MLT GlobeMOH exam preparation (UAE) – page 3
700 practice MCQs for the MOH medical laboratory exam. Level: Basic to intermediate.
Acetyl-CoA carboxylase makes malonyl-CoA, the first committed step of fatty acid synthesis. Which cofactor does it need?
Like other ATP-dependent carboxylases, acetyl-CoA carboxylase carries CO2 on biotin. Acyl carrier protein is used later, by fatty acid synthase.
A serum amylase method measures breakdown of a polysaccharide substrate. Which natural substrate does amylase hydrolyse?
Alpha-amylase cleaves alpha-1,4 glycosidic bonds in starch and glycogen. Sucrose and lactose are disaccharides, and the beta bonds in cellulose are not attacked.
After glycogen phosphorylase releases glucose-1-phosphate, which enzyme converts it to glucose-6-phosphate?
Phosphoglucomutase moves the phosphate from C-1 to C-6. Phosphoglucose isomerase converts glucose-6-phosphate to fructose-6-phosphate.
An enzyme is produced at a steady level whatever the growth conditions, and no inducer is needed. What is it called?
Constitutive enzymes are expressed continuously, usually for housekeeping. Inducible enzymes such as beta-galactosidase need an inducer.
Trypsinogen is secreted inactive and later cleaved to trypsin. What is this kind of precursor called?
A zymogen is an inactive enzyme precursor activated by limited proteolysis. An apoenzyme is the protein part that lacks its cofactor.
Which group of eicosanoids comes from arachidonic acid by the lipoxygenase pathway?
5-Lipoxygenase converts arachidonic acid to leukotrienes. Prostaglandins, thromboxanes and prostacyclin come from the cyclooxygenase pathway.
Pregnant women are warned against high-dose supplements of which vitamin because it is teratogenic?
Excess preformed vitamin A and retinoids such as isotretinoin cause craniofacial, cardiac and CNS defects. Folic acid is recommended in pregnancy to prevent neural tube defects.
Periconceptional supplements are advised to lower the risk of spina bifida and anencephaly. Which vitamin?
Folate is needed for nucleotide synthesis during neural tube closure, and folic acid supplements reduce neural tube defects. Raised maternal serum AFP is a screening marker for these defects.
A toddler has bowed legs, widened wrists, low phosphate and raised alkaline phosphatase. Which vitamin is deficient?
Rickets is poor mineralisation of growing bone, usually from vitamin D deficiency. Osteoblast activity raises ALP, and secondary hyperparathyroidism lowers phosphate.
Creatinine clearance is used clinically to estimate which kidney function?
Creatinine is freely filtered and only slightly secreted, so its clearance approximates GFR. Renal plasma flow is estimated with PAH clearance.
Low-dose aspirin prevents arterial thrombosis because it irreversibly inhibits which enzyme in platelets?
Aspirin acetylates a serine in COX-1, blocking thromboxane A2 for the life of the platelet (7–10 days). This is why aspirin affects platelet function assays.
Which statement about reticulocytes in a healthy adult is FALSE?
Normal reticulocytes are roughly 0.5–2.5% of red cells; 10% would indicate marked marrow response. They lack a nucleus but retain RNA, visible with supravital stains.
A normal mature red cell measures roughly how much across on a blood film?
Normal erythrocytes average about 7.2–7.5 µm in diameter, similar to the nucleus of a small lymphocyte, which is a handy size reference on films.
Which leukocyte is the most numerous in adult blood and contains primary, secondary and tertiary granules?
Neutrophils make up about 40–75% of leukocytes and carry azurophilic (primary), specific (secondary) and gelatinase (tertiary) granules. Lymphocytes are agranular.
A synovial fluid is examined for monosodium urate crystals. Which microscope setup is needed to show their birefringence?
Birefringent crystals rotate plane-polarized light; a polarizer, analyzer and red compensator reveal this and distinguish urate (negative) from calcium pyrophosphate (positive) crystals.
Which range is typical for the red cell count of a healthy adult woman?
Adult female RBC counts are usually around 4.0–5.2 × 10^12/L, slightly lower than men. Laboratories should use locally validated intervals.
After antigen stimulation, B lymphocytes differentiate into which cell that secretes large amounts of antibody?
Activated B cells become plasma cells, with abundant rough endoplasmic reticulum for immunoglobulin production. Some form memory B cells; T cells do not secrete antibody.
Which finding defines neutropenia?
Neutropenia is judged on the absolute neutrophil count (total WBC × neutrophil fraction), commonly below 1.5 × 10^9/L in adults; total WBC may be low for other reasons.
Which protein holds the readily mobilized storage iron of the body and is measured in serum to assess iron stores?
Ferritin is the soluble, readily available iron store and its serum level mirrors body stores. Hemosiderin is an insoluble, slowly released form; transferrin transports iron.
For a manual leukocyte count, 20 µL of blood is added to 380 µL of diluting fluid. What dilution factor is used in the calculation?
20 µL in a final volume of 400 µL gives a 1:20 dilution, the standard for manual WBC counts. A 1:200 dilution is used for manual RBC counts.