-Robbie Thomashow
diehardcubsfan93@comcast.net
Friday, March 25, 2011
Genes
At the beginning of chapter three, Shubin talks about what makes one cell different from the other. He explains that the answer lies in the DNA and what genes are actually turned on. In unit 10 we learned that this is because of the DNA transcription and translation. Using prior knowledge, review the process of gene expression in both eukaryotic and prokaryotic cells and include the role of RNAi and transcription factors.
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The DNA Transcription is the process of building RNA copy of a DNA sequence that occurs in the nucleus of the cell. The gene sequence is copied into messenger RNA (mRNA) The mRNA is single stranded and has 4 nucleotides like DNA, but instead of Thymine it has Uracil. Transcription continues until one entire gene has been converted to RNA After Transcription the whole mRNA strand is transported out of the nucleus to the cytoplasm. In the cytoplasm, the mRNA strand is translated into an amino acid.
ReplyDeleteDNA translation converts the mRNA sequence into amino acids that form protiens. This creates most of the protiens that make up cells. During DNA translation, messenger RNA, transfer RNA, and ribosomes work together to produce proteins. A ribosomal subunit attaches to a mRNA molecule. The Transfer-RNA transports the amino acid from the cytoplasm to the ribosome. The start codon attaches to at the stating point of the ribosomal unit and this starts making the protein.
RNA interference is when cells turn off or shut down a specific gene that is seen as harmful or dangerous. RNAi works by destroying the molecular messengers that carry information coded in genes to the cell’s protein factories. These messengers, called messenger RNAs (mRNAs), carry out a critical function, without which a gene is essentially inactive.Upon entering a cell, the double-stranded RNA molecules that trigger RNAi are cut into small fragments by an enzyme called Dicer. The small fragments then serve as guides, leading the cell’s RNAi machinery to mRNAs that match the genetic sequence of the fragments. The machinery then slices these cellular mRNAs, effectively destroying their messages and shutting off the corresponding gene.
(http://www.nigms.nih.gov/News/Extras/RNAi/factsheet.htm). A transcription factor is a protein needed to initiate the transcription of a gene. Some transcription factors bind to specific sequences of DNA (promoters and enhancers) while others bind to each other; many bind both to DNA as well as to other transcription factors. These transcription factors regulate the flow of protein synthesis by either deactivating or activating the RNA.
-Adnan Jahan
(adnanjahan@gmail.com)
Adnan did a good job with his explanation of translation and RNA interference but I would like to add more to his explanation about DNA transcription. Like he said, there are 4 paired nucleotides, adenine (A)thymine (T) and guanine (G) cytosine (C). There are three main steps to transcription. First, RNA polymerase binds to the DNA at the promoter region, or TATA box, or the upstream end. It is called the TATA box because the sequence of nucleotides at that region is T-A-T-A or a very similar version of that. Second, transcription factors unwind the DNA strand and allow RNA polymerase to transcribe only a single strand of DNA into a messenger RNA or mRNA. The region where the transcribing actually occurs is called the coding region. When DNA is converted into mRNA, thymine (T) is replaced with the nucleotide uracil (U). The last step in DNA transcription is termination. This occurs when RNA polymerase reaches the terminator sequence, or the downstream end. The RNA polymerase then releases the mRNA polymer and detaches from the DNA.
ReplyDeletehttp://www.elmhurst.edu/~chm/vchembook/583rnatrans.html