Ch.5 - Bio

Chapters 5 & 4 Overview

• Focus on cellular structures, membranes, and transport mechanisms.

Cell Membrane

• The cell membrane separates the cell from its environment, allowing for internal regulation.

• Key organelles include:

  • Mitochondrion: energy production.

  • Ribosomes: protein synthesis (free and bound to the rough endoplasmic reticulum).

  • Nucleus: houses DNA and controls cellular activities.

  • Golgi apparatus: modifies and packages proteins.

  • Endoplasmic reticulum (smooth and rough): synthesizes proteins and lipids.

  • Cytoskeleton: provides structural support.

Cell Theory

• Cell theory consists of three main principles:

  1. Cells are the fundamental units of life.

  2. All living organisms are composed of cells.

  3. All cells arise from preexisting cells.

• Additionally:

  • Hereditary information transfers from cell to cell.

  • All cells share a basic chemical composition.

  • Energy flows within cells.

Structure of Cells

• Cells are primarily composed of cytoplasm, which includes a jelly-like fluid with water, salts, and organic molecules.

• Cytosol is the aqueous component of cytoplasm containing organelles.

Membrane Composition

• Cell membranes are primarily made of a phospholipid bilayer:

  • Phospholipids are amphipathic:

    • Polar, hydrophilic heads face outward.

    • Nonpolar, hydrophobic tails face inward.

• Membrane components include:

  • Proteins (integral, peripheral, transmembrane).

  • Cholesterol: regulates membrane fluidity.

  • Carbohydrates: attached to proteins and lipids, important for cell recognition.

Fluid Mosaic Model

• Describes the cell membrane as a fluid structure with various proteins and lipids moving laterally.

• Lipids interact via weak van der Waals forces, enabling dynamic movement.

Membrane Fluidity

• Influenced by:

  • Lipid composition (short, unsaturated chains increase fluidity).

  • Temperature (higher temperatures increase fluidity).

  • Cholesterol's role during temperature fluctuations.

Transport Mechanisms

• Cell membranes are selectively permeable, allowing certain substances to cross:

  • Passive Transport:

    • Does not require energy, substances move down concentration gradients (simple diffusion, facilitated diffusion).

  • Active Transport:

    • Requires energy (ATP) to move substances against concentration gradients.

    • Types: Primary (direct ATP usage) and Secondary (ion gradient-driven).

Diffusion Basics

• Molecules move naturally from areas of high to low concentration.

• Factors affecting diffusion speed:

  • Molecule size, temperature, concentration gradient, surface area, and distance.

Osmosis

• The movement of water across membranes, driven by solute concentration differences.

  • Terms:

    • Isotonic: equal solute concentrations.

    • Hypotonic: lower solute concentration than the other solution.

    • Hypertonic: higher solute concentration than the other solution.

Endocytosis and Exocytosis

• Endocytosis: Cells ingest external materials by folding the membrane to form vesicles.

• Exocytosis: Materials packaged into vesicles are expelled out of the cell.

Types of Endocytosis

1. Phagocytosis: Engulfing large particles.

2. Pinocytosis: Taking in fluids and dissolved substances.

3. Receptor-mediated Endocytosis: Specific uptake of molecules via receptors.

Cytoskeleton

• Comprises protein filaments that provide structural support and shape.

• Types of filamentous structures:

  1. Microfilaments (actin): involved in movement and shape change.

  2. Intermediate filaments: robust structures resisting stress.

  3. Microtubules (tubulin): maintain shape and enable transport of organelles.

Organelles in Eukaryotic Cells

• Nucleus: Houses DNA and coordinates cell activities.

• Endoplasmic Reticulum (ER): Rough (protein synthesis) and smooth (lipid synthesis).

• Golgi Apparatus: Modifies, sorts, and packages proteins.

• Lysosomes: Digestive enzymes that break down waste materials.

• Mitochondria: Produce ATP through cellular respiration.

• Chloroplasts (in plants): Site of photosynthesis.

• Vacuoles: Storage and maintenance of turgor pressure in plant cells.

Extracellular Structures

• Cell wall: Provides structural support in plants, fungi, and bacteria (not in animals).

• Extracellular Matrix: Supports cell adhesion, communication, and structural integrity.

Cell Junctions

• Types of junctions in animal cells:

  1. Tight Junctions: Prevent leakages between cells.

  2. Desmosomes: Provide mechanical strength.

  3. Gap Junctions: Allow for communication between cells.

Prokaryotic vs Eukaryotic Cells

• Prokaryotic Cells: Lack a nucleus, organelles, and membrane-bound structures (e.g., bacteria).

• Eukaryotic Cells: Have a nucleus, organelles, and divide labor among compartments (e.g., plants, animals).

This structured overview provides a comprehensive foundation in cell biology for further study.