MCAT Biology : Amino Acids

Study concepts, example questions & explanations for MCAT Biology

varsity tutors app store varsity tutors android store

Example Questions

← Previous 1 3

Example Question #1 : Amino Acids

Integral proteins span the entire width of the plasma membrane. They are used to facilitate the diffusion of specific compounds across the membrane.

Which amino acid would you expect to find in the middle of an integral protein embedded in the phospholipid bilayer?

Possible Answers:

Arginine

Serine

Glutamine

Leucine

Correct answer:

Leucine

Explanation:

The middle of the phospholipid bilayer is composed of nonpolar fatty acid tails. As a result, we would expect to find a nonpolar amino acid in the middle of the bilayer as part of the integral protein. Leucine is a nonpolar amino acid, so it could be found in the middle.

All other amino acids listed are either polar or charged.

Example Question #1 : Amino Acids

Excluding the amino acid glycine, all other amino acids found within human proteins are __________.

Possible Answers:

of the L configuration

optically inactive

neutral at physiologic pH

essential

Correct answer:

of the L configuration

Explanation:

All amino acids with the exception of glycine are optically active, as they have four unique groups attached to their alpha-carbons and are situated in the L configuration (amino terminus oriented to the left and carboxyl terminus to the right of the alpha-carbon). Not all amino acids are neutral at physiologic pH, as lysine and arginine are positively charged and apartate and glutamate are negatively charged due to their respective side chains. Finally, only ten of the twenty amino acids are essential, thus, the correct answer is that the amino acids found within human proteins are of the L configuration.

Example Question #2 : Amino Acids

What is the reasoning behind the planar geometry of peptide bonds in proteins?

Possible Answers:

Hydrogen bonding

Proteins contain only L amino acids

Steric hindrance

The peptide bond is trans rather than cis

The carbon-nitrogen bond has partial double bond character

Correct answer:

The carbon-nitrogen bond has partial double bond character

Explanation:

The double bond character of the carbon-nitrogen bond results in a shorter bond compared to the normal length of a pure bond ( vs. ). The double bond resonance of peptide bonds aids to increase stability, while subsequently decreasing the rotation about that bond. The partial double bond results in the amide group being planar, thus allowing for either a cis or trans conformation of a peptide bond. Due to the preference for the trans orientation over the cis orientation, there is less steric hindrance between groups attached to the alpha-carbon atoms. Thus, the correct answer is that the carbon-nitrogen bond has partial double bond character.

Example Question #2 : Amino Acids

Which of the following amino acids is basic?

Possible Answers:

Proline

Phenylalanine

Alanine

Lysine

Correct answer:

Lysine

Explanation:

On the MCAT you must be able to recognize the following as basic amino acids: lysine, arginine, and histidine. Important acidic amino acids include aspartic acid (aspartate) and glutamic acid (glutamate). Important nonpolar amino acids include: methionine, alanine, isoleucine, proline, phenylalanine, tryptophan, valine, and leucine.

Example Question #1 : Amino Acids

Which two functional groups are included in every amino acid, and take part in amino acids binding together?

Possible Answers:

Sulfide group and carboxyl group

Amino group and sulfide group

Sulfide group and alcohol

Amino group and carboxyl group

Correct answer:

Amino group and carboxyl group

Explanation:

Every amino acid contains a carboxyl group and an amino group. These two functional groups are essential for amino acid binding and breaking.

While sulfide groups contribute to higher protein structure by forming disulfide bonds, they do not exist in every amino acid.

Example Question #1 : Amino Acids

What are the four categories of amino acids?

Possible Answers:

Nonpolar, polar, acidic, neutral

Nonpolar, polar, neutral, basic

Polar, neutral, acidic, basic

Nonpolar, polar, acidic, basic

Correct answer:

Nonpolar, polar, acidic, basic

Explanation:

Amino acids are categorized as nonpolar, polar, acidic, or basic. The category that an amino acid is placed into gives you an idea of where you might find the amino acid within a protein. For example, polar amino acids are commonly found on the outside of proteins, where other polar molecules (water) are likely to be found.

Example Question #2 : Amino Acids

A peptide bond is formed between __________.

Possible Answers:

two carboxyl groups

two aromatic groups

a carboxyl group and an amino group

an ester group and an amine group 

two amino groups

Correct answer:

a carboxyl group and an amino group

Explanation:

Each amino acid has an N and a C terminus. The N terminus contains an amino group and the C terminus contains a carboxylic acid group. In order to make a peptide linkage (and eventually create a polypeptide), a bond must form between the amino and carboxylic groups, with water as a byproduct.

Example Question #3 : Amino Acids

What would charge would you expect on alanine when placed in a solution with a pH of 1.00?

Possible Answers:

More information is needed to answer the question.

–1

+1

0 (neutral)

Correct answer:

+1

Explanation:

Since alanine is nonpolar, we know that the only parts of the amino acid that can be charged are the N-terminus and the C-terminus.

In an acidic solution, there is an excessive amount of protons available to protonate the amino acid. As a result, the carboxylic acid end and the amine end will both be fully protonated. This will result in an overall charge of +1, due to the nitrogen having three hydrogens attached.

Example Question #4 : Amino Acids

Which of the following components is not found in a nucleotide?

Possible Answers:

A phosphate group

A nitrogenous base

A sulfate group

A five-carbon sugar

Correct answer:

A sulfate group

Explanation:

Nucleotides are composed of a pentose sugar, phosphate group, and nitrogenous base. Nucleotides are the building blocks of nucleic acids, such as DNA and RNA. Phosphodiester bonds form between the phosphate group of one nucleotide and the 3' carbon of the pentose sugar on a second nucleotide to form a linkage. A nucleoside describes the molecule that is formed by a pentose sugar and nitrogenous base.

Sulfate groups are not found in nucleotides or nucleosides. 

Example Question #8 : Amino Acids

Which of the following amino acids is considered basic?

Possible Answers:

Tyrosine

Valine

Glutamic Acid

Lysine

Correct answer:

Lysine

Explanation:

Basic amino acids are those containing an amine group, while acidic contain a carboxylic acid group.

The basic amino acids are lysine (the correct answer), arginine, and histidine.

The acidic amino acids are glutamic acid (glutamate) and aspartic acid (aspartate).

← Previous 1 3
Learning Tools by Varsity Tutors

Incompatible Browser

Please upgrade or download one of the following browsers to use Instant Tutoring: