Prokaryotic Cells

Its cells lack a nucleus
1. The DNA is free floating in a circle
e.g. bacteria cell
1. Cell wall is made up of murein
Cell wall
1. Functions
  1. Excludes substances
  2. Protects against mechanical damage and osmotic lysis
Cell surface membrane
1. This is inside the cell wall
  1. It encloses the cytoplasm
2. Function
  1. Controls entry and exit of chemicals
    1. It has a permeable layer
Ribosomes
1. Size
  1. 70S in prokaryotic cells
2. Function
  1. Protein synthesis
Circular strand of DNA
1. (DNA is still a double helix)
2. It is not associated with proteins
  1. i.e. not wrapped around protein
3. Found in central area of the cell called the nucleoid
4. Function:
  1. Stores genetic information for replication of bacterial cells
Microscopy
1. Maginifcation
  1. This is how many times bigger the image is than the actual object
  2. Magnification = size of image/size of real object
2. Resolution
  1. This is the minimum distance apart two objects can be in order to appear as separate items
  2. The human eye has a resolution of 0.2mm
  3. The light microscope has a resolving power of 0.2 micro metres
  4. The best electron microscope has a resolution of 0.1nm
3. The light microscope
  1. Specimens must be thin sections of prepared tissue that has been stained with coloured pigments
    1. Or they can be small live specimens like Daphnia
    2. Sections must be thin to allow light to pass through and to make sure you are only looking at a single layer of cell
    3. They must be stained as sections are often transparent
  2. A beam of light is shone through the specimen through a series of lenses resulting in a magnified image
  3. Very little intracellular detail can be seen
  4. The eyepiece graticule
    1. Usually around 10mm long with 100 sub divisions
    2. Stage micrometer
      1. This is usually 1mm long it goes on the specimen stage
    3. Calibrating the eyepiece graticule
      1. Because the scale remains constant no matter what magnification you're on, you must change the eyepiece graticule
4. The electron microscope
  1. This uses a beam of electrons rather than light
    1. The electron beam has a shorter wavelength than light which means the resolving power is higher
  2. Transmission electron microscope (TEM)
    1. Ultra thin sections needed, must be stained and heavy metals are needed
    2. Where electrons pass thought the specimen the image appears bright and when the electrons are absorbed the image is dark
    3. A near vacuum is required
      1. Specimen must be dead
    4. 2D black and white images
  3. Scanning Electron Microscope (SEM)
    1. Electrons do not penetrate the specimen
      1. The beam is passed to and fro over the specimen surface in a regular pattern
        Electrons are scattered depending on the contours
    2. Produces a 3D image
      1. Black and white
    3. Resolution is lower than that of the TEM
5. Artefacts
  1. Due to all of the processes the specimens must undergo under microscopes, images may contain objects that shouldn't be there
  2. An artefact may be a break in a membrane, empty spaces in cells
    1. In the TEM heavy metal stains are used, so granular deposits may be seen
  3. It is therefore not possible to be sure what we see on an image is the actual natural specimen
Some prokaryotic cells have
1. Plasmid
  1. Small circular strand of DNA
  2. Function:
    1. Gives genes that aid survival
      1. e.g. they can reproduce with antibiotic resistance
  3. Used extensively as vectors
2. Capsule
  1. This is mucilaginous slime around the outside of the cell wall
  2. Functions:
    1. It stops bacteria being deteced
      1. This protected them from other cells
    2. It helps bacteria stick together for protection
3. Flagellum
  1. Function
    1. Used for locomotion
      1. Makes bacteria move
Viruses
1. This is an acellular, non living particle
2. Contains nucleic acids such as DNA or RNA as genetic material enclosed in a protein coat or capsid
  1. Capsid or envelope have attachment proteins
    1. These allow the virus to identify and attach to a host cell
3. Can only multiply inside a living host cell
4. May be surrounded by a living host cell

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Prokaryotic Cells

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	Created by Jacob Shepherd about 9 years ago