Biochem chapter 3

Lys

All of the following amino acids except _________ are classified as nonpolar aliphatic. Pro Lys Val Ile Ala

5.66

At which pH would the net electric charge of tyrosine be zero, given that its -COOH group has a pKa of 2.20, its -NH3+ group has a pKa of 9.11, and its R group has a pKa of 10.07?

Certain segments of a protein sequence that are found in the organisms of one taxonomic group but not in other groups

BEST defines a signature sequence?

An area of research focusing on the computerized analysis of biological data

BEST defines the term bioinformatics?

from N-terminus to C-terminus, left to right.

By convention, amino acid sequences of polypeptides are read:

is a thermodynamically favorable process.

Hydrolysis of a peptide bond:

11 kilodaltons

If a protein is composed of 100 amino acids, what would its approximate molecular weight be?

larger protein molecules appear in earlier fractions.

In size-exclusion chromatography:

Thr

Of the 20 common amino acids, only one lacks a chiral -carbon. Likewise, there is one amino acid that has a second chiral carbon within its side chain. Which amino acid is it? Leu Arg Thr Ser Pro

Asp

Of the following amino acids, which has the most acidic side chain group? Cys Asp Lys Arg His

Indirect derivation from the DNA sequences in genome databases

Of the methods available to determine amino acid sequence, which of the following is MOST commonly used today?

covalent; condensation

Peptide bonds are _______ bonds between the carboxyl group of one amino acid and the amino group of another amino acid and are formed by _______.

Glycoproteins

Prosthetic groups represent the non-amino-acid part of conjugated proteins. Which of the following conjugated proteins contains carbohydrates?

Cation exchange resin

The carboxymethyl (CM) group is a common functional group attached to what type of chromatography material?

iodoacetamide.

The following reagents can all be used to modify the cysteine thiol group in a protein except sodium dodecyl sulfate. maleimide. iodoacetamide. bromomethyl ketone. benzylbromide.

to make sure all disulfides are reduced.

The purpose of adding β-mercaptoethanol during a protein electrophoresis (SDS-PAGE) experiment is:

The peptide will be charged at pH 7.

What can be said about a single polypeptide containing: 5 Ala, 2 Glu, 1 Lys, 1 Gly, and 1 Cys?

(1.99+10.96)/2 = PI PI= 6.48

What is the pI of proline, given that its -COOH group has a pKa of 1.99 and its -NH3+ group has a pKa of 10.96?

It masks the intrinsic charge of the protein and contributes a large negative charge, giving each protein a similar charge-to-mass ratio AND it partially unfolds proteins, enabling separation of protein almost exclusively on the basis of mass.

What is the role of SDS in gel electrophoresis?

120

What is the total number of possible peptide pentamers that could be formed from five different amino acids? (Assume that each amino acid is present only once per peptide.)

a product of the reaction is water.

When a peptide bond is formed: content_hint: This is a condensation reaction.

Primary

Which level of protein structure describes the covalent backbone of a protein, including the sequence of amino acids?

Thr

Which of the following amino acids has an uncharged polar side chain at pH 7? C Glu Thr Ile Arg Pro

Estimation of the purity AND molecular weight of a protein sample.

Which of the following can be obtained through the process of SDS gel electrophoresis? Estimation of the purity of a protein sample Estimation of protein molecular weight Protein purification All of the above. Estimation of the purity AND molecular weight of a protein sample.

Some R-groups AND terminal alpha-amino groups

Which of the following groups can ionize and contribute to the total acid-base behavior of a peptide? Some R-groups Terminal alpha-amino groups Alpha-carboxyl groups involved in peptide bonds All of the above. Some R-groups AND terminal alpha-amino groups

Dialysis

Which of the following is a procedure in which small molecules are removed from a solution of a macromolecule by their diffusion through a semipermeable membrane into a suitable buffered solution?

Ala-Gly-Asn-Leu-Lys

Which of the following peptides would have a +1 charge at pH 7? Arg-Gln-Lys-Leu-Lys Ala-Glu-Asn-Leu-Lys Ala-Gly-Asp-Leu-Lys Ala-Glu-Arg-Leu-Pro Ala-Gly-Asn-Leu-Lys

β -mercaptoethanol

Which of the following reagents, commonly used in the laboratory, will break disulfide bonds in proteins?

They are found in the D-form in amino acids.

Which of the following statements is FALSE regarding amino acids? pH can influence the charge of an amino acid. They are found in the D-form in amino acids. They can be grouped according to the properties of their R groups. All amino acids have amino groups and carboxyl groups.

The 20 common amino acids generally occur in equal amounts in a protein.

Which of the following statements is FALSE regarding biologically active peptides and proteins? The 20 common amino acids generally occur in equal amounts in a protein. Hemoglobin is an example of a multisubunit protein. No generalizations can be made about function of a peptide and its molecular weight. An oligomeric protein is a multisubunit protein that has two or more identical polypeptide chains.

It refers to the total units of enzyme in a solution.

Which of the following statements is FALSE with regard to specific activity? It refers to the number of enzyme units per milligram of total protein. It is a measure of the purity of an enzyme. It increases during the purification of an enzyme. It refers to the total units of enzyme in a solution.

They are both sulfur-containing amino acids.

Which of the following statements is TRUE of both methionine and cysteine? They are both nonpolar, aliphatic amino acids. They are both polar, uncharged amino acids. They are both sulfur-containing amino acids. They are both nonpolar and sulfur-containing amino acids. They are both polar and sulfur-containing amino acids.

Mass spectrometry can be used for mixed samples.

Which of the following statements is TRUE regarding the methodologies available for obtaining protein sequence information? Mass spectrometry is a slower technique than Edman degradation. Edman degradation requires a smaller amount of protein than mass spectrometry. Mass spectrometry, and not Edman degradation, can identify changes in protein sequence that result from mRNA editing in eukaryotes. Mass spectrometry can be used for mixed samples.

The Cys side chain can act as an acid in its unprotonated form.

Which statement about the amino acid Cys is not true? The Cys side chain contains a redox active thiol group. The Cys side chain is a nucleophilie in its unprotonated form. The Cys side chain can act as an acid in its unprotonated form. The Cys side chain is ionizable. All of these are true.

glycine; proline

While most amino acids follow general rules regarding structure, there are a few exceptions. _______ does not have a chiral α-carbon, while _______ is a cyclic amino acid.

Selenocysteine

While there are 20 amino acids commonly found in proteins, over 300 different amino acids have been identified in cells. Which of the following is NOT created by a post-translational modification?

Environmental factors can influence pKa. Ionizable R groups can interact with other peptide R groups. There can be a loss of charge to alpha-carboxyl and alpha-amino groups.

Why can the pKa value for an ionizable R group change when an amino acid becomes incorporated into a peptide?

Ion exchange chromatograpy

You have isolated a crude sample of two related peptides (Peptide A and Peptide B). To separate the two, what protein purification method would be most effective? Peptide A: Ala-Ala-Gly-Glu-Asp-Ser-Glu-Ala Peptide B: Ala-Ala-Gly-Lys-Arg-Ser-His-Ala