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In 1953, Watson and Crick were credited with the discovery of the structure of DNA. It consists of long chains of chemical units called nucleotides, each of which is made of three parts: deoxyribose, phosphate, and nitrogenous bases. The shape of the DNA molecule is known as a double helix, the 'rungs' of which are arranged as follows: cytosine pairs with guanine, while thymine pairs with adenine. It is the sequence of these nitrogenous bases that determine the code of DNA. DNA does not build a protein directly but undergoes the process of transcription to create an mRNA molecule. The three key parts to this process are initiation, elongation, and termination. A key enzyme that guides this process is RNA polymerase. Following this, the next process, processing/splicing, takes place. During this process, introns are removed, and exons are spliced together. The final product, mRNA, is now ready to leave the nucleus. The next key process is translation, where the genetic code is converted from nucleic acid language to protein language. This process converts the information stored in mRNA to a polypeptide. There are a number of 'players' involved in this process. First, the tRNA carrying its amino acid cargo attaches to the mRNA at the small ribosomal subunit, and the process begins. The five stages of this process go in this order: initiation, elongation, and termination. During the process, the codons pick up their anticodons. These are carried to the ribosome, where the mRNA codon binds to the tRNA anticodon. This continues, and each new codon is attached to the growing polypeptide chain by a peptide bond. Now that the protein has been created, it needs to be sent to other locations to function. Proteins are critical to our functioning in many ways. One key importance is that these are the processes whereby genes control the structures and activities of cells, or thinking about what we learned in chapter 9, it is the way that genotype produces phenotype.

Added by Charlene T.

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