that's a dissenter to saying that ask me
mix - you're drinking milk
there's been great excitement of the
last couple of days about arsenic and
particular arsenic and bacteria because
of a paper that's just been published in
the journal Science this paper is about
bacteria that had been scooped out of
the mud in a lake in California
Lake Mono and they appear to be able to
live using arsenic instead of
phosphorous and that is really quite
surprising and the reason why it's so
surprising is because arsenic is
well-known as a poison there's a book
that was published this year which talks
about the century arsenic how Victorian
Britain was poisoned at home work and
play and everybody when they hear about
arsenic looked rather grim and thinks of
poison I've got a sample of arsenic here
which Neal brought to me and he looked
pretty grim wasn't sure whether she
should be giving a professor some
arsenic and you can see if I turn it
round you can see it's a grayish element
it's in the same group as phosphorus the
group 15 of the periodic table
phosphorus is essential to all life the
molecules that give us energy ATP
contains phosphorus our very DNA has
phosphorus in it and so it was strongly
believed that nothing could survive
without phosphorus so what these
scientists did was that they got some
bacteria from this lake in California
which has really quite high levels of
arsenic in the water the bacteria in the
mud they reasoned probably would not be
killed by arsenic because there was a
lot of arsenic in the water so what they
did was to take some bacteria out and
start growing it in the dish in solution
in which they didn't add any phosphorus
but they
added some arsenic what they did is
after the bacteria grown a bit they
poured away the water and transferred it
to some new water which had even less
phosphorus in it because they hadn't
added any and had more arsenic and they
did this several times the surprising
thing was that the bacteria still kept
growing but everybody would expect
without phosphorus the bacteria wouldn't
grow it's well known that bacteria and
algae grow really well if there's
phosphorus in the water but everybody
thought no phosphorus and happy bacteria
who couldn't divide and so on but what
this experiment showed or appears to
show because there still some people
have slight doubt is that the bacteria
not only grew and nobody can argue with
that but in the bacteria inside the
cells you could find arsenic now the
chemistry behind this is depend you can
understand quite easily about DNA you
probably all know that DNA consists of
two chains in the helix which are joined
together by groups here shown light by
these TAS and so on and this backbone of
the chain consists of a mixture of a
sugar deoxyribose that's the D and
phosphate so phosphate is a group that
has phosphorus in the middle and four
oxygens around it and the bacteria take
in phosphate and incorporates it in the
DNA and each time a bacteria divides
into two to make two new bacteria they
need to make more DNA so they need more
phosphate so what appears to have
happened in this case is that the in
absence of phosphorus they have
incorporated some arsenate exactly the
same molecule four oxygens but with
arsenic instead of phosphorus the reason
people are so excited is because it
overturns a belief that everybody has
had
for that phosphate is essential to life
or phosphorus is essential to life a so
called paradigm that something that all
the scientists believe the problem is
was been up till now that people thought
that if there was an environment that
did not contain phosphorus life as we
know it could not exist so this
restricts the areas in space or in the
universe where life could develop what
this experiment seems to show is that as
long as there is a group 5 element then
perhaps life could adapt that is the
life as we know it is more flexible than
we thought if there isn't any phosphorus
then you could use arsenic just like you
might use concrete blocks instead of
bricks when you're building your house
if the bricks run out may not look like
as beautiful but it still works now they
haven't proved for example how much
arsenic there is there's not pure our
cynical DNA but it has some of it in
there and this is what's really
surprising