Amino acids, peptides, and proteins | Practice Problems, Examples & Solutions

Introduction

Chemistry : An Introduction to General, Organic, and Biological Chemistry

A student in your class asks you for advice on learning chemistry. Which of the following might you suggest?
a. forming a study group
b. skipping a lecture
c. visiting the professor during office hours
d. waiting until the night before an exam to study
e. being an active learner

Chemistry in Our Lives

Learning Chemistry: A Study Plan

01:37

Chemistry : An Introduction to General, Organic, and Biological Chemistry

Identify each activity, $\mathbf{a}-\mathbf{f},$ as an observation (O), a hypothesis (H) an experiment (E), or a conclusion (C). Lucia wants to develop a process for dyeing shirts so that the color will not fade when the shirt is washed. She proceeds with the following activities:
a. Lucia notices that the dye in a design fades when the shirt is washed.
b. Lucia decides that the dye needs something to help it combine with the fabric.
c. She places a spot of dye on each of four shirts and then places each one separately in water, salt water, vinegar, and baking soda and water.
d. After one hour, all the shirts are removed and washed with a detergent.
e. Lucia notices that the dye has faded on the shirts in water, salt water, and baking soda, while the dye did not fade on the shirt soaked in vinegar.
f. Lucia thinks that the vinegar binds with the dye so it does not fade when the shirt is washed.

Chemistry in Our Lives

Scientific Method: Thinking Like a Scientist

09:29

Chemistry : An Introduction to General, Organic, and Biological Chemistry

Read the labels on products used to wash your dishes. What are the names of some chemicals contained in those products?

Chemistry in Our Lives

Chemistry and Chemicals

Structure and Stereochemistry of the A@Amino Acids

125 Practice Problems

00:35

Biochemistry

Although serine is a nonessential amino acid, serine deficiency syndrome has been observed in humans One such form of the syndrome is traceable to a deficiency in 3-phosphoglycerate dehydrogenase (see Figure 25.31). Individuals with this syndrome not only are serine-deficient but also are impaired in their ability to synthesize another common amino acid, as well as a class of lipids. Describe why.

Nitrogen Acquisition and Amino Acid Metabolism

03:53

Biochemistry

Compare and contrast the features and physiological advantages of each of the major classes of hormones, including the steroid hormones, polypeptide hormones, and the amino acid-derived hormones.

The Reception and Transmission of Extracellular Information

01:36

Biochemistry

The simple average molecular weight of the 20 common amino acids is $138,$ but most biochemists use 110 when estimating the number of amino acids in a protein of known molecular weight. Why do you suppose this is? (Hint: there are two contributing factors to the answer. One of them will be apparent from a brief consideration of the amino acid compositions of common proteins. See, for example, Figure 5.16 of this text.)

Amino Acids and the Peptide Bond

Acid–Base Properties of Amino Acids

8 Practice Problems

02:13

Biochemistry

REFLECT AND APPLY An amino acid mixture consisting of lysine, leucine, and glutamic acid is to be separated by ion-exchange chromatography, using a cation-exchange resin at $\mathrm{pH} 3.5$, with the eluting buffer at the same pH. Which of these amino acids will be eluted from the column first? Will any other treatment be needed to elute one of these amino acids from the column?

Protein Purification and Characterization Techniques

01:02

Biochemistry

REFLECT AND APPLY In each of the following two groups of amino acids, which amino acid would be the easiest to distinguish from the other two amino acids in the group, based on a titration?
(a) gly, leu, lys
(b) $\mathrm{glu},$ asp, ser

Amino Acids and Peptides

02:18

Biochemistry

MATHEMATICAL Sketch a titration curve for the amino acidd cysteine, and indicate the $\mathrm{p} K_{\mathrm{a}}$ values for all titratable groups. Also indicate the $\mathrm{pH}$ at which this amino acid has no net charge.

Amino Acids and Peptides

Isoelectric Points and Electrophoresis

4 Practice Problems

00:55

Biochemistry

What physical parameters of a protein control its migration on electrophoresis?

Protein Purification and Characterization Techniques

02:47

Principles of Biochemistry

Suppose you have four forms of a protein, all with identical amino acid sequence but containing zero, one, two, or three oligosaccharide chains, each ending in a single sialic acid residue. Draw the gel pattern you would expect when a mixture of these four glycoproteins is subjected to SDS polyacrylamide gel electrophoresis (see Fig. 3-18) and stained for protein. Identify any bands in your drawing.
(FIGURE CAN'T COPY)

Carbohydrates and Glycobiology

02:11

Organic Chemistry

Aspartame, a nonnutritive sweetener marketed under such trade names as Equal, NutraSweet, and Canderel, is the methyl ester of a simple dipeptide, Asp-Phe-OCH $_{3}$
(a) Draw the structure of aspartame.
(b) The isoelectric point of aspartame is $5.9 .$ Draw the principal structure present in aqueous solution at this pH.
(c) Draw the principal form of aspartame present at physiological $\mathrm{pH}=7.3$.

