Cell Division

The type of cell division where a parent cell divides to produce two genetically identical daughter cells.

The cell cycle (Interphase)

• Mitosis
  • Start and end of the cycle.
• Gap phase 1
  • Cell grows and new organelles and proteins are made - normal life functions.
• Synthesis
  • Cell replicates DNA.
  • DNA replicates --> chromosomes are double stranded.
  • Energy in form of ATP are saved.
• Gap phase 2 
  • Cell keeps growing and proteins needed for cell division are made.
  • Growth phase - cell checks for damage and repairs DNA.

• Interphase
• Chromosomes are not visible, membrane and nucleolus present.
• DNA replication, organelles are synthesised - increase rate of respiration and protien synthesis.
• Prophase
• Chromosomes are now visible.
• Chromosomes shorten and condense, nuclear envelope breaks down.
• Metaphase
• Chromosomes lined upon the middle of cell.
• Spindle fibres form, centromeres attach to spindle, chromosomes move along spindle fibres to centre of cell.
• Anaphase
• Set of chromatids at either end of the cell.
• Centromere of each chromosome splits, sister chromatids move to opposite poles, each chromoatid goes into a daughter cell.
• Telophase
• Two cells, chromosomes not visble.
• Nuclei reform, DNA becomes chromatin.

Tumour that invades tissue.

If there is a mutation in a gene that controls cell divsiion, the cells grow out of control

Treatments

• Designed to control rate of cell division in tumour cell cycle to kill the cells.
• They don't distinguish between normal cells so kill them too.... BUT, tumour cells divide more frequently than normal cells, so morel likely to kill them.
• Gap phase 1 - cell growth and protein production.
  • Prevents synthesis of enzymes needed for DNA replication therefore cell is unable to enter synthesis phase.
• S Phase - DNA replication
  • Radiation and drugs damage DNA - so cell kills itself.

Mitotic index = number of cells in mitosis

                           total number of cells

The type of cell division where a parent cell divides to create 4 genetically different haploid cells.

1) DNA replicates - two copies of each chromosome called chromatids.

2) DNA condenses to form double-armed chromosomes - each made from 2 sister chromatids.

3) Meiosis I - choromosomes arrange themselves into homologous pairs - half chromosome number when separated.

4) Meiosis II - pairs of chromatids are separated, centromere divides so 4 genetically different halpod cells are produced.

Importance of meiosis

• Produces haploids so during fertilisation diploid number is restored.
• Diploid number remains the same after every generation.
• Produces genetic variation in offspring which increases chance of survival.

1) Crossing over of chromatids

• During meioisis I - homologous chromosomes pair up and chromatids twist around each other.
• Setion of DNA breaks off, swaps positions and reattaches.
• Creates new combination of alleles.

2) Independent segregation of chromosomes

• During meiosis I - homologous chromosomes line up in pairs across the cell.
• Maternal and paternal chromosomes are produced in gametes.
• Creates different combinations of alleles.

Chromosome mutations

• Cells produced contain variations in the numebr of whole chromosomes or pairs.
• Can lead to inherited conditions because errors are present in gametes.
• e.g. chromosome non-disjunction --> failure of chromosomes to separate properly.

Binary fission is where the cell replication its genetic material before physically splitting into daughter cells.

1) Cicrular DNA and plasmid replicate.

2) Cell gets bigger and DNA moves to opposite sides.

3) Cytoplasm begins to divide - new cell wall begins to form.

4) Cytoplasm divides - two daughter cells are produced.

• Each daughter cell has one copy of circular DNA but vary in number of plasmids.

Viruses are not alive so do not undergo cell division.

1) Virus attaches to host cell receptor proteins.

2) Genetic material (DNA/RNA) is released into the host cell.

3) Genetic material and proteins are replicates by the host cell 'machinery'.

4) Viral DNA becomes part of the hosts DNA and becomes activated - results in transcription and translation.

5) Viral proteins are made.

6) New viral particles dissembled and burst out of the cell.