Chapter 5 – The Working Cell

Fluid-Mosaic Model of Membrane Structure

The Fluid-Mosaic Model describes the structure of cell membranes as a mosaic of diverse protein molecules embedded in a fluid bilayer of phospholipids. This model explains how membranes are selectively permeable and dynamic.

• Selective permeability: The ability of the membrane to allow some substances to pass while blocking others.

• Examples of molecules: Small nonpolar molecules (e.g., O2, CO2) can diffuse freely; ions and large polar molecules require transport proteins.

Membrane Transport Mechanisms

Cells use various mechanisms to move substances across membranes, often depending on concentration gradients and energy requirements.

• Passive transport: Movement of substances down their concentration gradient without energy input.

• Facilitated diffusion: Passive transport aided by membrane proteins.

• Active transport: Movement against the concentration gradient, requiring energy (usually ATP).

• Osmosis: Diffusion of water across a selectively permeable membrane.

Types of Solutions

Cells are affected by the tonicity of their environment, which can be classified as:

• Hypotonic: Lower solute concentration outside the cell; water enters the cell.

• Isotonic: Equal solute concentration; no net water movement.

• Hypertonic: Higher solute concentration outside; water leaves the cell.

Kinetic and Potential Energy in Cells

Cells transform energy to perform work, following the laws of thermodynamics.

• Kinetic energy: Energy of motion (e.g., movement of molecules).

• Potential energy: Stored energy (e.g., chemical bonds).

• Exergonic reactions: Release energy (e.g., cellular respiration).

• Endergonic reactions: Require energy input (e.g., photosynthesis).

Enzymes and Catalysis

Enzymes are biological catalysts that speed up chemical reactions by lowering activation energy.

• Catalytic cycle: Substrate binds to active site, reaction occurs, product released.

• Key terms: Catalyst, substrate, reactant, product, active site, activation energy.

ATP and ADP

ATP (adenosine triphosphate) is the main energy currency of the cell. Hydrolysis of ATP releases energy for cellular processes.

• ATP hydrolysis equation:

Factors Affecting Enzyme Activity

Enzyme activity is influenced by temperature, pH, substrate concentration, and inhibitors.

• Optimal conditions: Each enzyme has specific temperature and pH ranges for maximum activity.

Chapter 6 – Cellular Respiration & Fermentation

Cellular Respiration Overview

Cellular respiration is the process by which cells extract energy from glucose and other organic molecules, primarily using oxygen.

• Breathing vs. cellular respiration: Breathing is gas exchange; cellular respiration is the metabolic breakdown of molecules for energy.

Redox Reactions

Redox (oxidation-reduction) reactions transfer electrons between molecules, central to energy extraction in cells.

• Oxidation: Loss of electrons.

• Reduction: Gain of electrons.

• Electron carriers: NAD+, FAD, which shuttle electrons during respiration.

Summary Equation of Cellular Respiration

The overall reaction for aerobic cellular respiration is:

• Reactants: Glucose, oxygen

• Products: Carbon dioxide, water, ATP

Stages of Cellular Respiration

• Glycolysis: Occurs in cytoplasm; glucose split into pyruvate.

• Citric acid cycle (Krebs cycle): Completes breakdown of glucose; produces electron carriers.

• Electron transport chain & chemiosmosis: Electrons transferred to oxygen; ATP produced.

Fermentation

Occurs when oxygen is absent; produces less ATP and different end products (e.g., lactic acid, ethanol).

Key Terms

• Substrate level phosphorylation: Direct transfer of phosphate to ADP.

• Oxidative phosphorylation: ATP synthesis powered by electron transport chain.

• ATP synthase: Enzyme that synthesizes ATP.

Chapter 7 – Photosynthesis

Photosynthesis Overview

Photosynthesis is the process by which plants, algae, and some bacteria convert light energy into chemical energy stored in glucose.

• Comparison with cellular respiration: Photosynthesis stores energy; respiration releases energy.

Summary Equation of Photosynthesis

The overall reaction for photosynthesis is:

• Reactants: Carbon dioxide, water, light energy

• Products: Glucose, oxygen

Structure of Leaves and Chloroplasts

• Stomata: Openings in leaves for gas exchange.

• Chloroplast: Organelle where photosynthesis occurs; contains thylakoids and stroma.

Light Reactions and Calvin Cycle

• Light reactions: Convert solar energy to chemical energy (ATP, NADPH).

• Calvin cycle: Uses ATP and NADPH to synthesize glucose from CO2.

Photosynthetic Pigments

• Chlorophyll a: Primary pigment; absorbs mainly blue and red light.

• Accessory pigments: Chlorophyll b, carotenoids; broaden absorption spectrum.

Comparing Photosynthesis and Cellular Respiration

• Photophosphorylation: ATP synthesis using light energy in photosynthesis.

• Oxidative phosphorylation: ATP synthesis using electron transport in respiration.

Chapter 8 – Cell Cycle & Division

Cell Division in Prokaryotes and Eukaryotes

Cell division is essential for growth, repair, and reproduction. Prokaryotes divide by binary fission; eukaryotes by mitosis and meiosis.

• Binary fission: Prokaryotic cell division; produces identical cells.

• Mitosis: Eukaryotic cell division for growth and repair; produces identical daughter cells.

• Meiosis: Eukaryotic cell division for sexual reproduction; produces gametes with half the chromosome number.

Chromosome Structure and Terminology

• DNA: Genetic material.

• Chromatin: DNA and protein complex.

• Sister chromatids: Identical copies joined at centromere.

• Homologous chromosomes: Chromosome pairs with same genes.

Phases of the Cell Cycle

• Interphase: Cell growth and DNA replication.

• M phase: Mitosis and cytokinesis.

Mitosis Stages

• Prophase: Chromosomes condense, spindle forms.

• Metaphase: Chromosomes align at cell equator.

• Anaphase: Sister chromatids separate.

• Telophase: Nuclear envelopes reform.

Meiosis Stages

• Meiosis I: Homologous chromosomes separate.

• Meiosis II: Sister chromatids separate.

• Genetic variability: Crossing over, independent assortment.

Cytokinesis

• Animal cells: Cleavage furrow forms.

• Plant cells: Cell plate forms.

Errors in Cell Division

• Nondisjunction: Failure of chromosomes to separate properly; can lead to genetic disorders.

Comparison Table: Mitosis vs. Meiosis