Question

Match the following Column-I Column-II (a) Glycine (p) Forms chloroacetic acid with NOCl (b) Lysine (q) Neutral (c) Proline (r) Optically inactive (d) Glutamic acid (s) Basic (t) Isoelectric point

Short answer

(a) matches with (r), (b) with (s), (c) with (t), and (d) with (p).

Step-by-step solution

Analyze Glycine

Glycine is the simplest amino acid with the formula NH2CH2COOH. It does not contain a chiral center, making it optically inactive. Thus, the correct match is (a) with (r).

Analyze Lysine

Lysine is an amino acid with a basic side chain, specifically an alkyl amino side chain. This makes lysine a basic amino acid. Therefore, (b) matches with (s).

Analyze Proline

Proline is unique as an amino acid because its side chain forms a ring structure by bonding to the nitrogen in its amino group, which makes it a secondary amine. However, it is not neutral as it has an imine group affecting its properties. Thus, it does not match with neutral (q), but rather affects its isoelectric point differently than typical amino acids due to its ring structure making it match with (t).

Analyze Glutamic Acid

Glutamic acid contains a carboxylic acid functional group in its side chain, making it acidic in nature. It has the ability to form chloroacetic acid derivatives with reagents like NOCl. Hence, (d) corresponds to (p).

Key concepts

Glycine

Glycine is recognized as the simplest amino acid, characterized by its chemical formula NH extsubscript{2}CH extsubscript{2}COOH. A distinctive feature of glycine is the absence of a chiral center, as its side chain is simply a hydrogen atom. This lack of chirality leads to glycine being classified as optically inactive. Unlike most amino acids, which have more complex side chains, glycine's simplicity makes it a frequent subject of study in biochemistry.

• Chirality refers to a molecule's ability to exist in forms that are non-superimposable on their mirror images.
• In optically active compounds, chiral centers allow the molecule to rotate plane-polarized light, while glycine does not partake in such behavior.
• Glycine's simplicity does not compromise its importance; it serves various functions, such as starting points for protein synthesis and acting as a neurotransmitter.

Lysine

Lysine is an essential amino acid, meaning it must be ingested as the human body cannot synthesize it. Distinguished by its basic nature, lysine possesses an alkyl amino side chain, making it one of the few basic amino acids. This distinguishes it from acidic or neutral amino acids that do not possess this unique attribute.

• The basic side chain of lysine contains an additional amino group that can accept a proton, giving lysine a positive charge under physiological pH.
• Owing to its basic property, lysine is positively charged at neutral pH conditions, aiding in various biochemical interactions.
• Lysine is vital for protein formation and is crucial in maintaining proper body function.

Proline

Proline stands out among the amino acids due to its distinctive side chain, which forms a cyclic structure. This ring formation connects with the nitrogen of the amino group, resulting in a secondary amine. The rigidity of this structure impacts protein folding, making proline significant in determining protein conformation.

• Unlike other amino acids that have a linear side chain, proline's ring introduces a constraint that can influence the folding of proteins.
• Proline's influence on the protein's isoelectric point is also noteworthy, as the cyclic structure affects how the molecule interacts with its environment.
• This special attribute of proline is crucial for collagen, a structural protein that relies on proline for stability.

Glutamic Acid

Glutamic acid is one of the key amino acids renowned for its acidic nature. It contains a second carboxyl group in its side chain, making it an acid under physiological conditions. This additional carboxylic group allows the amino acid to engage in chemical reactions, such as forming chloroacetic acid derivatives.

• With its dual carboxyl groups, glutamic acid can donate a proton, imparting a negative charge at a neutral pH.
• The acidic nature of glutamic acid makes it essential for neurotransmitter synthesis and function.
• Glutamic acid plays pivotal roles in cellular metabolism and is critical for nitrogen transport in the body.

Optically Inactive Amino Acids

An amino acid classified as optically inactive does not possess a chiral carbon, which means it cannot rotate plane-polarized light. Glycine is a classic example of this category of amino acids. It stands out as the only standard amino acid that falls into this classification.

• Optical inactivity arises from the absence of four distinct substituents around a central carbon, the hallmark of chirality.
• This property affects biochemical interactions and can influence the overall activity of peptides and proteins.
• Amino acids without stereocenters, like glycine, often serve roles where chirality is a non-essential factor.