A-level notes series by
Emaan Atif
(Enzymes)
Chapter Outline
Enzyme Structure and Mode of Action
Enzyme Structure
Lock and Key Hypothesis vs. Induced Fit hypothesis
Mechanism of Enzymatic Reaction
Active site
Measuring the rate of reactions
Time course graph
Factors Affecting Enzymatic Reaction
1. enzyme concentration
2. Substrate concentration
3. Temperature
4. Ph.
5. Inhibitor concentration
Maximum rate of reaction (Vmax)
Michaelis-Menten constant (Km)- a measure of affinity
Competitive vs. Non-competitive Inhibition
Immobilized enzymes
, Enzymes are biological catalysts
1. ‘Biological’ because they function in living systems
2. ‘Catalysts’ because they speed up the rate of chemical reactions without being used up or changed
3. Can break down or synthesize products (catabolic e.g. Cellular respiration, hydrolysis, and anabolic
reactions such as protein synthesis and photosynthesis)
4. Specific: 1 enzyme to only one / few substrates of its complimentary shape thus The specificity of an
enzyme is a result of the complementary nature between the shape of the active site on the enzyme and
its substrate(s)
5. Complementary binding refers to when two molecules fit together to complete each other
6. Unchanged at the end of the reaction
7. Effective in small amounts
8. The number of substrates an enzyme can catalyze in one minute is called the enzyme's turnover number
9. Ph. and temperature can change the active site destroying the shape of active side and enzyme would be
no longer useful, inhibitors (stops enzymes from working) and cofactors (bind to active site so that
substrate can’t).
10. Low temperature makes enzymes inactive, high temperatures destroy active side (denatures).
11. Enzymes can be intracellular or extracellular referring to whether they are active inside or outside the
cell respectively
12. Intracellular enzymes are produced and function inside the cell
13. Extracellular enzymes are secreted by cells and catalyze reactions outside cells (e.g. digestive enzymes in
the gut)
How Do Enzymes Catalyze Reactions?
Enzymes lower the activation energy of chemical reactions, Activation energy (E₂) = Energy needed for a
chemical reaction to successfully form products, this provides an alternative pathway for reactions to occur. A
reaction with a lower activation energy will occur faster.
, All enzymes are globular proteins
1. Spherical / ball shape
2. Mostly tertiary structures , some quaternary
3. Have precise 3D structure due to interactions between R groups
4. Soluble because all Hydrophobic R groups are inside and Hydrophilic R groups faces outside.
All enzymes have an active site, A site where substrates bind to enzyme, The shape of the active site (and
therefore the specificity of the enzyme) is determined by the complex tertiary structure of the protein that
makes up the enzyme:
o Proteins are formed from chains of amino acids held together by peptide bonds
o The order of amino acids determines the shape of an enzyme
o If the order is altered, the resulting three-dimensional shape changes
o Bind = complementary in shape to substrate
o Only few catalytic amino acids at the active site!
o Precisely positioned, not necessarily beside each other in primary sequence.
Emaan Atif
(Enzymes)
Chapter Outline
Enzyme Structure and Mode of Action
Enzyme Structure
Lock and Key Hypothesis vs. Induced Fit hypothesis
Mechanism of Enzymatic Reaction
Active site
Measuring the rate of reactions
Time course graph
Factors Affecting Enzymatic Reaction
1. enzyme concentration
2. Substrate concentration
3. Temperature
4. Ph.
5. Inhibitor concentration
Maximum rate of reaction (Vmax)
Michaelis-Menten constant (Km)- a measure of affinity
Competitive vs. Non-competitive Inhibition
Immobilized enzymes
, Enzymes are biological catalysts
1. ‘Biological’ because they function in living systems
2. ‘Catalysts’ because they speed up the rate of chemical reactions without being used up or changed
3. Can break down or synthesize products (catabolic e.g. Cellular respiration, hydrolysis, and anabolic
reactions such as protein synthesis and photosynthesis)
4. Specific: 1 enzyme to only one / few substrates of its complimentary shape thus The specificity of an
enzyme is a result of the complementary nature between the shape of the active site on the enzyme and
its substrate(s)
5. Complementary binding refers to when two molecules fit together to complete each other
6. Unchanged at the end of the reaction
7. Effective in small amounts
8. The number of substrates an enzyme can catalyze in one minute is called the enzyme's turnover number
9. Ph. and temperature can change the active site destroying the shape of active side and enzyme would be
no longer useful, inhibitors (stops enzymes from working) and cofactors (bind to active site so that
substrate can’t).
10. Low temperature makes enzymes inactive, high temperatures destroy active side (denatures).
11. Enzymes can be intracellular or extracellular referring to whether they are active inside or outside the
cell respectively
12. Intracellular enzymes are produced and function inside the cell
13. Extracellular enzymes are secreted by cells and catalyze reactions outside cells (e.g. digestive enzymes in
the gut)
How Do Enzymes Catalyze Reactions?
Enzymes lower the activation energy of chemical reactions, Activation energy (E₂) = Energy needed for a
chemical reaction to successfully form products, this provides an alternative pathway for reactions to occur. A
reaction with a lower activation energy will occur faster.
, All enzymes are globular proteins
1. Spherical / ball shape
2. Mostly tertiary structures , some quaternary
3. Have precise 3D structure due to interactions between R groups
4. Soluble because all Hydrophobic R groups are inside and Hydrophilic R groups faces outside.
All enzymes have an active site, A site where substrates bind to enzyme, The shape of the active site (and
therefore the specificity of the enzyme) is determined by the complex tertiary structure of the protein that
makes up the enzyme:
o Proteins are formed from chains of amino acids held together by peptide bonds
o The order of amino acids determines the shape of an enzyme
o If the order is altered, the resulting three-dimensional shape changes
o Bind = complementary in shape to substrate
o Only few catalytic amino acids at the active site!
o Precisely positioned, not necessarily beside each other in primary sequence.
