MLT GlobeDOH exam preparation (Abu Dhabi)
700 practice MCQs for the DOH medical laboratory exam. Level: Basic to intermediate.
Subject mix: Chemistry 17%, Hematology 16%, Bacteriology 14%, Blood Banking 12%, Immunology & Serology 10%, Laboratory Operations 7%, Parasitology 7%, Urinalysis & Body Fluids 7%, Virology 5%, Mycology 5%
A person receives a booster dose of tetanus toxoid. Compared with the first exposure, the antibody response is:
Memory B cells produce a secondary response with a shorter lag, higher titres, more IgG and higher affinity than the primary response.
Which patient group is at greatest risk of pyridoxine (vitamin B6) deficiency?
Alcohol's metabolite acetaldehyde speeds breakdown of pyridoxal phosphate, and poor diet adds to the deficit. Isoniazid therapy is another classic cause.
A gout patient is started on a drug that lowers serum urate by blocking xanthine oxidase. The drug is:
Allopurinol (via oxypurinol) inhibits xanthine oxidase, reducing uric acid production. Probenecid increases urate excretion; colchicine only suppresses inflammation.
Dicoumarol and warfarin act as anticoagulants by opposing which vitamin?
Coumarins block vitamin K epoxide reductase, preventing γ-carboxylation of factors II, VII, IX and X. Menadione is a synthetic vitamin K.
Electron micrographs of relaxed chromatin show a 'beads-on-a-string' appearance. What are the beads?
Each bead is a histone octamer wrapped with DNA; linker DNA forms the string between them (the 10-nm fibre).
As the replication fork moves, strain builds in the DNA ahead of it. Which enzymes relieve this supercoiling?
Topoisomerases (e.g., DNA gyrase) cut and reseal strands to remove positive supercoils. Helicase unwinds the helix, which creates the strain.
Active vitamin D (calcitriol) is produced by sequential hydroxylation in which organs?
Liver 25-hydroxylase forms calcidiol; renal 1α-hydroxylase converts it to 1,25-dihydroxycholecalciferol. Renal failure therefore causes calcitriol deficiency.
Lack of vitamin D produces soft, poorly mineralised bone. In children and adults this is called, respectively:
Deficient calcitriol reduces calcium and phosphate absorption, impairing mineralisation of osteoid: rickets before growth plates close, osteomalacia afterwards.
Which best describes vitamins?
Vitamins are organic compounds required in trace amounts, often as coenzyme precursors, that the body cannot make adequately. They supply no significant energy.
Which fatty acid belongs to the omega-3 family?
α-Linolenic acid (18:3) has its last double bond three carbons from the methyl end. Linoleic and arachidonic acids are ω-6; palmitic acid is saturated.
NSAIDs such as ibuprofen reduce prostaglandin synthesis by inhibiting:
NSAIDs block the cyclooxygenase activity of PGH synthase. Corticosteroids inhibit phospholipase A2 indirectly; zileuton targets 5-lipoxygenase.
Which of these proteins is a digestive enzyme released into pancreatic juice?
Pancreatic acinar cells secrete ribonuclease along with amylase, lipase and proteases. Myoglobin, cytochrome c and ferritin are intracellular oxygen-, electron- and iron-handling proteins, not secreted enzymes.
During differential centrifugation of a tissue homogenate, which component sediments first at the lowest speed?
Nuclei are the largest, densest particles and pellet at about 600–1,000 g. Mitochondria need higher speed, while microsomes and ribosomes require ultracentrifugation.
In aqueous solution, D-glucose exists predominantly as:
Over 99% of glucose in solution is cyclic glucopyranose (α and β anomers). The open-chain aldehyde is a tiny fraction, and the furanose form is minor for glucose.
In a red blood cell, which lacks mitochondria, what is the net ATP yield from converting one glucose to lactate?
Anaerobic glycolysis produces 4 ATP but uses 2, giving a net 2 ATP per glucose. About 30 ATP requires complete oxidation through mitochondria.
Two cysteine residues join to form cystine through oxidation of their:
Oxidation links the –SH groups of two cysteines into a disulfide (–S–S–) bond. Cysteine has no hydroxyl side chain, and amino/carboxyl groups form peptide bonds.
At a plasma pH of 7.40, the ratio of bicarbonate to carbonic acid is approximately:
From Henderson–Hasselbalch, 7.40 = 6.1 + log(HCO3−/H2CO3), so the ratio is about 20:1. Reversing it (1:20) would describe severe acidosis.
In the collagen triple helix, which amino acid occupies every third position?
The Gly-X-Y repeat is needed because only glycine's tiny side chain fits inside the tight triple helix. Proline and hydroxyproline are common in X and Y positions but not every third residue.
The Michaelis constant (Km) of an enzyme is best defined as the:
Km is the [S] at which v = ½Vmax; it has concentration units, not velocity units. It is independent of enzyme amount but changes with pH and temperature.
Which iron-storage protein releases iron most readily and is measured in serum to assess body iron stores?
Ferritin holds readily mobilised iron, and serum ferritin reflects stores. Hemosiderin is an insoluble, slowly released aggregate; transferrin transports iron rather than storing it.