I achieved a high A* Grade in my final A-Level exams using these notes!!!
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a. Metabolism: series of enzyme controlled chemical reactions taking place in a cell
Anabolism: reactions that synthesise complex molecules from simple molecules
Catabolism: reactions that break down complex molecules into simple molecules
b. Globular proteins
c. Extracellular enzymes – work outside cell (human digestive enzymes)
Intracellular enzymes – work inside cell
d. active site (3D) – enzyme-substrate complex – successful collision
lock & key model: specific active site shape + complementary substrate shape – bind = ES complex
e. induced fit model – lysozyme: active site shape (tertiary structure) alters slightly to fit substrate – lowers E a
Lysozyme: anti-bacterial enzyme – tears & saliva
active site = groove – closes over & hydrolyses polysaccharides in bacteria cell wall
f. catalysis
- Increases rate of reaction
- Lowers activation energy: minimum amount of energy required for reaction to occur
Enzyme = biological (protein) catalyst of metabolic reactions
not used up / permanently altered
g. Rate
Temperature
molecules have more KE – move faster: more frequent successful collisions – more ES complexes = rate increases
Rate peaks at optimum temperature – human: 37-40˚C / plant: 25˚C
Enzyme denatures above optimum
pH – changes from optimum:
- small: reversible changes to active site shape
- extreme: denature
Enzyme & substrate concentration – more frequent successful collisions & ES complex forming = rate increases
- limiting factor: rate increases as it increases – rate proportional (until other limits)
o enzyme concentration = all active sites occupied (saturated)
- not: adding more won’t make a difference
Control experiment: boil enzyme solution – denatures enzymes: can’t catalyse any reaction
ensures enzyme action is the only factor influencing results
denaturation of enzymes: permanent change in enzyme structure
temperature beyond optimum – KE vibrations break H-bonds
extreme pH change away from optimum – breaks ionic/H-bonds
- disrupts tertiary structure = 3D shape of enzymes & active site changes
- active site no longer complementary to substrate: can’t form ES-complex – reduces rate & products formed
buffer: maintains constant pH
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