Re: Richard Dawkins - amusing quote

On Jan 27, 8:42 am, Vend <ven...@xxxxxxxxxxx> wrote:
On 26 Gen, 18:23, Friar Broccoli <Elia...@xxxxxxxxx> wrote:



On Jan 24, 9:23 pm, John Harshman <jharshman.diespam...@xxxxxxxxxxx>
wrote:

Friar Broccoli wrote:
On Jan 24, 3:39 pm, John Harshman <jharshman.diespam...@xxxxxxxxxxx>
wrote:
Friar Broccoli wrote:
On Jan 24, 11:24 am, Ernest Major <{$t...@xxxxxxxxxxxxxxxxx> wrote:
In message <il2mj.258977$S37.112...@xxxxxxxxxxxxxxxxxxxxxxxxx>, Tim
Tyler <seemy...@xxxxxxxxxxxxxx> writes
John Wilkins wrote:
Tim Tyler <seemy...@xxxxxxxxxxxxxx> wrote:
Bill Hudson wrote:
On Jan 23, 2:43 pm, Tim Tyler <seemy...@xxxxxxxxxxxxxx> wrote:
"The DNA molecule itself is not right- or left-handed [...]"
Richard Dawkins - RIVER OUT OF EDEN
http://macroevolution.narod.ru/river/river.html
Why is that amusing? He's not talking about the handedness of the
molecule, but the handedness of snail shells.
It's amusing because it's wrong - and Richard Dawkins is
a famous writer on biology - and Chair for the Public
Understanding of Science at Oxford University.
It's not wrong. There is nothing intrinsically left or right handed
specified in the DNA for coiling.
Uh, the DNA molecule under discussion is /actually/
chiral and right-handed.
To say it is "not right- or left-handed" is not correct.
The meaning of words depends on context. By forcing a claim of chirality
on Dawkins' words in this context you may not be as bad as those who
interpreted his reference to selfish genes as entailing the possession
of volition by genes, but you're not impressing me with your command of
English in doing so. It's one thing to be amused (rather too easily in
my opinion) by the observation that an overly literal interpretation of
his words is factually incorrect; it's another to insist that he was
actually making that claim.
--
alias Ernest Major
I agree with pretty much all of the above (both sides) and
think Dawkins may need a more agressive or more
knowledgable proof reader.
Do you know anything about HarshPerson's "left-coiling" form
DNA? That really puzzled me.
Google Z-DNA.

Thanks. As you've probably noted, Tim already found a
good article on the topic for me. I'm thinking that the copying
machinery must have fits when it gets to those sections.

Not really. DNA gets uncoiled before copying, whether you mean
trancription or replication.

The only thing I am (reasonably) sure of here is that DNA
strands retain their handedness when uncoiled for replication
because of the supporting deoxyribose backbone, and this
has some quite amazing consequences.

Here is page 40 (and a bit more) from: "Darwin in the Genome"
by Lynn Helena Caporale:

"Predictable mutations depend not only on the sequence of letters
in the DNA, but also on which side of the double helix is being
copied. Imagine that you are moving down the helical staircase,
one railing on your left, the other on your right, just ahead of
the machinery that is making a new copy of DNA. The "steps" that
you are using to go down the center of the double helix are, of
course, the letter pairs, A-T, T-A, G-C, and C-G. The railings
of the staircase form the structural framework that links the
two life-generating strings of letters. Each railing is a chain
of the sugar deoxyribose, the D in DNA, and atoms that connect
the sugars to each other. Because of the way the sugars are
linked together, the railing has a pattern.

The pattern is the same on both railings, but it has a
direction. It runs down the railing on one side of the helix,
and up the railing on the other side of the helix. This pattern
comes from the way the sugar backbones, the deoxyribose
molecules that connect the letters, are hooked together. (When
we talk about letters in DNA, like ATTCGG, we leave out the
connecting sugars, but in real DNA, they are there between the
letters, linking them to each other through hooks called
phosphates.) If the sugar patterns on both of the double helix's
two railings went in the same direction, they might be described
as parallel patterns; because the patterns go in opposite
directions, they are called antiparallel. These antiparallel
patterns complicate the copying of DNA.

