BIOL 32 Module 3 Cells

Overview of Cellular Composition and Function

Introduction to Cells

  • Cells as the smallest functional units of life.
  • Capable of carrying out all processes of life.

Components of a Cell

  1. Plasma Membrane

    • Basic definition: Structure that separates outside from inside a cell.
    • Made of
      • Phospholipids: Form a bilayer with:
      • Hydrophilic phosphate heads facing outward.
      • Hydrophobic lipid tails facing inward, creating a nonpolar barrier.
    • Also contains:
      • Cholesterol: Provides flexibility and temperature insensitivity.
      • Glycolipids: Lipids with carbohydrate tails, important for cell recognition and signaling.
    • Involves various types of proteins:
      • Integral Membrane Proteins: Span the width of the membrane (transmembrane proteins).
      • Peripheral Proteins: Located on one side of the membrane, do not span.
      • Glycoproteins: Proteins with carbohydrate attachments aiding in identification and signaling.

  2. Cytoplasm

    • Defined as the contents within the cell membrane but outside the nucleus.
    • Contains the cytosol:
      • A fluid mostly comprised of water and dissolved substances (ions, glucose, amino acids, etc.).
    • Comprises organelles (subcellular structures):
      • Ribosomes: Organelle responsible for protein synthesis (cytoprotein synthesis).
      • Endoplasmic Reticulum (ER):
      • Rough ER: Spotted with ribosomes and synthesizes proteins for export.
      • Smooth ER: Synthesizes lipids.
      • Golgi Complex:
      • Receives proteins/lipids from ER, modifies, packages and sends them out in vesicles.
      • Mitochondria:
      • Organelle that produces ATP (cellular energy).
      • Lysosomes:
      • Digestive organelle, breaks down waste and cellular debris.
      • Peroxisomes:
      • Contain enzymes for detoxifying harmful substances and metabolizing fatty acids.
      • Proteasomes:
      • Break down damaged proteins to maintain cellular health.
      • Cytoskeleton:
      • Network of protein filaments providing structural support.
      • Components:
        • Microfilaments: Smallest filaments, provide mechanical support and form cellular extensions like microvilli.
        • Intermediate Filaments: Provide strength, support organelle positioning, connect cells.
        • Microtubules: Largest components, contribute to shape, transport, and movement (cilia and flagella).
      • Centrosomes:
      • Organize microtubules and anchor cytoskeletal structures.

  3. Nucleus

    • Houses the majority of a cell's DNA, including genes.
    • Surrounded by a Nuclear Envelope:
      • Double membrane structure, continuous with the Rough ER.
    • Inside features:
      • Nucleolus: Site for ribosomal RNA synthesis.
    • DNA Organization:
      • DNA wraps around histones to form chromatin when cells are non-dividing.
      • Condenses into chromosomes during cell division (mitosis).
    • Gene Expression Process:
      • Involves transcription (DNA to RNA) in the nucleus.
      • Translation (RNA to protein) in the cytoplasm.

Cell Transport Mechanisms

Membrane Transport Mechanisms
  • Passive Transport:
    • Movement across the membrane without energy (e.g., diffusion, osmosis).
  • Active Transport:
    • Requires energy (e.g., transport proteins for glucose).

Cellular Division

  1. Mitosis (somatic cell division):
    • Phases of Mitotic Division:
      • Interphase:
      • Most of the cell's life, metabolic activity occurs.
      • Subphases:
        • G1 Phase: Cell growth; organelle duplication.
        • S Phase: DNA replication.
        • G2 Phase: Preparation for mitosis, synthesis of necessary components.
      • Prophase: Chromosomes condense, spindle apparatus forms.
      • Metaphase: Chromosomes align at the cell equator.
      • Anaphase: Sister chromatids are pulled apart.
      • Telophase: Nuclear membranes form around separated chromatid sets; cytokinesis begins.

Tissue Types and Functions

  1. Epithelial Tissue: Covers body surfaces and lines cavities.
  2. Connective Tissue: Supports, binds, and protects other tissues and organs.
    • Types: Adipose, dense connective, cartilage, blood (liquid connective tissue).
  3. Muscle Tissue: Responsible for movement (skeletal, smooth, cardiac).
  4. Nervous Tissue: Specialized for communication via electrical impulses.

Cellular Junctions

  • Specialized connections that link cells:
    1. Tight Junctions: Prevent leakage; found in epithelial tissues (e.g., lining of the stomach).
    2. Adherens Junctions: Protein plaques attaching to cytoskeleton for structural integrity.
    3. Desmosomes: Provide tissue strength; likened to buttons.
    4. Hemidesmosomes: Anchor cells to the basement membrane, allowing free apical surfaces.
    5. Gap Junctions: Allow communication; consist of connexins that form tunnels allowing ion passage.

Conclusion

  • Study of cells includes understanding structures, functions, transport mechanisms, division, and their roles in tissues. Each cellular component performs critical functions necessary for life and organismal health.