AP Biology : Understanding Amino Acids

Study concepts, example questions & explanations for AP Biology

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Example Questions

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Example Question #1 : Understanding Amino Acids

A point mutation during translation would most likely incorporate which of the following amino acids?

Possible Answers:

Valine

It depends on the newly created codon

Isoleucine

Proline

Tyrosine

Correct answer:

It depends on the newly created codon

Explanation:

The effect of a point mutation is not dependent on the amino acid—the amino acid's selection is entirely independent of its structure. The amino acid selection during translation depends only on the three base-pair codon read by the ribosome. For example, the start codon—AUG—recruits methionine. If a frameshift mutation lead to UGG as the codon instead, tryptophan would be recruited. No single amino acid is more likely to be incorporated after a point mutation.

Example Question #2 : Understanding Amino Acids

Amino acids are coded for by three-base mRNA sequences called codons. Although there are 64 possible combinations of three bases, the body only contains 22 standard amino acids. What genetics concept explains this fact?

Possible Answers:

Evolution has removed those amino acids thought to be unfavorable for an organism's fitness

The remaining combinations code for either start or stop codons

The genetic code is degenerate

This statement is false; the human body contains 64 distinct amino acids

The remaining combinations code for non-protein macromolecules such as lipids and carbohydrates

Correct answer:

The genetic code is degenerate

Explanation:

The degeneracy of the genetic code is a major concept relating to protein synthesis. This concept states that each codon codes for a single amino acid, but that an amino acid can have more than one codon. If each three-base codon corresponded to a different amino acid, 64 amino acids would be produced in the body. Instead, most amino acids are coded for by multiple codons; for example, lysine corresponds to both AAA and AAG. This concept is especially important with regard to mutations. If an AAA codon undergoes a point mutation to become an AAG codon, the same amino acid will be produced, and the organism will be unharmed.

Example Question #3 : Understanding Amino Acids

What are the components of an amino acid?

Possible Answers:

An “R” group, an amine, a carboxylic acid, and a hydrogen atom

An “R” group, an amine, and a hydrogen atom

An “R” group, an amine, a carboxylic acid, and a methyl group

An “R” group, an amine, a carboxylic acid, and a sulfhydryl group

Correct answer:

An “R” group, an amine, a carboxylic acid, and a hydrogen atom

Explanation:

Amino acids consist of an amine, a carboxylic acid, a hydrogen atom and a side chain (often simply referred to as an “R group”). Differences between these side chains are what differentiate amino acids from one another. These four components are bound to a central carbon atom, giving each amino acid a stereocenter. Amino acids form peptide bonds through condensation reactions between the carboxyl group of one residue and the amino group of another.

Example Question #2 : Understanding Amino Acids

What type of bonds are used to link amino acids into a chain?

Possible Answers:

Hydrogen bonds

Ionic bonds

Glycosidic bonds

Peptide bonds

Correct answer:

Peptide bonds

Explanation:

Peptide bonds are the uniquely named form of covalent bonds that hold together amino acids. These bonds are formed when the carboxylic acid of one amino acids reacts with the amino group of another amino acid. The result is a peptide polymer, known as a polypeptide, and a water molecule.

Glycosidic linkages are seen in sugars, and are used to bind monosaccharides. Hydrogen and ionic bonds are more general intermolecular forces. Hydrogen bonding helps shape the secondary and tertiary structure of proteins, but does not help in the formation of an amino acid chain.

Example Question #5 : Understanding Amino Acids

What is a similarity between all amino acids in the body?

Possible Answers:

All can be used as the first amino acid in a protein structure

All fit into the alpha-helix structure

All are used in every protein in the body

All contain side chains

All contain amino and carboxyl groups

Correct answer:

All contain amino and carboxyl groups

Explanation:

The amino acids, as denoted by the name, contain amino and carboxyl groups. Each amino acid has the amine group connected to a central carbon, which is then connected to a carboxyl group.

Amino acids may contain R-groups on the central carbon, and all amino acids have a specific R-group except for glycine, which is the simplest amino acid. Glycine is bound to an extra hydrogen atom in place of an R-group. Only methionine can start a protein structure; methionine is coded by the start codon on an mRNA sequence. Some amino acids are capable of forming alpha-helices, while others are capable of disrupting and breaking alpha-helices. Proline, for example, frequently disrupts this secondary structure. Each protein is coded by a specific sequence of amino acids; not all proteins will contain every amino acid.

Example Question #6 : Understanding Amino Acids

The genetic code consists of three base pairs per codon and allows for 64 unique amino acid combinations. If instead the genetic code were to contain four base pairs per codon, what would be the maximum number of amino acids that could be formed from this code?

Possible Answers:

Correct answer:

Explanation:

The number of codons can be found by raising the number of nitrogenous bases to the power of the codon length. In the genetic code, there are four bases and codons are three bases in length.

If codons were four bases in length, then the number of possible bases would be raised to the fourth power.

Example Question #7 : Understanding Amino Acids

Which of the following is not found on the central carbon of every amino acid?

Possible Answers:

All of these are found in every amino acid

A methyl group

An amino group

A carboxyl group

A hydrogen

Correct answer:

A methyl group

Explanation:

Every amino acid has a central carbon with an amino terminus and a carboxyl terminus. There is also a hydrogen attached to the central carbon. The last substituent varies between amino acids and determines how the particular amino acid will be used in proteins. This variable group is known as the "R-group." Only one amino acid, alanine, has a methyl group attached in the "R-group" position.

Example Question #3 : Understanding Amino Acids

Which of the following choices best characterizes the primary components of an amino acid?

Possible Answers:

Amine group, carboxylic acid group, and variable side chain 

Carboxylic acid group, alcohol group, and citric acid group 

Amine group, alcohol group, and variable side chain

Amine group, citric acid group, and variable side chain 

Correct answer:

Amine group, carboxylic acid group, and variable side chain 

Explanation:

Amino acids are compounds that make up proteins and polypeptide chains. They are made up of an amine group , a carboxylic acid group , and a variable side chain. The amine group is called the “N terminus” and the carboxylic acid group is called the “C terminus”. The N terminus of one amino acid and the C terminus of another amino acid can form a peptide bond through a condensation reaction.

Example Question #1 : Understanding Amino Acids

An amino acid typically contains which of the following functional groups?

Possible Answers:

Carboxylic acid and aldehyde

Carboxylic acid and alcohol

Carboxylic acid and amine

Aldehyde and amine

Alcohol and amine

Correct answer:

Carboxylic acid and amine

Explanation:

Amino acids are the building blocks of proteins. The general structure of an amino acid consists of a carboxylic acid and an amine group bonded to a carbon that contains. The carbon contains an R group that varies depending on the amino acid.

Example Question #4 : Understanding Amino Acids

What special bond is formed when two cysteine residues come together in a protein?

Possible Answers:

A dipole-dipole interaction

A covalent bond

A hydrogen bond

A disulfide bridge

An ionic bond

Correct answer:

A disulfide bridge

Explanation:

Cysteine is an amino acid that contain a sulfhydryl group . When two sulfhydryl groups come together and get oxidized they form a  bond, which is referred to as a disulfide bond or a disulfide bridge.

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