Foundations of Bio - Ch. 4: Exam 2 Notes

Foundations of Bio - Exam 2 Notes

Cellular Energy Concepts and Thermodynamics

Chapter 4: Overview of Cell Structure and Energy Chemistry

  • Definition of Energy in Biological and Physical Terms

    • Energy: Ability to do work.

    • Work: Specifically refers to moving matter.

    • Example: Walking across a room demonstrates energy used to move matter.

Forms of Energy

  • Energy exists in various states, specifically potential and kinetic energy:

    • Potential Energy:

    • Definition: Stored energy not currently being used.

    • Example: A compressed spring holds potential energy because it can do work when released.

    • Kinetic Energy:

    • Definition: Energy that is actively being used to move something.

    • Example: A released spring that moves a ball demonstrates kinetic energy.

Energy in Everyday Contexts

  • Energy exists not only in our bodies but also in objects around us:

    • Example: A hot cup of coffee contains energy due to its heat.

    • Cold objects, like an ice cream sundae, also possess energy, though in lesser amounts than hot objects.

Energy Transformation in Biological Processes

  • Distinction between potential and kinetic energy in biological systems:

    • Bodies utilize chemical energy stored in chemical bonds.

    • Formation of Chemical Bonds: Requires energy (similar to compressing a spring).

    • Breaking Chemical Bonds: Releases energy, as seen in consumption of sugar (glucose).

    • Example: When glucose is broken down, energy is captured and transformed into usable forms in the body.

Adenosine Triphosphate (ATP)

  • Significance of ATP in Energy Capture and Usage in Cells:

    • ATP: Known as the energy currency of the cell.

    • Allows cells to store energy from chemical reactions in a usable form.

    • ATP Structure Consists of:

    • Adenosine: (adenine base + ribose sugar)

    • Three Phosphate Groups.

    • Energy Release Mechanism:

    • When energy is needed, ATP donates a phosphate group to release energy, converting it to ADP (adenosine diphosphate).

    • Breaking the bond between the second and third phosphate groups releases energy for cellular work.

    • Analogy: ATP can be likened to cash used for cellular activities.

Laws of Thermodynamics

  • Overview of Thermodynamic Principles Relevant to Biology:

    • First Law of Thermodynamics:

    • Definition: Energy cannot be created or destroyed; it can only change forms.

    • Cells cannot create energy; they must convert energy they uptake from external sources.

    • Example: Plants convert solar energy into chemical energy during photosynthesis.

    • Second Law of Thermodynamics:

    • Definition: Every time energy is transformed (e.g., chemical reactions in cells), some energy is lost as heat.

    • Heat is considered unusable energy and leads to less efficiency in energy storage and transformation.

    • As usable energy decreases over time, all energy will eventually dissipate into heat if no new energy is supplied.

Concept of Entropy

  • Entropy as a Measure of Disorder in the Universe:

    • Definition: Entropy is related to the randomness or disorder of a system.

    • High Entropy: Indicates a more disordered system; Low Entropy: Indicates order.

    • Examples:

    • Mixing creamer into coffee increases entropy as liquids naturally mix without energy input.

    • It takes energy to maintain order (low entropy) in biological systems.

    • Cells expend energy to keep organized; without energy, systems tend toward chaos and higher entropy.

Conclusion

  • Importance of Entropy:

    • Entropy is a fundamental concept in understanding energy flow and organization in living systems.

    • Energy transformations and the laws of thermodynamics are vital for understanding metabolic processes in cells.

    • Essential Takeaway: Cells must consistently input energy to counteract entropy and maintain structure.

Overview of Chapter Four: Energy of Life

  • Focus on energy transformations, the laws of thermodynamics, and chemical reactions.

  • Energy Transformations:

    • Energy in biological cells is primarily stored in ATP (adenosine triphosphate) molecules.

    • ATP is crucial for various cellular processes.

