Bio Chapter 3 - Energy & Enzymes

Chapter 3: Energy and Enzymes

Energy

  • Definition: Capacity to do work or be transferred as heat.

  • Forms:

    • Kinetic Energy

    • Potential Energy

  • Conversion: Energy can be readily converted from one form to another.

  • Atomic Energy States: Electrons in an atom exist in discrete energy states, containing more or less energy depending on their distance from the atomic nucleus.

  • Molecular Potential Energy: Molecules contain potential energy in the bonds between atoms.

  • Thermodynamics: Study of energy and its transformations.

Types of Thermodynamic Systems

  • Open Systems: Most relevant to biology.

Conservation of Energy

  • First Law of Thermodynamics: Energy can be transferred or transformed from one form into another, but it cannot be created or destroyed.

  • Energy Transformation Equation:
    ext{Total energy before} = ext{Total energy after}

Second Law of Thermodynamics

  • Principle:

    • Each time energy is transferred or transformed, some is lost as entropy (becomes unavailable to do work).

  • Efficiency: Can never have 100% efficiency.

  • Entropy Increase: Increases the entropy (disorder) of a system and surroundings.

    • Examples:

    • Only ~25% of energy in gas converted into mechanical energy.

    • Only 40% of glucose energy is used for muscle contractions.

Section 3.2: Free Energy and Spontaneous Reactions/Processes

  • Spontaneous Reactions:

    • Occur without a constant input of energy.

    • Does not imply quick; they are energetically favorable.

    • Tend to have products with less potential energy than reactants or greater disorder (entropy).

  • Entropy (S): Amount of randomness or disorder.

Free Energy (ΔG)

  • Equation:
    G = H - TS

  • Definitions:

    • G: Free Energy (energy available to do work)

    • H: Enthalpy (total energy)

    • T: Temperature (absolute temperature in Kelvin)

    • S: Entropy (degree of disorder)

  • Change in Free Energy: ΔG = ΔH - TΔS

    • Where:

    • ΔG = change in free energy,

    • ΔH = change in enthalpy, and

    • ΔS = change in entropy.

Types of Reactions

  • Exergonic Reaction:

    • ΔG negative, spontaneous, releases energy.

    • Products contain less free energy than reactants.

  • Endergonic Reaction:

    • ΔG positive, non-spontaneous, requires an input of energy.

    • Products contain more free energy than reactants.

Metabolism

Definitions

  • Metabolic Pathways: Series of sequential reactions where products of one reaction are used as reactants for the next.

  • Catabolic Pathway: Energy is released by breakdown of complex molecules into simpler ones.

  • Anabolic Pathway: Consumes energy to build complex molecules from simpler ones.

Chemical Structure of ATP (Adenosine Triphosphate)

  • ATP Hydrolysis:

    • Hydrolysis of phosphate bonds results in the net release of free energy used by cells.

    • Exergonic Reaction:

    • ΔG = -7.3 ext{ kcal/mol}

Energy Coupling

  • Definition: The coupling of an endergonic reaction to an exergonic reaction.

    • Hydrolysis of ATP is an exergonic reaction that can drive otherwise non-spontaneous reactions.

    • Requires enzymes for coupling reactions.

ATP/ADP Cycle

  • Process: ATP used in coupling reactions is replenished; linking ATP synthesis to catabolic reactions.

  • Cycle: Continuous breakdown and resynthesis of ATP.

Section 3.5: Enzymes

Enzymes as Biological Catalysts

  • Definition: Special group of proteins that increase the rate of chemical reactions without being consumed.

  • Function: Bind to reactants (substrates) and facilitate conversion to products without altering themselves.

Activation Energy (EA)

  • Definition: Initial input of energy required to start a reaction, regardless if spontaneous.

  • Transition State: Molecules that acquire the necessary activation energy occupy this unstable state.

Enzyme Catalysis Mechanisms

  1. Proximity: Bringing reacting molecules together.

  2. Altered Environment: Exposing molecules to altered charge environments.

  3. Induced Fit: Changing the shape of substrate molecules to favor catalysis.

Enzyme Activity and Regulation

  • Concentration Effects:

    • In low substrate conditions: Enzyme activity slows due to infrequent collisions.

    • In high substrate conditions: Enzymes become saturated and reaction rates level off.

Enzyme Inhibition

  • Types:

    1. Competitive Inhibition: Inhibitor competes with substrate for active site.

    2. Noncompetitive Inhibition: Inhibitor binds elsewhere, reducing efficacy without competing for the active site.

Allosteric Regulation

  • General Definition: Occurs when a regulatory molecule binds to an allosteric site, affecting enzyme activity.

  • Example: An allosteric activator can convert an enzyme from low-affinity to high-affinity state, enhancing substrate binding.

Feedback Inhibition

  • Definition: Product of an enzyme-catalyzed pathway acts as a regulator, helping conserve resources.

Temperature and pH Effects

  • Optimal Conditions: Each enzyme has an optimal temperature and pH for peak efficiency.

    • Extreme conditions can denature enzymes, reducing reaction rates.

Chapter 4: Cell Membranes and Signaling

Selectively Permeable Membranes

  • Requirements:

    • Impermeability to most molecules and ions.

    • Ability to exchange specific molecules/ions.

    • Insolubility in water yet permeability to water.

Membrane Composition

  • Components:

    • Phospholipids, glycolipids

    • Sterols: Cholesterol (animals), ergosterols (fungi), phytosterols (plants)

    • Membrane Proteins: Integral and peripheral.

Fluid Mosaic Model

  • Concept: Membranes consist of a fluid lipid bilayer where proteins are embedded and can move freely.

  • Experimental Evidence: Membrane fusion experiments showing protein mixing support fluidity.

Water and Solubility

  • Polarity: Water's polarity leads to hydrogen bonding, aiding solubility of polar molecules.

    • Hydrophilic vs. Hydrophobic:

    • Hydrophilic substances: soluble in water (e.g., sugars, DNA)

    • Hydrophobic substances: insoluble in water (e.g., lipids).

Membrane Fluidity Maintenance

  • Factors Influencing Fluidity:

    • Lipid composition (degree of unsaturation)

    • Temperature.

  • Sterols as Buffers: Help stabilize membrane fluidity across temperature changes.