FMGE Biochemistry Flashcards

24 sample cards from the Biochemistry deck

Sampled from the end of the deck, so these are different cards from the ones shown on the syllabus page.

1. What is the defect in alkaptonuria and in classic galactosemia?

   Alkaptonuria: homogentisate oxidase deficiency - black urine, ochronosis, arthritis. Classic galactosemia: galactose-1-phosphate uridyltransferase (GALT) deficiency - cataracts, hepatomegaly, intellectual disability.

2. What enzyme is deficient in maple syrup urine disease and what accumulates?

   Branched-chain alpha-ketoacid dehydrogenase. Branched-chain amino acids (leucine, isoleucine, valine) and their ketoacids accumulate, giving urine a sweet/maple-syrup odor and causing neurotoxicity.

3. Describe the key features of DNA replication and name the enzyme that synthesizes the leading and lagging strands.

   Replication is semiconservative, bidirectional, and 5'->3'. DNA polymerase III (prokaryotes) synthesizes both strands; the lagging strand is made in Okazaki fragments joined by DNA ligase.

4. What enzyme carries out transcription and what is the role of the promoter and the TATA box?

   RNA polymerase synthesizes RNA 5'->3' using a DNA template. The promoter is the binding/start site; the TATA box (eukaryotes, ~-25) positions RNA polymerase II for accurate initiation.

5. Explain the wobble hypothesis and the direction of translation.

   Wobble: the third codon base (3' end) can pair loosely with the tRNA anticodon, so one tRNA reads several codons - this accounts for codon degeneracy. mRNA is read 5'->3' and protein synthesized N- to C-terminus.

6. Describe the lac operon as a model of gene regulation.

   An inducible operon: in the absence of lactose, a repressor binds the operator and blocks transcription. Lactose (allolactose) inactivates the repressor (induction). Low glucose raises cAMP, which with CAP enhances transcription (positive control).

7. Define and give an example of a point mutation: silent, missense, and nonsense.

   Silent: base change with no amino acid change (degeneracy). Missense: change to a different amino acid (e.g. sickle cell, Glu->Val). Nonsense: change to a stop codon, producing a truncated protein.

8. Name a DNA repair mechanism and the disease caused by its defect.

   Nucleotide excision repair (removes UV-induced thymine dimers); its defect causes xeroderma pigmentosum. Mismatch repair defects cause hereditary nonpolyposis colorectal cancer (Lynch syndrome).

9. What are the steps of a PCR cycle and what enzyme makes it possible?

   Denaturation (~94-95C, strand separation), annealing (~50-65C, primer binding), and extension (~72C, DNA synthesis). The heat-stable Taq polymerase (from Thermus aquaticus) allows repeated cycling.

10. What are restriction endonucleases and how are recombinant DNA molecules formed?

    Restriction enzymes cut DNA at specific palindromic sequences, often leaving 'sticky ends.' Fragments with complementary sticky ends are joined by DNA ligase into a vector (plasmid) to form recombinant DNA.

11. What is a balanced diet and the recommended distribution of energy from macronutrients?

    A diet supplying all nutrients in adequate proportion. Typically ~50-60% energy from carbohydrates, 20-30% from fats, and 10-15% from proteins.

12. State the physiological caloric (Atwater) values of carbohydrate, protein, fat, and alcohol per gram.

    Carbohydrate ~4 kcal/g, protein ~4 kcal/g, fat ~9 kcal/g, and alcohol ~7 kcal/g.

13. What are free radicals and which enzymatic antioxidants neutralize them?

    Free radicals are reactive oxygen species with unpaired electrons (superoxide, hydroxyl, H2O2) causing oxidative damage. Enzymatic antioxidants: superoxide dismutase (SOD), catalase, and glutathione peroxidase (uses selenium).

14. Which liver function tests indicate hepatocellular damage versus cholestasis (obstruction)?

    Hepatocellular damage: raised ALT and AST (ALT more liver-specific). Cholestasis/obstruction: raised alkaline phosphatase (ALP), GGT, and conjugated bilirubin.

15. Which biochemical markers are used to assess renal function?

    Serum creatinine, blood urea (BUN), and calculated GFR/creatinine clearance. Cystatin C is a newer marker. Raised urea and creatinine indicate reduced renal function (azotemia).

16. Name the major plasma protein fractions seen on serum electrophoresis and the largest.

    Albumin (largest), alpha-1, alpha-2, beta, and gamma globulins (gamma contains immunoglobulins). Albumin is the most abundant and maintains oncotic pressure.

17. What electrophoresis pattern is seen in multiple myeloma versus chronic inflammation?

    Multiple myeloma: a sharp narrow 'M spike' in the gamma region (monoclonal gammopathy). Chronic inflammation: a broad polyclonal increase in the gamma region with raised alpha-2 (acute-phase proteins).

18. How do you interpret arterial blood gases for the four primary acid-base disorders?

    Metabolic acidosis: low pH, low HCO3-. Metabolic alkalosis: high pH, high HCO3-. Respiratory acidosis: low pH, high PCO2. Respiratory alkalosis: high pH, low PCO2. Compensation moves the other parameter in the same direction as pH-correction.

19. What is the anion gap and what does a high anion gap metabolic acidosis suggest?

    Anion gap = Na+ - (Cl- + HCO3-), normal ~8-12 mEq/L. High anion gap acidosis: causes by MUDPILES (Methanol, Uremia, DKA, Propylene glycol, Iron/INH, Lactic acidosis, Ethylene glycol, Salicylates).

20. Match these tumor markers to their associated cancers: AFP, CEA, CA-125, PSA, CA 19-9.

    AFP - hepatocellular carcinoma & germ cell tumors; CEA - colorectal cancer; CA-125 - ovarian cancer; PSA - prostate cancer; CA 19-9 - pancreatic cancer.

21. Name the hormone assays used to evaluate thyroid function and the typical pattern in primary hypothyroidism.

    TSH, free T4, and free T3. Primary hypothyroidism: high TSH with low free T4. Secondary (pituitary) hypothyroidism: low TSH with low free T4.

22. Describe calcium homeostasis: the roles of PTH, vitamin D, and calcitonin.

    PTH raises serum calcium (bone resorption, renal Ca reabsorption, activates vitamin D). Active vitamin D (calcitriol) increases intestinal Ca and phosphate absorption. Calcitonin lowers calcium (inhibits osteoclasts).

23. What are the consequences of iron and iodine deficiency, and which protein stores iron?

    Iron deficiency causes microcytic hypochromic anemia; iron is stored as ferritin and transported by transferrin. Iodine deficiency causes goiter and hypothyroidism (cretinism in infants).

24. State the functions of zinc, copper, and selenium as trace minerals.

    Zinc: cofactor for many enzymes (carbonic anhydrase, DNA polymerase); deficiency causes acrodermatitis enteropathica. Copper: cofactor for cytochrome oxidase, lysyl oxidase (deficient in Menkes; excess in Wilson). Selenium: glutathione peroxidase cofactor.

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