Part 2: http://dialoguewithdisability.blogspot.com/2013/05/how-do-parkinsons-researchers-discover_29.html
TOOL 2 – DNA sequencing
It is crucial to know the sequence
of subunits in DNA because it is this sequence that forms specific proteins and
these proteins carry out specific roles in the cell.
A clever modification of DNA
replication makes sequencing possible: modified subunits are used that allow
partner binding (A-T and C-G) but doesn’t allow the next subunit in the row to
become glued to the modified subunit; thereby stopping replication at this
point. For example, imagine the DNA to be read is made up of ATCGATCG. Four separate
PCRs are set up with each containing a modified subunit (*) along with all four
normal subunits. In the T* reaction replication will be stopped at two places:
AT* and ATCGAT*; these can be distinguished by size. Therefore, taken together
all four reactions will generate the following bits of DNA:
A* reaction T*
reaction C*
Reaction G*
Reaction
A*
AT*
ATC*
ATCG*
ATCGA*
ATCGAT*
ATCGATC*
ATCGATC*
ATCGATCG*
Therefore, the sequence is read
left to right as ATCGATCG. This technique formed the basis of the Human Genome
Sequencing Project and is therefore one of the most important innovations in
human history.
Finding the criminal
Genes within a region are sequenced
in sufferers and non-sufferers. For example, gene X in non-sufferers has the
sequence TTTATTCCG and in sufferers it is TTTGTTCCG: the fourth subunit A has
been replaced by G. This is an A to G mutation (any subunit can be replaced by
any other subunit). The criminal has been caught!
Mutations can have a range of
affects: stopping the protein from being made, protein is made but it has lost
its function, function is subtly altered or the change has no affect. One of
the most important ways a mutation has an affect is changing the order of
subunits (called amino acids) in proteins. It is the different strings of amino
acids that give proteins their specific jobs in the cell.
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