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Magazine Chapter 3: Problem 5
Match each amino acid in the left-hand column with the appropriate side-chain type in the right-hand column. \(\sqrt{1}\). (a) Leu____________________ (b) Glu__________________ (c) Lys_____________ (d) Ser_________________ (e) Cys_____________ (f) Trp________________ 1\. hydroxyl-containing 2 . acidic 3\. basic 4\. sulfur-containing 5 . nonpolar aromatic 6 .nonpolar aliphatic
Short Answer
Expert verified
a-6, b-2, c-3, d-1, e-4, f-5.
Step by step solution
01
Identify Leu (Leucine)
Leucine is a nonpolar aliphatic amino acid, which means it does not have polar side chains and is not aromatic. Therefore, Leu is matched with side-chain type 6.
02
Identify Glu (Glutamic Acid)
Glutamic Acid is an acidic amino acid. It has a side chain with a carboxylic acid group, making it acidic in nature. Therefore, Glu is matched with side-chain type 2.
03
Identify Lys (Lysine)
Lysine is a basic amino acid, as it contains an amino group in its side chain that can accept a proton. Thus, Lys is matched with side-chain type 3.
04
Identify Ser (Serine)
Serine has a hydroxyl group in its side chain, making it a hydroxyl-containing amino acid. Therefore, Ser is matched with side-chain type 1.
05
Identify Cys (Cysteine)
Cysteine contains a sulfur atom in its side chain, specifically a thiol group, making it sulfur-containing. Thus, Cys is matched with side-chain type 4.
06
Identify Trp (Tryptophan)
Tryptophan is a nonpolar aromatic amino acid due to the presence of an indole ring, which is an aromatic structure. Therefore, Trp is matched with side-chain type 5.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Side-Chain Type
Amino acids are the building blocks of proteins, and each amino acid has a unique side chain. The side chain, often referred to as the 'R group', differs among the 20 standard amino acids and determines the chemical properties and nature of the amino acid. It can affect how proteins interact with each other and how they fold. The side chains can be categorized into different types based on their characteristics, such as polarity, charge, and the presence of specific elements like sulfur. Understanding the side-chain type is essential for predicting the behavior of proteins in different environments, which is crucial in biochemistry and molecular biology.
Nonpolar Aliphatic
Nonpolar aliphatic amino acids have side chains that are non-aromatic and mostly consist of carbon and hydrogen atoms. These amino acids are hydrophobic, meaning they do not interact well with water, allowing proteins to fold in such a way that the hydrophobic residues are tucked away inside the protein structure. An example is Leucine (Leu), which is classified as nonpolar aliphatic due to its side chain that lacks polar groups, making it hydrophobic. Understanding these properties helps clarify why nonpolar aliphatic amino acids are often found in the interior of protein structures.
Acidic Amino Acids
Acidic amino acids have side chains that contain a carboxylic acid group, which can donate a proton, making them negatively charged at physiological pH. These amino acids are polar and interact well with water. Glutamic acid (Glu) exemplifies this category, as it has a carboxyl group in its side chain, allowing it to release hydrogen ions into the solution. This property is important in enzyme active sites and for protein binding, where the charge can affect how the amino acid interacts with other molecules or ions.
Basic Amino Acids
Basic amino acids include those with side chains that have an amino group capable of accepting a proton, giving them a positive charge at physiological pH. Lysine (Lys) is a prime example of a basic amino acid; it has an extra amino group in its side chain, allowing it to accept an additional proton. This basic property makes such amino acids crucial for forming ionic bonds with negatively charged molecules, impacting protein structure and function. Basic amino acids often play roles in facilitating hydrogen bonding and electrostatic interactions in protein structures.
Hydroxyl-Containing
Hydroxyl-containing amino acids are characterized by having an -OH group in their side chains, making them polar and capable of forming hydrogen bonds. Serine (Ser) is a hydroxyl-containing amino acid, which provides sites for phosphorylation, a common post-translational modification that regulates protein activities. The presence of a hydroxyl group increases the amino acid's solubility in water, which can influence the protein's secondary structure and interaction with other molecules. These amino acids often facilitate enzyme activity and promote structural stability through hydrogen bonding.
Sulfur-Containing
Sulfur-containing amino acids have side chains that include sulfur, offering unique properties such as the ability to form disulfide bonds essential for protein stability. Cysteine (Cys), which contains a thiol group (-SH), is a notable sulfur-containing amino acid. The thiol group can form disulfide bridges with other cysteine residues, stabilizing protein structures by linking different parts of the protein molecule. These bonds are crucial in maintaining the three-dimensional structure of proteins, especially those secreted outside of the cell, by providing resilience against environmental changes.
Nonpolar Aromatic
Nonpolar aromatic amino acids contain side chains with aromatic rings. These structures are planar and cyclic, allowing them to absorb ultraviolet light, which can be used to study proteins. Tryptophan (Trp) is an example of a nonpolar aromatic amino acid, known for its indole ring, which contributes to its hydrophobic properties. While aromatic, the nonpolar nature means these amino acids are often buried within protein structures. They play a role in stabilizing proteins through hydrophobic interactions and are involved in protein-protein interactions due to their ability to stack with other aromatic rings.
