### Amino Acid Localization in Membrane ProteinsThe image above displays four amino acid structures labeled as A, B, C, and D. The task is to determine which amino acid is most likely to be located in the transmembrane domain of an integral membrane protein.#### Structure Descriptions:- **Amino Acid A:** - Structure: \(^+\text{H}_3\text{N} - \text{CH} - \text{COO}^-\) - Side Chain: Three CH\(_2\) groups with a terminal amino group (\(+\text{H}_3\text{N} - \text{CH}_2\))- **Amino Acid B:** - Structure: \(^+\text{H}_3\text{N} - \text{CH} - \text{COO}^-\) - Side Chain: Three CH\(_2\) groups with a terminal carboxylate group (\(\overset{O}{\underset{O}{\vert}}\text{C} - \text{O}^-\))- **Amino Acid C:** - Structure: \(^+\text{H}_3\text{N} - \text{CH} - \text{COO}^-\) - Side Chain: One CH\(_2\) group with a terminal hydroxyl group (-OH)- **Amino Acid D:** - Structure: \(^+\text{H}_3\text{N} - \text{CH} - \text{COO}^-\) - Side Chain: One CH group bonded to two methyl groups (\(\text{H}_3\text{C} - \text{CH}_3\))#### Question:Of the four amino acids shown, which one would most likely be located in the transmembrane domain of an integral membrane protein?#### Answer:- **Amino Acid D** is the correct choice. The presence of nonpolar side chains, such as the two methyl groups in Amino Acid D, makes it more hydrophobic and suitable for the lipid bilayer environment of a transmembrane domain.

Answered: +H₂N-CH-COO™ 1 CH₂ I CH₂ I CH₂ I…

Biochemistry

9th Edition

ISBN:9781319114671

Author:Lubert Stryer, Jeremy M. Berg, John L. Tymoczko, Gregory J. Gatto Jr.

Publisher:Lubert Stryer, Jeremy M. Berg, John L. Tymoczko, Gregory J. Gatto Jr.

Chapter1: Biochemistry: An Evolving Science

Section: Chapter Questions

Problem 1P

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Question

### Amino Acid Localization in Membrane Proteins

The image above displays four amino acid structures labeled as A, B, C, and D. The task is to determine which amino acid is most likely to be located in the transmembrane domain of an integral membrane protein.

#### Structure Descriptions:

- **Amino Acid A:**
- Structure: \(^+\text{H}_3\text{N} - \text{CH} - \text{COO}^-\)
- Side Chain: Three CH\(_2\) groups with a terminal amino group (\(+\text{H}_3\text{N} - \text{CH}_2\))

- **Amino Acid B:**
- Structure: \(^+\text{H}_3\text{N} - \text{CH} - \text{COO}^-\)
- Side Chain: Three CH\(_2\) groups with a terminal carboxylate group (\(\overset{O}{\underset{O}{\vert}}\text{C} - \text{O}^-\))

- **Amino Acid C:**
- Structure: \(^+\text{H}_3\text{N} - \text{CH} - \text{COO}^-\)
- Side Chain: One CH\(_2\) group with a terminal hydroxyl group (-OH)

- **Amino Acid D:**
- Structure: \(^+\text{H}_3\text{N} - \text{CH} - \text{COO}^-\)
- Side Chain: One CH group bonded to two methyl groups (\(\text{H}_3\text{C} - \text{CH}_3\))

#### Question:

Of the four amino acids shown, which one would most likely be located in the transmembrane domain of an integral membrane protein?

#### Answer:

- **Amino Acid D** is the correct choice. The presence of nonpolar side chains, such as the two methyl groups in Amino Acid D, makes it more hydrophobic and suitable for the lipid bilayer environment of a transmembrane domain.

Expert Solution

Step 1: Classification of amino acids based on the chemical nature of their side group

Amino acids are biomolecules that have a hydrogen atom, an amino group and a carboxyl group linked to the same carbon called alpha carbon. Other than the amino and carboxyl groups, amino acids have a chemically diverse side chain linked to the alpha carbon. Amino acids differ from each other in the side group that is linked to the alpha carbon.

Based on the chemical nature of the side groups, amino acids can be classified into the following:

Non-polar, aliphatic side groups: side chains are not ionizable and consist of aliphatic groups that do not form hydrogen bonds. Glycine (G), Alanine (A), Valine (V), Proline (P), Leucine (L), Isoleucine (I) and Methionine (M) are non-polar aliphatic amino acids.
Aromatic side group: side chains have an aromatic group. Phenylalanine (F), Tyrosine (Y) and Tryptophan (W) are aromatic amino acids. Only tyrosine is polar out of the three.
Polar uncharged side groups: side chains are non-ionizable but they do form hydrogen bonds. Serine (S), Cysteine (C), Threonine (T), Asparagine (N) and Glutamine (Q) are polar amino acids. Cysteine can ionise at high pH.
Positively charged side groups: side chain has an ionizable group that is positively charged at neutral pH. They are also called basic amino acids. Lysine (K), Arginine (R) and Histidine (H) are positively charged amino acids.
Negatively charged side groups: side chain has an ionizable group that is negatively charged at neutral pH. They are also called acidic amino acids. Only two amino acids are negatively charged: Aspartate (D) and Glutamate (E)