characteristic of the histidine R group?

What is the pI, and how is it determined for amino acids that have nonionizable R groups?

The following reagents are often used in protein chemistry. Match the reagent with the purpose for which it is best suited. Some answers may be used more than once or not at all; more than one reagent may be suitable for a given purpose. (a) CNBr (cyanogen bromide) (e) performic acid (b) Edman reagent (phenylisothiocyanate) (f) chymotrypsin (c) Sanger reagent (FDNB) (g) trypsin (d) reducing agent (dithiothreitol) (h) iodoacetamide ___ hydrolysis of peptide bonds on the carboxyl side of Lys and Arg ___ cleavage of peptide bonds on the carboxyl side of Met ___ breakage of disulfide (-S-S-) bonds ___ modification of sulfhydryl groups of Cys ___ determination of the amino acid sequence of a peptide ___ determining the amino-terminal amino acid in a polypeptide

The amino acid histidine has three ionizable groups, with pK_a values of 1.8, 6.0, and 9.2. (a) Which pK_a corresponds to the histidine side chain? (b) In a solution at pH 5.4, what percentage of the histidine side chains will carry a positive charge?

According to the diagram, does this amino acid have a titratable R-group?

In a conjugated protein, a prosthetic group is: