Pathogens & antibiotics formulas

Operons, nitrogen fixation, pathogens, antibiotics and viruses. 3 formulas for GATE BT General Biology, each with when to use it. Each is explained in the topic notes.

All 3 Pathogens & antibiotics formulas

NITROGENASE REACTION (CONVENTIONAL STOICHIOMETRY)

N_{2} + 8 H^{+} + 8 e^{-} + 16 ATP + 16 H_{2} O \to 2 NH_{3} + H_{2} + 16 ADP + 16 P_{i}

Convention: 2 ATP hydrolysed per electron transferred; 8 electrons per N₂ (6 to make 2 NH₃ and 2 for the obligatory H₂), so 16 ATP per N₂. In cells the cost is often higher because extra H₂ is made.

PLAQUE ASSAY TITER

Titer (PFU/mL) = \frac{number of plaques}{dilution \times volume plated (mL)}

Use a plate with a countable number of plaques (conventionally 30 to 300). The dilution is the fraction of the original stock in the plated sample (such as $1 0^{- 6}$ ).

MULTIPLICITY OF INFECTION (POISSON DISTRIBUTION)

P (k) = \frac{m ^{k} e ^{- m}}{k !}, P (0) = e^{- m}, fraction infected = 1 - e^{- m}

m is the multiplicity of infection (phage added per bacterium), assuming random adsorption. P(k) is the fraction of cells infected by exactly k phages.

Where this was asked: 2019 (2), 2020 (1), 2022 (1), 2023 (4), 2024 (2), 2026 (1). See the 11 previous-year questions on Pathogens & antibiotics. This shows what was asked, not what will be asked.

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Pathogens & antibiotics: the notes and 11 solved previous-year questions