<aside> 💡 An introduction to Cells & Microscopy

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1. To consider the concepts which underpin the cell theory

   1. Cells are the basic structural and functional units of living organisms

   2. Cells are alive

      • Cells must be able to adapt, grow & reproduce.

      

   3. Cells are activity dictates activity of organism (complementarity of structure)

      1. Biochemical activities of cels depend on specific sub cellular structures
      2. Principle of complementary structure

   4. Cell Cycle

      

      

      Interphase:

      • DNA is present as uncondensed chromatin (not visible under microscope)
      • DNA is contained within a clearly defined nucleus
      • Centrosomes and other organelles have been duplicated
      • Cell is enlarged in preparation for division

      Prophase:

      • DNA supercoils and chromosomes condense (becoming visible under microscope)
      • Chromosomes are comprised of genetically identical sister chromatids (joined at a centromere)
      • Paired centrosomes move to the opposite poles of the cell and form microtubule spindle fibres
      • The nuclear membrane breaks down and the nucleus dissolves

      Metaphase:

      • Microtubule spindle fibres from both centrosomes connect to the centromere of each chromosome
      • Microtubule depolymerisation causes spindle fibres to shorten in length and contract
      • This causes chromosomes to align along the centre of the cell (equatorial plane or metaphase plate)

      Anaphase:

      • Continued contraction of the spindle fibres causes genetically identical sister chromatids to separate
      • Once the chromatids separate, they are each considered an individual chromosome in their own right
      • The genetically identical chromosomes move to the opposite poles of the cell

      Telophase:

      • Once the two chromosome sets arrive at the poles, spindle fibres dissolve
      • Chromosomes decondense (no longer visible under light microscope)
      • Nuclear membranes reform around each chromosome set
      • Cytokinesis occurs concurrently, splitting the cell into two

   • 3 main features of cells

     

     1. Plasma/cell membrane

        • Allowing cells to be self contained and forming a barrier

          

     2. Cytoplasm

        • Intracellular solution containing organelles and structures for functioning

          

     3. Nucleus

     

2. To consider the value of cell biology, and the biological sciences, in the study and practice of medical science

   1. Anatomy
      1. Structure of cells and their communities
   2. Physiology
      1. Functions and interactions of cells and their communities
   3. Microbiology & Immunology
      1. The structure/function/interaction between human and nonhuman cells
   4. Molecular Biology & Biochemistry
      1. The processes required for cells to survive, adapt and regulate themselves
   5. Genetics
      1. How developmental and adaptive processes are regulated within cells
   6. Pathology
      1. The effects of damage to cells and how this creates illness
   7. Pharmacology
      1. Chemical interactions between cells and “drugs”
   8. Histology
      1. A branch of anatomy concerned with the study of the microscopic structures of animal and plant tissue.
         1. The resolving power of a light microscope is limited to about 0.2 μm (200 nm) and the study of ultrastructure of the cell is only possible using electron microscopy (EM) techniques (with a much better resolution of around 1.0 nm)
      2. Histotechniques

         1. Tissue collection

            1. Tissue specimens biopsied
               1. living
               2. Non living
            2. The tissue type collected will often determine the method of tissue collection.

         2. Fixation

            1. Preserves tissues, antigenicity and enhances refractive index of tissue constituents
            2. Occurs immediately after removal and collection to prevent autolysis and putrefaction of tissues
            3. Fixative: formaldehyde

         3. Tissue Processing

            processed of preparing tissue to be sectioned

            1. Dehydration
               1. Wet fixed tissues (in aqueous solutions) cannot be directly infiltrated with paraffin.
               2. water in tissues must be dehydrated using series of alcohols (70% to 95% to 100%)
            2. Clearing
               1. removal of dehydrant with a substance that will be miscible with embedding medium (paraffin)
            3. Embedding
               1. “embedding” the tissue in an embedding agent/media (almost always paraffin) that will support the tissue structure and allow sectioning
                  1. paraffin similar in density to tissue, can be sectioned at anywhere from 3 to 10 microns (μm), usually 6-8 routinely.
                  2. Paraffins can be purchased that differ in melting point, for various hardnesses, depending upon how histotechnologist preference and climate (warm vs. cold).
      3. Sectioning
         1. Cut into sections by a microtome (knife with mechanism for advancing paraffin block standard distances across it.
         2. A very sharp knife is a necessity
         3. Common artefacts: tearing, ripping, holes, folding
         4. Once sections are cut, float in warm water bath to remove wrinkles
         5. Picked up on microscope slide and placed in warm oven for 15 min to help section adhere to slide
      4. Staining: embedding process must be reversed to get paraffin wax out of tissue and allow water-soluble dyes to penetrate sections = deparaffinized
      5. Mounting (coverslips): stained section on slide must be covered with a thin piece of plastic/glass to protect tissue from being scratched
      6. Microscope

3. To discuss the basic functions and properties of cells

4. Compare and contrast the features of prokaryotic and eukaryotic cells

5. List the major type of microbial organisms & outline the major structural and functional characteristics of bacteria and viruses