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One DNA nucleotide is made up of:
-Phosphate sugar
-Deoxyribose sugar
-Bases- A.T & C.G
*DNA nucleotide join together by condensation reaction to form
a poly-nucleotide chain. *DNA is made up of two poly-
nucleotide chains linked together by hydrogen bonds between
the bases.
1. DNA unwinds + unzips- enzyme Helicase breaks the
hydrogen bonds between bases. Each parent strand is a
template for a new strand
2. Free floating nucleotides pair up with exposed bases
according to complementary base pairing rule
3. New strand is built up using the enzyme DNA
polymerase- phosphodiester bond is formed between the…read more

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Slide 3

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Type of Cell division- formation of genetically identical cells
each with the same chromosome numbers
Mitosis is important in multi-cellular organisms
because it is used for:
- REPAIRING damaged or lost cells
Form of Asexual reproduction.
Phases of cell cycle:
G1- 1st growth phase- protein made- used to build up cell
Synthesis- DNA replicated
G2- 2nd growth phase- cell organelles grow+ divide- builds
up energy stores- mitochondria
Mitosis- Cell division.…read more

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· Cell is not going under cell division
· Chromosomes coil up, become dark + visible
· the nuclear envelope breaks down
· centrioles move to opposite poles of the cell.
· Spindle fibres form from the centrioles
· Chromosomes line up at the equator of the cell
· They're attached to the spindle fibres by their
· Chromosomes are split
· Spindle fibres shorten + sister chromatids are pulled
to opposite poles of the cell- centromere first.
Telepahase- Cytokinesis…read more

Slide 5

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Haploid cells- (23 chromosomes-gametes)
produced to maintain the same chromosome
number when they fuse. If diploid (46
chromosomes) cells were to fuse there would be
double chromosomes which would happen every
Genetic make up of Daughter cell and original
parent cell:
- Both have same number of chromosomes +
same genes
- They're genetically identical…read more

Slide 6

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Apoptosis- Programmed cell death; needed for
normal foetal development and needed for the
removal of cancerous cells.
P53 tumour suppressor gene which leads to cells
going under apoptosis. If it is mutated it could lead
to continuous cell division
Proto-oncogenes- Regulate cell division- if they were
mutated they would form oncogenes- these
permanently switch on cell division which could lead
to cancer.
Cancer- Changes that occur in a cell cause it to
become cancerous. Mutation in a cell can occur if:…read more

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