Lecture 6 - Metabolism

Energy and Enzymes: An Introduction to Metabolism

• Cellular Respiration: Drives the cell’s economy by extracting energy stored in fuels (e.g., sugars) for work.

Metabolism: Key Concepts

• Metabolism Definition: Transform matter and energy subject to thermodynamics.

• Free Energy Change (ΔG): Determines spontaneity of reactions; negative ΔG indicates spontaneous actions, while positive ΔG requires energy input.

• ATP Role: Powers cellular work through coupling exergonic (spontaneous) and endergonic (non-spontaneous) reactions.

• Enzyme Function: Accelerates metabolic reactions by lowering energy barriers.

• Factors Affecting Enzymes: Local conditions (temperature and pH) and other regulators (activators and inhibitors).

Overview of Metabolism

• Sum of Chemical Reactions: Metabolism encompasses all chemical reactions in an organism, linked through pathways.

• Pathway Types:

  • Catabolic Pathways: Release energy by breaking down complex molecules (e.g., glucose oxidation).

  • Anabolic Pathways: Consume energy to synthesize complex molecules from simpler ones (e.g., sugar synthesis in photosynthesis).

Complex Metabolic Pathways

• Metabolic pathways can become complex, encompassing various molecules from food.

• A network map can illustrate metabolic pathways in typical cells.

Energy Transformations in Chemical Reactions

• Chemical Energy: Stored in the position of electrons; outer-shell electrons have higher potential energy.

• Electron Transfer: During reactions, electrons can move to lower energy states, releasing energy during chemical transformations.

• High Energy Organic Molecules: Organic molecules like sugars have many high-energy electrons due to C-H bonds.

Changes in Potential Energy and Entropy

• Potential Energy Movement: Electrostatic forces held tightly in products indicate lower potential energy compared to reactants.

• Spontaneity: Reactions that release energy are often spontaneous, especially when product molecules are less ordered (higher entropy).

Classification of Reactions

• Exergonic Reactions: Spontaneous with energy release.

• Endergonic Reactions: Non-spontaneous with required energy input.

  • Example: Glucose oxidation releases 2870 kJ/mol of energy.

Work of Cells

• Cellular Work: Activities requiring energy include motor functions, active transport, and synthesis of complex molecules.

• ATP: The primary energy currency of metabolism.

Hydrolysis of ATP

• Hydrolysis Process: Breaking bonds in ATP releases inorganic phosphate and significant energy (ΔG = -30.5 kJ/mol).

• Structure of ATP: Comprises three phosphate groups, ribose sugar, and adenine; high potential energy due to repelling phosphate groups.

Phosphorylation and Enzyme Activation

• Phosphate Group Transfer: Energy release from ATP hydrolysis can activate or change the shape of substrates, thus triggering processes in cells.

• Phosphorylation: Adds a phosphate group to proteins, altering their function.

Energetic Coupling

• Coupling Reactions: Exergonic reactions can drive non-spontaneous endergonic ones (energetic coupling).

• Examples include combined reactions that navigate energy dynamics.

ATP Cycle and Regeneration

• Continuous Energy Provision: Catabolic processes regenerate ATP through phosphorylation.

• Turnover Rate: Cells use ATP for 30 seconds to a few minutes; cells turn over around 10 million ATP molecules every second!

Rate of Reactions and Activation Energy

• Activation Energy (EA): Required to achieve transition states in chemical reactions; involves higher energy states.

• Catalysis by Enzymes: Enzymes lower EA and increase reaction rates by various mechanisms.

Enzyme Mechanisms

• Enzyme Specificity: Each enzyme usually catalyzes a specific reaction; they are dynamic and change shape upon substrate binding.

• Three-Step Process of Enzyme Action:

  1. Initiation: Reactants bind to active sites.

  2. Transition State Facilitation: Lowers EA.

  3. Termination: Products released, enzyme unchanged.

Enzyme Regulation

• Regulatory Molecules: Can activate or inhibit enzymes through various mechanisms, including competitive inhibition and allosteric regulation.

• Cofactors Requirement: Many enzymes need metal ions or coenzymes for function.

Factors Affecting Enzyme Activity

• Michaelis-Menten Kinetics: Describes the reaction rates through substrate concentration levels leading to saturation kinetics.

• Local Environment: Conditions such as pH and temperature affect enzyme functioning.

SIMPLIFIED

Energy and Enzymes: An Introduction to Metabolism

Metabolism is how our cells manage energy and chemical reactions to keep living organisms functioning. Here’s a simplified overview:

What is Metabolism?

• Metabolism includes all the chemical reactions in a living organism.

• These reactions are divided into two main types:

  • Catabolic Pathways: These break down larger molecules into smaller ones, releasing energy (for example, breaking down glucose).

  • Anabolic Pathways: These build larger molecules from smaller ones, spending energy (like how plants create sugars during photosynthesis).

Cellular Respiration

• This is the process where cells extract energy from food (like sugars) to do work, almost like a business uses money.

Energy in Reactions

• Free Energy Change (ΔG) tells us whether a reaction can happen on its own.

  • Negative ΔG means the reaction can occur spontaneously (with no added energy).

  • Positive ΔG means we need to add energy for the reaction to happen.

ATP: The Energy Currency

• ATP (Adenosine Triphosphate) is the main molecule that provides energy for many cellular processes.

• When ATP is broken down, it releases energy that can be used to perform work in the cell, such as moving materials or making new molecules.

Enzymes: Helpers of Reactions

• Enzymes are special proteins that speed up chemical reactions by lowering the energy needed for them to occur.

• They work like catalysts that help reactions go faster and make it easier for the cell to react to changes.

Factors Affecting Enzymes

• Enzyme activity can be affected by nearby conditions like temperature and pH level (how acidic or basic something is).

• Some molecules can also help or hinder the activity of enzymes, called activators or inhibitors.

How Reactions Happen

• Enzymes work by binding to substances (called reactants) at their active sites, changing the shape and lowering energy hurdles, which makes it easier for the reaction to happen.

• After the reaction, the products are released, and the enzyme can be used again.

Reaction Types

• Exergonic Reactions: These release energy and happen naturally.

• Endergonic Reactions: These require energy input to happen.

The ATP Cycle and Energy Regeneration

• Our cells continuously regenerate ATP so they can keep running smoothly.

• On average, a cell uses about 10 million ATP molecules every second!

By keeping track of these processes, cells can perform various functions efficiently, keeping the organism alive and functioning properly.