Ficha de revisão: Enzymes and Metabolism

📋 Course Outline

1. Metabolism and Reaction Types
2. Energy in Living Organisms
3. Enzyme Structure and Active Sites
4. Induced Fit and Catalysis
5. Activation Energy and Collisions
6. Specificity and Denaturation
7. Factors Affecting Enzyme Rates

📖 1. Metabolism and Reaction Types

🔑 Key Concepts & Definitions

• Metabolism : The sum of all chemical reactions that occur in living organisms, converting reactants into products.
• Anabolic reactions : Form macromolecules from monomers by condensation reactions and require energy, making them endergonic.
• Catabolic reactions : Hydrolyse macromolecules into monomers and release energy, making them exergonic.

📝 Essential Points

• Examples of anabolic reactions include protein synthesis, glycogen formation, and photosynthesis.

• Examples of catabolic reactions include digestion and oxidation of substrates during respiration.

💡 Memory Hook

Build or break

📖 2. Energy in Living Organisms

🔑 Key Concepts & Definitions

• Kilocalorie : The amount of heat energy needed to increase the temperature of 1 g of water by 1°C.

📝 Essential Points

• The forms of energy important to living organisms are kinetic energy, potential energy, thermal energy, and chemical energy.

• The energy currency used in cells is ATP.

📖 3. Enzyme Structure and Active Sites

🔑 Key Concepts & Definitions

• Enzyme : A globular protein with catalytic properties that increases the rate of a biochemical reaction by lowering its activation energy.
• Active site : The region of an enzyme where a specific substrate binds and the reaction occurs.

📝 Essential Points

★ Must-know

• Enzymes are proteins made of amino acids with a complex three-dimensional globular structure containing an active site composed of only a few amino acids.

Further detail

• The shape of an enzyme's active site closely matches the shape of its specific substrate.

📖 4. Induced Fit and Catalysis

📝 Essential Points

★ Must-know

📌 The lock-and-key model proposes that the substrate fits a rigid enzyme active site, whereas the induced-fit model proposes that substrate binding changes the enzyme's conformation and moulds the active site precisely.

🔄 Process — During enzyme catalysis, the substrate binds to the active site to form an enzyme-substrate complex, is converted into product to form an enzyme-product complex, and then the enzyme and product separate.

• The enzyme is not consumed during catalysis and can catalyse another substrate after releasing the product.

Further detail

🔄 Process — Substrate binding induces a conformational change that creates a suitable chemical environment and stretches substrate bonds, making the reaction easier.

💡 Memory Hook

Bind, mould, react, release

📖 5. Activation Energy and Collisions

🔑 Key Concepts & Definitions

• Activation energy : The initial energy input required to start a chemical reaction by destabilising existing substrate bonds.

📝 Essential Points

★ Must-know

• Enzymes lower activation energy, allowing biochemical reactions to proceed rapidly without using potentially damaging high temperatures as another catalyst.

🔄 Process — Successful enzyme catalysis requires substrate molecules to collide with the active site in the correct orientation and with enough energy to bind.

Further detail

• During the activation-energy stage, the reacting molecules are in a transition state.

• Enzyme-controlled reactions proceed approximately 10^8 to 10^11 times faster than corresponding non-enzymic reactions.

📌 Collision frequency can be increased by raising thermal energy, which increases kinetic energy, or by increasing the concentration of enzyme or substrate particles.

📖 6. Specificity and Denaturation

🔑 Key Concepts & Definitions

• Enzyme specificity : The selective activity of an enzyme for its substrate, determined by the three-dimensional shape and chemical properties of its active site.
• Denaturation : A change in the shape of an enzyme or other protein that prevents the active site from binding its substrate and stops or reduces catalysis.

📝 Essential Points

📐 Formula — The enzyme reaction can be represented as E + S ↔ ES ↔ E + P, where E is enzyme, S is substrate, ES is the enzyme-substrate complex, and P is product.

📖 7. Factors Affecting Enzyme Rates

📝 Essential Points

★ Must-know

📌 Increasing temperature generally increases enzyme reaction rate because molecules move faster, causing more collisions, until the enzyme's optimum temperature is exceeded.

📌 Above the optimum temperature, enzyme bonds and three-dimensional structure can alter or denature, changing the active site so the reaction rate slows or stops; denaturation may be temporary or permanent.

📌 Each enzyme has an optimal pH, and extreme acidity or basicity can alter ionisation, disrupt substrate binding, break internal bonds, denature the enzyme, and stop the reaction.

📌 Increasing substrate concentration increases reaction rate through more enzyme-substrate collisions until all enzyme molecules are occupied and the maximum rate, Vmax, is reached.

Further detail

• For most enzymes the optimum temperature is about 30°C, most enzymes are fully denatured at 70°C, and some bacterial enzymes withstand temperatures up to 100°C.

• Cold-water fish can die at 30°C because their enzymes denature at that temperature.

• Most human enzymes function best at approximately pH 7, although enzymes in different body locations have different optimal pH levels.

💡 Memory Hook

Temperature, pH, concentration

📊 Synthesis Tables

Anabolic and Catabolic Reactions

Feature	Anabolic	Catabolic
Molecular change	Form macromolecules from monomers	Hydrolyse macromolecules into monomers
Energy	Require energy; endergonic	Release energy; exergonic
Examples	Protein synthesis, glycogen formation, photosynthesis	Digestion, substrate oxidation in respiration

⚠️ Common Pitfalls & Confusions

1. Anabolic reactions build molecules, whereas catabolic reactions break them down.
2. ATP is the cellular energy form identified in the course, whereas a kilocalorie measures heat energy.
3. An enzyme accelerates a reaction but is not consumed by it.
4. The induced-fit model replaces the older rigid lock-and-key explanation.
5. Activation energy is required to initiate the reaction, not the total energy released or absorbed by it.
6. Specificity concerns which substrate binds, whereas denaturation concerns loss of the active-site shape.
7. Increasing substrate concentration does not increase the rate beyond the saturation point when Vmax has been reached.