AS Revision - DNA Replication

Mitosis: (used for growth and repair, including the growth of the foetus)

2 daughter cells produced

Identical to original (parent) cell and to each other, unless a mutation occurs.

Importance:

• Increase in number of cells
• 2 haploid cells fuse to make a diploid cell
• Differentiation
• Replacing cells (when they're damaged or die new cells must form to be genetically identical to function effectively)

Interphase: (cell not dividing, when replication of DNA occurs)

• cell continues its normal function
• prepares to divide
• Cells DNA is unravelled and replicated - genetic content is doubled
• Organelles replicated so there's spares
• ATP content increased

Prophase:

• Chromosomes condense (they get shorter and fatter)
• Centrioles start moving towards opposite ends of the cell forming a network of protein fibres across it (forms the spindle)
• Nuclear envelope breaks down
• Chromosomes are free in the cytoplasm

Nuclear envelope: membrane around the nucleus

Centrioles: tiny bundles of protein

Metaphase:

• Chromosomes (each have two chromatids) line up along the middle of the cell
• become attached to the spindle via their centromere

Anaphase:

• Centromeres divide
• separating each pair of sister chromatids
• spindle contracts
• Pulls chromatids to opposite ends of the cell (first the centromere)

Telophase:

• Chromatids reach opposite poles on the spindle
• uncoil and become long and thin again
• They're now called chromosomes again
• Nuclear envelope forms around each group of chromosomes so there are now 2 nuclei
• Cytoplasm divides
• FORMING: 2 daughter cells genetically identical to the original cell and to each other

Mitosis is now finished and each daughter cell starts interphase and the whole cycle repeats.

Mitotic index = the number of cells carrying out mitosis (visible chromosomes)/ total number of cells on the slide

Cancer:

(result of uncontrolled cell division)

• cell growth and cell division controlled by genes
• cancer is a tumour that invades surrounding tissue
• cells keep on dividing to make more tissue (the tumourr)

Chemotherapy:

• prevent the synthesis of enzymes needed for DNA replication
• Not specific- can kill normal cells, steps taken to reduce the impact on normal cells
• A large portion of the tumor is removed using surgery
• Repeated treatments (ie not one big dose), treatment breaks in between. 

G1- cell growth and protein production

specifically for AQA Biology AS Unit 2