Cenozoic Park: Cloning the Tasmanian Tiger

Mirk writes "The Australian Museum reports a breakthrough in their plans to clone the Tasmanian Tiger. The ``tiger'', actually a carnivorous marsupial, became extinct in 1936, when the last known specimen died in captivity. Er, did I say ``extinct''? Now it looks like what everyone thought was an extinction may be ``a 70-year hiccup'', to quote the press release. The museum's Evolutionary Biology Unit have successfully replicated individual Tasmanian Tiger genes using a process known as PCR (Polymerase Chain Reaction)."

Comments

How PCR works (b/c I'm bored)

[sam_handelman]

I'm capped, and yet I still whore.

DNA, as I'm sure we all know, is double stranded. One strand is a complement of the other. A complements T and C complements G. So, if one strand is:
5' ATTTC 3'

then the other strand is:
3' TAAAG 5'

The DNA is "read" from 5' to 3'. 5' and 3' refer to particular atoms on the sugar backbone that are attached to one another via a phosphate.

When DNA is replicated, you split it into two strands:
5' ATTTC 3' and 5' GAAAT 3'

(notice that the two complements read in opposite directions)

and each strand has it's complement added.

5' ATTTC 3' and 5' GAAAT 3'
3' TAAAG 3' and 3' CTTTA 5'

The problem with this is, in order for this happen to DNA, you need an RNA "primer." This primer is a complement to the beggining of what you want to replicate. So, for example, if you have (RNA bases I'm putting in bold. U is the same as T:)

UAA

floating around in solution, which compliments ATT, then any sequence beggining with ATT will be replicated, but other sequences will NOT be replicated, because no RNA primer is available to get them started.

So, if you have a whole mess of DNA, including a piece that you're interested in, which reads:

5' ATTTG (long space........) TCGTC 3'
3' TAAAC (long space........) AGGAG 5'

and you add:
TAAAC and TCGTC

You get a chain reaction; the sequence flanked by the complements of the two things you add (the sequence printed above) is replicated, and then the replication product is replicated, and so on and so on. Other sequences, which are flanked by only one compliment (only ATTTG, say) will be replicated occasionally, but there replication products cannot in turn replicate, so you get no chain reaction.

More history here.

A thermophile (heat loving organism), thermus aquaticus, provided a polymerase (an enzyme which polymerises, that is to say replicates sequences of, nucleic acids like DNA and RNA) that works extremely fast at high temperatures. In general, the higher the temperature you run a reaction at, the faster it goes. However, most biological enzymes (from, say, a person) cease to function when temperatures rise (this is one of the ways heat kills you.) Thermophiles, bacteria that live in geysers and in volcanic ocean vents, have evolved enzymes that continue to function at higher temperatures.