DNA replication in ~5' to 3' direction; (2023)

Hi to all!

I have a DNA replication bioassay tomorrow and I have a quick question. (I'm in eighth grade now)

I don't understand when the textbook says that DNA can only be replicated from the 5' to 3' direction.

If it is

PT。 B -> 5' ---------- 3'

3' ---------- 5' <- PT. A

Can't there be a polymerase that works from point A and point B at the same time? Because everything starts in the 5' direction?

(I read Yggdrasil's answer to a similar question, but it's a bit unclear to me...)

If you have time, it would be great if you could also add a brief summary of DNA replication!

Yggdrasil and so on. I would appreciate it if you could prepare a quick and easy to understand summary on this topic. Thanks!

When the textbook says that DNA can only be replicated in the 5' to 3' direction, it means DNA synthesis. Each DNA strand has a 5' end and a 3' end. To make this strand longer, you can imagine adding new DNA to the 3' end of the strand or to the 5' end of the strand. It turns out that DNA polymerase can only add new nucleotides to the 3' end of the strand and not the 5' end, so DNA is synthesized in the 5' --> 3' direction.

Your thinking is correct in your example. Both strands of DNA can be copied, and when they are copied, DNA polymerase will move in opposite directions. During top strand synthesis, DNA polymerase can only synthesize from left to right (5' to 3'), while during bottom strand synthesis, the polymerase will move from right to left. It is not possible for the leading strand to be synthesized by a right-to-left polymerase because DNA polymerases cannot work in the 3' to 5' direction.

Why cannot polymerase add nucleotides to the 5' end of DNA? DNA synthesis is driven by the release of pyrophosphates (the last two phosphates in nucleotide triphosphates) that occur during DNA synthesis. These phosphates are attached to the 5' end of the nucleotide. These triphosphate groups are somewhat unstable and sometimes self-dissociate. If nucleotides are added to the 5' end of DNA, accidental loss of the 5' triphosphate is a major problem. Without the 5' triphosphate, DNA synthesis cannot proceed. However, it does not matter if the 5' triphosphate of the DNA strand is damaged if new nucleotides are added to the 3' end of the DNA. For 5' to 3' synthesis, loss of triphosphate from nucleotides can cause problems, but there are so many nucleotides in cells that the low rate of loss of triphosphate from nucleotides does not affect the rate of DNA synthesis.

I hope this answers your question. Please let me know if anything is unclear.

I guess you're asking why you can't stop the DNA strand from growing with -5'PPP at the end, then the mononucleoside 5'-triphosphate condenses its 3'-OH on itself and eliminates the pyrophosphate that will extend the strand one nucleotide from 5'PPP at the end, ready to do it again.

Watson in his textbook gives much the same explanation as Ygggdrasil, except for the accidental loss of terminal phosphates or pyrophosphates, which he calls proofreading, an exonuclease that consumes new strands to correct errors. This is by far the preferred hydrolysis, and if the PPP is to leave the end of the chain being eaten, it must be a largely ATP-driven pyrophosphate transfer at each step. As awkward as it sounds, it's hard to imagine being favored.

If the problem is that you cannot get mononucleoside 3'-triphosphates that condense on the 5'OH end of the growing DNA and thus extend in the 3'->5' direction, I don't know if anyone can give a reason. Actually, I'd say you can, but in life on Earth, that's not the case.

remember it is5'(Monophosphates, diphosphates, and triphosphates are the queens, queens, and aces of geobiochemistry. Think ATP-5'ATP. I think this is even reflected in the terminology. You can think of a DNA strand as a polymer of 5' or 3' nucleoside phosphates. But given the 5' king, you mentally split the chain into 5'-PN-3'OH monomers, thus defining the 5'->3' direction, which is the only way I've found that the terminology isn't confusing.

5'-Empire is not a chemical event. The energy transferred by the phosphate or pyrophosphate of the 3'- or 5'-NTP or dNTP should be about the same. This is a biological fact. enzymethey understandAnd we catalyze the reaction with 5'-P compounds. The reasons for this must be sought in the origin and early history of life. I guess the 5' with extra O-C-O- allows exploring larger volumes and complementary structures for different interactions, so the catalyst has a better chance to evolve.

I've never heard anyone think that way - it's not something that's encouraged in biology. If it reflects on someone, IMHO, it doesn't beg the question.

I suspect that the reason the triphosphate is at the 5' end is because the 5' triphosphate is much more stable than the 3' triphosphate for ribonucleotides.

In ribonucleotides, the 2' hydroxyl group is adjacent to the 3' hydroxyl group, capable of nucleophilic attack on the 3' triphosphate, resulting in loss of pyrophosphate and formation of a 2',3'-cyclic phosphate intermediate (see examplehttp://www.scripps.edu/news/scientificreports/sr2001/images/fedor1.gif). Thus, 3'-rNTPs catalyze their own hydrolysis over time to 3'-rNMPs, while 5'-rNTPs do not exhibit this problem.

That said, there are exceptions to every rule in biology. It turns out that there are some polymerases that can add nucleotides to the 5' end of substrates (for example seehttp://www.pnas.org/content/early/2013/12/04/1321312111.abstract)