radiation, carcinogens, and oxidation can all modify DNA. Nucleases can cleave or
degrade the DNA molecule. Methylation happens three ways in the DNA molecule. Cytosine can be methylated in two ways to make two types of methylcytosine molecules, while adenine can be methylated in one way. Sometimes, methylation can occur not
because of enzymes but because of exposure to carcinogens. Natural methylation is important to bacterial and archaeal immune systems by protecting DNA from being fragmented by restriction endonucleases. Methylation also prevents mistakes in the process of DNA replication. Methylation will inactivate the gene associated with the piece of DNA and will control differentiation in embryos. Five-
methylcytosine can be mutagenic because it can lead to a GC pair becoming an AT pair. Nucleases will break the phosphodiesterase bond in DNA. There are endonucleases that make cleavage points in the middle of the chain, while exonucleases act on the end of the chain. Restriction endonucleases are used to make recombinant DNA pieces in
recombinant DNA technology. Circular DNA has the ability to supercoil. This happens when one strand is broken and winds many times around its complementary strand until it becomes a tight ball taking up very little space. This can be reversed. There are topoisomerases and gyrases, which are enzymes that unwind and relax the supercoiled DNA. Supercoiling happens to some degree in eukaryotic linear chromosomes as well. The goal is to compact the DNA so it
fits within the nucleus. DNA can now be sequenced. The sequence is based on the different chemical reactivities of the bases on the DNA strand. DNA fragments are separated through gel electrophoresis, which separates the bases. Fluorescent labeling is done to determine
which base pair is located on which part of the DNA molecule.
RNA RNA is also a nucleic acid type but has A, C, G, and U as its bases. There are ribose sugars connected to other ribose sugars by phosphodiesterase linkages between the ribose hydroxyl groups. RNA is largely single-stranded but this gives it the ability to be synthesized correctly by binding to a strand of DNA and creating a matching RNA
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