Question:
Question about DNA??
Sienna
2010-05-16 19:03:32 UTC
When DNA replicates, where do the single bases which attach onto the then separated strands of DNA come from? How are they available?

I am currently getting a little confused about what is the basic building blocks inside our body. I know that DNA is the information which allows our body to create protein that make us up, but what tells the DNA polymerase to attach the spare nitrogen bases, who commands replication and translation????

How does the DNA polymerase make the bases stick on? and where does the extra backbone come from during replication?

this whole study on DNA is starting to really confuse me...especially the basics and reasoning so if anyone can help me...
thankkyouuU!!
Four answers:
DNAunion
2010-05-16 19:24:03 UTC
Some simple answers to most of your questions, followed by a detailed answer to one of them.



The DNA nucleotides are free, floating around in the nucleus (not in the cytoplasm as the other person wrongly stated).



The bases "stick" to one another via hydrogen bondings.



There is no extra backbone: the backbone of a DNA strand is a repeating sugar-phosophate pattern. Each incoming nucleotide already has a single suger-phosphate unit in it: adding the new nucleotide extends the sugar-phosphate backbone by one unit.







There is no "who" in the cell. It's all chemistry and physics. Here is an explanation of how the cell transitions from the G1 phase into the S phase.



Cyclins

As their name suggests, cyclins are a group of proteins whose concentrations repeatedly “cycle” up and down over the course of multiple rounds of division (one “up” and one “down” per cell cycle).



Cdks

Cdks (cyclin-dependent kinases) are protein kinases that require binding of cyclins in order to be activated (a protein kinase is a protein that phosphorylates other proteins). Their concentration remains relatively constant throughout cell division.



Cdk1 (Cdc2)

Cdk1 (cyclin-dependent kinase 1) and Cdc2 (cell-division-cycle 2) are two names for the same protein: the first name is the newer one, but you may see either in literature (especially for genes and proteins that were named before the renaming of Cdc2 to Cdk1). Cdk1 is a mitotic Cdk found in all eukaryotes studied and is highly conserved: human Cdc2 is about 60% to 65% identical to the yeast homolog, and the human cdc2 gene can rescue yeast with a non-functional gene.



MPF

MPF (maturation-promoting factor) is a Cdk1-cyclin B complex that causes cells to exit G2 and enter mitosis.





G1-S Transition



The Restriction Point

In multicelluar animals, cells remain in G1 (or G0) until they receive a message to begin division: that is, they must be signaled to pass through the restriction point before the cell cycle begins. E2F is a transcription factor that activates transcription of genes needed for DNA replication, such as the gene for cyclin E. cyclin E combines with Cdk2 to form Cdk2-cyclin E complexes, which activate MCM helicases at replication origins, triggering the initiation of DNA synthesis.



However, in G1 (and G0), although E2F binds to its target DNA sequences, it is inactivated by being bound by the inhibitory Rb protein (The Rb gene is a tumor-suppressor gene. It gets its name from retinoblastoma, the first cancer known to be caused by mutations in the gene). The restriction point is passed when Rb dissociates from the E2F transcription factor, allowing E2F to begin activating the genes needed for DNA replication.



1. The binding of growth factors to cell-surface receptors initiates a Ras/Raf/MEK/ERK pathway that leads to the synthesis of cyclin D, and thereby formation of Cdk4, 6 / cyclin D (consisting of either Cdk4 or Cdk6 complexed with cyclin D), which is also called the G1 Cdk-cyclin complex. Cyclin D is rapidly degraded, so is present only when the cell is actively being stimulated by the growth factors.



2. The activated G1 Cdk-cyclin complex then phosphorylates the Rb protein.



3. The phosphorylated Rb protein dissociates from E2F.



4. The freed E2F transcription factor activates the genes needed for DNA synthesis, leading to the G1-S transition.



5. Later, during mitosis, Rb is dephosphorylated, and so rebinds to E2F, inactivating it.
K
2010-05-16 19:35:24 UTC
Ok so i am going to attempt to be as thorough in answering your questions as possible (hopefully explaining more than you asked) but it will be in a different order.



DNA------transcription------->mRNA-------translation--------->protein------------->polypetide (3+ bonds)

(ATGC) (AUGC) (amino acids)



Needed for DNA transcription:

1) RNA polymerase-adds on free RNA nucleotides to 3' end of growing mRNA

2) DNA template-info to copy

3) Free RNA nucleotides-to build 3' mRNA



Transcription:

-occurs in the nucleus

5' mRNA is read when a promoter is seen, helicase unwinds the double strands so it is readable, ends with a terminator sequence. There is a waiting period where Exons are Expressed and introns are spliced out of the sequence. A polyAtail protects the 3' end and a 5' cap protects the other end.



Leaves through a nuclear pore...



Needed for Translation:

1) mRNA-codons/instructions

2) tRNA-bring Amino acids (AA) in (can be recycled)

3) ribosomes-formation of proteins (have 2 cites: P and A site, which hold the tRNA next to each other while peptide bonds form)

4) enzymes

5) free AA



Translation (made of 3 phases):

-occurs in the cytoplasm

-Phase 1: initiation-mRNA is brought into P site of ribosome

-Phase 2: elongation-tRNA (anticodon) is matched with the correct mRNA (codon), peptide bond forms between the AA, everything shifts over 1 codon (also the tRNA is moved to the A site) and the process repeats until...

-Phase 3: termination-stop codons expressed



When the DNA is replicated it can be condensed and DNA strands can wrap around histones (which are like beads and the DNA can be compared to a string).



I hope this doesn't confuse you and gives you more info than you needed! Let me know if you have any more questions!
yutgoyun
2010-05-16 19:24:37 UTC
The single bases are freely floating in the cytoplasm, as nucleotide triphosphates.



Gene/cell regulation is another topic on its own which you can spend a lifetime studying. In general, whether a protein (in this case DNA polymerase and its associated proteins) is active or not is dependent on 1. whether or not it is present. This is transcriptional/translational regulation at the DNA/RNA level. In other words, DNA replication does not occur because DNA polymerase is not present. 2. Repression. Proteins can be made inactive with modifications. 3. You can also have more complex situations where the substrate is inactive (remember DNA is wound up in histones, so in those situations you can't replicate it).



DNA replication is primarily regulated by the 1st one. Note that many processes are regulated by a combination of all of these, and of course you can get even more specific. (Transcriptional regulation occurs through mRNA repression, modification, digestion, transcriptional repression, activation, etc...)



http://en.wikipedia.org/wiki/DNA_replication#Regulation_of_replication



The bases stick on because of DNA structure. Review your DNA structure! The bonding energy of the phosphates of the dNTPs (dideoxy nucleotide triphosphates) provide the energy for DNA replication. One P remains as the backbone.



Very good questions.
?
2016-06-03 06:08:42 UTC
Native Americans are not East Asians AT ALL. There is a tendency among Eurocentric scholars based on superficial likeness to assimilate Native Americans with East Asians. They have a very different DNA. Eurocentric scholars do that a lot; maybe they want to prove that Native Americans are not so "Native" after all and that they are descendants of East Asians who crossed the Bering Strait thousands of years ago. The same Eurocentric scholars don't do the same thing with Melanesians, papuans or even the Olmecs (who appear to have "African features"). They NEVER ask whether Melanesians, papuans or even Olmecs are African based on their features. Equating Native Americans with East Asians proves that Eurocentric scholars and those who have been brainwashed by them have a racist agenda.


This content was originally posted on Y! Answers, a Q&A website that shut down in 2021.
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