« on: May 14, 2014, 10:52:20 pm »
Also a convenient place for me to drop stuff specifically relating to genetics rather than biology as a whole, since I'm taking genetics in two weeks.
So, just as a quick run-down of how DNA and RNA work together before getting deep into the protein bits:
-DNA and RNA are strands of genetic instruction, the main difference between them being that the sugar molecules in their bases differ by one oxygen atom.
-Both use 4 nucleotides (bases), Adenine, Cytosine, and Guanine for both (differing only in that one oxygen atom, natch) and DNA uses Thymine where RNA uses Uracil. Cytosine always pairs with Guanine. Adenine always pairs with Thymine or Uracil. This is basically due to whether or not they can form 2 or 3 hydrogen bonds on the center of the double helix.
-Nucleotides are made up of a phosphate group, a sugar (ribose/deoxyribose/other- more on that in a bit), and a nitrogenous base. The phosphate group of one forms a phosphodiester bond with the sugar of the one next to it, this creates the strand, and nitrogenous bases, which determine what nucleotide it is, forms weaker (and therefore, easy to unzip) hydrogen bonds with the nitrogenous base of its counterpart.
-There are more than one kind of nucleotide, and more than one kind of nucleic acid. ATP, for example, which is the fuel our cellular processes, is basically a modified adenine molecule with three phosphate groups. Further, there are nucleotides that form XNA- nucleic acids that for some reason or another, life on Earth decided not to bother incorporating, but can be used it the fields of synthetic biology and biotechnology (creating exotic nucleic acids that won't interact with ours if it got loose, or even in capping off replication early in biotech). XNA sounds intriguing to me and I think I'll read about it more in my own time as well.
-DNA is an instruction manual, genes are particular tasks in the instruction manual, RNA is the instruction being read outloud, and proteins are the end result of the instructions.
-Triplet sequences of nucleotides code for one of twenty amino acids, or tell you to stop coding. There are 64 possible combinations for codons. Only one sequence codes for "Start" and "Methionine." SIX code for Leucine, and three code for "stop". I'm not exactly sure how these redundancies work, or why Methionine gets no redundancy. Most get 2 or 3. The redundancies help mitigate the chance of damaging mutation. If a syllable can be coded for in a couple of different ways, spelling errors don't have to be that nonsensical.
-DNA unzips, messenger RNA gets grafted on to the exposed nitrogenous bases, and makes a mirror copy. Since most DNA doesn't actually code for anything, the mRNA needs to get edited. The edited mRNA then gets paired with transfer RNA. tRNA is what ends up going on to synthesizing amino acid sequences, which then fold around and create 3 dimensional proteins.
I'll address some of your questions in the next post.