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Cell Structures and Functions

Unit 3: Cell Structures

  • Slideshow based on:
    • Campbell Book: Chapters 6 & 7
    • Miller Levine Book: Chapter 8

Lesson 6.1 & 6.2: Life is Cellular

  • Internal organization of eukaryotic cells allows them to perform vital functions through:
    • Energy and matter transformations through a system of internal membranes that synthesize and modify proteins, lipids, and carbohydrates.
    • Chloroplasts that convert light energy to chemical energy.
    • Mitochondria that break down molecules generating ATP.
    • Internal membranes divide the cell into compartments for specific chemical reactions.
    • DNA in the nucleus provides instructions for protein synthesis, with ribosomes as the sites.
    • Plasma membrane regulates cellular interaction with the environment, with plant cells possessing a protective cell wall.

Cell Theory

  • Key Principles:
    • All living things are composed of cells.
    • All cells arise from pre-existing cells.
    • The cell is the fundamental unit of life; nothing living is smaller than a cell.

Historical Contributions to Cell Theory

  • Early Discoveries:
    • Most cells are microscopic.
    • The microscope was instrumental in revealing cells (invented by Zacharias Janssen and his father).
  • Key Scientists:
    • Robert Hooke (1665): Observed cork cells using a three-lens microscope; termed cells as compartments.
    • Anton Van Leeuwenhoek (1674): Enhanced microscope power, first to describe living cells ('animalcules') from pond water.
    • Matthias Schleiden (1838): Proposed all plants are composed of cells.
    • Theodor Schwann (1839): Stated all living things consist of cells.
    • Rudolph Virchow (1855): Asserted cells originate from existing cells.

Understanding Cells: Microscopy

  • Microscopes:

    • Used for visualizing cells, light microscopy passes light through specimens resulting in magnification.
    • Key Parameters:
      • Magnification: Ratio of image size to actual size.
      • Resolution: Clarity of the image, minimum distance between distinguishable points.
      • Contrast: Visible differences in brightness within the sample.

  • Types of Microscopes:

    • Light Microscopes (LM): Magnification up to 1,000x; contrast enhanced through staining techniques.
    • Electron Microscopes (EM):
      • Scanning Electron Microscopes (SEM): Provide 3D images by focusing a beam of electrons on the surface.
      • Transmission Electron Microscopes (TEM): Electrons pass through specimens for internal structure imaging.
    • Cryo-electron microscopy (cryo-EM): Preserves specimens at low temperatures, revealing structures without preservatives.

Cell Fractionation

  • Technique: Used to separate major organelles for study.

    • Centrifugation is applied for differential separation of cellular components.
    • Helps link structure to function in cellular components.

  • Prokaryotic vs Eukaryotic Cells:

    • Common Features for All Cells:
      • Plasma membrane.
      • Cytosol (semi-fluid substance).
      • Chromosomes (genetic material).
      • Ribosomes (sites of protein synthesis).
    • Eukaryotic Cells:
      • Larger, possess membrane-bound organelles, and a nucleus.
      • Include organisms from Protista, fungi, plants, and animals.
    • Prokaryotic Cells:
      • Lack nucleus and organelles, simpler, and smaller.
      • Exist in two forms: eubacteria and archaebacteria.

Characteristics of Living Cells

  • Cells contain structures facilitating essential life functions such as:
    • Energy acquisition.
    • Reproduction.
    • Adaptation.
    • Homeostasis maintenance.
    • Single-celled organisms conduct all processes independently; multicellular organisms have specialized functions.
    • All cells contain genetic material (DNA), cytoplasm, plasma membrane, and ribosomes.

Detailed Comparison of Prokaryotic vs Eukaryotic Cells

  • Organelles in Eukaryotes:
    • Nucleus with a double-membrane-bound structure.
    • Membrane-bound organelles: mitochondria, endoplasmic reticulum, Golgi apparatus.
    • Generally larger than prokaryotic cells.
  • Prokaryotic Characteristics:
    • No nucleus or membrane-bound organelles.
    • DNA in the form of a single circular chromosome in the nucleoid region.
    • Many are unicellular.

Size & Surface Area of Cells

  • Most cells are small due to metabolism which sets limits on size for effective nutrient exchange.
  • As size increases, volume increases faster than surface area, thus impacting cellular efficiency.

Eukaryotic Cell Functions: Overview

  • Organelles: Nucleus, ribosomes, endoplasmic reticulum, Golgi apparatus, lysosomes, vacuoles, mitochondria, and chloroplasts.
  • Nucleus: Contains genetic material, site of RNA synthesis, enclosed by a double membrane.
  • Ribosomes: Make proteins either freely in the cytoplasm or attached to the endoplasmic reticulum.
  • Endoplasmic Reticulum: Synthesizes lipids and proteins; can be rough (with ribosomes) or smooth (lacking ribosomes).
  • Golgi Apparatus: Modifies, sorts, and packages proteins for secretion.
  • Lysosomes: Contain hydrolytic enzymes for breaking down macromolecules.
  • Peroxisomes: Contain enzymes for metabolic reactions, including the conversion of hydrogen peroxide.
  • Cytoskeleton: Maintains cell shape, facilitates movement, anchors organelles.
  • Plasma Membrane: Phospholipid bilayer controlling material exchange.

Cell Walls and Extracellular Components

  • Plant cells have cell walls made of cellulose, providing protection and maintaining shape.
  • Animal cells possess an extracellular matrix (ECM) comprised of glycoproteins, regulating cellular behavior and communication.
  • Cell Junctions: Include tight junctions (prevent leakage), desmosomes (anchor cells together), and gap junctions (allow communication between cells).

Homeostasis in Cells

  • The plasma membrane ensures homeostasis by regulating entry and exit of substances.
  • Mechanisms include passive processes (diffusion, facilitated diffusion, osmosis) and active transport requiring ATP.

Types of Transport Mechanisms

  • Passive Transport: Does not require energy, includes:
    • Diffusion: Movement from high to low concentration.
    • Osmosis: Specific to water movement across a selectively permeable membrane.
  • Active Transport: Requires energy to move substances against a concentration gradient.
  • Bulk Transport:
    • Endocytosis: Engulfing large molecules into cells (phagocytosis, pinocytosis).
    • Exocytosis: Exporting substances from cells

Summary of Key Differences

  • Plant Cells: Have cell walls, chloroplasts, and large vacuoles, undergo photosynthesis.
  • Animal Cells: Lack cell walls, contain centrioles, and small vacuoles; do not perform photosynthesis.
    • Both types have mitochondria and a variety of common organelles but differ in structure and function due to adaptation to their environments.

Endosymbiosis Theory

  • Suggests eukaryotes arose through symbiotic relationships between prokaryotes.
  • Mitochondria are believed to have originated from heterotrophic bacteria, while chloroplasts derived from cyanobacteria.

Final Notes

  • Review all provided diagrams and figures to understand the structural components of cells and organelles visually.
  • Connect the functions of the organelles with their structures for a comprehensive understanding of cellular biology.