AP1 - 1.3 - The Cell

Overview of Cells

  • Cells are the basic structural and functional units of the body.
  • Cells vary in structure and function but all contribute to forming tissues.
  • They come in various shapes and sizes, each specialized for different tasks.

Classification of Cells

Prokaryotic Cells

  • Definition: Cells without a nucleus.
  • These are not human body cells but exist as pathogens or beneficial microorganisms.
  • Examples:
    • Pathogens that cause diseases.
    • Beneficial bacteria in the gut that assist in digestion.

Eukaryotic Cells

  • Definition: Cells that contain a nucleus and are membrane-bound.
  • Key Characteristics:
    • Contain DNA inside a defined nucleus.
    • Membrane-bound organelles.
  • Importance: Eukaryotic cells make up human body tissues.

Cell Structure and Organelles

Plasma Membrane

  • Function: Surrounds all cells, allowing selective movement of substances.
  • Dynamic Nature:
    • Composed of specialized pumps and gates to regulate what enters and exits the cell.
    • Not a solid barrier; allows constant movement and fluidity.

Nucleus

  • Known as the control center of the cell.
  • Main Regions:
    • Nuclear Envelope: Outer boundary that regulates movement of materials in and out of the nucleus.
    • Nucleolus: Central region involved in ribosome production.
    • Chromatin: Genetic material that condenses to form chromosomes during cell division.

Interstitial Fluid

  • Definition: Fluid that fills the spaces between cells in tissues.
  • Importance: Provides nutrients and facilitates waste removal for cells.

Cytoskeleton Components

Microtubules
  • Structure: Made of tubulin subunits and form a network from the centrosome.
  • Function: Help maintain cell shape and provide support.
Microfilaments
  • Location: Found along the outer edges of the cell.
  • Function: Assist in maintaining the structure and shape of the cell.

Genetic Material and Protein Synthesis

Chromosomes

  • Definition: Packaged form of DNA containing genetic information.
  • Nucleotides: Composed of adenine (A), thymine (T), guanine (G), and cytosine (C).
  • Genes: Segments of DNA that code for proteins.

Transcription and Translation

  • Messenger RNA (mRNA): Transfers genetic information from DNA to ribosomes.
  • Types of RNA:
    • tRNA (Transfer RNA): Assists in protein synthesis by delivering amino acids to ribosomes.
  • Codons: Groups of three nucleotides that correspond to a specific amino acid.
  • Significance: Defines cell uniqueness through protein production.

Organelles Involved in Protein Processing

Endoplasmic Reticulum (ER)

  • Rough Endoplasmic Reticulum (RER):

    • Characterized by ribosomes on its surface.
    • Involved in protein synthesis.

  • Smooth Endoplasmic Reticulum (SER):

    • Lacks ribosomes, involved in lipid synthesis and detoxification (especially in liver cells).

Golgi Apparatus (Golgi Complex)

  • Structure: Series of flattened sacs (cisternae).
  • Function: Packages proteins and directs them to their destinations, either within the cell or for secretion.
    • Options for vesicles:
    • Remain inside for internal use.
    • Fuse with cell membrane for incorporation.
    • Form secretory vesicles to export materials outside the cell.

Lysosomes

  • Function: Contain digestive enzymes that act as the cell's recycling center.
  • Processes: Break down large biomolecules, pathogens, and cell debris for reuse or excretion.
  • Example of Dysfunction: Tay-Sachs disease - a genetic disorder caused by the lack of a specific lysosomal enzyme, leading to lipid accumulation in the brain.

Proteasomes

  • Definition: Non-membrane-bound organelles responsible for protein recycling.
  • Function: Degrade damaged or unnecessary proteins into peptides for reuse.

Cellular Energy and Mitochondria

ATP (Adenosine Triphosphate)

  • Definition: The primary energy currency of the cell.
  • Importance: Provides the energy necessary for cellular activities.

Aerobic Cellular Respiration

  • Definition: The process by which cells generate ATP in the presence of oxygen.
  • Required Ingredients:
    • Oxygen and glucose are the main reactants.
  • By-products include carbon dioxide and water.
    • Summary Reaction:
      Glucose + O_2
      ightarrow CO_2 + H_2O + ATP

Mitochondria

  • Structure: Organelles with a double membrane, highly folded inner membrane to maximize surface area for reactions.
  • Function: Site of aerobic respiration, producing ATP efficiently.

Cell Membrane and External Features

Cell Coat

  • Definition: The external layer of the plasma membrane, consisting of glycoproteins and glycolipids.

Surface Area to Volume Ratio

  • Importance: Smaller cells generally have a higher surface area to volume ratio, allowing more efficient transport of materials.
  • Implication: Cells must balance size to maximize efficiency in function.

Conclusion

  • Cells are crucial to the functioning of living organisms, carrying out essential processes required for life. They maintain tissue health through their diverse roles and complex interactions within the body.