Ch. 6 Exam Objectives

Chapter 6a: Metabolism

Key Terms

• Bioenergetics: Study of the energy flow through living systems.

• Metabolism: Totality of an organism's chemical reactions, consisting of anabolic and catabolic pathways.

• Metabolic Pathway: Series of chemical reactions occurring within a cell.

• Anabolism: Metabolic pathways that construct molecules from smaller units, usually requiring energy.

• Catabolism: Metabolic pathways that break down molecules into smaller units, generally releasing energy.

• Kinetic Energy: Energy of an object in motion.

• Potential Energy: Stored energy based on an object's position or state.

• Chemical Energy: Energy stored in chemical bonds, a form of potential energy.

• Free Energy: Energy available to do work in a biological system.

• Exergonic: Reactions that release energy, resulting in a negative change in free energy.

• Endergonic: Reactions that require energy input, resulting in a positive change in free energy.

• Thermodynamics: Study of energy transformations in matter.

Differences in Reactions

• Anabolic Reactions vs. Catabolic Reactions:

  • Anabolic reactions build larger molecules and require energy.

  • Catabolic reactions break down larger molecules and release energy.

Types of Reactions

• Photosynthesis: An endergonic reaction where solar energy is converted into chemical energy.

• Cellular Respiration: An exergonic reaction that releases energy by breaking down glucose.

Energy Types

• Relationship of Kinetic and Potential Energy: Potential energy can be converted into kinetic energy through movement; for example, a rock at the edge of a cliff possesses potential energy which converts to kinetic energy as it falls.

• Chemical Energy Relation to Potential Energy: Chemical energy is a form of potential energy stored in molecular bonds that can be released during chemical reactions.

High-Energy Molecules

• ATP (Adenosine Triphosphate): Primary energy carrier in cells.

• NADH (Nicotinamide Adenine Dinucleotide): Electron carrier in cellular respiration.

• NADPH (Nicotinamide Adenine Dinucleotide Phosphate): Electron carrier used in photosynthesis.

Free Energy in Reactions

• Exergonic Reactions: Release free energy, resulting in products with lower energy than reactants.

• Endergonic Reactions: Consume free energy, resulting in products with higher energy than reactants.

• Anabolism is typically endergonic while catabolism is typically exergonic.

Thermodynamics Laws

• First Law of Thermodynamics: Energy cannot be created or destroyed, only transformed (conservation of energy).

• Second Law of Thermodynamics: Energy transformations increase the entropy (disorder) of the universe.

• Energy lost during transfers is often in the form of heat.

Energy Currency

• ATP is the main energy currency of living organisms, necessary for various cellular processes such as muscle contraction and active transport.

ATP Structure

• AMP Structure: Composed of a ribose sugar, adenine base, and a single phosphate group.

• Differences from ADP & ATP: AMP has one phosphate, ADP has two phosphates, and ATP has three phosphates.

Energy Bonds in ATP

• Chemical Bonds Storing Energy: The bonds between the second and third phosphate groups in ATP store the majority of transferable chemical energy.

Phosphorylation Processes

• Phosphorylation: Addition of a phosphate group to a molecule, generally activating the molecule.

• Dephosphorylation: Removal of a phosphate group, usually deactivating the molecule.

• Energy Coupling: Process where the energy released from an exergonic reaction is used to drive an endergonic reaction, often via ATP hydrolysis.

ATP Usage

• Sodium-Potassium Pump: Cells use a significant percentage of ATP to maintain gradients across membranes through this pump.

• Instability of ATP: The instability arises from the high-energy bonds between phosphate groups, making ATP readily usable for energy transfer.

• The regeneration of ATP from ADP is endergonic, as it requires an energy input.

Substrate-Level Phosphorylation

• Definition: Direct transfer of a phosphate group to ADP to form ATP during specific enzymatic reactions.

• Sodium-Potassium Pump Example: This pump utilizes ATP hydrolysis to carry out substrate-level phosphorylation.

• ATP Regeneration: Approximately 90% of ATP is regenerated through oxidative phosphorylation in cellular respiration.

Location of ATP Regeneration

• Eukaryotic Cells: Occurs primarily in the mitochondria.

• Prokaryotic Cells: Occurs across the plasma membrane since they lack mitochondria.

Chapter 6b: Enzymes

Key Terms

• Activation Energy: Minimum energy required for a chemical reaction to proceed.

• Catalyst: Substance that increases the rate of a reaction without being consumed.

• Enzyme: Biological catalyst that accelerates chemical reactions in living organisms.

• Substrate: The reactant on which an enzyme works.

• Denaturation: Structural alteration of an enzyme due to environmental changes that affect its activity.

• Cofactor: Non-protein chemical compounds that assist enzyme activity.

• Coenzyme: Organic molecules required by some enzymes for activity, often derived from vitamins.

Factors Affecting Enzymatic Reactions

• Various factors influencing reaction rate include substrate concentration, enzyme concentration, temperature, and pH.

• Higher Activation Energy: Results in a slower reaction rate since more energy is required to start the reaction.

Activation Energy Sources

• The source of activation energy for most reactions is heat energy, but living cells cannot use ambient heat due to their specific reaction conditions.

Enzyme Function

• Enzymes lower activation energy by providing an alternative reaction pathway, increasing reaction speeds without being consumed in the process.

• Active Site: Specific region of the enzyme where substrates bind; its particular shape and chemical environment give enzymes their specificity for certain substrates.

Specificity Benefits and Drawbacks

• High specificity allows precise control of reactions, minimizing unwanted side reactions, but can limit flexibility and speed of metabolic processes.

Environmental Factors and Models

• Environmental changes such as temperature spikes or pH changes can denature enzymes.

• Lock and Key Model: Suggests that substrates fit perfectly into the enzyme's active site.

• Induced Fit Model: Proposes that the enzyme changes shape slightly to better fit the substrate after binding.

Enzyme Behavior

• Enzymes can be reused after catalyzing a reaction without undergoing permanent changes.

• Competitive Inhibition: Occurs when an inhibitor competes with the substrate for the active site, helping regulate reaction rates by reducing substrate binding.

• Non-Competitive Inhibition: Involves inhibitors binding elsewhere on the enzyme, changing its shape and rendering it inactive without competing for the active site.

• Allosteric Inhibition: Inhibitor binds to an allosteric site causing a conformational change that decreases enzyme activity.

• Allosteric Activation: Activator binds inducing a conformational change that enhances activity.

Cofactors and Coenzymes

• Purpose: Assist enzymes in reactions, often necessary for enzymatic activity.

• Similarities: Both are non-protein molecules that help enzymes function.

• Differences: Cofactors are typically metal ions while coenzymes are organic molecules.

Regulation of Enzymatic Reactions

• Compartmentalization: Eukaryotic cells regulate reactions by segregating enzymes into different compartments, enhancing reaction efficiency and specificity.

• Feedback Inhibition: A mechanism whereby the end product of a metabolic pathway inhibits an earlier step, regulating the overall pathway activity.