Prokaryotes vs Eukaryotes

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  • 1. STRUCTURE, FUNCTION & GROWTH OF PROKARYOTIC & EUKARYOTIC CELLS
  • 2. Prokaryotic and Eukaryotic Cells
    • All living creatures are made up of CELLS , small membrane bound units filled with aqueous solutions of chemicals, which have the ability to create copies of themselves by growing and dividing.
    • [The sizes of cells and organelles]
  • 3.
    • Living organisms can be classified into 3 major domains:
    • Bacteria
    • Archaea
    • Plant cells
    • Animal cells
    • Prokaryotes and Eukaryotes are 2 distinct cell types with STRUCTURAL differences
    PROKARYOTES EUKARYOTES
  • 4. The Prokaryotic Cell
    • Simply stated, prokaryotes are molecules surrounded by a membrane and cell wall.
    1 um
  • 5. Prokaryotes
    • Lack a membrane bound nucleus enclosing the DNA
    • DNA is present as a single circular molecule called a BACTERIAL CHROMOSOME
    • DNA is naked having no associated histone proteins
    • No membrane bound organelles
    • Apart from the DNA nucleoid, there is little internal structure apart from dissolved substances and a large number of RIBOSOMES essential for PROTEIN SYNTHESIS
    • The cytosol is an effective site for bacterial cell metabolism. This allows bacteria to adapt quickly to changing nutritional conditions, but means the regulation of genetic and metabolic activity has to be tightly regulated.
    • Divide by BINARY FISSION
    • Some prokaryotic cells have external whip-like FLAGELLA for locomotion or hair like PILI for adhesion.
    • Prokaryotic cells come in multiple shapes: cocci (round), baccilli (rods), and spirilla or spirochetes (helical cells).
  • 6. External Prokaryotic Structures
    • Cell Wall
    • Contains PEPTIDOGLYCAN (only found in bacteria). Large complex molecule consisting of polysaccharide polymers cross-linked by short chains of amino acids
    • Capsules
    • Sometimes the cell wall is further surrounded by a gelatinous polysaccharide sheath called an attach CAPSULE , GLYCOCALYX or SLIME LAYER
    • Plasma Membrane
    • Basic structure of the phospholipid bilayer is the same for all bacteria
    Flagella Motile bacteria usually have long, thin appendages called FLAGELLA . These protein sub-units are used to propel bacteria through liquids
  • 7.
    • Pili or Fimbrae
    • A pilus ( Latin ; plural : pili ) is a hairlike protein structure on the surface of a bacterial cell, required for bacterial conjugation (transfer of genetic material)
    • A fimbrium (Latin; plural: fimbria ) is a short pilus that is used to attach the cell to a surface. Mutant bacteria that lack fimbria cannot adhere to their usual target surfaces and, thus, cannot cause diseases.
  • 8. Spores & Cysts
    • These are produced by some bacteria to survive unfavourable environmental conditions. Dormant forms are metabolically inactive and only germinate under suitable conditions
    ENDOSPORES : a dormant , tough, non-reproductive structure produced by a small number of bacteria . The primary function of most endospores is to ensure the survival of a bacterium through periods of environmental stress. They are therefore resistant to ultraviolet and gamma radiation , desiccation , lysozyme , temperature , starvation , and chemical disinfectants . Endospores are commonly found in soil and water, where they may survive for long periods of time e.g. Clostridium (tetanus, gas gangrene), Bacillus (anthrax) CYSTS : also dormant, but unlike endospores are not resistant to heating at high temperatures
  • 9. Classifying Prokarotes
    • Main method is using the GRAM’S STAIN
    • This separates bacteria into GRAM-POSITIVE (purple) and GRAM-NEGATIVE (red) depending on the percentage of PEPTIDOGLYCAN in the cell walls
    • - GRAM-POSITIVE bacteria have a cell wall only 1 layer thick
    • - GRAM-NEGATIVE bacteria have a cell wall several layers thick
  • 10. Eukaryotes
    • More complex multicellular organisms e.g. plants, animals, fungi and also many single-celled organisms e.g. amoeba, yeast
    • Possess an NUCLEUS and other organelles all of which are surrounded by a MEMBRANE , which divided the cell up into compartments
    COMPARTMENTALISATION: very important !
