Question

For each of the following, name an amino acid in which the \(\mathrm{R}\) group contains it: a hydroxyl group, a sulfur atom, a second chiral carbon atom, an amino group, an amide group, an acid group, an aromatic ring, and a branched side chain.

Short answer

Serine, Cysteine, Isoleucine, Lysine, Asparagine, Aspartic acid, Phenylalanine, Valine.

Step-by-step solution

Identify an amino acid with a hydroxyl group in the R group

Serine (Ser, S) is an amino acid with a hydroxyl group (-OH) in its R group.

Identify an amino acid with a sulfur atom in the R group

Cysteine (Cys, C) is an amino acid with a sulfur atom in its R group.

Identify an amino acid with a second chiral carbon atom

Isoleucine (Ile, I) is an amino acid that contains a second chiral carbon atom.

Identify an amino acid with an amino group in the R group

Lysine (Lys, K) is an amino acid with an amino group (-NH2) in its R group.

Identify an amino acid with an amide group in the R group

Asparagine (Asn, N) is an amino acid with an amide group (-CONH2) in its R group.

Identify an amino acid with an acid group in the R group

Aspartic acid (Asp, D) is an amino acid with an acid group (-COOH) in its R group.

Identify an amino acid with an aromatic ring in the R group

Phenylalanine (Phe, F) is an amino acid with an aromatic ring in its R group.

Identify an amino acid with a branched side chain

Valine (Val, V) is an amino acid with a branched side chain.

Key concepts

Hydroxyl Group

A hydroxyl group (-OH) is a functional group consisting of an oxygen atom bonded to a hydrogen atom. This group plays a key role in the reactivity of molecules. In amino acids, the hydroxyl group can lead to water solubility and participate in various biochemical reactions.

Serine (Ser, S) is an example of an amino acid containing a hydroxyl group in its R group. This makes serine unique as it can form hydrogen bonds, which are critical for protein structure and function.

Sulfur Atom

The presence of a sulfur atom in an amino acid can significantly affect its chemical properties. Sulfur atoms are larger than oxygen and nitrogen, making sulfur-containing amino acids distinctive. Sulfur atoms can form disulfide bonds, critical for protein stability.

Cysteine (Cys, C) contains a sulfur atom in its R group. This sulfur can form disulfide bonds with another cysteine, stabilizing the protein's three-dimensional structure.

Chiral Carbon

A chiral carbon is a carbon atom that is attached to four different groups, making it a center of asymmetry. Most amino acids have one chiral carbon at the alpha position, but some can have more.

Isoleucine (Ile, I) is an amino acid with a second chiral carbon atom in its side chain. This additional chirality introduces more stereoisomers, increasing the diversity of protein structures.

Amino Group

An amino group (-NH2) is a functional group containing nitrogen and hydrogen. It is basic and can accept protons, playing a vital role in the acid-base chemistry of amino acids.

Lysine (Lys, K) possesses an amino group in its R group. This additional amino group makes lysine a strongly basic amino acid, often involved in protein interactions and enzyme activity.

Amide Group

An amide group (-CONH2) is a functional group consisting of a carbonyl group linked to a nitrogen atom. Amides are generally stable and resistant to hydrolysis.

Asparagine (Asn, N) features an amide group in its R group. The presence of the amide makes asparagine polar and capable of forming hydrogen bonds, contributing to the protein's solubility and stability.

Acid Group

An acid group (-COOH) is a functional group with a carbon double-bonded to an oxygen (carbonyl) and single-bonded to a hydroxyl group. This group grants the amino acid acidic properties.

Aspartic acid (Asp, D) includes an acid group in its R group. This acid group allows aspartic acid to donate protons and participate in ionic interactions, crucial for enzyme catalysis and ion transport.

Aromatic Ring

An aromatic ring is a cyclic, planar molecule with alternating double bonds that create a stable ring. Aromatic side chains add to the hydrophobicity and provide distinctive chemical properties.

Phenylalanine (Phe, F) has an aromatic ring in its R group, making it hydrophobic. The ring can participate in pi stacking interactions, which are important in stabilizing protein structures and interactions.

Branched Side Chain

A branched side chain is an R group that branches away from the main chain of the amino acid. This structure can affect the molecule's hydrophobicity and reactivity.

Valine (Val, V) exemplifies an amino acid with a branched side chain. The branching makes valine hydrophobic, playing a crucial role in the folding and stability of proteins by promoting hydrophobic interactions in the core of the proteins.