Biology A-level Notes from an A* student.
Topic 8 can be a bit challenging, however these notes helped simplify the information for me and also my friends.
Sequencing projects read the genomes of a wide range of organisms,
including humans.
Determining the genome of simpler organisms allows the sequences of the
proteins that derive from the genetic code of the organism to be determined.
This may have many applications, including the identification of potential
antigens for use in vaccine production.
In more complex organisms, the presence of non-coding DNA and of
regulatory genes means that knowledge of the genome cannot easily be
translated into the proteome.
The proteome is all the proteins that the genome can code for. However due
to selective gene expression not all of these proteins will be found in every
cell in the body.
Gene sequencing allows for genome-wide comparisons between individuals
and between species. Comparing genomes between species is significant as
it allows evolutionary relationships between species to be determined, and it
is also beneficial to medical research.
Comparing genomes of individuals enables differences to be identified which
can then be used for development of personalised medicine tailored to a
particular genome, as well as in studies of human diseases.
Apart from allowing genome-wide comparisons to be made, gene sequencing
has allowed for the sequences of amino acids in polypeptides to be predicted
and has allowed for the development of synthetic biology.
The Human Genome Project is an international scientific project which has
successfully determined the sequence of bases of a human genome.
Potential applications include: screening for mutated sequences, carriers and
pre-implantation screening as well as screening for disorders such as
Huntington’s disease before the symptoms appear.
However, there are many ethical concerns regarding the Human Genome
Project, such a s people being discriminated against as well as regarding the
misuse and ownership of the genetic information.
, Recombinant DNA technology
Recombinant DNA technology involves many ways of manipulating DNA, t
ccvbbb c bg hese processes are all detailed below.
This allows us to make working versions of DNA that act as genes, by
extracting mRNA from cells where that gene is being expressed.
Using reverse transcriptase to make DNA. The enzyme reverse transcriptase
is a enzyme that is found in only some viruses and bacteria and catalyses
the formation of a double strand of DNA from a single strand on RNA.
Using restriction endonucleases to cut DNA fragments. Restriction
endonucleases are enzymes, extracted from bacteria, that cut DNA at
specific sequences, usually six base pairs in length.
The most useful restriction endonucleases are those that make staggered
cuts, as they leave sticky ends on the DNA.
Sticky ends are important because if the same restriction endonuclease is
used to cut two DNA fragments then the ends will be complementary. This
allows them to attach together before stronger covalent bonds form.
In-vivo gene cloning If a DNA fragment was placed in a cell it would be
digested by enzymes and therefore a vector is used to insert DNA into cells.
They are the plasmids from bacterial cells that naturally occur.
Isolated DNA fragments can be placed in plasmids in a following way:
1. Plasmid and gene are cut with the same restriction enzyme to create
complementary ends sticky ends. This means that the inserted DNA
and vector are complementary and can be joined.
2. The fragments are incubated with the plasmids. If a plasmid takes up
the insert, base pairing takes place between the complementary ends
which are then sealed with the use of DNA ligase which forms
phosphodiester linkages. A recombinant DNA molecule is created.
Electroporation
In the formation of transgenic microorganisms (organisms whose genetic
material has been altered using recombinant DNA technology),
electroporation is used to stimulate bacterial cells to take up plasmids.
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