GATE Biotechnology General Biology Flashcards

24 sample cards from the General Biology deck

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

1. Contrast allosteric regulation with covalent modification of enzyme activity.

   Allosteric: reversible binding of effectors at a site distinct from the active site shifts conformation/activity (often cooperative, sigmoidal kinetics). Covalent modification: reversible attachment of groups (e.g., phosphorylation) switches activity on/off.

2. Write the Michaelis–Menten equation and define each term.

   $$v_0 = \frac{V_{max}[S]}{K_m + [S]}$$ where $v_0$ is initial velocity, $V_{max}$ is maximum velocity, $[S]$ is substrate concentration, and $K_m$ is the substrate concentration at half $V_{max}$.

3. What does the Michaelis constant $K_m$ indicate about an enzyme?

   $K_m$ equals the $[S]$ at which $v_0 = \tfrac{1}{2}V_{max}$; a low $K_m$ indicates high apparent affinity for substrate, a high $K_m$ indicates low affinity.

4. Write the Lineweaver–Burk (double-reciprocal) equation.

   $$\frac{1}{v_0} = \frac{K_m}{V_{max}}\cdot\frac{1}{[S]} + \frac{1}{V_{max}}$$ giving a straight line with slope $K_m/V_{max}$, y-intercept $1/V_{max}$, and x-intercept $-1/K_m$.

5. Define the catalytic efficiency of an enzyme and its expression.

   Catalytic efficiency is $\dfrac{k_{cat}}{K_m}$, where $k_{cat}=V_{max}/[E]_T$ is the turnover number; the diffusion-limited upper bound is about $10^{8}$–$10^{9}\ \text{M}^{-1}\text{s}^{-1}$.

6. How does a competitive inhibitor affect $K_m$ and $V_{max}$?

   It increases the apparent $K_m$ but leaves $V_{max}$ unchanged, because the inhibitor competes at the active site and can be overcome by high $[S]$.

7. How does a pure non-competitive inhibitor affect $K_m$ and $V_{max}$?

   $V_{max}$ decreases while $K_m$ stays unchanged; the inhibitor binds equally to E and ES at an allosteric site and cannot be overcome by adding substrate.

8. How does an uncompetitive inhibitor affect $K_m$ and $V_{max}$?

   Both $K_m$ and $V_{max}$ decrease (their ratio stays constant); the inhibitor binds only to the enzyme–substrate (ES) complex, giving parallel lines on a Lineweaver–Burk plot.

9. On a Lineweaver–Burk plot, how do you distinguish competitive, non-competitive, and uncompetitive inhibition?

   Competitive: lines intersect on the y-axis (same $1/V_{max}$). Non-competitive: lines intersect on the x-axis (same $-1/K_m$). Uncompetitive: parallel lines (same slope).

10. State the basis of the Gram stain and what differentiates Gram-positive from Gram-negative bacteria.

    Gram-positive cells have a thick peptidoglycan layer that retains the crystal violet–iodine complex (stain purple); Gram-negative cells have thin peptidoglycan plus an outer membrane, lose the dye on decolorization, and counterstain pink with safranin.

11. Which gene/molecule is used as the standard molecular marker for bacterial classification and phylogeny?

    The $16S$ ribosomal RNA gene, because it is universal, has conserved and variable regions, and is rarely subject to horizontal transfer.

12. Distinguish the three domains of life proposed by Carl Woese.

    Bacteria, Archaea, and Eukarya — defined chiefly by rRNA sequence differences; Archaea share some molecular features with eukaryotes (e.g., RNA polymerase) despite a prokaryotic cell plan.

13. Define a microbial extremophile and give three examples by habitat.

    An extremophile thrives in extreme conditions: thermophiles/hyperthermophiles (high temperature), halophiles (high salt), acidophiles/alkaliphiles (extreme pH), barophiles (high pressure), psychrophiles (cold).

14. Define mutualism, commensalism, parasitism, and amensalism in microbial interactions.

    Mutualism: both partners benefit (+/+). Commensalism: one benefits, the other unaffected (+/0). Parasitism: one benefits at the other's expense (+/−). Amensalism: one is harmed, the other unaffected (−/0).

15. What are syntrophy and quorum sensing in microbial communities?

    Syntrophy: metabolic cooperation where one organism's product is another's substrate (e.g., interspecies $\ce{H2}$ transfer). Quorum sensing: cell-density-dependent gene regulation via diffusible autoinducer signals.

16. What are the essential structural components of a virus, and what defines an enveloped virus?

    A nucleic acid genome (DNA or RNA) enclosed in a protein capsid (made of capsomeres); an enveloped virus additionally has a host-derived lipid membrane with viral glycoprotein spikes.

17. On what two main criteria does the Baltimore classification group viruses?

    On the nature of the viral genome (dsDNA, ssDNA, dsRNA, +ssRNA, −ssRNA, RNA-RT, DNA-RT) and the pathway used to produce mRNA; it defines seven classes (Groups I–VII).

18. Differentiate the lytic and lysogenic cycles of a bacteriophage.

    Lytic: phage replicates immediately, lyses the host, and releases progeny. Lysogenic: phage DNA integrates as a prophage and is replicated passively with the host genome until induced into the lytic cycle.

19. What is the principle of the streak-plate method and pour-plate method in microbiology?

    Both isolate pure colonies: the streak plate dilutes cells mechanically across an agar surface so single cells form separate colonies; the pour plate mixes serially diluted sample with molten agar so colonies grow within and on the medium (also enabling counts).

20. Differentiate selective and differential media with an example each.

    Selective media suppress unwanted organisms and favor target growth (e.g., MacConkey inhibits Gram-positives). Differential media distinguish organisms by colony appearance via indicators (e.g., EMB or blood agar showing hemolysis).

21. Name the four phases of a bacterial batch growth curve.

    Lag phase (adaptation, no division), log/exponential phase (maximal balanced growth), stationary phase (growth rate = death rate, nutrient depletion), and death/decline phase.

22. Write the equation for exponential bacterial growth in terms of number and generation time.

    $$N = N_0 \times 2^{\,n}, \quad n = \frac{t}{g}$$ where $N_0$ is initial cell number, $n$ is the number of generations, $t$ is elapsed time, and $g$ is the generation (doubling) time.

23. Classify microbes by their carbon and energy sources (the four nutritional types).

    Photoautotroph (light energy, $\ce{CO2}$ carbon), photoheterotroph (light energy, organic carbon), chemoautotroph/chemolithotroph (chemical energy, $\ce{CO2}$ carbon), and chemoheterotroph (chemical energy, organic carbon).

24. What is biological nitrogen fixation, which enzyme catalyzes it, and why is it oxygen-sensitive?

    It is the reduction of atmospheric $\ce{N2}$ to ammonia by the nitrogenase enzyme complex: $$\ce{N2 + 8H+ + 8e- + 16ATP -> 2NH3 + H2 + 16ADP + 16Pi}$$ Nitrogenase is irreversibly inactivated by $\ce{O2}$, so fixers use protective strategies (e.g., leghemoglobin, heterocysts).

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