3.1.23 · Enzymes
Enzyme Action — Cambridge AS & A Level Biology 9700 Revision Notes & Topical Questions
5 min read 7 parts Lesson 4 of 17 1 quiz
Lesson summary
3.1.2 Enzyme Action — CAMBRIDGE AS & A LEVEL BIOLOGY 9700 — REVISION NOTES notes: Explain enzyme specificity, enzyme–substrate complexes and how enzymes lower activation energy.Binding — a specific substrate binds to the active site to form an enzyme–substrate complex.Complementa…
- Complementary shape
- Origin of shape
- Collisions
- Denaturation
- Definition
- Enzyme effect
Section 1 of 7Active site and specificity
Binding
- Binding a specific substrate binds to the active site to form an enzyme–substrate complex.
Complementary shape
- Complementary shape the active site has a shape that fits a specific substrate.
Origin of shape
- Origin of shape the amino acid order determines the tertiary structure and so the active site.
- Changing the order changes the shape of the enzyme and active site.
Example
- Example catalase binds hydrogen peroxide because it is complementary, whereas DNA polymerase does not.
Section 2 of 7Enzyme–substrate complex
Temporary
- Temporary the complex forms briefly, the enzyme catalyses the reaction, and the products are released.
Collisions
- Collisions the substrate must collide with the active site in the correct orientation and with enough speed.
Denaturation
- Denaturation extremes of heat or pH change the active site, so the substrate cannot bind.
Section 3 of 7Catabolic and anabolic reactions
Catabolic
- Catabolic one substrate is drawn into the active site and split into two or more products, as in respiration and hydrolysis.
Anabolic
- Anabolic two or more substrates are drawn in, bonds form between them, and a single product is released, as in protein synthesis and photosynthesis.
Section 4 of 7Activation energy
Definition
- Definition the energy a substrate needs to become unstable enough to react.
Enzyme effect
- Enzyme effect enzymes destabilise bonds in the substrate, making it more reactive.
Result
- Result the activation energy is lowered and an alternative energy pathway is provided.
Section 5 of 7More from the specification
More from the specification
Tertiary structure and catalytic function
- Tertiary structure and catalytic function specific conformational folding of enzyme polypeptide chains forms active sites critical for biological catalytic function.
Induced-Fit Hypothesis and Enzyme-Substrate Complexes
- According to the induced-fit hypothesis, an enzyme's active site undergoes conformational changes upon substrate binding,
- forming an enzyme-substrate complex that strains chemical bonds to lower activation energy.
Hydrolysis of Starch by Amylase
- The digestive enzyme amylase catalyzes the breakdown of starch polysaccharides into maltose disaccharides by hydrolyzing α-1,4-glycosidic bonds in solution.
Colorimetric Measurement of Enzyme Reaction Rates
- A colorimeter can measure the progressive hydrolysis of starch by amylase over time, tracking the percentage transmission of light through an iodine-starch solution as dark blue coloration disappears.
Serial Dilutions for Quantitative Assays
- Preparing a series of known starch concentrations via serial dilution enables the construction of a calibration curve,
- allowing researchers to measure unknown enzyme kinetics in living cells or extracts.
Induced-Fit Hypothesis and Enzyme-Substrate Complexes
- According to the induced-fit hypothesis, an enzyme's active site undergoes conformational changes upon substrate binding,
- forming an enzyme-substrate complex that strains chemical bonds to lower activation energy.
Hydrolysis of Starch by Amylase
- The digestive enzyme amylase catalyzes the breakdown of starch polysaccharides into maltose disaccharides by hydrolyzing α-1,4-glycosidic bonds in solution.
Colorimetric Measurement of Enzyme Reaction Rates
- A colorimeter can measure the progressive hydrolysis of starch by amylase over time, tracking the percentage transmission of light through an iodine-starch solution as dark blue coloration disappears.
Serial Dilutions for Quantitative Assays
- Preparing a series of known starch concentrations via serial dilution enables the construction of a calibration curve,
- allowing researchers to measure unknown enzyme kinetics in living cells or extracts.
Enzyme-substrate complex
- The temporary structure formed when a substrate binds to an enzyme's active site.
Induced-fit hypothesis
- The active site changes shape to fit the substrate.
Lock-and-key hypothesis
- Rigid enzyme and substrate fit exactly.
Iodine solution
- Orange-brown reagent that turns blue-black with starch.
Globular protein
- A rounded, usually soluble protein, such as an enzyme or insulin.
Extracellular enzyme
- An enzyme secreted to work outside cells.
Amylase
- Enzyme that breaks starch into maltose.
Starch
- An insoluble polysaccharide of glucose used by plants for energy storage.
Hypothesis
- A testable prediction with a scientific explanation.
Colorimeter
- An instrument that measures light absorbed by a solution.
Transmission
- The amount of light passing through a sample.
Absorbance
- A measure of the light absorbed by a sample.
Section 6 of 7Key terms
| Term | Meaning |
|---|---|
| Enzyme–substrate complex | The temporary complex of an enzyme and its substrate. |
| Specificity | An enzyme acting on only one type of substrate. |
| Complementary | Having a matching shape. |
| Catabolic | Breaking down complex molecules. |
| Anabolic | Building complex molecules. |
| Activation energy | The energy required to start a reaction. |
Section 7 of 7Exam technique
1
Saying all substrates fit any enzyme — each enzyme is specific to its substrate.
2
Saying the enzyme provides activation energy — it lowers it.
3
Forgetting the role of orientation in collisions — correct orientation is needed.
4
Saying the enzyme–substrate complex is permanent — it is temporary.
Marked practiceQuizzes for this lesson
Last updated: