The simplest amino acid is?

Appeared in: HPSSC Staff Nurse - 2021

Explanation

Glycine is the simplest of the 20 standard amino acids found in proteins.
Its structure is unique because its side chain (R-group) consists of only a single hydrogen atom.
This makes Glycine the only standard amino acid that is achiral, as its alpha-carbon is bonded to two hydrogen atoms.
Due to its small size, Glycine provides rotational flexibility to the polypeptide chain and can fit into tight corners in a protein's three-dimensional structure.

Option B: Lysine has a large, complex side chain containing a terminal amino group, making it a basic amino acid, not the simplest.
Option C: Tyrosine is a large amino acid with a bulky aromatic (phenol) ring as its side chain, making it structurally complex.
Option D: Aspartic acid has a side chain containing a carboxyl group, which is significantly larger than Glycine's hydrogen atom and classifies it as an acidic amino acid.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Structure and classification of amino acids as background academic context rather than a clinical decision trigger.
The unique properties of amino acids, determined by their side chains, are fundamental to protein folding, structure, and function. For example, Glycine's flexibility is crucial for the structure of collagen, the most abundant protein in the human body.
Glycine also functions as an inhibitory neurotransmitter in the central nervous system, primarily in the spinal cord and brainstem.
Defects in amino acid metabolism can lead to serious genetic disorders, such as Phenylketonuria (PKU), which involves the inability to metabolize Phenylalanine.

How to Approach the Question

This is a factual recall question from biochemistry.
First, identify the core concept: the definition of the 'simplest' amino acid.
Recall that the complexity of an amino acid is determined by its side chain (R-group), which is the variable part of its structure.
The simplest possible side chain is a single hydrogen atom.
Mentally review the structures of the options or recall which amino acid has the hydrogen side chain. This is Glycine.
Eliminate the other options as they have more complex side chains (basic, acidic, or aromatic groups).

Concept Tested & Keywords

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E6 Textbook of Biochemistry for medical StudentsDM Vasudevan Part 1 (pp 26-370 of 370) p. 287-289

E6 Biochemistry U Satyanarayana— Part 1 (pp 26-420 of 840) pp. 34-36, 340-342

Practise the full HPSSC Staff Nurse - 2021

Attempt every question from this paper in a timed mock, then review the full solution for each one.