MLT GlobeDOH exam preparation (Abu Dhabi) – page 20
700 practice MCQs for the DOH medical laboratory exam. Level: Basic to intermediate.
Thymidylate synthase needs a one-carbon donor derived from which vitamin?
N5,N10-Methylene-tetrahydrofolate supplies the methyl group that turns dUMP into dTMP. B12 deficiency affects this only indirectly by trapping folate as methyl-THF.
Pantothenic acid forms part of coenzyme A and of the acyl carrier protein used in:
Its 4′-phosphopantetheine arm is the acyl carrier of fatty acid synthase. Pyruvate carboxylase uses biotin, and glycolysis needs no CoA.
The Schilling test has been withdrawn. Which test is now used to show pernicious anaemia as the cause of B12 deficiency?
Intrinsic factor antibodies are highly specific for pernicious anaemia; parietal cell antibodies are more sensitive but less specific. Ferritin, electrophoresis and osmotic fragility investigate other anaemias.
Which human enzyme needs a vitamin B12 coenzyme?
Humans have two B12 enzymes: methylmalonyl-CoA mutase (adenosylcobalamin) and methionine synthase (methylcobalamin). Human ribonucleotide reductase uses iron and thioredoxin, not B12.
Lingual lipase, which starts fat digestion in the mouth, is secreted from where?
Lingual lipase comes from serous (von Ebner) glands on the dorsal tongue. Gastric lipase, a separate enzyme, is secreted by gastric chief cells.
During fasting, lipolysis releases glycerol from adipocytes. Where is most of this glycerol used?
Adipocytes have little glycerol kinase, so glycerol goes to the liver. There it is phosphorylated and used for gluconeogenesis.
Which enzyme links amino acid nitrogen to carbon metabolism by reversibly converting glutamate to alpha-ketoglutarate and NH4+?
Glutamate dehydrogenase uses NAD(P)+ to release free ammonia and form a TCA-cycle intermediate. Aminotransferases move amino groups but release no ammonia.
In the pyruvate dehydrogenase complex, which cofactor accepts the acetyl group and passes it to coenzyme A?
Lipoamide on E2 forms an acetyl-thioester and transfers the acetyl group to CoA. TPP carries a hydroxyethyl group earlier, and FAD and NAD+ reoxidise lipoamide.
Human mitochondrial DNA encodes only 13 proteins. Where are nearly all other mitochondrial proteins made?
Over 1000 mitochondrial proteins are nuclear-encoded and imported through TOM/TIM translocases. mtDNA encodes 13 respiratory chain subunits, 2 rRNAs and 22 tRNAs.
A neonate is well at birth, then feeds poorly, becomes lethargic and has urine smelling of burnt sugar by the end of the first week. What is the likely diagnosis?
BCKD deficiency causes branched-chain amino acids and alloisoleucine to build up within days of feeding. PKU and alkaptonuria do not cause an acute neonatal crisis.
How many carbon atoms does cholesterol have, the parent structure for bile acids and steroid hormones?
Cholesterol is C27H46O. Progestogens and corticosteroids are C21, androgens C19 and bile acids C24, all made by shortening the side chain.
Which fatty acid synthase activity joins the growing acyl chain to a malonyl group, releasing CO2?
The condensing enzyme (KS) joins acyl and malonyl units and releases CO2, which drives the reaction. The transacylases only load substrates onto ACP.
Which system is the current standard for classifying leukemias using morphology, immunophenotype and genetics together?
The WHO 5th edition integrates genetic, immunophenotypic and morphological data. FAB was morphology-only and is now historical; Rai stages CLL and Ann Arbor stages lymphoma.
A positive direct antiglobulin test indicates what?
The DAT detects in vivo sensitization of red cells, as in hemolytic disease of the newborn or autoimmune hemolysis. The indirect test detects serum antibodies binding in vitro.
Both vitamin B12 and folate deficiency cause megaloblastic anemia. Which feature points to B12 deficiency specifically?
B12 is needed for myelin maintenance, so neurological damage occurs only in B12 deficiency. Glossitis, macrocytosis and hypersegmentation occur in both.
Supravital staining of a G6PD-deficient patient's blood after an oxidant drug shows round inclusions at the membrane. What are they?
Oxidized hemoglobin precipitates as Heinz bodies, seen with supravital stains. Howell–Jolly bodies are DNA remnants; stippling is aggregated ribosomes.
Hydroxyurea, used in sickle cell disease and myeloproliferative neoplasms, acts mainly by inhibiting which enzyme?
Hydroxyurea blocks ribonucleotide reductase, preventing deoxyribonucleotide formation and DNA synthesis. It also raises HbF. Methotrexate inhibits dihydrofolate reductase.
Which condition would NOT typically raise the eosinophil count?
Acute bacterial infections and stress raise cortisol, which lowers eosinophils. Allergy, helminths and Hodgkin lymphoma are recognized causes of eosinophilia.
Which of these conditions is recognized as a cause of eosinophilia?
Hodgkin lymphoma cells release IL-5 and other cytokines, raising eosinophils. Corticosteroids and acute sepsis lower eosinophils; tuberculosis is not a typical cause.
A patient has anemia with spherocytes and raised bilirubin. Which test shows whether the hemolysis is antibody-mediated?
A positive DAT shows immunoglobulin or complement on red cells, confirming immune hemolysis. Osmotic fragility is raised in both hereditary and immune spherocytosis.