Which is an essential amino acid?

Appeared in: SGPGI Nursing Officer-2022

Explanation

Lysine is an essential amino acid, meaning the human body cannot synthesize it in sufficient quantities to meet metabolic needs.
It must be obtained through dietary sources. Good sources include meat, fish, dairy products, eggs, and legumes like soybeans.
Lysine plays a vital role in protein synthesis, calcium absorption, and the production of hormones, enzymes, and antibodies.
Cereal-based diets are often deficient in lysine, which is why combining cereals with pulses (like rice and dal) is important for obtaining a complete protein profile.

Option A: Purine is not an amino acid. It is a heterocyclic aromatic organic compound that consists of a pyrimidine ring fused to an imidazole ring. Purines (adenine and guanine) are fundamental components of nucleic acids (DNA and RNA).
Option C: Glutamine is a non-essential amino acid, meaning the body can typically synthesize it from other compounds, particularly glutamic acid. It is the most abundant free amino acid in human blood.
Option D: Alanine is a non-essential amino acid. The body can easily synthesize it from pyruvate, a product of glucose metabolism, through a process called transamination.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Classification of Amino Acids (Essential vs. Non-essential) as background academic context rather than a clinical decision trigger.
Nurses assess dietary intake to ensure patients, especially those with wounds, infections, or malnutrition, receive adequate essential amino acids for tissue repair and immune function.
A deficiency in lysine can lead to fatigue, poor concentration, hair loss, anemia, and impaired growth.
What if? If a patient is on a strict vegan diet, the nurse must educate them on combining plant-based protein sources (like grains with legumes) to ensure a complete amino acid profile, as many plant sources are low in lysine.

How to Approach the Question

First, understand the question is asking to identify an 'essential' amino acid.
Recall the definition: Essential amino acids cannot be made by the body and must come from food.
Evaluate each option against this definition.
Option A, Purine, is a component of DNA/RNA, not an amino acid. Eliminate it.
Options C (Glutamine) and D (Alanine) are common examples of non-essential amino acids that the body can produce.
This leaves Option B, Lysine, which is a well-known essential amino acid, crucial for protein synthesis.

Concept Tested & Keywords

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E6 Textbook of Biochemistry for medical StudentsDM Vasudevan Part 1 (pp 26-370 of 370) p. 300-302

E6 Biochemistry U Satyanarayana— Part 1 (pp 26-420 of 840) p. 362-364

E6 Pharmacology Nursing Lilley 11e Part 3 p. 231-233

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