amino acids
3.4 | Protein Synthesis By the end of this section, you will be able to: Explain how the genetic code stored within DNA determines the protein that will form Describe the process of transcription Describe the process of translation Discuss the function of ribosomes It was mentioned earlier that DNA provides a blueprint for the cell structure and physiology. This refers to the fact that DNA contains the information necessary for the cell to build one very important type of molecule: the protein. Most structural components of the cell are made up, at least in part, by proteins and virtually all the functions that a cell carries out are completed with the help of proteins. One of the most important classes of proteins is enzymes, which help speed up necessary biochemical reactions that take place inside the cell. Some of these critical biochemical reactions include building larger molecules from smaller components such as occurs during DNA replication or synthesis of microtubules and breaking down larger molecules into smaller components such as when harvesting chemical energy from nutrient molecules . Whatever the cellular process may be, it is almost sure to involve proteins. Just as the cells genome describes its full complement of DNA, a cells proteome is its full complement of proteins. Protein synthesis begins with genes. A gene is a functional segment of DNA that provides the genetic information necessary to build a protein. Each particular gene provides the code necessary to construct a particular protein. Gene expression, which transforms the information coded in a gene to a final gene product, ultimately dictates the structure and function of a cell by determining which proteins are made. The interpretation of genes works in the following way. Recall that proteins are polymers, or chains, of many amino acid building blocks. The sequence of bases in a gene that is, its sequence of A, T, C, G nucleotides translates to an amino acid sequence. A triplet is a section of three DNA bases in a row that codes for a specific amino acid. Similar to the way in which the three-letter code d-o-g signals the image of a dog, the three-letter DNA base code signals the use of a particular amino acid. For example, the DNA triplet CAC cytosine, adenine, and cytosine specifies the amino acid valine. Therefore, a gene, which is composed of multiple triplets in a unique sequence, provides the code to build an entire protein, with multiple amino acids in the proper sequence Figure 3.25 . The mechanism by which cells turn the DNA code into a protein product is a two-step process, with an RNA molecule as the intermediate.