Biomolecules: Amino Acids, Peptides, and Proteins

Synthesis of Amino Acids

11 Practice Problems

05:32

Introduction to General, Organic and Biochemistry

(Chemical Connections $26 \mathrm{A}$ ) Why is selenocysteine called the twenty-first amino acid? Why were amino acids such as hydroxyproline and hydroxylysine not counted as additional amino acids?

Gene Expression and Protein Synthesis

02:59

Introduction to General, Organic and Biochemistry

What is an amino sugar? Name the three amino sugars most commonly found in nature

Carbohydrates

02:22

Chemistry

Draw the structure of an alternating copolymer of these two amino acids, showing at least two repeating units:

Modern Materials

Resolution of Amino Acids

2 Practice Problems

01:22

Introduction to General, Organic and Biochemistry

Which amino acids in Table $22-1$ have more than one stereocenter?

Proteins

03:49

Introductory Chemistry

An amino acid on a protein strand hydrogen-bonds to another amino acid that is four amino acid units away. The next amino acid on the chain does the same, hydrogen bonding to an amino acid that is four amino acids away from it. This pattern repeats itself over a significant part of the protein chain. The resulting pattern in the protein is an example of what kind of structure? (primary, secondary, tertiary, or quaternary)

Biochemistry

Reactions of Amino Acids

18 Practice Problems

00:49

Biochemistry

RECALL What is the relationship between $\alpha$ -ketoglutarate, glutamate, and glutamine in amino acid anabolism?

The Metabolism of Nitrogen

01:19

Biochemistry

Sulfanilamide and related sulfa drugs were widely used to treat diseases of bacterial origin before penicillin and more advanced drugs were readily available. The inhibitory effect of sulfanilamide on bacterial growth can be reversed by $p$ aminobenzoate. Suggest a mode of action for sulfanilamide.

The Metabolism of Nitrogen

01:26

Introduction to General, Organic and Biochemistry

Which amino acids have the most possible codons? Which have the fewest?

Gene Expression and Protein Synthesis

Structure and Nomenclature of Peptides and Proteins

50 Practice Problems

03:49

Biochemistry

The central rod domain of a keratin protein is approximately 312 residues in length. What is the length (in $\AA$ ) of the keratin rod domain? If this same peptide segment were a true $\alpha$ -helix, how long would it be? If the same segment were a $\beta$ -sheet, what would its length be?

Proteins: Secondary, Tertiary, and Quaternary Structure

03:29

Biochemistry

Amino acid analysis of an oligopeptide 7 residues long gave
$\begin{array}{lllll}\text { Asp } & \text { Leu } & \text { Lys } & \text { Met } & \text { Phe } & \text { Tyr }\end{array}$
The following facts were observed:
a. Trypsin treatment had no apparent effect.
b. The phenylthiohydantoin released by Edman degradation was
c. Brief chymotrypsin treatment yielded several products, including a dipeptide and a tetrapeptide. The amino acid composition of the tetrapeptide was Leu, Lys, and Met.
d. Cyanogen bromide treatment yielded a dipeptide, a tetrapeptide, and free Lys. What is the amino acid sequence of this heptapeptide?

Proteins: Their Primary Structure and Biological Functions

00:11

Biochemistry

REFLECT AND APPLY Are chaperones the only proteins that aid in correct protein folding?

Protein Synthesis: Translation of the Genetic Message

Peptide Structure Determination

14 Practice Problems

02:41

Biochemistry

A sample of a peptide of unknown sequence was treated with trypsin; another sample of the same peptide was treated with chymotrypsin. The sequences (N-terminal to C-terminal) of the smaller peptides produced by trypsin digestion were as follows:
$$Met-Val-Ser Thr-Lys$$
$$Val-Ile-Trp-Thr-Leu-Met-Ile$$
$$Leu-Phe-Asn-Glu-Ser-Arg$$
The sequences of the smaller peptides produced by chymotrypsin digestion were as follows:
$$Asn-Glu-Ser-Arg-Val-Ile-Trp$$
$$Thr-Leu-Met-Ile$$
$$Met-Val-Ser-Thr-Lys-Leu-Phe$$
Deduce the sequence of the original peptide.

Protein Purification and Characterization Techniques

0:00