Metabolism and Cellular Processes

Chapter 6: Metabolism

Energy Definitions

  • Energy: The capacity to do work or to produce change; exists in various forms.

Energy Sources in Living Systems

  • Most living systems primarily derive their energy from the sun through photosynthesis.
  • Energy capture occurs via the process of photosynthesis in plants.

Chemical Bonds and Energy

  • Energy is intricately related to the breaking and formation of chemical bonds.
    • The breaking of bonds releases energy, while forming bonds requires energy.

Energy Transformation in Chemical Reactions

  • In chemical reactions, energy transformations occur when reactants transition to products, especially evident in reactions that result in a more ordered state, such as photosynthesis.
    • Example: Photosynthesis transforms light energy into chemical energy stored in glucose.

Laws of Thermodynamics

  • First Law of Thermodynamics: Energy cannot be created or destroyed, only transformed from one form to another.
  • Second Law of Thermodynamics: In every energy transfer, some energy is lost as heat, leading to increased entropy in a closed system.

Free Energy and Chemical Reactions

  • Free Energy (G): The energy in a system that can be used to do work at constant temperature and pressure.
    • Changes in free energy () during a chemical reaction dictate spontaneity.

Types of Reactions

  • Endergonic Reactions: Reactions that absorb energy and have a positive change in free energy (G > 0).
  • Exergonic Reactions: Reactions that release energy and have a negative change in free energy (G < 0).
  • Graphing Free Energy Changes: Understand how to graph changes in free energy from reactants to products for both endergonic and exergonic reactions.

Activation Energy

  • Activation Energy (Ea): The minimum energy required for a chemical reaction to occur.
    • Relates to reaction rates; higher activation energy generally results in slower reactions.

Catalysts

  • Catalysts: Substances that increase the rate of a chemical reaction without being consumed in the process.
    • Their presence lowers the activation energy required for a reaction.
  • Diagram the difference between catalyzed and uncatalyzed chemical reactions.

ATP (Adenosine Triphosphate)

  • Structure: Composed of adenine, ribose, and three phosphate groups.
  • Energy Storage: ATP stores energy in the high-energy bonds between phosphate groups.
  • ATP Hydrolysis: The process where ATP is broken down into ADP and inorganic phosphate, releasing energy for cellular processes.
  • Cycle of ATP: ATP is regenerated from ADP and inorganic phosphate in cellular respiration.

Enzymes

  • Structure: Typically proteins that catalyze biochemical reactions.
  • Factors Influencing Function: Temperature, pH, and substrate concentration can affect enzyme activity.
  • Allosteric Enzymes: Enzymes whose activity is regulated by the binding of an effector molecule at a site other than the active site.

Metabolism

  • Anabolic Reactions: Processes that build larger molecules from smaller ones, requiring energy input.
    • Example: Protein synthesis.
  • Catabolic Reactions: Processes that break down larger molecules into smaller ones, releasing energy.
    • Example: Cellular respiration.
  • Biochemical Pathways: Series of chemical reactions occurring within cells. Feedback inhibition is often used to regulate these pathways.

Chapter 7: Cellular Respiration

Energy Harvesting in Organisms

  • Different organisms harvest energy through cellular respiration, which can vary by organism based on metabolic needs and environment.

Oxidations and Dehydrogenations

  • Oxidation involves the loss of electrons or hydrogen, while dehydrogenation specifically involves the removal of hydrogen atoms.

Overview of Cellular Respiration

  • Cellular Respiration Defined: The complete oxidation of glucose to produce energy in the form of ATP.

Steps of Respiration

  • Respiration occurs in steps to efficiently capture and conserve energy.
  • By breaking down glucose through multiple steps, cells manage energy release and minimize waste.

Types of Respiration

  • Aerobic Respiration: Requires oxygen; final electron acceptor is oxygen.
  • Anaerobic Respiration: Occurs without oxygen; different final electron acceptors (e.g., sulfate, nitrate).
  • Fermentation: An anaerobic process that partially breaks down glucose to generate ATP, producing byproducts like ethanol or lactic acid.

Importance of Electron Carriers

  • Electron Carriers: Molecules that transport electrons during cellular respiration.
    • Key Electron Carriers: NAD+ (Nicotinamide Adenine Dinucleotide) and FAD+ (Flavin Adenine Dinucleotide) play vital roles in transferring electrons.

Stages of Cellular Respiration

  1. Glycolysis: The breakdown of glucose into pyruvate, occurs in the cytoplasm.
  2. Pyruvate Oxidation: Converts pyruvate into Acetyl-CoA, releasing CO2 and producing NADH.
  3. Citric Acid Cycle (Krebs Cycle): Completes the oxidation of glucose derivatives, producing ATP, NADH, and FADH2.
  4. Electron Transport Chain (ETC): Uses high-energy electrons from NADH and FADH2 to produce ATP through oxidative phosphorylation.
    • Chemiosmosis: Proton gradient generated across the mitochondrial membrane drives ATP synthesis via ATP synthase.

