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DNA is the genetic material of all living cells.
The sequence of nucleotides in DNA forms a code that determines the sequence of amino acids in
the proteins of an organism.
DNA is largely confined to the nucleus.
Sections of the DNA code are transcribed onto a single-stranded molecule called…

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Ribonucleic Acid (RNA) Structure

RNA is a polymer made up of repeating mononucleotide subunits.

It forms a single strand that is made up of:
· Ribose sugar
· One of the organic bases
· A phosphate group

The two types of RNA that are important in protein synthesis are:

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DNA never leaves the nucleus, but proteins are synthesised in the cytoplasm, so a copy of each gene is
made to carry the "message" from the nucleus to the cytoplasm.
This copy is mRNA, and the process of copying is called transcription.

1. The enzyme DNA helicase acts on a…

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DNA is made up of sections of introns and exons.

Exons Code for proteins
Introns Do not code for proteins and interfere with the synthesis of a polypeptide

In the pre-mRNA of eukaryotic cells, these non-functional introns are removed and the functional
exons are joined together in a process called…

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Once mRNA has passed out of the nuclear
pore it determines the synthesis of a

A ribosome becomes attached to the
starting codon at one end of the mRNA

The tRNA molecule with the
complimentary anti-codon sequence
moves to the ribosome and pairs up with
the sequence on…

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Any change to the base sequence of DNA is called a mutation.

Mutations arise in body cells are not passed on to the next generation.
Mutations occurring during the formation of gametes may be inherited, often producing sudden and
distinct differences between individuals.
They are therefore the basis of discontinuous…

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Deletion of bases

A gene mutation by deletion arises when a nucleotide is lost from the normal DNA sequence.
The loss of a single nucleotide from the thousands in a typical gene may seem a minor change but
the consequences can be considerable.

Usually the amino acid sequence of the…

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Cell division is controlled by genes.
Most cells divide at a fairly constant rate to ensure that dead or worn out cells are replaced.
In normal cells, this rate is tightly controlled by two genes:

Proto-oncogenes that stimulate cell division
Tumour suppressor genes that slow cell division


Proto-oncogenes stimulate…




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