Biochemistry : Identification by Structure

Study concepts, example questions & explanations for Biochemistry

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Example Questions

Example Question #41 : Identification By Structure

Which of the following structures is methionine?

Possible Answers:

Arginine

Threonine

Methionine

Leucine

Aspartic acid

Correct answer:

Methionine

Explanation:

Methionine is a non-polar amino acid. It is one of two amino acids that contain sulfur, the other is cysteine.

Example Question #42 : Identification By Structure

Name the given structure.

Leucine

Possible Answers:

Leucine

Alanine

Lysine

Isoleucine

Valine

Correct answer:

Leucine

Explanation:

Leucine is a non-polar amino acid with a  R-group.

Example Question #43 : Identification By Structure

Which of the following is a polar amino acid?

Possible Answers:

Leucine

Phenylalanine

Alanine

Threonine

Cysteine

Correct answer:

Threonine

Explanation:

The polarity of an amino acid is determined by the R-group. The electronegativity difference between oxygen and carbon creates a dipole with the partial positive being on carbon and the partial negative being on oxygen. The dipole makes the molecule polar.

Example Question #5 : Identifying Specific Protein Structures

Which of the following is a basic amino acid?

Possible Answers:

Phenylalanine

Methionine

Aspartic acid

Arginine

Cysteine

Correct answer:

Arginine

Explanation:

Bases, according to the Bronsted-Lowry definition, are substances that  accept 

Arginine is a base

Example Question #41 : Identification By Structure

Identify the given amino acid.

Asparagine

Possible Answers:

Glutamine

Glutamic acid

Aspartic acid

Glycine

Asparagine

Correct answer:

Glutamine

Explanation:

Glutamine is one of two amino acids that are amides. The nitrogen bonded to a carbon-oxygen double bond makes it an amide. 

Example Question #42 : Identification By Structure

Describe the solubility of the given amino acids.

Phenylalanine and Tyrosine

Possible Answers:

Cannot be determined without knowing the temperature of the solution

Neither are soluble

Both are equally soluble

Tyrosine < Phenylalanine

Phenylalanine < Tyrosine

Correct answer:

Phenylalanine < Tyrosine

Explanation:

Although tyrosine is hydrophobic, it is more soluble than phenylalanine. The only difference between the two amino acids is the hydroxyl group present on tyrosine. The hydroxyl is much more acidic than the hydrogen, and so it is more likely to ionize. The ability to ionize makes it more soluble (think electrolytes). 

Example Question #43 : Identification By Structure

Identify the given amino acid.

Aspartic acid

Possible Answers:

Myristic acid

Asparagine

Alanine

Aspartic acid

Glutamic acid

Correct answer:

Aspartic acid

Explanation:

Aspartic acid is an acidic amino acid, meaning it contains  in its R-group. The R-group of aspartic acid is .

Example Question #46 : Identification By Structure

Identify the given structure.

Phenylalanine

Possible Answers:

Phenylalanine

Proline

Tryptophan

Tyrosine

Histidine

Correct answer:

Phenylalanine

Explanation:

Phenylalanine is a non-polar amino acid. The structure of this amino acid is literally alanine with a phenyl group attached.

Example Question #44 : Identification By Structure

Which of the following structures is threonine?

Possible Answers:

Aspartic acid

Asparagine

Alanine

Threonine

Arginine

Correct answer:

Threonine

Explanation:

Threonine is a polar uncharged amino acid with a  R-group.

Example Question #48 : Identification By Structure

Identify the given structure.

Arginine

Possible Answers:

Arginine

Leucine

Aspartic acid

Alanine

Lysine

Correct answer:

Arginine

Explanation:

Arginine is a basic amino acid. The charge on the amine in the functional group makes this structure basic. While lysine is also a basic amino acid, it has a different R-group.

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