ATP Production from Glucose

  • Theoretical maximum ATP yield from one glucose molecule is approximately 36-38 ATP depending on conditions.
  • Most ATP is produced during the electron transport chain and chemiosmosis phases of cellular respiration.

Chapter 8: Photosynthesis

Photosynthesis Overview

  • Definition: The process by which green plants, algae, and some bacteria convert light energy into chemical energy stored in glucose.
  • Location: Primarily occurs in plant chloroplasts.

Chloroplast Structure

  • Components: Inner and outer membranes, thylakoids (where light-dependent reactions occur), and stroma (where the light-independent reactions occur).
  • Photosystem Structure: Proteins and pigments organized in thylakoid membranes that capture light energy.

Light-Dependent Reactions

  • Location: Occur in the thylakoid membranes.
  • Energy Harvesting Contribution: Converts solar energy into chemical energy; oxygen is produced as a byproduct.

Photosystems Organization

  • Photosystem II: Generates charged electrons for transport and pumps protons, contributing to the proton gradient.
  • Photosystem I: Accepts electrons from Photosystem II to reduce NADP+ to NADPH.

Electron Sources for Photosystems

  • Photosystem II: Electrons are obtained through hydrolyzing water.
  • Photosystem I: Electrons come from electron transport from Photosystem II.

Light-Independent Reactions (Calvin Cycle)

  • Purpose: Uses inorganic carbon (CO2) to synthesize organic molecules (glucose).
  • **Key Stages:
    • Carbon Fixation
    • Reduction phase (producing G3P)
    • Regeneration of RuBP to continue the cycle.**
  • Cycles Required: Three turns of the Calvin Cycle are necessary to produce one G3P, while six cycles yield one glucose molecule.

Interplay Between Photosynthesis and Cellular Respiration

  • Diagram the cycle of energy to understand how photosynthesis and aerobic cellular respiration feed into each other.

Chapter 9: Cell Communication

Importance of Cell Communication

  • Enables cells to respond to environmental changes and coordinate functions vital for survival.

Requirements for Cell Signaling

  • Ligands: Signaling molecules like proteins, lipids, gases, or ions that initiate communication.
  • Receptor Proteins: Molecules that bind to ligands and trigger signal transduction pathways that convert the signal into a cellular response.

Binding Process

  • The binding of ligands to receptor proteins leads to the formation of a receptor-ligand complex, which activates signal transduction.

Mechanisms of Cell Communication

  1. Direct Contact: Cells communicate directly through physical connections.
  2. Paracrine Signaling: Signals released from one cell affect nearby cells.
  3. Endocrine Signaling: Hormones travel through the bloodstream to distant targets.
  4. Synaptic Signaling: Neurotransmitters released from neurons affect neighboring neurons.

Signal Transduction and Cellular Response

  • Signal transduction results in changes in protein activity, often mediated by phosphorylation events (adding/removing phosphate groups).
  • Receptor Proteins: Classified by location (e.g., membrane, intracellular receptors).
    • Types of Membrane Proteins: Ion channels, enzymatic receptors, and G-protein coupled receptors (GPCRs).

Hormonal Signaling

  • Hormones can induce changes in gene expression and metabolic activity, impacting cell function.

Turning Off Signaling Pathways

  • Mechanisms exist to deactivate signaling pathways and prevent overstimulation of cellular responses.

G-Protein Coupled Receptors (GPCRs)

  • A common type of membrane receptor involved in many signaling pathways, known for their role in activating G-proteins and downstream signaling components.

Secondary Messengers

  • Secondary Messengers: Intracellular signaling molecules that relay signals received by cell surface receptors. An example is cyclic AMP (cAMP), a common secondary messenger in many signaling pathways.

Chapter 10: Cell Division

Binary Fission

  • Definition: Asexual reproduction method used by prokaryotic organisms.
  • Process: Involves the replication of a single chromosome starting from the origin of replication, continuing to the termination site, followed by septum formation resulting in two identical daughter cells.

Comparison to Eukaryotic Cell Division

  • Binary fission is simpler and generally occurs in a single step, whereas eukaryotic cell division (mitosis) involves multiple phases.

Structure of Eukaryotic Chromosomes

  • Chromosomes consist of chromatin (DNA and associated proteins) which condense to form visible chromosomes during cell division.

Chromosomal Changes During Division

  • Sister Chromatids: Duplicated chromosomes that are joined together before cell division.

Phases of the Cell Cycle

  • Interphase: The cell cycle phase where the cell grows and prepares for division, consisting of G1, S, and G2 phases.
  • M Phase: The phase where cell division occurs, including mitosis and cytokinesis.

Events in Mitosis

  • Be able to diagram and describe events occurring during each phase of mitosis (prophase, metaphase, anaphase, and telophase).