Cell cycle, Mitosis, DNA replication Flashcards
Cell division
All complex organisms originated from a single fertilised egg.
Every cell in your body started here.
Through cell division the numbers are increased.
Cells then specialise and change into their various roles.
Mitosis
Mitosis is somatic (body) cell division.
Cells divide in order to make two identical new cells (‘daughter’ cells) for growth and repair of the body
Somatic (body) cells are diploid which means they have 2 copies of the genetic material (1 of each chromosome from each parent).
Mitosis produces two exact copies of the parent cell.
The new daughter cells also have the diploid number of chromosomes.
In humans, somatic cells have 46 chromosomes (23 pairs) so in mitosis we start with 1 cell that has 46 chromosomes, and end up with 2 cells that each have 46 chromosomes.
Mitosis stages
Interphase: Normal cell functions, DNA replication happens prior to mitosis
Prophase: DNA begins to condense and form chromosomes
Metaphase: Chromosomes line up along centre (equator) of cell
Anaphase: Chromosome pairs are pulled to opposite ends of cell by spindle fibres
Telophase: Membrane forms around new ‘daughter’ cells and begin to divide
Cytokinesis: Cells completely separate
(Mitosis does not create variation)
DNA Replication
The DNA of the cell must be copied (replicated) before the cell can divide.
Base pairing means that the DNA can be copied exactly.
Replication (copying) occurs in a series of steps each controlled by enzymes.
Two identical DNA molecules form.
Each has one strand from the original molecule and one new strand.
This is called semi-conservative replication.
DNA Replication steps
1)The DNA helix unwinds.
2)Hydrogen bonds between the bases break (the strands unzip).
3)New nucleotides bind to their base pairs to form a new strand (A-T, G-C).
4)The semi-conservative strands wind into their double helix.
5)Two identical DNA molecules are formed.
