Question

RECALL 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, Threonine, Lysine, Asparagine, Aspartic Acid, Phenylalanine, Valine.

Step-by-step solution

- Identify Amino Acids with Hydroxyl Groups

Amino acids with hydroxyl groups in their \(\text{R}\) group include Serine and Threonine.

- Identify Amino Acids with Sulfur Atoms

Amino acids with sulfur atoms in their \(\text{R}\) group include Cysteine and Methionine.

- Identify Amino Acids with a Second Chiral Carbon Atom

The amino acids with a second chiral carbon atom in their \(\text{R}\) group include Threonine and Isoleucine.

- Identify Amino Acids with an Amino Group

Amino acids with an extra amino group in their \(\text{R}\) group include Lysine.

- Identify Amino Acids with an Amide Group

Amino acids with an amide group in their \(\text{R}\) group include Asparagine and Glutamine.

- Identify Amino Acids with an Acid Group

Amino acids with an acid group in their \(\text{R}\) group include Aspartic Acid and Glutamic Acid.

- Identify Amino Acids with an Aromatic Ring

Amino acids with an aromatic ring in their \(\text{R}\) group include Phenylalanine, Tyrosine, and Tryptophan.

- Identify Amino Acids with a Branched Side Chain

Amino acids with branched side chains in their \(\text{R}\) group include Valine, Leucine, and Isoleucine.

Key concepts

amino acids with hydroxyl groups

Amino acids with hydroxyl groups have an -OH group attached to the side chain, or \( \text{R} \) group. These hydroxyl groups make these amino acids polar and capable of forming hydrogen bonds. Two common amino acids with hydroxyl groups are:

• Serine (Ser, S): Found in various proteins, playing crucial roles in metabolism and enzyme function.
• Threonine (Thr, T): An essential amino acid important for protein synthesis and maintaining proper protein balance in the body.

Bonds between hydroxyl groups and other molecules are significant for protein structure and function.

amino acids with sulfur atoms

Sulfur-containing amino acids have sulfur atoms in their side chains. These amino acids are particularly important due to their ability to form disulfide bonds, which contribute to protein stability. Two amino acids with sulfur atoms are:

• Cysteine (Cys, C): It can form disulfide bonds with other cysteine molecules, providing structural stability to proteins.
• Methionine (Met, M): An essential amino acid used as the starting amino acid in protein synthesis (AUG codon). It contains a sulfur atom in a thioether linkage.

The presence of sulfur allows these amino acids to perform unique functions in cellular processes.

amino acids with second chiral carbon atoms

Amino acids with a second chiral carbon atom have an additional asymmetric center in their side chain, making them important in stereochemistry. Such amino acids include:

• Threonine (Thr, T): one of the two amino acids with two chiral centers due to its side chain structure.
• Isoleucine (Ile, I): another essential amino acid, with a complex side chain leading to its having two chiral centers.

The extra chiral center results in additional stereoisomers, influencing the way these amino acids interact with other biochemical molecules.

amino acids with extra amino group

Certain amino acids have an additional amino group on their side chain, imparting extra basic properties to them. A key example of such an amino acid is:

• Lysine (Lys, K): An essential amino acid notable for its long side chain capped with an extra amino group (−NH₂), contributing to its role in binding to various protein and nucleic acid structures.

This extra amino group makes lysine very basic and allows it to participate in ionic interactions crucial for protein structure and function.

amino acids with amide group

Amino acids with amide groups contain a side chain with the amide functional group (−CONH₂). These groups help in hydrogen bonding and offer structural features. Examples include:

• Asparagine (Asn, N): Derived from aspartic acid, asparagine is involved in protein biosynthesis and metabolism.
• Glutamine (Gln, Q): Similar to asparagine, but with a longer side chain, it is important for nitrogen metabolism and serves as a nitrogen donor in various biosynthetic processes.

The amide group makes these amino acids uncharged under physiological conditions while providing hydrogen bond donors and acceptors.

amino acids with acid group

Amino acids with acid groups feature carboxylic side chains, introducing negative charges at physiological pH. These acids play significant roles in enzyme active sites and ionic interactions. They include:

• Aspartic Acid (Asp, D): A dicarboxylic amino acid involved in the active sites of many enzymes due to its acidic properties.
• Glutamic Acid (Glu, E): Similar to aspartic acid but with a longer side chain, contributing to its roles in neurotransmission and metabolism.

These carboxylic side chains make these amino acids highly polar and reactive.

amino acids with aromatic rings

Aromatic amino acids contain ring structures that allow for absorption of UV light and engage in hydrophobic interactions. Examples are:

• Phenylalanine (Phe, F): Contains a benzyl side chain, crucial for protein structure by stabilizing interactions through hydrophobic effects.
• Tyrosine (Tyr, Y): It has a phenolic side chain that can be phosphorylated, making it vital for signal transduction.
• Tryptophan (Trp, W): With an indole side chain, it participates in protein-protein interactions and is a precursor for serotonin.

These aromatic side chains contribute extensively to protein structure and function through π-π interactions and UV absorption.

amino acids with branched side chains

Branched-chain amino acids (BCAAs) play essential roles in protein synthesis and muscle metabolism. These amino acids have non-linear side chains, including:

• Valine (Val, V): A hydrophobic amino acid with a branched aliphatic side chain, crucial for muscle structure and function.
• Leucine (Leu, L): Known for promoting protein synthesis and muscle repair, containing an isobutyl side chain.
• Isoleucine (Ile, I): This isomer of leucine participates in energy production and muscle metabolism.

These amino acids are particularly significant in sports and bodybuilding for their roles in muscle protein synthesis and recovery.