MLT GlobeDOH exam preparation (Abu Dhabi) – page 2
700 practice MCQs for the DOH medical laboratory exam. Level: Basic to intermediate.
Which vitamin, after hydroxylation in liver and kidney, stimulates intestinal calcium absorption?
Cholecalciferol becomes 1,25-dihydroxyvitamin D, which induces calcium-binding transport proteins in enterocytes. Vitamin K carboxylates bone and clotting proteins but does not drive absorption.
A man living mainly on maize develops a photosensitive skin rash, diarrhoea and confusion. Deficiency of which vitamin is most likely?
Dermatitis, diarrhoea and dementia define pellagra, caused by niacin deficiency; maize niacin is poorly available and low in tryptophan. Thiamine deficiency causes beriberi and Wernicke encephalopathy without rash.
Compared with the primary response, a secondary antibody response to a protein antigen is characterised by:
Memory B and T cells give a rapid, larger response dominated by class-switched, affinity-matured IgG. Such switching and maturation require T-cell help; IgM predominance is typical of a primary response.
Which bilirubin fraction gives a direct van den Bergh reaction and is the main pigment excreted in bile?
Hepatic UGT1A1 conjugates bilirubin with glucuronic acid; this water-soluble form reacts directly with diazo reagent and enters bile. Unconjugated bilirubin needs an accelerator; urobilinogen forms in the gut.
Which sugar gives a negative Benedict's test because it has no free anomeric carbon?
In sucrose, the glycosidic bond joins the anomeric carbons of glucose and fructose, so it cannot reduce Cu2+. Lactose and maltose keep one free anomeric carbon and are reducing.
Under current ADA criteria, which fasting plasma glucose range is considered normal in an adult?
Normal fasting glucose is below 100 mg/dL (5.6 mmol/L). 100–125 mg/dL is impaired fasting glucose, ≥126 mg/dL on repeat testing indicates diabetes, and values below 70 suggest hypoglycaemia.
Which animal-derived food is essentially free of cholesterol?
Egg cholesterol is concentrated in the yolk; albumen is almost pure protein and water. Milk and fish, being animal tissues or secretions, contain cholesterol.
The enzyme complexes of the respiratory electron transport chain are located in the:
Complexes I–IV and ATP synthase are embedded in the folded inner membrane (cristae). The matrix holds Krebs cycle and β-oxidation enzymes; the outer membrane is porous.
Glutelins, plant storage proteins such as glutenin, are found mainly in:
Glutelins and prolamins are the main storage proteins of wheat, rice and other cereals and form gluten. Milk is rich in caseins, eggs in albumins.
In mammalian cells, most ribosomal RNA is transcribed in the:
RNA polymerase I transcribes rRNA genes in the nucleolus, where subunits are assembled before export. Ribosomes use rRNA but do not make it.
Which laboratory marker is now preferred for diagnosing acute myocardial infarction?
The universal definition of MI relies on a rise and/or fall of cardiac troponin, preferably high-sensitivity assays. CK-MB is less specific; AST and LDH are obsolete for this purpose.
Mammalian cell lines, including transformed cells, are usually cultured at:
Human and other mammalian cells grow best at body temperature, usually with 5% CO2. Lower temperatures slow growth; 42 °C causes heat stress.
Eggs supply many vitamins but contain virtually none of which water-soluble vitamin?
Eggs provide riboflavin, B12 and some thiamine, but no meaningful vitamin C, which comes mainly from fruit and vegetables.
Endemic goitre in inland mountain regions is caused mainly by dietary deficiency of:
Without iodine the thyroid cannot make enough hormone; rising TSH enlarges the gland. Iodised salt prevents this. Copper metabolism relates to Wilson disease, not goitre.
A blood film shows macro-ovalocytes and hypersegmented neutrophils, with low serum folate. The anaemia is:
Folate deficiency impairs DNA synthesis, giving large red cells with immature nuclei and hypersegmented neutrophils. Microcytic hypochromic anaemia points to iron deficiency.
Adjacent strands of a β-pleated sheet are held together by:
Backbone hydrogen bonds link neighbouring strands, whether parallel or antiparallel. Disulfide bridges can cross-link chains but do not define the sheet; glycosidic bonds join sugars.
Which glycolytic enzyme is the main control point, allosterically inhibited by high ATP and citrate?
PFK-1 catalyses the committed step and is inhibited when ATP and citrate signal energy abundance; AMP and fructose-2,6-bisphosphate activate it. Hexokinase is inhibited by its product glucose-6-phosphate.
Ninhydrin produces a purple colour with release of CO2 when it reacts with:
Ninhydrin oxidatively deaminates and decarboxylates free α-amino acids, forming Ruhemann's purple. Peptide bonds are detected by the biuret reaction instead.
Transamination reactions catalysed by ALT and AST require which coenzyme?
PLP (from vitamin B6) accepts the amino group, forming pyridoxamine phosphate, then passes it to the keto acid. Biotin serves carboxylases; CoA carries acyl groups.
Coenzyme A carries acetyl groups into the citric acid cycle. Which B vitamin forms part of its structure?
Coenzyme A is built from pantothenic acid, ATP and cysteamine. Biotin is the carboxylation cofactor, not part of CoA.