    • ADVANTAGES:
    • Molecules are ‘concentrated’ together, increases rate of reactions
    • Keeps reactive molecules away from other parts of the cell that may be affected by them
    • Large work surface area … many enzymes are bound in membranes
  • 11. Eukaryotes
    • The basic eukaryotic cell contains the following:
    • - membrane-bound nucleus
    • - plasma membrane
    • - glycocalyx (components external to the plasma
    • membrane)
    • - cytoplasm (semifluid)
    • - cytoskeleton – microfilaments, intermediate filaments and
    • microtubules that suspend organelles, give
    • shape, and allow motion
    • - presence of characteristic membrane
    • enclosed subcellular organelles e.g.
    • mitochondria, golgi, rER, sER etc
  • 12. Plant & Animal Cells
    • For ANIMAL CELLS only:
          • Peroxisomes & Lysosomes often present
          • Some have microvilli on their surface
          • Centrioles organise spindle fibres during cell division
    • For PLANT CELLS only:
          • Cell walls made from cellulose
          • Communication with neighbouring cells occurs through plasmodesmata
          • Usually a large central vacuole
          • Photosynthesis occurs in cells containing chloroplasts
    [Stick in & label plant & animal cell diags]
  • 13. Plasma Membrane
    • Plasma Membrane
    • A lipid/protein/carbohydrate complex, providing a barrier and containing transport and signalling systems.
  • 14. Nucleus
    • Nucleus
    • Double membrane surrounding the chromosomes and the nucleolus. Pores allow specific communication with the cytoplasm. The nucleolus is a site for synthesis of RNA making up the ribosome
  • 15. Mitochondria
    • Mitochondria
    • Surrounded by a double membrane with a series of folds called cristae.
    • Functions in energy production through metabolism.
    • Contains its own DNA, and is believed to have originated as a captured bacterium.
  • 16. Rough endoplasmic reticulum (RER)
    • Rough endoplasmic reticulum (RER)
    • A network of interconnected membranes forming channels within the cell.
    • Covered with ribosomes (causing the "rough" appearance) which are in the process of synthesizing proteins for secretion or localization in membranes.
    • Ribosomes
    • Protein and RNA complex responsible for protein synthesis
  • 17. Golgi Apparatus
    • Golgi apparatus
    • A series of stacked membranes. Vesicles (small membrane surrounded bags) carry materials from the RER to the Golgi apparatus.
    • Vesicles move between the stacks while the proteins are "processed" to a mature form.
    • Vesicles then carry newly formed membrane and secreted proteins to their final destinations including secretion or membrane localisation.
  • 18. Centrioles
    • Centrioles
    • Centrioles are found only in animal cells. They function in cell division.
  • 19. Lysosymes
    • Lysosymes
    • A membrane bound organelle that is responsible for degrading proteins and membranes in the cell, and also helps degrade materials ingested by the cell.
  • 20. Peroxisomes
    • Peroxisomes or Microbodies
    • Produce and degrade hydrogen peroxide, a toxic compound that can be produced during metabolism
  • 21. Chloroplasts
    • Chloroplasts
    • Surrounded by a double membrane, containing stacked thylakoid membranes.
    • Responsible for photosynthesis, the trapping of light energy for the synthesis of sugars.
    • Contains DNA, and like mitochondria is believed to have originated as a captured bacterium.
  • 22. Vacuoles
    • Vacuoles
    • Membrane surrounded "bags" that contain water and storage materials in plants.
  • 23. Cell wall
    • Cell wall
    • Plants have a rigid cell wall in addition to their cell membranes. They provide support for the plant.
  • 24. Similarities between P & E cells
    • Prokaryotes & Eukaryotes are CHEMICALLY & METABOLICALLY similar:
      • Both have genetic material
      • Both have a cell membrane
      • Both have a cytosol
      • Both have ribosomes
      • Both contain nucleic acids, proteins, carbohydrates & lipids
      • Both use similar reactions for storing energy and metabolic activities e.g. building proteins
  • 25. Differences between P & E cells
    • Main differences are STRUCTURAL :
    Cell size ranges from 10 – 150um Cell size ranges from 0.5um to 100um No mucilaginous capsule present (numerous internal structures present including microtubules, ER, Golgi, secretory vesicles etc) Mucilaginous capsule Have cilia or flagella (for movement) Have pili & fimbriae (for adhesion) and flagella (for propulsion) Membrane bound organelles (compartmentalisation) No membrane bound organelles Cell walls, if present, made of cellulose (chitin in fungi) Cell walls made of peptidoglycan (Thickness of wall depends on whether the cell is Gram +ve or –ve) Membrane bound nucleus No membrane bound nucleus EUKARYOTES PROKARYOTES
  • 26. Comparison of Prokaryotic and Eukaryotic Cells