Re: DNA, RNA and Protein questions

On Mar 15, 7:03 am, Bill <spintro...@xxxxxxxxxxx> wrote:
On Mar 15, 3:50 am, hersheyh <hershe...@xxxxxxxxx> wrote:



On Mar 14, 9:23 pm, Bill <spintro...@xxxxxxxxxxx> wrote:

On 15 Mar, 01:06, hersheyh <hershe...@xxxxxxxxx> wrote:

On Mar 14, 8:03 pm, "Simon \(Dark Angel\)"

<darkangel5STOPTHES...@xxxxxxxxxxx> wrote:
OK, here's some novice questions.

A person I am arguing with claims that DNA, RNA and Proteins must have all
been formed at the same time as none can exist without the other.

Now, I have very little understanding in this field, but have been doing
some googling around. From what I've read on the Talk Origins website, it
was my understanding that RNA was the precursor to both DNA and proteins,
but other articles have got me totally confused on this issue as they're say
that RNA is made from DNA.

Actually it is the other way around. The deoxynucleotide phosphates
are made, biochemically, by reduction of ribonucleoside diphosphates
to the deoxyribonucleotide form of the sugar (the reaction involves
NADP as the H receptor).  Since the ribose purine is uridine (base
pairs to adenine) and the deoxyribose purine equivalent is thymidine,
there is yet another enzyme that converts dUMP to dTMP by methylation
(tetrahydrofolate is the methyl donor).  IOW, the substrate components
of DNA are synthesized from the substrate components of RNA.  This is
part of the evidence that RNA preceded DNA.

In short. RNA is turned into DNA.

I did not say that.  I said that DNA's constituent monomers are made
by modification of RNA's constituent monomers.

So 'again', "RNA is turned into DNA.

As I previously said, and you apparently cannot understand, RNA and
DNA are what chemists call "polymers". That is, they are composed of
a chain (in this case, a linear chain) of subunits that are called
"monomers" (in this case, either NTPs for RNA or dNTPs for DNA). In
synthesizing either RNA or DNA, one adds monomers to the growing
polymer chain one monomer at a time, usually directed by the sequence
of a template strand. That is the case whether the template upon
which the new chain is made is DNA or RNA or even if there is no
template at all (non-template directed synthesis). I am pointing out
that the *monomers* that are the basis of either RNA and DNA are
manufactured biochemically by cells, and that the manufacture of
*monomers* needed to make DNA is accomplished by modifying *monomers*
needed to make RNA. That is, the *monomers* for RNA are made first,
biochemically, and subsequently modified into *monomers* for making
DNA.

RNA is NOT converted into DNA after or during the formation of the
polymer. The monomers that go into making RNA are biochemically
converted after their synthesis into the monomers that go into making
DNA. Then the appropriate monomers are used in making the respective
polymers.

RNA can be transcribed off a DNA template. DNA can be replicated (DNA
off a DNA template). RNA can also be replicated off an RNA template
(in viruses). And DNA can be reverse transcribed off an RNA
template. In fact, in the synthesis of DNA off DNA (DNA replication),
the process always starts with a short stretch of RNA with a switch to
DNA, since there are no enzymes that can initiate DNA replication
directly off a DNA template. The initiating stretch of RNA is later
removed by nucleases with subsequent ligation of the DNA fragments.
Again, evidence that RNA comes first and DNA second.

 That is, the dNTPs
(deoxyribonucleotide triphosphates) used to make DNA are modifications
of the NTPs (ribonucleotide triphosphates) used to make RNA.  That
makes RNA's constituent monomers a necessary precursor to the
biosynthesis of DNA's constituent monomers.  That is, RNA first.

And by that logic, this is evidence that RNA preceded DNA?

Yes.  It says to make DNA by linking dNTPs an organism must already be
able (have the enzymes) needed to make RNA's NTPs.

So by that logic, "It says that to make mRNA by transcribing DNA an
organism
must already be able (have the proteins) to make DNA.

Not at all. mRNAs are also made off an RNA template in some viruses.
Again, DNA, as a polymer, seems largely limited to the role of genome
and a few structural features related to genomes, like telomers and
centromeres in organisms (it can be enzymatic to a limited extent, but
the examples I know of are artificial constructs). RNA, OTOH, not
only can act as a genome, but can also act as an enzyme (and there are
examples of such in living cells, including the ribosome and certain
RNA ligase activities) and as a template translatable into a protein
sequence. IOW, RNA has the ability to act as genome and enzymes
needed for repliction of RNA. DNA is largely constrained to being
specialized for a genome. Protein is largely specialized for
structure and enzymatic activity. RNA is inherently multifunctional.
DNA and protein are specialized.

So since the premise of your logic gives two conflicting results, the
premise is flawed.

Namely: "precurser's in synthesis, illustrate antecedent".

.

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