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Translation/Transcription 10/13/2011

DNA transcription can be describes in a simple way. It is when cells transcribe the genetic material codes from the DNA molecule into a RNA molecule. RNA is a working copy of DNA that. The initiator factor of transcription is when a RNA Polymerase binds to a DNA molecule at the promoter site, located within the major grove, of DNA and it then unwinds the DNA molecule. RNA Polymerase does not need the aid of a Ligase or a Primer to accomplish this task. After the unwinding of the DNA molecule, the RNA Polymerase then goes into the elongation. In elongation, a single strand of DNA molecule is then transcribed into a single RNA molecule. Using the base complementary pair rule of nucleotides, Chargaff’s Rule. If a cytosine is present in DNA then the complementary pair in RNA would be guanine and vice versa. If an adenine is present in DNA, then a uracil will be present in the RNA strand according to Chargarr’s rule. Uracil takes the place of thyamine because it is not present in RNA and is only present in DNA. The newly formed strand of RNA can now be called the messenger RNA (mRNA) when the RNA Polymerase reaches a specifically coded termination point on the DNA molecules.

Before a mRNA is released from the nucleus into the cytoplasm to undergo protein synthese, it must first be proofread and edited and then submitted as the final copy, kind of like a thesis paper. This editing occurs withing the nucleus and after DNA transcription has occured. The mRNA has areas on it that are called introns and exons and essentially the nucleus only wants for the good genetic information to be presented and these are the exons. To accomplish this, there are specific enzymes involved in this process known as spliceosome and it scans the informations from the 3′ end and after all introns are removed it then does the 5′ end on the mRNA. When the splicing is complete the mRNA is now a mature mRNA and can now be released from the nucleus into the cytoplasm of the cell to deliver the message of the DNA as to what to proteins to produce.

In DNA translation, the mRNA is released from the nucleus of the cell and is then released into the cytoplasm of the cell where the translation of the mRNA is then converted into functional proteins with the help ribosomes. While the mRNA is in the cytoplasm it then comes into contact with a 30s ribosome with the matching complementary base pairing of its first three anitcodon nucleotides. Once this bonding occurs, they are then joined with a 50s ribosomal and the translation can now begin within three active sites. E (exit), P (peptidyl) site and A (aminoacyl) site. With the first codon paired in the P site, another transfer RNA (tRNA), then enters into the ribosome with the next matching anticodon and the two tRNA present in the two ribosomal subunits then bond to create a peptide bond and the ribosome shifts one codon. The tRNA that was in the P site is then moved to the E site and is released leaving behind the bonded amino acid. The next matching tRNA enters the ribosome in the A site and then creates peptide bond with the tRNA now in the P site and the ribosome shifts one codon releasing the tRNA in the P site to the E site and this process continues until the ribosome reaches the termination point or the codon with the stop message and the two subunits of ribosomes unpair and the protein is released as well as the mRNA.

This complex process occurs in all of us and it the means of a cell knowing the appropriate genetic information like which proteins to produce to help with metabolic functions and essentially gene building. We need this genetic information to live and to make us who we are!

 
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Posted by on October 14, 2011 in Biology

 

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Cell Replication 10/11/2011

When you look at someone, all you are seeing is the finished product of a very complicated and meticulous process known as DNA replication. Cells go through several stages and restriction points when they undergo cytokinesis. On of the most important and complicated processes occur in the S-Phase (synthesis) stage. DNA replication takes place in this phase.

There were three proposed models of how DNA is replicated and they are the dispersive model in which the original strand of DNA would produce two DNA molecules with sections of both old and new DNA along each new strand of DNA, the conservative model states that the original DNA molecule will remain intact but a completely new strand will generate but the most logically plausible model is the one we use today called the semi conservation model in which would produce molecules with both old and new DNA, but each molecule would be composed of one old strand and one new one.

In this semi conservation model, a DNA Helicase binds to DNA and unwinds the DNA molecule from itself. To maintain the stability of the DNA molecule, single-stranded DNA binding proteins bind to the exposed purines and pyrimidines. The double helix shape of the DNA have “gaps” of six to eight visible nucleotides that are called the DNA’s major grove region so that DNA Polymerase 3 can bind to the DNA molecule and begin the continuous replication process of the leading strand of the DNA molecule. DNA Polymerases 3 can only read from the 5’-3’direction and since DNA is antiparallel this makes replicating the lagging or the 3’-5’ end a little more complex. This 3’-5’ end forms in Okazaki fragments where a RNA primase attaches to this strand and lays down the RNA primer and then DNA Polymerase 3 comes and makes DNA in the 5’-3’ direction and then DNA Polymerase 1 comes in and converts the RNA primers into base complementary pair DNA and finally Ligase comes in to fill the gaps of each fragment and this is the continuous method is repeated until the whole lagging strand is replicated.

 
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Posted by on October 11, 2011 in Biology

 

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