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I have a, probably stupid, question.
Please explain to me as if I was a 5-year old and I might
actually understand this. Thank you!
Q: The DNA chain is polymerized in the 5' --> 3' direction. Always.
But WHY? I've been given two different answers, and I understand neither
of them.
According to wikipedia: If the Dna were synthesized in the 3'->5' direction, the energy
would come from the 5' end of the growing strand rather than from free nucleotides.
Well, I don't really see why this would be a problem. Splitting of a phosphate group
from 5' should give some energy. This + energy from ATP --> ADP + P, could then be used to
add a new nucleotide. It would be a bit strange to take something OFF of the DNA strand, only
to add something again thereafter, but I don't see why energetics would not allow it.
The second explanation why it should be from 5'--->3' , I got from Essential cell biology
by Alberts et al. It says: The proofreading mechanism of DNA polymerase explains why DNA
polymerase synthesize DNA only in the 5' to 3' direciton. A hypothetical DNA polymerase synthesizing
in the other direction would be unable to proofread: if it removed an incorrectly paired nucleotide,
the polymerase would create a chain end that is chemically dead, in the sense that it could no
longer be elongated.
Well, who is right? Wiki or Essential cell biology? Aren't they talking about the same thing but
what Essential says is just a consequence of something that is in a certain way b/c of what was
said in wiki?
Anyway, the explanation in Essential is another one I don't understand. Still, why can't we just split
off the phospate from the "chemically dead" 5' end and build from there?
Please explain to me as if I was a 5-year old and I might
actually understand this. Thank you!
Q: The DNA chain is polymerized in the 5' --> 3' direction. Always.
But WHY? I've been given two different answers, and I understand neither
of them.
According to wikipedia: If the Dna were synthesized in the 3'->5' direction, the energy
would come from the 5' end of the growing strand rather than from free nucleotides.
Well, I don't really see why this would be a problem. Splitting of a phosphate group
from 5' should give some energy. This + energy from ATP --> ADP + P, could then be used to
add a new nucleotide. It would be a bit strange to take something OFF of the DNA strand, only
to add something again thereafter, but I don't see why energetics would not allow it.
The second explanation why it should be from 5'--->3' , I got from Essential cell biology
by Alberts et al. It says: The proofreading mechanism of DNA polymerase explains why DNA
polymerase synthesize DNA only in the 5' to 3' direciton. A hypothetical DNA polymerase synthesizing
in the other direction would be unable to proofread: if it removed an incorrectly paired nucleotide,
the polymerase would create a chain end that is chemically dead, in the sense that it could no
longer be elongated.
Well, who is right? Wiki or Essential cell biology? Aren't they talking about the same thing but
what Essential says is just a consequence of something that is in a certain way b/c of what was
said in wiki?
Anyway, the explanation in Essential is another one I don't understand. Still, why can't we just split
off the phospate from the "chemically dead" 5' end and build from there?