To follow along, you could draw two railings with antiparallel
patterns, perhaps arrows running in opposite directions or
something more creative. Now imagine separating the strands and
copying each of them, as was illustrated in Figure 2.1. When DNA
is copied, the strands separate, and a copy is made of each
strand. Conceivably, this could have been done differently.
It could have been that when DNA is copied, the result would be
a completely new double helix, leaving the original double helix
intact, but it doesn't work that way. The strands separate and
are copied, and each copy remains with the strand that it was
copied from, the strand that was its template. The two original
template strands, each with its new partner strand, leave each
other, giving us two half-new DNA double helices.

The enzyme machine that builds a new copy of DNA is designed to
work in one direction, always building the pattern from left to
right. But, here's a problem for the DNA copying machinery:
Because of the antiparallel railing patterns on the original
helix, when the double helix opens up at one end for copying,
the copying machinery is at the right end of the pattern on one
strand of the helix and at the left end of the pattern on the
other strand. The railing pattern on a new strand built from
left to right starting at one end of the original helix will
have the required antiparallel pattern, right to left on the
original strand and left to right on its new partner. The
problem is on the other side of the helix, where the helix
railing pattern runs left to right. If it too is copied from the
left using the DNA copying machine, which builds a copy with a
left-to-right pattern, the new railing patterns will be
parallel, not antiparallel as they need to be.

This is how the problem is solved: To make a copy of the problem
strand, the DNA copying enzyme machine slips a bit down the
helix from the open end, then works its way back up, making a
small piece of DNA called an Okazaki fragment after the husband
and wife team that figured this out. Then the copying machinery
slips even further down the open helix and, moving up again,
makes another small piece of DNA until it reaches the Okazaki
fragment it made just before. This new fragment of DNA is then
attached to the first fragment, and so on down the helix. So,
one strand is copied in this discontinuous, jumpy way. Because
the machinery slips down a bit and copies up, the second strand
of DNA can be copied with a backbone pattern that is
antiparallel to the original, as it should be."

I am having considerable difficulty getting my mind around all
this so I don't know whether such insanity makes copying left
handed strand sections easier or harder, but it seems to me
that the forward direction replicators would have to begin
behaving like the reverse direction ones and vice versa, but
chances are really good that I am even more confused than
normal.

And then there's the question of why The Designer didn't
provide us with enzymes for copying the reverse direction
strands?

Friar Broccoli
Robert Keith Elias, Quebec, Canada Email: EliasRK (of) gmail * com
Best programmer's & all purpose text editor:http://www.semware.com

--------- I consider ALL arguments in support of my views ---------


DNA replication animation:http://highered.mcgraw-hill.com/sites/0072556781/student_view0/chapte...

This is extremely clear.
I was going to wait to thank you until I had more time to
study it, but by that time this thread might be long forgotten.

So thanks now.

.

Relevant Pages

  • Re: Richard Dawkins - amusing quote
    ... specified in the DNA for coiling. ... but also on which side of the double helix is being ... the railing has a pattern. ... and each copy remains with the strand that it was ...
    (talk.origins)
  • Re: Richard Dawkins - amusing quote
    ... specified in the DNA for coiling. ... but also on which side of the double helix is being ... the railing has a pattern. ... and each copy remains with the strand that it was ...
    (talk.origins)
  • Re: Richard Dawkins - amusing quote
    ... specified in the DNA for coiling. ... but also on which side of the double helix is being ... the railing has a pattern. ... and each copy remains with the strand that it was ...
    (talk.origins)
  • Re: Richard Dawkins - amusing quote
    ... specified in the DNA for coiling. ... but also on which side of the double helix is being ... the railing has a pattern. ... and each copy remains with the strand that it was ...
    (talk.origins)
  • Re: Richard Dawkins - amusing quote
    ... specified in the DNA for coiling. ... but also on which side of the double helix is being ... the railing has a pattern. ... and each copy remains with the strand that it was ...
    (talk.origins)