MCAT (Medical College Admission Test) Biological and Biochemical Foundations of Living Systems Flashcards

24 sample cards from the Biological and Biochemical Foundations of Living Systems deck

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

1. Why is DNA replication described as semiconservative?

   Each daughter double helix contains one original (parental) strand and one newly synthesized strand.

2. What is the function of DNA polymerase, primase, helicase, and ligase in replication?

   Helicase unwinds the helix; primase lays RNA primers; DNA polymerase adds nucleotides 5' to 3'; ligase joins Okazaki fragments on the lagging strand.

3. What is the difference between the leading and lagging strands?

   The leading strand is synthesized continuously toward the replication fork; the lagging strand is synthesized discontinuously in Okazaki fragments away from the fork.

4. Name two DNA repair mechanisms and what they correct.

   Mismatch repair fixes replication errors missed by proofreading; nucleotide excision repair removes bulky lesions like thymine dimers; base excision repair removes single damaged bases.

5. What are the three stages of transcription?

   Initiation (RNA polymerase binds the promoter), elongation (RNA synthesized 5' to 3' from the template strand), and termination (RNA released).

6. What three modifications convert eukaryotic pre-mRNA to mature mRNA?

   Addition of a 5' guanine cap, addition of a 3' poly-A tail, and splicing out of introns (keeping exons).

7. What is the role of tRNA and the codon-anticodon relationship in translation?

   tRNA carries a specific amino acid and has an anticodon that base-pairs with the complementary mRNA codon, ensuring the correct amino acid is added.

8. What are the start and stop codons of translation?

   Start codon: AUG (codes for methionine). Stop codons: UAA, UAG, UGA (signal termination, code for no amino acid).

9. How do the lac and trp operons differ in regulatory logic?

   The lac operon is inducible (turned ON by lactose/allolactose, a catabolic pathway); the trp operon is repressible (turned OFF when tryptophan is abundant, an anabolic pathway).

10. How do eukaryotes regulate gene expression through chromatin and epigenetics?

    Histone acetylation loosens chromatin and activates transcription; DNA methylation and histone deacetylation condense chromatin and silence genes.

11. State Mendel's laws of segregation and independent assortment.

    Segregation: the two alleles for a trait separate during gamete formation. Independent assortment: alleles of different genes assort independently (for unlinked genes).

12. What is the difference between incomplete dominance and codominance?

    Incomplete dominance: heterozygote shows a blended intermediate phenotype (red x white = pink). Codominance: both alleles are fully and simultaneously expressed (AB blood type).

13. How is recombination frequency used to map genes?

    Recombination frequency between two loci is proportional to the distance between them; 1% recombination = 1 map unit (centimorgan). Linked genes recombine less frequently.

14. What does PCR do and what are its three temperature steps?

    PCR amplifies a specific DNA sequence. Steps: denaturation (~95C, separates strands), annealing (~55C, primers bind), and extension (~72C, Taq polymerase synthesizes DNA).

15. What is the principle of gel electrophoresis?

    DNA/RNA/protein fragments are separated by size and charge in a gel under an electric field; negatively charged nucleic acids migrate toward the positive electrode, smaller fragments moving faster.

16. Compare Southern, Northern, and Western blots.

    Southern detects DNA, Northern detects RNA, Western detects protein (using antibodies).

17. List three structures found in eukaryotic but not prokaryotic cells.

    Membrane-bound nucleus, mitochondria, and other membrane-bound organelles (e.g., ER, Golgi, lysosomes).

18. What are the functions of the rough ER, smooth ER, and Golgi apparatus?

    Rough ER synthesizes/folds proteins (has ribosomes); smooth ER synthesizes lipids and detoxifies; Golgi modifies, sorts, and packages proteins for secretion.

19. What are the phases of the cell cycle and the key checkpoints?

    G1, S (DNA synthesis), G2 (collectively interphase), and M (mitosis). Checkpoints: G1/S (restriction point), G2/M, and the spindle (metaphase) checkpoint.

20. What is apoptosis and how does it differ from necrosis?

    Apoptosis is programmed, controlled cell death (cell shrinks, no inflammation) executed by caspases. Necrosis is uncontrolled death from injury, causing cell swelling and inflammation.

21. Compare lytic and lysogenic viral life cycles.

    Lytic: virus replicates immediately and lyses the host cell. Lysogenic: viral DNA integrates into the host genome as a provirus/prophage and replicates passively until induced into the lytic cycle.

22. How does an action potential propagate along a neuron?

    Depolarization opens voltage-gated Na+ channels (influx), then K+ channels open (efflux) to repolarize; the wave travels down the axon, jumping between nodes of Ranvier in myelinated neurons (saltatory conduction).

23. What is the difference between the systemic and pulmonary circulation, and which side of the heart drives each?

    Pulmonary circulation (right heart) sends deoxygenated blood to the lungs; systemic circulation (left heart) sends oxygenated blood to the body.

24. Trace the path of a nephron's filtrate and the main function of each segment.

    Glomerulus (filtration) to proximal tubule (bulk reabsorption) to loop of Henle (concentration gradient) to distal tubule (regulated Na+/K+) to collecting duct (water reabsorption via ADH).

What this deck covers

Biological and Biochemical Foundations of Living Systems flashcards FAQ