Pre-Clinical 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. List the main factors affecting enzyme activity.

   Substrate concentration, enzyme concentration, temperature, pH, and presence of activators or inhibitors (including cofactors).

2. How do temperature and pH affect enzyme activity?

   Activity rises with temperature up to an optimum, then falls sharply as the enzyme denatures. Each enzyme has an optimum pH (e.g., pepsin ~2, trypsin ~8); deviations reduce activity by altering ionization/structure.

3. Classify carbohydrates into their three main groups with examples.

   Monosaccharides (glucose, fructose), disaccharides (sucrose, lactose, maltose), and polysaccharides (starch, glycogen, cellulose).

4. What is the difference between glycolysis's location and its net ATP yield?

   Glycolysis occurs in the cytoplasm and converts glucose to 2 pyruvate, with a net gain of 2 ATP and 2 NADH per glucose molecule.

5. Write the overall net reaction of glycolysis.

   $$\ce{Glucose + 2 NAD^+ + 2 ADP + 2 P_i -> 2 Pyruvate + 2 NADH + 2 H^+ + 2 ATP + 2 H2O}$$

6. What is gluconeogenesis and where does it occur?

   Gluconeogenesis is the synthesis of glucose from non-carbohydrate precursors (lactate, glycerol, glucogenic amino acids); it occurs mainly in the liver (and kidney) cytoplasm and mitochondria.

7. How is glycolysis regulated, naming the key regulatory enzyme?

   Regulated at three irreversible steps; the main control point is phosphofructokinase-1 (PFK-1), which is activated by AMP and fructose-2,6-bisphosphate and inhibited by ATP and citrate.

8. What are the two hormones that reciprocally regulate blood glucose, and their effects?

   Insulin lowers blood glucose (promotes glucose uptake, glycogenesis, glycolysis); glucagon raises blood glucose (stimulates glycogenolysis and gluconeogenesis).

9. Classify lipids into their major categories.

   Simple lipids (fats/oils, waxes), compound lipids (phospholipids, glycolipids, lipoproteins), and derived lipids (fatty acids, steroids, cholesterol, ketone bodies).

10. Where does β-oxidation of fatty acids occur and what does each cycle produce?

    In the mitochondrial matrix; each round shortens the fatty acyl chain by 2 carbons and yields 1 acetyl-CoA, 1 FADH2, and 1 NADH.

11. What is the role of carnitine in fatty acid metabolism?

    Carnitine shuttles long-chain fatty acyl groups across the inner mitochondrial membrane (via the carnitine shuttle) so they can undergo β-oxidation in the matrix.

12. Name the three ketone bodies and the clinical condition of their excess.

    Acetoacetate, β-hydroxybutyrate, and acetone; their excess causes ketoacidosis, notably diabetic ketoacidosis.

13. What is the rate-limiting enzyme of cholesterol synthesis and its target by statins?

    HMG-CoA reductase; statins competitively inhibit it, lowering cholesterol synthesis.

14. Clinically, what does an elevated LDL versus HDL indicate for cardiovascular risk?

    High LDL ("bad" cholesterol) deposits cholesterol in arteries and raises atherosclerosis/CVD risk; high HDL ("good" cholesterol) removes cholesterol (reverse transport) and is protective.

15. What is the structure of DNA according to the Watson–Crick model?

    A right-handed antiparallel double helix of two polynucleotide strands, with a sugar-phosphate backbone outside and complementary base pairs (A–T, G–C) hydrogen-bonded inside; ~10 base pairs per turn.

16. State Chargaff's rules for base composition in DNA.

    In double-stranded DNA, the amount of adenine equals thymine ($A = T$) and guanine equals cytosine ($G = C$); thus purines equal pyrimidines ($A+G = T+C$).

17. How many hydrogen bonds form between A–T and G–C base pairs?

    Adenine–Thymine form 2 hydrogen bonds; Guanine–Cytosine form 3 hydrogen bonds (making G–C pairs more stable).

18. Compare the structural differences between DNA and RNA.

    DNA: deoxyribose sugar, thymine base, usually double-stranded, stable. RNA: ribose sugar (2'-OH), uracil instead of thymine, usually single-stranded, less stable.

19. Name the three main types of RNA and their functions.

    mRNA carries the genetic code from DNA to ribosomes; tRNA delivers amino acids matching codons; rRNA forms the structural and catalytic core of the ribosome.

20. Define the central dogma of molecular biology.

    The flow of genetic information: DNA is replicated and transcribed into RNA, which is translated into protein ($\ce{DNA -> RNA -> Protein}$).

21. What is the difference between transcription and translation?

    Transcription synthesizes RNA from a DNA template (in the nucleus, by RNA polymerase); translation synthesizes protein from an mRNA template (on ribosomes, using tRNA).

22. How is gene expression regulated in prokaryotes via the lac operon?

    The lac operon is transcribed only when lactose is present and glucose is low: lactose (allolactose) inactivates the repressor, and low glucose raises cAMP–CAP to activate transcription of lactose-metabolizing genes.

23. Name the four fat-soluble vitamins and one key function of each.

    Vitamin A (vision/epithelial health), Vitamin D (calcium/phosphate homeostasis and bone mineralization), Vitamin E (antioxidant), and Vitamin K (blood clotting factor synthesis).

24. What deficiency diseases result from lack of vitamins A, D, and K?

    Vitamin A deficiency causes night blindness/xerophthalmia; Vitamin D deficiency causes rickets in children and osteomalacia in adults; Vitamin K deficiency causes bleeding disorders (impaired clotting).

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