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: 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. Kinetic energy is energy of motion, while potential energy is stored energy.

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

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

Exergonic and Endergonic Reactions

Biochemical reactions are classified by their energy changes:

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

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

• Activation energy: The energy required to start a reaction.

ATP and Enzyme Function

ATP (Adenosine Triphosphate) is the cell's main energy currency. Enzymes are biological catalysts that speed up reactions by lowering activation energy.

• ATP hydrolysis: releases energy.

• Enzyme structure: Includes active site, substrate, and product.

• Factors affecting enzyme activity: Temperature, pH, substrate concentration.

Chapter 6 – Cellular Respiration & Fermentation

Cellular Respiration Overview

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

• Breathing vs. cellular respiration: Breathing exchanges gases; cellular respiration uses O2 to produce ATP.

• Redox reactions: Transfer electrons between molecules; oxidation is loss, reduction is gain of electrons.

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

Cellular respiration occurs in three main stages:

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

• Krebs Cycle (Citric Acid Cycle): Occurs in mitochondria; completes breakdown of glucose.

• Electron Transport Chain: Uses electrons to produce ATP via oxidative phosphorylation.

Electron Carriers and ATP Synthesis

Electron carriers (NAD+, FAD) transport electrons to the electron transport chain, where ATP is synthesized.

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

• Oxidative phosphorylation: ATP synthesis powered by electron transport and chemiosmosis.

• ATP synthase: Enzyme that produces ATP from ADP and inorganic phosphate.

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.

• Photosynthesis vs. 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

Photosynthesis occurs in the chloroplasts, mainly in the leaves.

• Stomata: Pores in leaves for gas exchange.

• Chloroplast structure: Includes thylakoids, grana, and stroma.

Light Reactions and Calvin Cycle

Photosynthesis consists of two main stages:

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

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

Photosynthetic Pigments

Pigments absorb light energy for photosynthesis.

• Chlorophyll a: Primary pigment.

• Accessory pigments: Chlorophyll b, carotenoids (absorb different wavelengths).

Comparing ATP Production

Photosynthesis and cellular respiration both produce ATP, but via different mechanisms.

• Photophosphorylation: ATP synthesis during photosynthesis.

• Oxidative phosphorylation: ATP synthesis during cellular 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: Simple division in prokaryotes.

• Mitosis: Produces identical daughter cells for growth and repair.

• Meiosis: Produces gametes for sexual reproduction; introduces genetic variation.

Chromosome Structure and Terminology

Chromosomes carry genetic information and undergo duplication before cell division.

• DNA: Genetic material.

• Chromatin: DNA and protein complex.

• Sister chromatids: Identical copies joined at the centromere.

Cell Cycle Phases

The cell cycle consists of interphase (G1, S, G2) and mitotic phase (mitosis and cytokinesis).

• Interphase: Cell growth and DNA replication.

• Mitosis: Division of the nucleus; includes prophase, metaphase, anaphase, telophase.

• Cytokinesis: Division of the cytoplasm.

Meiosis and Genetic Variation

Meiosis reduces chromosome number by half and increases genetic diversity.

• Homologous chromosomes: Chromosome pairs with the same genes.

• Crossing over: Exchange of genetic material between homologs.

• Independent assortment: Random distribution of chromosomes.

• Stages of meiosis: Meiosis I (reduction division), Meiosis II (equational division).

Errors in Cell Division

Errors such as non-disjunction can lead to abnormal chromosome numbers (e.g., Down syndrome).

• Non-disjunction: Failure of chromosomes to separate properly.

• Consequences: Genetic disorders due to extra or missing chromosomes.

Comparison Table: Mitosis vs. Meiosis

Additional info: Key figures referenced in the notes (e.g., Figure 6.6, 7.2, 8.16) are likely from the course textbook and can be reviewed for visual understanding of these processes.