I did not understand primer. Does anyone
08 Jul 2006, 06:08
You just need to look at the terms and functions.
Telomerase is supposed to prevent the shortening of the chromosomes. So nucleotide sequences that do not contain any genetically relevant information are appended to the end. Why?
this relevant information would be called telomeres. They are essential structural elements of DNA for the stability of chromosomes. Each time a cell divides, a piece of the telomeres is lost. By restoring telomeres, telomerase prevents chromosomes from getting shorter with each cell division, which would eventually lead to cell death. (so no apoptosis, but senescence)
So: Telomerase = enzyme of the cell nucleus (protein and long RNA portion) -> but can only be used in cells during d. Find germline, or cancer cells / unicellular organisms.
Telomere: Chromosome ends of linear chromosomes / important for folding to the secondary structure / sometimes anchoring point on the cell nucleus wall
The textbooks say that the primer is degraded and since the DNA polymerase cannot attach anything to a 5'-end, there is a gap at the end of the newly reduplicated strand. So far so good. A few pages beforehand, however, is in the same books:
The primer consists of RNA and is replaced by DNA by the DNA polymerase.
There is nothing there about a gap and if RNA is exchanged for DNA, everything should be fine. When it comes to telomerase, it always says that the primer is removed, not replaced.
Problem 1: Concept (technical term) - structure -> function
(= Nucleotide sequence that serves as the starting point for DNA-replicating enzymes such as DNA polymerase | short RNA molecule = starter molecule with free OH group)
3'OH end !!! -> (DNA polymerases need a hydroxyl group as a starting point)
Primers can consist of both DNA and RNA. (Prokaryotes / eukaryotes only have one RNA to replicate.) The polymerases ALWAYS start at the 3 'end. The primers are assembled beforehand by primases.
Viewing at Prokaryotes
Replication on the template: primase forms primer DNA polymerase III synthesized continuously from 3 'to 5' -clear
Sequence: 5 'to 3' -> the primases start at certain sequences (knowledge gap for me) form primers -> discontinuous polymerisation process by DNA polymerase III-> the so-called Okazaki fragments are created (1000-2000 nucleotides long)
DNA polymerase I. removes the primers and fills in the gaps between the fragments with additional deoxynucleotides. A DNA ligase links the individual fragments (phosphodiester bonds, etc.: happy:), so that ultimately a complete DNA strand, the subsequent strand, is created.
In eukaryotes similar - only the exact name of the enzyme is different. I think the multifunctional polymerase messed you up. (PolymeraseChainReaction, Exonuclease etc.) - also ligase is not explicit: D
PICTURES you can find HERE
Replicants were such space mutants, zombies with blue crosshair contacts, if I understood the television correctly ...
Replicants at Stargate, silicants at Space 2063-> those were the AIs with the blue cross lenses. well-known actor: David Duchovny (aka Agent Mulder) in the guest role, episode "The Bachus"
This post was made by myrmikonos: 08 Jul 2006, 06:13 edited
08 Jul 2006, 18:39
Quote (trannoc @ Jul 08 2006, 12:19 pm)
Thank you, this is described very well, but the question doesn't really answer that (or I don't get it ...).
"DNA polymerase I removes the primers and fills in the gaps between the fragments with additional deoxynucleotides. A DNA ligase links the individual fragments (phosphodiester bonds, etc.), so that ultimately a complete DNA strand, the subsequent strand, is created."
So the primers are completely replaced. Why are there teleomers that are supposed to prevent the shortening of the DNA when there is no shortening at all, since all primers are replaced?
The telomeres only play a role in cell reproduction, i.e. when all of the DNA is replicated. One strand of the DNA is completely replicated from top to bottom (great verb ;-). The other one would have to be replicated the other way round, but since it has to happen at the same time and the replication can only take place at one point at the same time, small pieces are always replicated and then the "gaps" are filled by the DNA polymerase I (primer away, correct DNA towards). However, the pieces need a certain minimum length and since everything happens randomly in the large cell soup, it would be a very large coincidence if it works out at the end of the DNA so that the last primer starts right at the end of the DNA.
So let's say the last primer is 5 nucleotides before the end of the replication works backwards, so away from the end to the next primer that is somewhere maybe 1500 nucleotides further in front and some ne -ase fixes the whole thing together.
Now the next primer would have to start somewhere at the last 5 nucleotides (primers are (I think) at least 3 nucleotides long) and that is not enough space to start a stable strand and then connect it to the rest. So in this example you are losing 5 nucleotides. And telomerase can then attach it again.
Maybe it's a bit confused now, but maybe it will help.
08 Jul 2006, 8:13 pm
so I'll try to explain:
it is correct that the primers are broken down during replication and then the gaps are closed
it has also been said that the polymerase that does just that needs a 3 'end to do this
So: this can only take place within the molecule, but not at the end where there is no 3 'end ...
the result is that the strand gets shorter and shorter ... at some point the teleomeres, which apparently do not carry any genetic information, are gone and then each time something of the coding sequence goes away ... that leads to a disturbance in the cell ... and at some point to death
another picture will come soon
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