PGIMER Entrance 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. Classify amino acids as glucogenic, ketogenic, or both, with examples.

   Purely ketogenic: Leucine and Lysine. Both glucogenic and ketogenic: Ile, Phe, Trp, Tyr, Thr. The rest are glucogenic.

2. What is the enzyme defect and accumulated substance in phenylketonuria (PKU)?

   Deficiency of phenylalanine hydroxylase (or BH4 cofactor); phenylalanine accumulates and is converted to phenylketones, causing intellectual disability if untreated.

3. What enzyme deficiency causes alkaptonuria, and what is its hallmark sign?

   Homogentisate oxidase deficiency; homogentisic acid accumulates, causing dark urine on standing and ochronosis (dark connective tissue/cartilage).

4. What enzyme deficiency causes maple syrup urine disease (MSUD)?

   Deficiency of branched-chain alpha-ketoacid dehydrogenase, causing accumulation of branched-chain amino acids (Leu, Ile, Val) and their keto-acids; urine smells like maple syrup.

5. Distinguish leading and lagging strand synthesis in DNA replication.

   The leading strand is synthesized continuously 5'→3' toward the replication fork; the lagging strand is synthesized discontinuously as Okazaki fragments away from the fork, later joined by DNA ligase.

6. What are the main enzymes of DNA replication and their functions?

   Helicase (unwinds DNA), Primase (RNA primers), DNA polymerase (synthesizes 5'→3'), Topoisomerase/gyrase (relieves supercoiling), DNA ligase (seals nicks), Single-strand binding proteins (stabilize).

7. Name the three RNA polymerases in eukaryotes and what each transcribes.

   RNA Pol I → rRNA; RNA Pol II → mRNA (and most snRNA); RNA Pol III → tRNA and 5S rRNA.

8. What are the key post-transcriptional modifications of eukaryotic mRNA?

   5' capping (7-methylguanosine), 3' polyadenylation (poly-A tail), and splicing (removal of introns, joining of exons).

9. Describe the role of the genetic code's properties: degeneracy and wobble.

   Degeneracy: multiple codons encode the same amino acid (64 codons, 20 amino acids). Wobble: the third codon base can pair flexibly with the tRNA anticodon, allowing one tRNA to read multiple codons.

10. What are the start and stop codons in translation?

    Start codon: AUG (methionine). Stop codons: UAA, UAG, UGA (no corresponding tRNA; recognized by release factors).

11. Explain the lac operon's regulation in E. coli.

    It is an inducible operon; in the absence of lactose, a repressor binds the operator blocking transcription. Lactose (allolactose) inactivates the repressor (induction). Low glucose raises cAMP, which with CAP enhances transcription (positive control).

12. Classify gene mutations: silent, missense, nonsense, and frameshift.

    Silent: no amino acid change. Missense: one amino acid changed. Nonsense: codon changed to a stop codon (truncated protein). Frameshift: insertion/deletion not a multiple of 3, altering the reading frame.

13. Define transition vs transversion point mutations.

    Transition: substitution of a purine for a purine or pyrimidine for a pyrimidine (A↔G, C↔T). Transversion: substitution of a purine for a pyrimidine or vice versa.

14. What are the three steps of each PCR cycle and their approximate temperatures?

    Denaturation (~94-95°C, separates strands), Annealing (~50-65°C, primers bind), and Extension (~72°C, Taq polymerase synthesizes new strands).

15. Match each blotting technique to the molecule it detects: Southern, Northern, Western.

    Southern blot → DNA; Northern blot → RNA; Western blot → protein (detected with antibodies).

16. What are restriction endonucleases and their role in recombinant DNA technology?

    Enzymes that cut DNA at specific palindromic recognition sequences, often producing 'sticky ends'; used to cut DNA and vectors for cloning, with DNA ligase joining fragments into recombinant DNA.

17. List the fat-soluble vitamins and a key deficiency of each.

    Vitamin A (night blindness/xerophthalmia), Vitamin D (rickets/osteomalacia), Vitamin E (hemolytic anemia/neuropathy), Vitamin K (bleeding/impaired coagulation).

18. What deficiencies result from lack of vitamin C, niacin (B3), and thiamine (B1)?

    Vitamin C: scurvy (impaired collagen, bleeding gums). Niacin: pellagra (dermatitis, diarrhea, dementia). Thiamine: beriberi and Wernicke-Korsakoff syndrome.

19. What is the role of vitamin B12 and folate, and what deficiency do they share?

    Both are needed for DNA synthesis (one-carbon metabolism); deficiency of either causes megaloblastic anemia. B12 deficiency additionally causes neurological damage (subacute combined degeneration).

20. Name key functions and deficiency signs of iron, iodine, and zinc.

    Iron: hemoglobin/oxygen transport (deficiency → microcytic anemia). Iodine: thyroid hormone synthesis (deficiency → goiter/hypothyroidism). Zinc: cofactor for many enzymes (deficiency → poor wound healing, dermatitis, hypogeusia).

21. What are reactive oxygen species (ROS), and name three major examples.

    Highly reactive oxygen-containing molecules that damage lipids, proteins, and DNA; examples: superoxide anion (O2·-), hydrogen peroxide (H2O2), and hydroxyl radical (·OH).

22. Name the three major enzymatic antioxidant defenses and the reactions they catalyze.

    Superoxide dismutase (SOD): converts O2·- to H2O2; Catalase: converts H2O2 to H2O + O2; Glutathione peroxidase (selenium-dependent): reduces H2O2 and lipid peroxides using glutathione.

23. Name important non-enzymatic antioxidants.

    Vitamin C (ascorbate), Vitamin E (tocopherol, lipid-phase), beta-carotene, glutathione (GSH), and uric acid.

24. What is the Warburg effect in cell metabolism?

    The tendency of cancer cells to preferentially use aerobic glycolysis (converting glucose to lactate even with oxygen present) rather than oxidative phosphorylation.

What this deck covers

Biochemistry flashcards FAQ