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:
Initiation: Reactants bind to active sites.
Transition State Facilitation: Lowers EA.
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.