Cell Structure and Function Summary

Cell Structure

  • Cell Definition: Key structural unit of all living organisms.
Prokaryotic Cells
  • Characteristics: 0.2 to 2 µm diameter, unicellular, no nucleus, no membrane-bound organelles.
  • Reproduction: Mitosis or binary fission.
  • DNA: Circular DNA (plasmid) and linear DNA.
  • Examples: Bacteria and Archaea.
Eukaryotic Cells
  • Characteristics: 10 to 100 µm diameter, unicellular and multicellular, contains nucleus, has membrane-bound organelles.
  • Reproduction: Mitosis and meiosis.
  • DNA: Linear only.
  • Examples: Plant, animal, fungi, protista cells.

Characteristics of Life

  1. Growth & Development: Organisms grow and develop complexity.
  2. Energy Metabolism: Acquire energy through eating, breathing, waste excretion.
  3. Homeostasis: Maintain internal balance.
  4. Adaptation: Evolve over time through natural selection.
  5. Response to Stimuli: React to environmental changes.
  6. Cells: Composed of at least one cell with complex structures.
  7. Reproduction: Offspring generation with new DNA combinations.

Cell Organelles

  • Common Structures (all cells): Ribosomes, chromosomes, cytoplasm, cell membrane.
  • Membrane-bound Organelles: Found only in eukaryotes (e.g., mitochondria, Golgi apparatus, endoplasmic reticulum).
  • Double Membrane Organelles: Mitochondria, chloroplasts, nucleus.
Ribosomes
  • Site of protein synthesis, composed of RNA and proteins, visible only via electron microscopy.
Cytoskeleton
  • Network of protein filaments (microtubules and microfilaments)
    • Microtubules: Thick tubes; form cilia, flagella, centrioles.
    • Microfilaments: Made of actin; aid in cell movement and muscle contraction.
Nucleus
  • Eukaryotic control center, surrounded by a double membrane, contains chromatin and nucleolus.
Endoplasmic Reticulum (ER)
  • Network of membranes in eukaryotic cells.
    • Rough ER: Associated with ribosomes, synthesizes and transports proteins.
    • Smooth ER: Lacks ribosomes, synthesizes lipids, detoxifies, metabolizes carbohydrates.
Golgi Apparatus
  • Modifies, stores, and packages proteins from the ER, creates lysosomes and vesicles.

Mitochondria and Chloroplasts

  • Mitochondria: Site of cellular respiration, contains ribosomes and own DNA.
  • Chloroplasts: Site of photosynthesis in plants and algae, green due to chlorophyll.

Cell Membrane

  • Selective Permeability: Controls entry/exit of substances; consists of phospholipid bilayer, proteins, cholesterol, and carbohydrates.
  • Fluid Mosaic Model: Membrane structure where components move within the layer.
Cell Wall
  • Structural layer outside cell membrane; found in bacteria (peptidoglycan), fungi (chitin), and plants (cellulose).

Cell Transport

  • Passive Transport: Does not require energy; involves diffusion (simple, facilitated) and osmosis.
  • Active Transport: Requires ATP; moves substances against the gradient (e.g., Na+/K+ pump).
  • Endocytosis and Exocytosis: Processes for molecules entering/leaving the cell.

Surface Area to Volume Ratio

  • Cells divide when surface area is insufficient for nutrient intake. Folds in membranes increase efficiency.