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Summary Biology (9700): Chapter 3, Enzymes
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Complete and concise notes on enzymes for A Level Biology (9700) with supporting syllabus points referenced to respective content.
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🔑Chpt 3: Enzymes
What are enzymes?
Globular proteins that act as biological catalysts by reducing the activation energy of a chemical reaction
(making it easier to induce a reaction) inside cells, or outside cells
Inside cells: intrinsic/intracellular enzymes
Outside: extrinsic/extracellular enzymes
Explain the mode of action of enzymes (lock and key hypothesis)
Substrate acts as the key, fitting in the lock of the enzyme's active site
The substrate has a complementary fit to the enzyme's active site, and is held in place by temporary bonds
form between substrate and enzyme r groups; forming an enzyme substrate-complex
Explain the induced fit mechanism
Binding of substrate: resulting in a temporary change in the substrate and the active site = providing a more exact
fit
As a result of hydrogen bonds within active site and substrate being temporarily broken down, resulting in
a slight temporary change in shape
Chpt 3: Enzymes 1
, Allowing the substrate to fit into the active site like a mould
How do you investigate the progress of enzyme-catalysed reactions using H2O2 and Catalase?
Catalase breaks down H2O2 into H2O and O2
2H2O2 —> 2H2O + O2
Can be measured by:
1. Counting bubbles produced by the reaction
Count bubbles with a slow-motion video recorder for a more accurate result
2. Using a closed gas system: using gas syringe
Using a bung (surrounded by petroleum jelly), delivery tube and gas syringe
How do you investigate the progress of enzyme-catalysed reactions using amylase?
Use a colorimeter and iodine solution
1. During the reaction, take small samples at set intervals to test for starch using an iodine solution
As starch is converted to maltose, conc. of starch decreases = colour of sample tested will change from
blue-black, to brown and remain pale brown (as starch is absent)
What is the use of a colorimeter
Used to measure a colour change quantitatively
Colorimeter provides numbers that can be plotted on a graph
Mechanism of colorimeter
The colour of a solution is measured by measuring the absorption of different wavelengths of light
Chpt 3: Enzymes 2
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