Topic: Key Biochemical Reactions and Equations in BIO-02

1. Lactic Acid Fermentation (Lactobacillus)

$C_{6}H_{12}O_{6}$ → 2 $CH_{3}CHOHCOOH$
Glucose → 2 Lactic Acid
[No $CO_{2}$ produced — no gas in curd]

2. Alcoholic Fermentation (Saccharomyces cerevisiae)

$C_{6}H_{12}O_{6}$ → 2 $C_{2}H_{5}OH$ + 2 $CO_{2}$
Glucose → 2 Ethanol + 2 Carbon dioxide
[$CO_{2}$ causes bread to rise; ethanol is the alcohol in wine/beer]

3. Propionate Fermentation (Propionibacterium shermanii)

3 $CH_{3}CHOHCOOH$ → 2 $CH_{3}CH_{2}COOH$ + $CH_{3}COOH$ + $CO_{2}$ + $H_{2}O$
3 Lactic acid → 2 Propionic acid + Acetic acid + $CO_{2}$
[$CO_{2}$ trapped in cheese = Swiss cheese holes]

4. Acetic Acid Fermentation (Acetobacter aceti)

$CH_{3}C$$H_{2}O$H + $O_{2}$ → $CH_{3}COOH$ + $H_{2}O$
Ethanol + Oxygen → Acetic acid (Vinegar) + Water
[Requires aerobic conditions]

5. Biological Nitrogen Fixation (Rhizobium, Azotobacter, Anabaena)

$N_{2}$ + 8$H^{+}$ + 8$e^{-}$ + 16 ATP → 2 $NH_{3}$ + $H_{2}$ + 16 ADP + 16 Pi
[Catalyzed by nitrogenase; requires 16 ATP per $N_{2}$ molecule]
[$O_{2}$ DESTROYS nitrogenase — anaerobic micro-environment required]

6. Methanogenesis (Methanobacterium)

$CH_{3}COOH$ → $CH_{4}$ + $CO_{2}$ (acetoclastic methanogenesis)
4 $H_{2}$ + $CO_{2}$ → $CH_{4}$ + 2 $H_{2}O$ (hydrogenotrophic methanogenesis)
[Both pathways produce methane in anaerobic digesters]

7. HMG-CoA Reductase Reaction (inhibited by lovastatin)

HMG-CoA + 2 NADPH → Mevalonate + 2 NA$DP^{+}$ + CoA
[Rate-limiting step of cholesterol synthesis; BLOCKED by statins]