From Genes to Proteins
08/11/2010 § 1 Comment
During today’s class, we started learning about RNA and protein and how these molecules transcribe and translate the information from DNA and produce meaning out of it. In this section of the textbook, we started getting closer to our essay question, which was not discussed in my last blog. As a refresher, our essay question was: How does information produce meaning?
At one point in class, we were able to translate the question and replace the words information and meaning. Another word for “information” can be “nucleotides” and “meaning” can be “proteins.” So if we switch around these words, the essay question can be reworded to: How do nucleotides produce proteins? This makes sense in terms of our original essay question because nucleotides contain nitrogen bases which code for amino acids that make proteins. Proteins, in turn, are responsible for many things in an organism. Some responsibilities they have include structural capabilities (determining someone’s eye color, hair color, everything that makes them look as they do), being able to fight off infections or bacteria, moving muscles to enable an organism to move, and many other tasks.
So in a way, the reworded essay question still makes sense.
In class, we learned that both transcription and translation contain three important stages: Initiation, Elongation and Termination. In transcription, an RNA polymerase binds to a DNA molecule’s promoter region, which is around the front of the gene and where transcription starts. The RNA unwinds and unzips the DNA. This is initiation. Elongation is when the RNA polymerase begins adding nucleotides via the complementary base pairing rule (A=U, G=C). Behind the polymerase, immediately after it adds a corresponding nucleotide to the lengthening mRNA, the DNA molecule zips up again and rewinds. Elongation and the matching of nucleotides continue until termination. This is when the mRNA that is being made reaches a stopping codon; a termination sequence. When transcription is completed, the mRNA is simply released to find a ribosome to do translation.
During translation, all the action happens inside ribosomes (which are made of ribosomal RNA and lots of proteins). The process of translation can be thought of as taxis dropping off guests at a party in Sannomiya. (Or wherever). First, the ribosome (kind of like the bellboy and the parking lot at the same time), mRNA (the guest list that determines who gets to come to the … party) and tRNA (tRNA are all taxis)—carrying the amino acid for the anticodon that corresponds to the start codon—all bind together. The tRNA carrying the start anticodon binds to the P site. Another tRNA comes along with the right anticodon and matching amino acid for the next codon shown on the mRNA. It attaches to the A-site. The two amino acids now link together with a peptide bond made by the ribosome. Then the [now empty] tRNA in the P-site leaves and the tRNA that was on the A-site moves to take its spot. A new tRNA comes in to fill the A-site and more amino acids are added to the growing chain. This process is continued until a stop codon is reached and the protein is finished and released to be used in the cell.
Going back to the essay question, we just used nitrogen bases (nucleotides) and genetic information to make proteins that will work around the cells and in an organism’s body to form its structure, help it move, enable it to think, feel, and do many more things. Clearly, proteins help an organism mean something. In the processes of transcription and translation, we kind of just figured out how information helps make meaning.