Laws of Thermodynamics

  • First Law of Thermodynamics:

    • Definition: Energy cannot be created or destroyed, only transformed.

    • Example: In biological systems, energy changes form but is not created or destroyed.

    • Note: Not strictly true in all contexts (e.g., nuclear reactions).

  • Second Law of Thermodynamics:

    • Definition: During energy transformations, some energy is lost as unusable heat.

    • Results in overall increase in disorder, known as entropy.

    • Over time, usable energy in a closed system diminishes.

    • Connection to Earth: Earth is not a closed system; it receives energy from the sun.

Entropy

  • Definition: A measure of disorder in a system; energy tends to spread out and become less organized.

  • Visual Example: Mixing coffee and cream increases disorder (high entropy).

    • Conversely, separate cream and coffee represent low entropy.

Importance

  • Relevance to Chemical Reactions:

    • Entropy is crucial when discussing chemical reactions and energy usage in biological systems.

Chemical Reactions

Definition of Chemical Reactions

  • Any process involving the making or breaking of chemical bonds.

    • Primarily concerned with covalent and ionic bonds, excluding non-permanent bonds like hydrogen bonds.

Key Terms

  • Reactants/Substrates: Molecules that enter a chemical reaction.

  • Products: Molecules that result from a chemical reaction.

  • Metabolism: The sum of all chemical reactions within a cell.

Energy and Chemical Reactions

Types of Energy in Reactions

  • Energy is stored in chemical bonds (potential energy) and released when bonds are broken (kinetic energy).

Types of Reactions

  • Endergonic Reactions:

    • Definition: Reactions that absorb energy, resulting in products with higher energy than reactants.

    • Example: Photosynthesis converts low-energy reactants (CO₂) into high-energy products (sugar).

  • Exergonic Reactions:

    • Definition: Reactions that release energy, resulting in products with lower energy than reactants.

    • Example: Breakdown of sugar to release energy.

Spontaneity of Reactions

  • Spontaneous Reactions (Exergonic): Tend to increase entropy (disorder).

  • Reactions that Decrease Entropy (Endergonic): Require energy input and are non-spontaneous.

Activation Energy

  • Definition: The minimum energy needed for a reaction to occur.

  • Characteristic: All reactions require activation energy, regardless of being endergonic or exergonic.

  • Analogy: Requires some energy (like climbing a hill) to initiate a reaction before it can proceed spontaneously.

Enzymes

Definition and Function

  • Enzymes: Biological catalysts that speed up chemical reactions without being consumed.

    • All enzymes are proteins.

    • Function: They lower the activation energy needed for reactions.

Mechanism of Enzyme Action

  • Enzymes bind to specific substrates at their active sites, akin to a key fitting a lock.

  • Example: Sucrase enzyme breaks down sucrose into glucose and fructose by stressing bonds and lowering activation energy.

Types of Enzyme Catalysis

  • Enzymes can either:

    • Break down substrates.

    • Synthesize them into larger products.

Identifying Enzymes

  • Naming Convention: Enzymes typically end with the suffix -ase (e.g., sucrase, lactase, DNA polymerase).

Coenzymes

Definition

  • Coenzymes: Non-protein molecules that assist enzymes; can be vitamins or metals.

    • Not consumed in reactions and help stabilize enzyme structure or participate in reactions by accepting electrons.

Regulation of Enzyme Activity

Reasons for Regulation

  • Resource Management:

    • Cells require energy (ATP) to perform reactions.

    • Continuous maximal speed reactions can waste resources unnecessarily.

    • Different pathways utilize substrates like glucose; cells may prioritize breaking down glucose for energy over forming sucrose from it.

Methods of Regulation

  • Denaturation: Loss of the three-dimensional structure of enzymes, affecting their functionality without breaking covalent bonds within the enzyme.

  • Inhibition: A temporary halt in enzyme activity, which can be achieved in two ways:

    • Competitive Inhibition:

    • A substrate mimics and competes for the active site of the enzyme.

