Ch.3

ANATOMY & PHYSIOLOGY - Third Edition Study Notes

Chapter 3: The Cellular Level of Organization

Overview of Cellular Components

  • Key Parts of the Cell: Slide Overview

    • Membranes and transport across a plasma membrane

    • Active Transport

    • Passive Transport

    • Organelles

    • Gene Structure and Function

    • Cell Cycle

    • Mitosis and Meiosis

Cytoskeleton and Cellular Structures

  • Cytoskeleton

    • Microtubule: Hollow structures providing shape and support.

    • Microfilament: Thinnest filaments involved in muscle contraction and cell movement.

    • Intermediate Filament: Fibers providing structural stability to cells.

    • Microvilli: Projections that increase surface area for absorption.

  • Centrosome:

    • Pericentriolar Material: Area surrounding the centrioles, involved in microtubule organization.

    • Centrioles: A pair of small cylindrical structures involved in cell division.

  • Plasma Membrane:

    • Selective barrier allowing passage of substances in and out of the cell.

  • Cytoplasm:

    • Comprises cytosol and organelles excluding the nucleus.

  • Nucleus:

    • Large organelle housing chromosomes (DNA associated with proteins).

Membrane Structure

  • Lipid Bilayer:

    • Composed of phospholipids, cholesterol, and glycolipids.

    • Fluid Mosaic Model: Describes the plasma membrane’s flexibility and composition of various proteins and lipids.

    • Phospholipid:

    • Hydrophilic Head: Polar part facing extracellular fluid or cytosol.

    • Hydrophobic Tails: Nonpolar fatty acid tails facing inward.

    • Function: Allows lipid-soluble molecules to pass; creates a barrier to charged/polar molecules.

  • Membrane Proteins:

    • Integral Proteins: Extends across the membrane, often functioning as channels or carriers.

    • Peripheral Proteins: Loosely attached to the membrane surface, involved in signaling and maintaining cell structure.

Functions of Membrane Proteins

  • Ion Channels: Allow specific ions to pass through.

  • Carriers: Transport polar molecules across the membrane.

  • Receptors: Bind to ligands, initiating cellular responses.

  • Enzymatic Activity: Catalyze reactions on membrane surfaces.

  • Linkers: Anchor proteins to cells or the cytoskeleton.

  • Cell Identity Markers: Involved in recognition during tissue formation.

Membrane Characteristics

  • Fluidity: Components can move laterally within the membrane, promoting growth and healing.

  • Selective Permeability:

    • Allows nonpolar molecules to diffuse while requiring proteins for selective passage of polar/charged molecules.

  • Gradients:

    • Concentration Gradient: Difference in molecule quantity.

    • Electrochemical Gradient: Difference in ion charge distribution.

Transport Across Plasma Membrane

  • Critical for Cell Life:

    • Substances enter to support metabolism and wastes/products exit.

  • Active Transport: Requires ATP to move substances against gradients.

    • Examples:

    • Sodium-potassium pump (Na^+/K^+ ATPase): Maintains concentration gradients by moving Na+ out and K+ into cells.

  • Passive Transport: Movement along concentration gradients without energy.

    • Types:

    • Simple Diffusion: Movement of nonpolar substances through the lipid bilayer.

    • Channel-Mediated: Ions move through integral proteins, can be gated.

    • Carrier-Mediated: Specific proteins shape change to carry molecules across.

Osmosis:

  • Definition: The diffusion of water across a semipermeable membrane toward higher solute concentration.

  • Hydrostatic Pressure: Force exerted by water.

  • Osmotic Pressure: Force exerted by solute concentration opposing hydrostatic pressure.

Osmotic Concentration Types

  • Isotonic: Equal solute concentrations.

  • Hypertonic: Higher solute concentrations.

  • Hypotonic: Lower solute concentrations.

  • Aquaporins facilitate faster water transport.

Active Transport Mechanisms

  • Active transport is necessary for maintaining cellular environments.

Types of Active Transport

  1. Primary Active Transport: Direct ATP usage to transport substances (e.g., Na+/K+ pump).

  2. Secondary Active Transport: Utilizes energy stored in other gradients created by primary active transport.

    • Antiporters: Move substances in opposite directions.

    • Symporters: Move substances in the same direction.

  3. Vesicular Transport: May involve receptor proteins.

    • Endocytosis: Moving substances into the cell.

    • Exocytosis: Releasing substances from the cell.

    • Transcytosis: Transport across cells.

Details of Endocytosis Types

  • Receptor-Mediated Endocytosis: Highly specific, involving receptors.

  • Phagocytosis: Engulfing large particles.

  • Bulk-Phase Endocytosis: Non-specific intake of fluids and solutes.

Cellular Organelles

  • Organelles: Structures within cells performing specified functions.

  • Mitochondria:

    • Double membranes; involved in ATP production via the electron transport system.

    • Contain their own DNA and self-replicate.

Endoplasmic Reticulum (ER)

  • Rough ER (RER): Studded with ribosomes; synthesizes proteins.

  • Smooth ER (SER): Lacks ribosomes; involved in lipid synthesis and detoxification.

Golgi Apparatus

  • Function: Modifies, sorts, and packages proteins and lipids.

  • Processed products: Vesicles transport to final destinations.

Vesicular Organelles

  • Lysosomes: Contain enzymes for digestion.

  • Peroxisomes: Involved in detoxifying harmful substances.

  • Proteasomes: Break down proteins.

Cytoskeleton Functions

  • Provides structural framework and facilitates movement.

  • Contains three main components:

    • Microfilaments: Provide mechanical strength and support.

    • Intermediate Fibers: Stabilize organelles.

    • Microtubules: Determine cell shape and transport organelles.

Nucleus and Gene Structure

  • Nucleus: Contains genetic material; site for transcription.

  • Chromatin: DNA and associated proteins in non-dividing cells.

    • Chromosomes: Formed during cell division; made up of chromatin.

Gene Expression

  • Transcription: Process where DNA is copied into mRNA by RNA polymerase.

  • Translation: Process of converting mRNA into a protein via ribosomes.

Exons and Introns

  • Exons: Coding regions for proteins.

  • Introns: Non-coding regions; removed from mRNA during processing.

Eukaryotic Cell Cycle

  • Consists of phases G1, S, G2, M, and C (cytokinesis).

  • Mitosis: Process of cell division divided into five phases: Prophase, Prometaphase, Metaphase, Anaphase, Telophase.

    • Key events occur in each phase, including chromatid separation and nuclear envelope formation.

Comparison of Meiosis and Mitosis

  • Meiosis: Two divisions producing four genetically distinct cells (haploid).

  • Mitosis: Single division creating two genetically identical cells (diploid).

  • Crossing-over occurs during meiosis, enhancing genetic diversity.