The essential amino acid which is not synthesized in our body is?

Appeared in: DSSSB - 29 August 2019 (Shift-2)

Explanation

Histidine is one of the nine essential amino acids that the human body cannot produce on its own.
It must be supplied through dietary sources like meat, fish, eggs, and dairy products.
Histidine is a precursor for histamine, a vital molecule involved in immune responses, digestion, and sleep-wake cycles.
It also plays a role in maintaining the myelin sheaths that protect nerve cells.

Option B: Tyrosine is a non-essential amino acid because the body can synthesize it from another amino acid, Phenylalanine.
Option C: Proline is a non-essential amino acid that the body can synthesize from the precursor molecule, glutamate.
Option D: Arginine is considered conditionally or semi-essential. While healthy adults can synthesize it in the urea cycle, the amount may be insufficient during periods of rapid growth (infancy), trauma, or metabolic stress.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Classification of Amino Acids as background academic context rather than a clinical decision trigger.
Nurses must assess the nutritional status of patients, ensuring adequate intake of essential amino acids, especially in those with high metabolic demands (e.g., burn victims, post-operative patients) or poor dietary intake.
Understanding amino acid metabolism is crucial for managing patients with inborn errors of metabolism like Phenylketonuria (PKU), where dietary restriction of phenylalanine and supplementation of tyrosine is life-saving.
What if? If the question was about an infant, both Histidine and Arginine would be considered essential. An infant's metabolic pathways are not mature enough to produce sufficient Arginine to support their rapid growth and development.

How to Approach the Question

First, identify the core of the question: it asks to find the 'essential' amino acid, which is defined as one the body cannot make.
Recall the three classifications of amino acids: essential, non-essential, and conditionally essential.
Use a mnemonic for the nine essential amino acids, such as 'PVT TIM HALL' (Phenylalanine, Valine, Threonine, Tryptophan, Isoleucine, Methionine, Histidine, Arginine, Leucine, Lysine). Note that Arginine is semi-essential.
Evaluate each option against this knowledge.
Histidine is on the essential list.
Tyrosine and Proline are synthesized in the body (non-essential).

Concept Tested & Keywords

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E6 Harper's Illustrated Biochemistry2023 (pp 26-793 of 813) p. 258-260

E6 Medicine Davidson Principles Practice 24e p. 717-719

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

Practise the full DSSSB - 29 August 2019 (Shift-2)

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