In-depth section 2.5 notes for IB Biology HL students. I took my exams in July 2022 and got a 7 in Biology HL. The notes are a combination of information from lots of different sources with a main focus on the IB Biology Textbook.
2.5 Enzymes
Objectives:
❏ Understanding:
❏ Enzymes have an active site to which specific substrates bind
❏ Enzyme catalysis involves molecular motion and the collision of substrates with the active site
❏ Temperature, pH and substrate concentration affect the rate of activity of enzymes
❏ Enzymes can be denatured
❏ Immobilised enzymes are widely used in industry
❏ Applications:
❏ Methods of production of lactose-free milk and its advantages
❏ Skills:
❏ Design of experiments to test the effect of temperature, pH and substrate concentration on the
activity of enzymes
❏ Experimental investigation of a factor affecting enzyme activity
❏ Nature of Science
❏ Experimental design: accurate quantitative measurements in enzymes experiments require
replicates to ensure reliability
Active sites and enzymes:
- Enzymes
- Large polypeptide proteins with a tertiary or quaternary structure
- Globular proteins that work as catalysts (speed up chemical reactions without being altered
themselves)
- Enzymes are called biological catalysts because they are made by living cells and speed up biochemical
reactions
- Substrate = substances that enzymes convert into products in reactions
- General equation for an enzyme-catalysed reaction is:
E + S → ES → EP → E + P
- Found in
all living
cells and
secreted
by some
cells to
work
outside
, - Enzymes are not changed or consumed by the reactions they catalyse and thus can be reused
- Living organisms produce many different enzymes (thousands)
- Many enzymes are needed as enzymes only catalyse only one biochemical reaction
- Thousands of reactions take place in cells, nearly all of which need to be catalysed
- Enzymes-substrate specificity = ability of an enzyme to choose exact substrate from a group of similar
chemical molecules
- Active site = a special region on an enzyme that binds to a protein or other substance during a reaction
- Shape and chemical properties of the active site and the substrate match each other (only a specific
substrate is capable of binding to a particular enzyme’s active site)
- Substrates are converted into products while they are bound to the active site and the products are
then release, freeing the active site to catalyse another reaction
Enzyme activity:
- Enzyme activity is the catalysis of a reaction by an enzyme. There are 3 stages:
1. The substrate binds to the active site of the enzyme
a. Some enzymes have two substrates that bind to different parts of the active site
2. While the substrates are bound to the active site they change into different chemical substances
(the products of the reaction)
3. The products separate from the active site, leaving it vacant for substrates to bind again
- A substrate molecule can only bind to the active site if it is in close physical proximity
- Collision Theory
1. Particles must collide
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