Problem 34 - Objective Biology for NEET

Question

Which of the following is correct about amino acid? (a) It is a compound containing amino and acidic group \((-\mathrm{COOH})\). (b) It is a substitute and is methane. (c) It is based on the nature of ' \(\mathrm{R}\) ' group they are of many types. (d) All the above

Step-by-Step Solution

Answer

The correct statements about amino acids are (a) It is a compound containing amino and acidic group \((-\mathrm{COOH})\), and (c) It is based on the nature of ' \(\mathrm{R}\) ' group they are of many types.

Step 1: Understanding Amino Acid Structure

An amino acid is an organic molecule that is made up of a basic amino group \((-\mathrm{NH2})\), an acidic carboxyl group \((-\mathrm{COOH})\), and an organic R group (side chain) that is unique to each amino acid.

Step 2: Evaluating Statement A

Statement A mentions that amino acids contain amino and acidic (carboxyl) groups, which is correct.

Step 3: Evaluating Statement B

Statement B states that an amino acid is a substitute and is methane. This is incorrect as amino acids are not substitutes for methane nor are they methane.

Step 4: Evaluating Statement C

Statement C places focus on the 'R' group stating that due to its variabilities, there are many types of amino acids. This is true as it is the variations in the 'R' group (side chain) that make each amino acid unique.

Step 5: Evaluating Statement D

Statement D suggests that all the above statements are correct. However, statement B was found to be incorrect, hence, statement D is also incorrect.

Key Concepts

Amino Acid Structure

Understanding the structure of an amino acid is fundamental in biology, as these molecules are the building blocks of proteins. An amino acid typically consists of a central carbon atom, also known as the \( \alpha \) carbon, to which four different groups are attached: a hydrogen atom, an amino group \( -\mathrm{NH2} \), a carboxyl group \( -\mathrm{COOH} \), and a distinctive \( R \) group. Each of these components plays a crucial role in the function and characteristics of the amino acid.

The amino group, a basic group, has a tendency to attract a proton giving it a positive charge under physiological conditions. Meanwhile, the acidic carboxyl group can lose a proton, which confers a negative charge. The central carbon atom, apart from being a connecting point for these groups, also binds to a hydrogen atom and the distinctive \( R \) group which can range from a simple hydrogen to a complex ring structure, determining the amino acid's properties.

Carboxyl Group

The carboxyl group, with the formula \( -\mathrm{COOH} \), is an acidic functional group present in amino acids. This group is composed of a carbon atom double-bonded to an oxygen atom and also bonded to a hydroxyl group \( -OH \). In an aqueous environment, the carboxyl group can dissociate to release a proton \( (H^+) \), resulting in a negatively charged carboxylate ion \( (-\mathrm{COO}^-) \).

This capacity to donate a proton is what makes the carboxyl group acidic. How easily this proton is donated in biological systems affects the amino acid's behavior, particularly in proteins, where the charge of the carboxyl group can influence the protein's structure and function.

Amino Group

The amino group, typically noted as \( -\mathrm{NH2} \), is a basic functional group that plays an integral role in the structure of amino acids. Comprising a nitrogen atom attached to two hydrogen atoms, this group can accept a proton \( (H^+) \), making it positively charged \( (NH3^+) \), depending on the surrounding environment. This feature becomes especially significant during the formation of peptides and proteins, where amino groups of one amino acid bond with carboxyl groups of another, forming peptide bonds through dehydration synthesis.

R Group Variability

One of the most distinct aspects of amino acids is the variability found in their \( R \) groups, which is referred to as the side chain. This component is what differentiates one amino acid from another. The \( R \) group can include structures as simple as a single hydrogen atom, making it glycine, or as complex as a benzyl group, as in the case of phenylalanine.

The chemical nature of the \( R \) group can dictate the amino acid's characteristics, such as hydrophobicity, charge, and size. This influence extends to proteins where these amino acids comprise the primary structure, ultimately determining a protein’s three-dimensional shape and function. These diverse side chains allow for a wide variety of amino acids, each with unique properties that contribute to the diversity of proteins in living organisms.