2.2 Structure of Prokaryotic Cells and Viruses

• There are four main structures by all prokaryotic cells:

  1. Plasma membrane
  2. Cytoplasm
  3. 70S Ribosomes
  4. Genetic material (DNA and RNA)
• Some prokaryotic cells contain structures like a murein cell wall, mesosome, pili, slime capsule, and flagella.
• The cell wall is a physical barrier that excludes certain substances and protects against mechanical damage and osmotic lysis.
• The capsule protects bacterium from other cells and helps groups of bacteria to stick together for further protection.
• The cell surface membrane controls what goes in and out and is a differentially permeable layer.
• The genetic material possesses the genetic information for the replication of bacterial cells.
• Plasmids possess genes and may aid the survival of bacteria in adverse conditions (e.g. produce enzymes which breakdown antibiotics).
• The mesosome is the infoldings of the plasma membrane which helps bacteria with cell division.
• The pilus is an extension of the bacterial cell envelope used to attach bacteria to surfaces and for bacterial conjugation.
• The flagellum is a thread like structure which allows prokaryotes to move.
• Bacteria divide by binary fission.
• How do bacteria divide?

  Binary fission.
• What happens in binary fission?

  1. First, the circular DNA is replicated and both copies attach to the cell membrane on opposite sides.
  2. Then, the plasmids are replicated and space themselves out in the cytoplasm.
  3. The cell membrane begins to grow between the two DNA molecules and begins to pinch inwards, which divides the cytoplasm in two.
  4. A new cell wall forms between the two molecules, dividing each of the cells into two identical daughter cells, each with a single copy of the circular DNA and variable numbers of plasmids.
• Binary Fission:

  1. Circular DNA is replicated.
  2. Plasmids replicate.
  3. Circular DNA moves to opposite sides of the cell.
  4. Plasmids space cut in the cytoplasm.
  5. Plasma membrane folds in until it joins and when it joins, it separates.
  6. If present, the cell wall reforms.
• Viruses are acellular, as they are not cells.
• Viruses are non-living.
• Why are viruses non-living?

  They lack:

  1. Movement
  2. Respiration
  3. Sensation
  4. Growth
  5. Reproduction
  6. Excete
  7. Nutrition
• Viruses are non-living, so do not undergo cell division.
• Viruses need a host cell.
• Viruses contain genetic material (RNA/DNA) to hold the information to make viral components.
• If the virus has a reverse transcriptase enzyme, then the genetic material is RNA. If not, then it is DNA.
• The reverse transcriptase enzyme is only found in viruses that contain RNA e.g. HIV.
• The reverse transcriptase enzyme converts RNA to DNA, so it can be used to make more copies of the virus.
• Viruses have attachment proteins to attach to a host cell.
• Viruses have a protein capsid, which protects the genetic material.
• Viruses have a lipid envelope which surrounds the virus and holds the attachment proteins in place.
• Viruses have a matrix, which is the fluid around the viral components, it does nothing as it is not as advanced as the cytoplasm.
• Viruses are between 20nm and 200nm in size.