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FCPS Part 1 Biochemistry and Genetics MCQs
Biochemistry and genetics questions test metabolic pathways and their enzyme defects, vitamins, lipid and protein metabolism, inheritance patterns, chromosomal disorders and molecular techniques.
Below are 5 free single-best-answer questions drawn from the most frequently examined biochemistry and genetics concepts, each with the answer and a rationale for every option. The full bank has 194 biochemistry and genetics concepts, each asked several different ways.
Free biochemistry and genetics questions
Question 1
Intellectual disability, elongated face, big ears, enlarged testes in a boy:
- A. Turner syndrome
- B. Klinefelter syndrome
- C. Williams syndrome
- D. Prader-Willi syndrome
- E. Fragile X syndrome
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Answer: E. Fragile X syndrome
A CGG expansion in FMR1 above 200 repeats causes hypermethylation and silencing, so FMRP is lost. The result is intellectual disability with a long face, large jaw and ears, and macro-orchidism.
Why not the others: Klinefelter syndrome: small testes, tall stature. Prader-Willi syndrome: paternal 15q deletion, hyperphagia. Williams syndrome: elfin face, supravalvular aortic stenosis. Turner syndrome: 45,XO, short stature.
High-yield: Fragile X = CGG repeat in FMR1, giant gonads, long face.
Question 2
Macrocytic anaemia with distal paraesthesia in a patient taking metformin for years suggests lack of:
- A. Folic acid
- B. Vitamin B1
- C. Vitamin B12
- D. Iron
- E. Vitamin B6
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Answer: C. Vitamin B12
B12 binds intrinsic factor and is absorbed in the terminal ileum. It is a cofactor for methionine synthase and methylmalonyl-CoA mutase, so deficiency causes megaloblastic change and myelin damage.
Why not the others: Folic acid: macrocytosis without neurology. Iron: microcytic anaemia. Vitamin B6: sideroblastic anaemia, neuropathy. Vitamin B1: beriberi and Wernicke encephalopathy.
High-yield: Macrocytic anaemia + neurology = B12; without neurology = folate.
Question 3
Defective hepatic enzyme in classic PKU:
- A. Tyrosinase
- B. Phenylalanine hydroxylase
- C. Galactose-1-phosphate uridyltransferase
- D. Homogentisate oxidase
- E. Branched-chain alpha-ketoacid dehydrogenase
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Answer: B. Phenylalanine hydroxylase
Phenylalanine hydroxylase converts phenylalanine to tyrosine using tetrahydrobiopterin. Deficiency lets phenylalanine accumulate, impairs melanin and neurotransmitter synthesis, and makes tyrosine essential.
Why not the others: Tyrosinase: melanin synthesis, albinism when absent. Homogentisate oxidase: alkaptonuria. Branched-chain alpha-ketoacid dehydrogenase: maple syrup urine disease. Galactose-1-phosphate uridyltransferase: galactosaemia. Tyrosine hydroxylase: catecholamine synthesis.
High-yield: PKU = phenylalanine hydroxylase deficiency; treat with low-phenylalanine diet and avoid aspartame.
Question 4
Single-base change behind HbS:
- A. Guanine to adenine
- B. Cytosine to guanine
- C. Adenine to thymine
- D. Thymine to adenine
- E. Adenine to guanine
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Answer: C. Adenine to thymine
GAG (glutamate) becomes GTG (valine): adenine is replaced by thymine, a transversion causing a missense mutation. HbS polymerises when deoxygenated.
Why not the others: G→A and C→T are transitions, the commonest point mutations generally but not in HbS. T→A describes the template strand. A→G would not create valine.
High-yield: HbS: Glu6Val, GAG→GTG, A→T transversion, missense.
Question 5
Lipoprotein with the highest proportion of cholesterol by composition:
- A. VLDL
- B. IDL
- C. LDL
- D. Chylomicrons
- E. HDL
Show answer
Answer: C. LDL
LDL forms from IDL, is the most cholesterol-rich lipoprotein, and delivers cholesterol to cells through LDL receptors. When receptors are defective, LDL accumulates in plasma.
Why not the others: VLDL: carries hepatic triglyceride. Chylomicrons: dietary triglyceride from the gut. HDL: reverse cholesterol transport. IDL: transient intermediate between VLDL and LDL. Free fatty acids on albumin: no cholesterol core.
High-yield: Highest cholesterol = LDL; highest triglyceride = chylomicrons; reverse transport = HDL.
Keep going with biochemistry and genetics
Anaesgen brings every concept back on a spaced-repetition schedule timed to your exam date, as a different question each time, with full mock papers for Paper 1 and 2.
Get full access Try the 5 sample questionsHigh-yield biochemistry and genetics one-liners
The most-tested biochemistry and genetics concepts, as a clue and the answer it points to:
- Long face, large testes, CGG repeat in FMR1 → fragile X syndrome.
- Metformin, vegan, ileal resection, gastrectomy with neuropathy → vitamin B12.
- PKU, musty odour, phenylalanine to tyrosine, BH4 → phenylalanine hydroxylase.
- HbS: GAG→GTG, A→T transversion, Glu6Val.
- Highest cholesterol, liver to tissues, familial hypercholesterolaemia → LDL.
- Dermatitis, diarrhoea, dementia, maize, Hartnup, carcinoid → niacin.
- Streak ovaries, high FSH, lymphoedema, coarctation, horseshoe kidney → 45,XO.
- Adipose store, fatty liver droplets, chylomicrons → triglycerides.
- AB blood group, both alleles shown → codominance.
- Fasting past glycogen stores, lactate/alanine/glycerol, metformin target → gluconeogenesis.
- Non-essential, PKU, catecholamines, melanin, thyroxine → tyrosine.
- Collagen hydroxylation, iron reduction, perifollicular bleeding → vitamin C.
- Abdominal pain, neuropsychiatric, port-wine urine, raised PBG → acute intermittent porphyria.
- Gut dietary fat, milky post-meal plasma, low-fat diet → chylomicrons.
- Transamination donor and collector, fast pain afferent transmitter → glutamate.
- AD parent × unaffected, EDV 2× ESV → 50%.
- Li-Fraumeni, guardian of genome, G1 arrest, HPV E6 → p53.
- Low AFP with high hCG, flat facies, palmar crease → trisomy 21.
- Brushfield spots, AVSD, hypotonia → trisomy 21.
- Night blindness, Bitot spots, xerophthalmia → vitamin A.
Other FCPS Part 1 subjects
AnatomyPharmacologyPathologyCardiovascularNeurophysiologyMicrobiologyHaematologyGeneral PhysiologyImmunologyEndocrineRespiratoryEmbryologyObstetrics & GynaeRenal & Acid-BaseHistologyGI & LiverPhysicsBiostatistics
New to the exam? Read the FCPS Part 1 exam guide: dates, format and a 12-week study plan.