    • Effectiveness correlated with relative amounts of competing substrates and inhibitors.

    • Non-competitive Inhibition:

    • An inhibitor binds to an allosteric site, resulting in a conformational change that prevents the substrate from binding to the active site.

    • This is not dependent on substrate concentration.

Environmental Factors Influencing Enzyme Activity

Optimal Conditions

  • Enzymes function best under specific conditions like temperature and pH.

    • Example:

    • Human enzymes generally operate at body temperature (37°C or 98.6°F).

    • Bacterial enzymes often have different optimal temperatures (e.g., 25°C or 70°F).

    • pH Levels:

    • Different enzymes work at varying pH levels:

      • Stomach enzymes: low pH (acidic).

      • Salivary amylase: neutral pH.

      • Arginase in kidneys: alkaline environment.

Biochemical Pathways

Definition

  • Biochemical Pathway: A biochemical pathway consists of interconnected chemical reactions in a specific order to achieve a cellular outcome that a single reaction cannot accomplish.

    • Example: Glycolysis is a 10-step metabolic pathway for energy production in cells, requiring that all steps happen sequentially for effective ATP synthesis.

Functional Dynamics

  • Different enzymes usually catalyze each step, generally one enzyme per step in a pathway.

  • Directionality:

    • Some enzymes may operate bidirectionally, while others (e.g., phosphofructokinase) are unidirectionally specific.

Redox Reactions

Definition

  • Redox Reaction: Revolves around the transfer of electrons between molecules.

    • Oxidation vs. Reduction:

    • Oxidation: Loss of electrons by a species (considered oxidized).

    • Reduction: Gain of electrons by a species (considered reduced).

    • Mnemonic: OIL RIG:

      • Oxidation Is Loss | Reduction Is Gain.

  • Chemical Understanding:

    • Example: If molecule A loses electrons (oxidized), molecule B gains them (reduced).

    • Reducing Agent: A substance that donates electrons and thus gets oxidized.

Cell Membranes and Transport Mechanisms

Functionality

  • Cell membranes serve multiple roles, including compartmentalization and selective permeability.

Components

  • Primarily composed of phospholipids with hydrophilic heads and hydrophobic tails, forming a bilayer.

Transport Types

  • Passive Transport:

    • Relies on diffusion with no energy required (moving from high to low concentration).

  • Facilitated Diffusion:

    • Protein channels assist transport without energy use.

  • Active Transport:

    • Requires energy (ATP) to move substances against their concentration gradient from low to high.

  • Endocytosis and Exocytosis:

    • Endocytosis: Transport of large particles into the cell using vesicles.

    • Pinocytosis: Cellular "drinking" involving smaller vesicles.

    • Exocytosis: Release of substances from the cell by vesicles fusing with the cell membrane.

Osmosis

  • Definition: Osmosis is the specific case of diffusion concerning the movement of water across a semipermeable membrane to equalize solute concentrations.

Types of Solutions

  • Isotonic: Equal concentration of solutes inside and outside the cell.

  • Hypertonic: Higher concentration of solutes outside the cell (causes cell to shrivel).

  • Hypotonic: Lower concentration of solutes outside the cell (can cause cells to burst).

Summary of Key Points from Chapter 4

  • Energy in cells primarily exists in chemical bonds.

  • ATP (Adenosine Triphosphate) is the primary energy currency in living cells.

  • The laws of thermodynamics govern energy transformations within cellular processes:

    • 1st Law: Energy cannot be created or destroyed, only transformed.

    • 2nd Law: Energy transformations lead to increased entropy.

  • Enzymes significantly lower activation energy and enable fast biochemical reactions.

  • Coenzymes function to assist in enzyme action, often derived from vitamins or metals.

  • **Biochemical pathways consist of numerous sequential steps that can influence overall cellular function.