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Week 5 (Epithelial Tissue (Junctions (Desmosomes are strong adhesions…

- - - - These are multipotential embryonic cells.
  - - - Found in the dermis of the skin and in the walls of veins and arteries.
    - - Adipose tissue contains adipocytes which have the main role of storing nutrients, providing insulation, and providing support.
      - White fat contains a single, large droplet of fat, and brown fat contains adipocytes and small lipid droplets and mitochondria.
    - - Contains Type III collagen fibres that support tissues.
    - - Found in tendons and ligaments as these structures require to be pulled in one direction in order to allow for bones to move.
    - - This type of tissue is 'packing material' and allows for blood vessels, nutrients, wastes, and nerves to pass through. It surrounds and supports glands, muscles, nerves, and is a medium through which the body fights against pathogens.
    - - This tissue contains the papillary dermis which is loose areolar connective tissue, and the reticular dermis which is dense, irregular connective tissue. Fibres run in all directions in this tissue and therefore give strength in all directions.
- - - - Nucleus: Contains all of the genetic information for the operation and eventual duplication of the cell. The nucleus is contained within the nuclear membrane and within it contains the nucleolus, which is responsible for the synthesis of ribosomal units (for the production of ribosomes). The nucleus also is able to synthesise mRNA, tRNA, and rRNA. The nucleus is also responsible for RNA transcription.
        Endoplasmic Reticulum: The rough endoplasmic reticulum is responsible for facilitating protein synthesis with ribosomes and also packaging these proteins into vesicles to be sent to the Golgi apparatus. The smooth endoplasmic reticulum on the other hand has many roles as it is able to convert glycogen into glucose for use as energy, it is able to detoxify the cell from alcohols, and can also synthesise sex hormones and cholesterol.
        Golgi Apparatus: The Golgi apparatus is the 'traffic controller' of the cell and is responsible for the packaging and distribution of proteins around the cell. It may add certain functional groups to the protein if necessary to alter their function.
        Mitochondrion: The mitochondrion is responsible for the generation of energy for the cell. It contains many cisternae which have the function of generating ATP, and is able to replicate itself independently from the genetic material of the nucleus as it contains some genetic material within itself.
        Vacuole: Vacuoles have the function of being places for storage within the cell. The vacuole is also able to maintain homeostasis within the cell as it is able to alter the pH of the cell, and also the concentration of water.
        Peroxisome: Peroxisomes have the role of detoxifying the cell. This is through the process of turning free radicals, which may also arise from alcohols, into hydrogen peroxide, which can be later broken down into water.
        Lysosome: Lysosomes contain digestive enzymes, stored within an acidic environment, which are able to break down the waste products or foreign contaminants of the cell. These enzymes break down the substance and the organelle is essentially able to consume the waste.
    - - Outer Membrane: The outer membrane is the protective layer of gram-negative bacteria and is encased in lipopolysaccharides, which are molecules responsible for inciting an inflammatory response from the host when in contact. Depending on the cell, the outer-most membrane (peptidoglycan layer in gram-positive bacteria) can contain fimbriae or pili, which are essential for the reproduction and position of prokaryotic cells. Cilia and flagella can also be present as cellular projections to assist in the motility of the cell.
        Cell Wall (Peptidoglycan Layer): The peptidoglycan layer is the main protective border more so for gram-positive bacteria than gram-negative bacteria as it is thicker than the one found in gram-negative bacteria, and that gram-positive bacteria do not contain an outer membrane. It is made of inter-weaving n-acetylmuramic acid and n-acetylglucosamine with linking proteins to bind these together. It allows the cell to also interact with its surroundings as gram-positive bacteria also contain teichoic acid channels which allow for the transfer of substances across this layer. Antibiotics such as penicillin are able to specifically target the linking proteins in the peptidoglycan layer, therefore weakening it and allowing for bacteria to be controlled. As the peptidoglycan layer of gram-negative bacteria is sandwiched between the inner and outer membranes, it is said to have endotoxins, whilst as the peptidoglycan layer of gram-positive bacteria is present at the surface, it has exotoxins. Gram-negative bacteria also contain lipoproteins which are responsible for adhesion as well. Both gram-positive and gram-negative bacteria also contain porin proteins which are proteins that are able to pass molecules through the peptidoglycan layer.
        Cytoplasmic membrane: The cytoplasmic membrane is the inner-most protective layer of gram-negative and gram-positive bacteria. It is similar to a plasma membrane in a eukaryotic cell in that it is made up of a lipid bilayer that allows for protection and the passage of molecules or solutes through the membrane. This membrane also carries out functions that are done by organelles in a eukaryotic cell such as production of energy and secretion of proteins and enzymes.
        Cytoplasm: The cytoplasm is the main medium at which cellular activities take place. Although prokaryotic cells do not contain any true organelles, they do contain a grouping of DNA in the centre of the cell called a nucleoid, and plasmids, which code for the characteristics of the cell such as antibiotic resistance. Prokaryotic cells contain no cytoskeleton.
        Nucleoid: The nucleoid contains the genetic material of the prokaryotic cell for its reproduction.
        Ribosomes: Ribosomes are responsible for the production of proteins in a prokaryotic cell. These organelles are smaller than the ones in eukaryotic cells (70S compared to 80S).
        Storage granules: Storage granules are responsible for the storage of solutes and molecules in the prokaryotic cell. Also just called nutrient reserves.
        Fimbriae and Pili: Fimbriae are only present in gram-negative bacteria and are responsible for the bacterial cells' adherence to surfaces. They play a major role in the virulency of bacteria as without this fimbriae, bacteria would not have been able to cause infection (no way to adhere to surfaces). Pili on the other hand are longer than fimbriae but shorter than flagella and can be either used as grappling hooks for the bacterium to move around, or for reproduction in which the bacteria can transfer genetic material to another by docking pili
        Flagellum: These are long extensions from the bacterium and are responsible for the motility of the cell.
      - The five modes of action for antibiotics: Inhibition of cell wall synthesis, inhibition of protein synthesis, inhibition of nucleic acid replication and transcription, injury to plasma membrane, and inhibition of the synthesis of essential metabolites.
      - Gram-positive bacteria stain purple and gram-negative bacteria stain pink.