Applied biochemistry is about 3% of NRE Step I, roughly 6 of 200 items, and PM&DC's published table gives 6 for it. The syllabus covers proteins, enzymes, carbohydrate and lipid metabolism, vitamins and nutrition, haem and porphyrias, inborn errors, molecular biology and PCR, and electrolytes with acid-base. Stems present a patient or a laboratory result and ask which enzyme, vitamin or pathway is at fault. With only six items it is the cheapest domain to prepare, because the same 15 or so themes recur and can be learned as clinical pictures rather than pathways.
Weight and expected item count
Six items is about six minutes of paper time, and fifteen subtopics in the syllabus map. That ratio says you cannot know every pathway, and you do not need to. A short revision plan aimed at the clinical pictures gets most of the marks.
What is tested
| Block | Topics |
|---|---|
| Macromolecules | Amino acids, protein structure and electrophoresis; enzyme kinetics, inhibition and clinical enzymology; plasma proteins, tumour markers and liver and renal function tests |
| Energy metabolism | Bioenergetics, the TCA cycle and oxidative phosphorylation; carbohydrate metabolism and glycogen storage diseases |
| Lipids and nutrition | Lipid metabolism, lipoproteins and dyslipidaemia; vitamins and mineral deficiencies; nutrition, protein-energy malnutrition and obesity |
| Inborn errors | Amino acid metabolism (PKU, MSUD, homocystinuria); purine and pyrimidine metabolism and gout; lysosomal storage disorders |
| Haem | Haem synthesis, porphyrias and haemoglobinopathies |
| Molecular biology | DNA replication, PCR and genetic techniques |
| Acid-base and endocrine | Electrolyte and acid-base biochemistry (anion gap); endocrine and hormone biochemistry |
Local guideline points
- Malnutrition and micronutrients: protein-energy malnutrition and micronutrient deficiency (iron, vitamin A, vitamin D, zinc, iodine) are public-health priorities in Pakistan, and the syllabus links nutrition to community medicine. The same facts appear here as biochemistry and in community medicine as programmes.
- Haemoglobinopathies: thalassaemia is a major burden. Know the globin chain change, the electrophoresis pattern and the iron overload consequence of repeated transfusion.
- Diabetes and lipids: common local problems make glycaemic and lipid biochemistry high-use in clinical stems.
- Reference ranges: use SI units (mmol/L) but expect mg/dL where Pakistani laboratories report in it, as the units are stated in the question.
Three typical traps
- Learning pathways without the enzyme-to-disease link. A child with an odour, a developmental problem or hypoglycaemia is a question about a named enzyme deficiency. Memorise the clinical picture, the metabolite that accumulates and the dietary or other management.
- Mixing up vitamin deficiency syndromes. Beriberi, pellagra, scurvy, rickets and night blindness are separated by specific features (neuropathy or heart failure, dermatitis-diarrhoea-dementia, gum bleeding, bone changes, xerophthalmia). A simple table prevents most errors.
- Calculating the anion gap wrongly or applying it wrongly. Know the formula (sodium minus chloride and bicarbonate) and that a raised gap means unmeasured acids, such as lactate, ketones, renal failure or toxins. Match the gap to the clinical stem.
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How to revise it
| Session | Do this |
|---|---|
| 1 | Enzymes and clinical enzymology; plasma proteins; liver and renal function tests |
| 2 | Carbohydrate and glycogen storage; TCA cycle and oxidative phosphorylation in outline |
| 3 | Lipids and lipoproteins; vitamins and minerals; malnutrition |
| 4 | Inborn errors: PKU, MSUD, homocystinuria, gout, lysosomal storage; haem synthesis and porphyrias |
| 5 | Molecular techniques and acid-base chemistry; 25 mixed questions |
Five sessions are enough if every session ends with questions. Revisit the vitamin table and inborn-error list weekly. The study plan shows where to place biochemistry.
Core facts to state without notes
| Deficiency | Classic picture |
|---|---|
| Thiamine (B1) | Beriberi and Wernicke encephalopathy |
| Niacin (B3) | Pellagra: dermatitis, diarrhoea, dementia |
| Vitamin C | Scurvy: bleeding gums, poor wound healing |
| Vitamin D | Rickets in children, osteomalacia in adults |
| Vitamin A | Night blindness, xerophthalmia |
| Folate and B12 | Megaloblastic anaemia; B12 also causes neurological damage |
- Phenylketonuria: phenylalanine hydroxylase deficiency, a musty odour, intellectual disability if untreated, managed by a low-phenylalanine diet.
- Maple syrup urine disease: branched-chain amino acid metabolism defect with sweet-smelling urine.
- Homocystinuria: marfanoid habitus, downward lens dislocation and thrombosis; some cases respond to pyridoxine.
- Von Gierke disease: glucose-6-phosphatase deficiency with fasting hypoglycaemia and hepatomegaly. Pompe disease causes cardiomegaly.
- Lesch-Nyhan syndrome: HGPRT deficiency with hyperuricaemia, gout and self-injury.
- Familial hypercholesterolaemia: an LDL receptor defect with very high LDL and early coronary disease.
- Lysosomal storage: Tay-Sachs disease has a cherry-red macular spot; Gaucher disease causes hepatosplenomegaly and bone disease.
- Anion gap: sodium minus the sum of chloride and bicarbonate, with a normal range of about 8 to 12 mmol/L depending on the laboratory.
Reading a biochemistry stem
Biochemistry stems follow a predictable shape: a patient, a laboratory finding and a request to identify the deficient step, the accumulating compound or the best next test. Four questions keep you on track.
- What is the organ pattern? Liver and spleen enlargement, brain, muscle, heart or bone each narrow the group of enzyme disorders.
- What is the age? A newborn who feeds poorly and has a strange odour points to an aminoacidopathy; a child with fasting hypoglycaemia and a big liver points to glycogen storage; an adult with a joint attack points to uric acid.
- What is the one abnormal laboratory value? Ammonia, lactate, uric acid, a specific amino acid or an abnormal electrophoresis band is usually the key.
- What would the management be? Diet, supplement, enzyme replacement or avoidance of a trigger. The stem sometimes asks for this directly.
| Can you say, in one sentence each... | Mark |
|---|---|
| Which vitamin deficiency causes each classic syndrome | red, amber or green |
| The enzyme, the compound that accumulates and the diet for PKU | red, amber or green |
| How to calculate and interpret an anion gap | red, amber or green |
| What PCR does and when it is used in diagnosis | red, amber or green |
Links to other domains
Biochemistry underlies physiology (acid-base), pathology (haemoglobinopathies, genetics), paediatrics (inborn errors, malnutrition) and medicine (diabetes, lipids).
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Frequently asked questions
How many biochemistry questions are in NRE Step I?
PM&DC's published blueprint table gives applied biochemistry 6 items, about 3% of the 200-question paper.
Do I need to memorise metabolic pathways?
Learn them as clinical pictures: the enzyme deficiency, the accumulating metabolite and the presenting features. PM&DC describes the items as aimed at higher cognition, not pathway recall.
Which biochemistry topics matter most?
Inborn errors, vitamin and mineral deficiencies, lipid and lipoprotein disorders, enzymes and clinical enzymology, haemoglobinopathies and acid-base chemistry. This is our reading of the syllabus, not a frequency list.
Is molecular biology included?
Yes. The syllabus lists DNA replication, PCR and genetic techniques.
How long should I spend on biochemistry?
Five focused sessions with questions are usually enough, plus weekly review of the vitamin table and inborn-error list.