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The cells that make up organisms are always derived from
existing cells by the process of division. Cell division occurs in
two main stages:
Nuclear division is the process by which the nucleus divides.
There are two types of nuclear division, mitosis and meiosis.
Cell division follows nuclear division and is the process by which
the whole cell divides.
Before a nucleus can divide its DNA must be replicated. This is to
ensure that all the daughter cells have the genetic information
to produce the enzymes and other proteins they need.
The process of DNA replication is clearly very precise because all
the new cells are more or less identical to the original one. This
is a remarkable achievement when one considers the
complexity of the DNA molecule.…read more

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For semi-conservative replication to take place there are four
requirements:
The four types of nucleotide, each with their bases
adenine, guanine, cytosine and thymine, must be
present.
Both strands of the DNA molecules must act as a
template for the attachment of these nucleotides.
The enzyme DNA polymerase is needed to catalyse the
reaction.
The source of chemical energy is required to drive the
process.…read more

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The process of semi-conservative replication takes place as follows:
The enzyme DNA helicase breaks the hydrogen bonds linking the base
pairs of DNA.
As a result the double helix separates into its two strands and
unwinds.
Each exposed polynucleotide stand then acts as a template to which
complementary nucleotides are attracted.
Energy is used to activate these nucleotides.
The activated nucleotides are joined together by the enzyme DNA
polymerase to form the `missing' polynucleotide strand on each of the
two original polynucleotide strands of DNA.
Each strand of the new DNA molecule contains one of the original
DNA strands, i.e. Half the original DNA has been saved and built into
each of the new DNA molecules. The process is therefore termed `semi
conservative replication'.…read more

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