Problem 30 - A Complete Resource Book in Chemistry for JEE Main

Question

An example of a sulphur containing amino acid is (a) lysine (b) serine (c) cysteine (d) tyrosine

Step-by-Step Solution

Answer

The sulphur-containing amino acid is cysteine (c).

Step 1: Identifying Characteristics

Sulfur-containing amino acids are those that have sulfur in their side chains. These amino acids have properties distinct from amino acids that do not contain sulfur.

Step 2: Analyzing each option

Look at the given options: (a) Lysine: This amino acid does not contain a sulfur atom. (b) Serine: This amino acid also lacks sulfur. (c) Cysteine: This amino acid contains sulfur in its thiol side chain (-SH). (d) Tyrosine: This amino acid does not contain sulfur.

Step 3: Selecting the Correct Answer

Based on the analysis of each option, cysteine is identified as the only amino acid among the given choices that contains sulfur in its side chain.

Key Concepts

Cysteine

Cysteine is a noteworthy amino acid because it contains sulfur, a relatively rare element in amino acids. This element is present in the form of a thiol group (-SH) in cysteine's side chain. Due to the presence of this thiol group, cysteine can form disulfide bonds, which are crucial for protein structure and stability. These bonds occur when two cysteine molecules oxidize and form a covalent bond between their sulfur atoms, turning into cystine. The ability of cysteine to form disulfide bonds makes it essential in the formation of the three-dimensional structure of proteins. This structural feature is particularly important in proteins that function in varying environments, such as extracellular enzymes and proteins that undergo conformational changes.

Amino Acid Structure

Amino acids are the building blocks of proteins, playing a vital role in numerous biological processes. Each amino acid consists of a central carbon atom, known as the alpha carbon (b1-carbon), bonded to four groups:

• An amino group (-NH\(_2\))
• A carboxyl group (-COOH)
• A hydrogen atom
• A distinctive side chain or R-group, which varies among different amino acids

The unique properties of each amino acid, such as its polarity, charge, and functional reactivity, are largely determined by the nature of its R-group. Cysteine's R-group contains a thiol group, which imparts unique attributes like the ability to engage in redox reactions and contribute to protein structure through disulfide bond formation. Understanding amino acid structure is fundamental in fields like biochemistry and molecular biology, where the function and behavior of proteins are studied extensively.

Organic Chemistry

Organic chemistry is the scientific study of the structure, properties, composition, reactions, and preparation of carbon-containing compounds. Amino acids, including cysteine, fall under organic chemistry as they are organic molecules containing carbon, hydrogen, nitrogen, oxygen, and often sulfur, as seen in cysteine. Cysteine's thiol group makes it an interesting subject in organic chemistry due to its reactivity. It is prone to oxidation, forming disulfide bonds, and can act as a nucleophile in various chemical reactions. Understanding the principles of organic chemistry, such as functional group chemistry and reaction mechanisms, is crucial for comprehending how amino acids like cysteine contribute to biochemical pathways and processes. Through these principles, we gain insights into how biological molecules behave and interact with each other, laying the groundwork for advances in biotechnology, pharmaceuticals, and biochemistry.