3.1.1Additional lessons
Metabolism: Enzymes and Reactions — IB Biology SL Revision Notes & Topical Questions
5 min read 5 parts Lesson 50 of 142
Curriculum Equation Key قوانين الرقم الهيدروجيني والاتزان الأيوني - pH & Acid-Base Equilibrium FormulasFast Exam Solution
pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴
Word Equation & Conditions: الرقم الهيدروجيني = -لوغاريتم تركيز أيون الهيدروجين | pH + pOH = 14
Location & Specifications: الاتزان الأيوني، كيمياء 3 ثانوي، التحصيلي، و AP Chemistry.
Section 1 of 5Metabolism
Metabolism
- Metabolism The sum of all the enzyme-catalysed chemical reactions that take place inside a living organism.
Anabolic reactions
- Anabolic reactions Build large molecules from smaller ones by condensation reactions, and require a supply of energy.
Catabolic reactions
- Catabolic reactions Break large molecules into smaller ones, as in hydrolysis, and usually release energy.
Metabolic pathways
- Metabolic pathways Reactions occur in chains or cycles, where the product of one step is the substrate for the next.
Control
- Control Each step is catalysed by its own enzyme, so the cell can regulate the pathway at several points.
Section 2 of 5Why Cells Need Enzymes
1
Most reactions in cells would be too slow at body temperature without help from a catalyst.
2
Cells cannot use high temperature, extreme pH or high pressure to speed reactions, because these would damage them.
3
Enzymes are globular proteins that act as biological catalysts, speeding up reactions at mild conditions.
4
They lower the activation energy of a reaction, so more collisions between molecules are successful.
5
Enzymes are not used up in the reaction, so a small amount can catalyse a large amount of substrate.
Section 3 of 5Where Enzymes Work
Where Enzymes Work
Intracellular
- Intracellular Enzymes working inside cells include those of cell respiration, which occur in the cytoplasm and mitochondria.
Extracellular
- Extracellular Enzymes such as amylase and trypsin are secreted and work outside the cells that make them.
Specificity
- Specificity Each enzyme usually catalyses only one type of reaction because of the shape of its active site.
Examples
- Examples Amylase digests starch to maltose, and catalase breaks down hydrogen peroxide into water and oxygen.
| Type | Anabolic | Catabolic |
|---|---|---|
| Direction | Small to large molecules | Large to small molecules |
| Reaction type | Condensation | Hydrolysis |
| Energy | Taken in | Usually released |
| Example | Protein synthesis | Digestion of starch |
Section 4 of 5Examples of Metabolic Pathways
Examples of Metabolic Pathways
Respiration
- Respiration Glucose is broken down in a series of steps, each catalysed by a different enzyme, to release energy.
Photosynthesis
- Photosynthesis Carbon dioxide is built into sugars in a cycle of enzyme-catalysed reactions in the chloroplast.
Protein synthesis
- Protein synthesis Amino acids are joined by condensation reactions to build polypeptides, an anabolic process.
Section 5 of 5Exam Checklist & Tips
3.1.1 – Key Points for the Exam
- Metabolism All the chemical reactions occurring in an organism.
- Enzyme A protein that acts as a biological catalyst.
- Anabolism Building up of complex molecules from simpler ones.
- Catabolism Breaking down of complex molecules into simpler ones.
Common Mistakes
- Writing that enzymes are used up during a reaction; they are unchanged at the end.
- Saying that enzymes provide energy for reactions, when they only lower the activation energy.
- Calling all metabolism catabolism; both anabolic and catabolic reactions are part of it.
- Believing that enzymes can catalyse any reaction, ignoring specificity.
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