Mitosis, bacterial and viral replication

• Mitosis produces two genetically identical daughter cells that have the same number of chromosomes as the parent cell.
• Meiosis produces four daughter cells, each with half the number of chromosomes of the parent cell.
• Interphase always precedes the first stage of mitosis. In this stage, DNA in the cell is replicated to produce two copies joined by a centromere.
• The first stage of mitosis is prophase. In this phase, the chromosomes first become visible as long thin threads. The centrioles move to opposite poles of the cell. From each centriole, spindle fibres develop and span the cell from pole to pole.
• The second stage of mitosis is metaphase. Metaphase is when chromosomes can be seen to be made up of two chromatids joined by a centromere, with each being an identical copy of DNA. Some microtubules from the poles attach to the centromeres, and the chromosomes are pulled along the spindle apparatus and arrange themselves across the equator of the cell.
• The third stage of mitosis is anaphase. In this phase, the centromeres divide in two and the spindle fibres pull the individual chromatids apart. The chromatids move to their respective poles and become chromosomes. The energy for this process is supplied by mitochondria surrounding the spindle apparatus.
• The fourth stage of mitosis is telophase and cytokinesis. In this phase, the chromosomes reach their respective poles and become longer and thinner, hence invisible. They leave behind chromatin. The spindle fibres disintegrate, the nuclear envelope and nucleolus reform. Finally, the cytoplasm divides in cytokinesis to produce two daughter cells.
• Cell division in prokaryotes takes place by the process of binary fission.
• The first stage of binary fission involves the circular DNA molecule being replicated and both copies attaching to the cell surface membrane. The plasmids also replicate.
• The second stage of binary fission involves the cell membrane beginning to grow between the two DNA molecules and begin to pinch inwards, dividing the cytoplasm in two. A new cell wall forms between these DNA molecules, dividing the original cell into two daughter cells, each with a single copy of the circular DNA and plasmids.
• Viruses are replicated through attacking and overtaking a host cell. They do this by firstly attaching to a host cell with the attachment proteins on their surface, then injecting their nucleic acids into the host cell.
• The second stage of viral replication is when the genetic information on the nucleic acids provides the instructions for the host cells metabolic processes, which causes the host cell to manufacture viral components, proteins and nucleic acids. These are then assembled into new viruses.