Metabolism is all chemical reactions in a living organism. (p.86)
Catabolism breaks complex substances into simple ones and releases energy (e.g. glucose breakdown in respiration). (p.86)
Anabolism builds complex molecules from simple ones and uses energy (e.g. photosynthesis). (p.86)
5.2 Enzymes
An enzyme is an organic catalyst, mostly protein, produced by living cells; the substrate binds to the active site forming an enzyme-substrate complex. (p.86)
Enzyme names are formed by adding "-ase" to the substrate name (e.g. lactase); exceptions include trypsin, pepsin and renin. (p.87)
Characteristics: speed up reactions, needed in small amounts, reusable, unchanged after reaction, specific, reversible reactions, act rapidly. (p.87)
Inhibitors (e.g. lead, mercury) slow or stop enzymes; cofactors (e.g. vitamin B, magnesium ion) help some enzymes. (p.87)
Intracellular enzymes work inside the cell (e.g. hexokinase in glycolysis); extracellular enzymes are secreted (e.g. trypsin). (p.88)
Extracellular enzyme production: ribosome → rough ER → transport vesicle → Golgi apparatus → secretory vesicle → plasma membrane. (p.88)
Lock and key hypothesis: the enzyme (lock) has an active site that fits a specific substrate (key). (p.89)
Temperature: rate rises up to the optimum (37°C in humans), roughly doubling per 10°C; above optimum enzymes denature (activity stops at about 60°C). (p.90)
pH: most enzymes work best at pH 6–8 (salivary amylase 6.8); pepsin pH 1.5–2.5; trypsin about pH 8.5. (p.90)
Extreme pH breaks bonds and denatures the enzyme. (p.91)
Substrate concentration: rate increases until enzyme concentration becomes limiting. (p.91)
Enzyme concentration: rate increases with more active sites until substrate becomes limiting. (p.91)
Amylase experiment: starch and amylase at 20–60°C, time for starch hydrolysis found with iodine test. (p.92)
Pepsin experiment: albumen suspension with HCl, distilled water or NaOH at 37°C; clarity shows pH effect. (p.94)
5.3 Application of Enzymes in Daily Life
Immobilised enzymes combine with inert insoluble substances, resist pH and temperature changes and can be separated from products easily. (p.95)
Uses: digestive enzymes in medicine, pectinase and cellulase in juice, lactase in lactose-free milk, protease for fish skin, bio detergents (amylase, lipase, protease, cellulase), trypsin for leather. (p.95)