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Information is adapted from http://www.biologyguide.net/unit1/2_enzymes.htm
Secondary 1/2 Level
What are enzymes?
- All enzymes are globular proteins → spherical in shape (Fig 3)
- Control biochemical reactions in cells
- They have the suffix “-ase“
- Intracellular enzymes are found inside the cell
- Extracellular enzymes act outside the cell (e.g. digestive enzymes)
- Enzymes are catalysts → speed up chemical reactions (Fig 1 & Fig 2)
- Reduce activation energy required to start a reaction between molecules
- Substrates (reactants) are converted into products
- Reaction may not take place in absence of enzymes (each enzyme has a specific catalytic action)
- Enzymes catalyse a reaction at max. rate at an optimum state
Fig.1
Fig.2
Lock and key theory
- Only one substrate (key) can fit into the enzyme’s active site (lock)
- Both structures have a unique shape
- Enzyme is not used up in the reaction (unlike substrates)
Fig.3
Enzyme Activity
- Changes in pH
- Ionic bonds can break and change shape → enzyme is denatured (not able to perform its intended function)
- Optimum pH (enzymes work best)
- pH 7 for intracellular enzymes
- Acidic range (pH 1-6) in the stomach for digestive enzymes (pepsin)
- Alkaline range (pH 8-14) in oral cavities (amylase)
- pH measures the conc. of hydrogen ions → higher conc. will give a lower pH
- Increased Temperature
- Increases speed of molecular movement → chances of molecular collisions
- At 0-42°C rate of reaction is proportional to temp
- Enzymes have optimum temp. for their action (usually 37°C in humans)
- Above ≈42°C, enzyme is denatured due to heavy vibration that breaks -H bonds
- Shape is changed → active site can’t be used anymore
- Decreased Temperature
- Enzymes become less and less active, due to reductions in speed of molecular movement
- Below freezing point
- Inactivated, not denatured
- Regain their function when returning to normal temperature
Secondary 3/4 Level
