from dm vasudevan a textbook of Biochemistry for Medical Students, 11t

from dm vasudevan a textbook of Biochemistry for Medical Students, 11th edition. Write a 2-mark reasoning answer for. A) Phenylketonuria should be diagnosed as early as possible. B) Statin group of drugs are given for treatment of Hypercholesterolemia. C) Patients with Porphyria should not be given Barbiturates D) Alcohol ingestion precipitates an acute attack of gout.

Reading File

Finding Sources

I have sufficient information from the biochemistry textbooks to write detailed, accurate 2-mark reasoning answers aligned with DM Vasudevan's approach. Let me now compose the answers.

Here are the 2-mark reasoning answers based on DM Vasudevan's Textbook of Biochemistry for Medical Students (11th edition):

A) Phenylketonuria Should Be Diagnosed as Early as Possible

Reason: Phenylketonuria (PKU) is caused by a deficiency of the enzyme phenylalanine hydroxylase, which converts phenylalanine to tyrosine. As a result, phenylalanine accumulates in the blood and tissues. Excess phenylalanine is transaminated to phenylpyruvate and other toxic metabolites (phenyllactate, phenylacetate), which impair normal brain development and myelination. If left untreated, this leads to irreversible intellectual disability (mental retardation), seizures, and developmental delay. However, since the brain is still developing in the neonatal period, early diagnosis (within the first 7-10 days of life via Guthrie test/newborn screening) followed by a low-phenylalanine diet can completely prevent neurological damage. Once brain damage occurs (after several weeks), it cannot be reversed. Hence, early diagnosis is essential to institute dietary therapy before irreversible neurological damage sets in.

B) Statin Group of Drugs Are Given for Treatment of Hypercholesterolemia

Reason: Cholesterol biosynthesis in the liver proceeds via the mevalonate pathway. The rate-limiting and committed step is the conversion of HMG-CoA (3-hydroxy-3-methylglutaryl CoA) to mevalonate, catalyzed by the enzyme HMG-CoA reductase. Statins (e.g., lovastatin, atorvastatin, simvastatin) are structural analogs of HMG-CoA and act as competitive inhibitors of HMG-CoA reductase. By blocking this rate-limiting enzyme, statins reduce endogenous cholesterol synthesis in the liver. This lowered intracellular cholesterol causes upregulation of LDL receptors on hepatocytes, which increases uptake of circulating LDL from the blood. The net result is a significant reduction in plasma LDL-cholesterol levels. Since elevated LDL-cholesterol is the primary driver of atherosclerosis and cardiovascular disease, statins are the drug of choice in hypercholesterolemia.

C) Patients with Porphyria Should Not Be Given Barbiturates

Reason: In porphyrias (e.g., Acute Intermittent Porphyria, Variegate Porphyria), there is an inherited defect in one of the enzymes of the heme biosynthesis pathway, causing accumulation of toxic porphyrin precursors (ALA, PBG). The synthesis of heme is regulated by negative feedback: heme inhibits ALA synthase (ALAS1), the rate-limiting enzyme of the pathway. Barbiturates are potent inducers of cytochrome P-450 (a hemoprotein) in the liver. When barbiturates are administered, the liver requires more cytochrome P-450, thereby consuming heme. This depletes the free heme pool, which in turn derepresses (activates) ALAS1 - the very enzyme that drives the pathway. The result is a massive increase in porphyrin precursor synthesis, precipitating a life-threatening acute attack of porphyria with abdominal pain, neurological manifestations, and psychiatric symptoms. Therefore, barbiturates are absolutely contraindicated in porphyria patients.

D) Alcohol Ingestion Precipitates an Acute Attack of Gout

Reason: Alcohol (ethanol) precipitates gout through two complementary mechanisms that raise serum uric acid levels:

Increased uric acid production: Ethanol is metabolized to acetaldehyde and then to acetate, consuming NAD⁺ and raising the NADH:NAD⁺ ratio. This increased NADH promotes the conversion of pyruvate to lactate (lactic acidosis). Additionally, the rapid turnover of ATP during ethanol metabolism leads to increased purine nucleotide catabolism, generating more uric acid.
Decreased renal excretion of uric acid: The lactic acid produced competes with urate for secretion via the organic acid transporter in the renal tubules, thereby reducing uric acid excretion. Similarly, ketoacidosis from alcohol consumption causes further inhibition of urate secretion.

The combined effect of increased uric acid production and decreased renal excretion leads to hyperuricemia, which causes monosodium urate crystals to deposit in joints, triggering an acute gouty attack.

This is a shared conversation. Sign in to Orris to start your own chat.