Other Types of Cellular Division

• Bacteria reproduce through binary fission, which is a form of asexual reproduction, very similar to mitosis, but is much similar
• How do bacteria reproduce?

  Through binary fission
• What type of reproduction is binary fission?

  Asexual
• Binary fission is very similar to mitosis
• Binary fission is much simpler than mitosis
• Bacteria possess a single circular DNA molecule and plasmids, which are smaller, circular DNA molecules that are also replicated and inherited.
• The number of copies of plasmids that each cell inherits can vary, although this number is regulated
• The DNA of a prokaryotic cell is not linear and it does not condense into chromosomes because it does not associate with histone proteins, it is a singular loop of circular DNA.
• What is the process of binary fission?

  1. The DNA is replicated along with any plasmids, the number of ribosomes also increases
  2. The cell then elongates
  3. The cytoplasm divides, similar to cytokinesis in plant cells as the cell wall has to be reformed along the centre
  4. The product is two new cells each with a single identical copy of the circular DNA loop
• What is the product of binary fission?

  Two new cells with a single identical copy of the circular DNA loop
• There are mechanisms to ensure that all daughter cells inherit a copy of the single, circular DNA molecule along with some plasmids during binary fission
• During bianry fission, if a daughter cell does not receive the single DNA molecule or at least one copy of a plasmid they will die
• What happens if a daughter cell doesn’t recieve any DNA during binary fission?

  Dies
• Bacteria divide via binary fission at regular intervals, as long as there are enough resources to maintain growth.
• As bacteria replicate at regular intervals, mathematical calculations can be made in order to predict how many bacteria will be present in a given time
• How to calculate the number of bacteria that replicates over a given time?

  Number of bacteria at the beginning of the growth period x 2^ the number of divisions
• What are viruses?


  Non-cellular infectious particles that straddle the boundary between living and non living
• Viruses are much smaller than prokaryotic cells, between 20 and 300nm in diameter
• What is the size of viruses?

  Between 20 and 300nm in diameter
• Viruses are very simple in structure
• Unlike prokaryotic cells, viruses do not have a plasma membrane, cytoplasm or ribosomes
• What is the structure of viruses?

  • A nucleic acid core
  • A protein coat known as a capsid
  • Some viruses have an outer layer known as an envelope, formed usually from the membrane of the cell it has replicated from
• Some viruses have an outer layer known as an envelope, which is formed usually from the membrane of the host cell from which they have replicated themselves
• Being non-living, viruses do not undergo cell division, only being able to reproduce by infecting living cells known as host cells
• What are the living cells that viruses infect called?

  Host cells
• How do viruses replicate?

  • Use attachment proteins on its surface to bind to complementary receptor proteins on the surface of a host cell
  • The virus then injects its DNA or RNA into the host cell
  • The host cell then uses its nucleic acid and ribosomes to produce new viral particles
• How are viral particles released?

  • The host cell bursts open, releasing all the new viral particles at once
  • The viral particles leave individually through the host cell membrane via a process known as budding, often taking a section of the membrane with them
• The host cell, containing viral particles can burst open, this releases all the viral particles at once into the extracellular fluid it is in
• Viral particles can leave host cells individually through the host cell membrane via a process known as budding, often taking a section of the membrane with them
• The exiting of viruses damages their host cells, causing disease
• When newly replicated HIV particles exit the cell, the host cells are destroyed, over time this severely damages the immune system of the individual with HIV, leading to a disease called aids