Thursday, 30 May 2013

How do Parkinson's researchers discover new knowledge? Part 3

Part 1:

Part 2:

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


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example, gene X in non-sufferers has the sequence TTTATTCCG and in sufferers it is TTTGTTCCG: the fourth subunit A has been replaced by G. This is an A to G mutation (any subunit can be replaced by any other subunit).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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