Nucleic Acid Functions

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DNA and RNA are types of organic molecules known as nucleic acids. In this lesson, we'll look at their functions. DNA, or deoxyribonucleic acid, is found inside of the nuclei of your cells and it encodes your genetic information in structures of DNA called genes. These genes determine what protein your cells can make. You can think of DNA as being like the master instructions for how to make all of the proteins in your body. Proteins are built by linking together basic units called amino acids. Proteins differ by what amino acids they contain and the specific order in which those amino acids are linked together. That organization is determined by the genes in your DNA. RNA, or ribonucleic acid, carries out the DNA's instructions. RNA comes in three varieties: ribosomal RNA, or rRNA; messenger RNA, or mRNA; and transfer RNA, or tRNA. Proteins are built out of the cell organelle called a ribosome. You can think of a ribosome as being something like a worktable where amino acids are linked together, one by one, to build a desired protein. Ribosomal RNA, or rRNA, as its name implies, is part of the ribosome structure. DNA, with the genes that determine which proteins your cells can make, resides in the cell nucleus. But ribosomes, where the proteins are actually built, are instead located in the cell cytoplasm. That means that the information contained in the DNA must somehow make its way from the nucleus out to the ribosomes where the instructions are carried out. That job is done by the messenger RNA, or mRNA. mRNA is built inside of the nucleus, forming as a coded copy of the information that is contained in one gene in the DNA. This step in protein synthesis is called transcription. The DNA's information or message is coded or transcribed into a new strand of mRNA. The mRNA then leaves the DNA and the nucleus carrying the DNA's instructions or message to the ribosomes so that the protein can be built correctly. Thus, messenger RNA is the messenger who brings DNA's message to the ribosomes so the desired protein can be built. Once the mRNA is in the cytoplasm, ribosomes attach to the mRNA strand and slide along it so it can be read, so to speak, and the protein is built according to the coded instructions. For this to happen, transfer RNA, or tRNA, molecules pick up amino acids in the cytoplasm and carry them to a ribosome that is attached to a mRNA strand. Each tRNA molecule carries or transfers only one type of amino acid, one at a time, to a ribosome, and then searches the mRNA strand for a place where that amino acid might be needed. If it is needed, the tRNA lines up the amino acid that it is carrying with others that have already arrived until the amino acid attaches to the others. Thus the protein is stitched together one amino acid at a time, each placed in its specific location according to the original DNA instructions. This process is called translation. The coded information contained in the mRNA is translated to form a protein. To summarize, simply put the functions of the different nucleic acids can be viewed as follows. DNA contains the specific instructions for building every protein that your cells can make. Messenger RNA is formed from the DNA and carries a coded copy of the DNA's message from the nucleus to the ribosome where the protein will be built. Ribosomal RNA is actually a part of the ribosome that will move along the mRNA strand. And finally, transfer RNA transfers amino acids to the ribosome aligning them as needed according to the coded information in the mRNA strand so that the amino acids can be linked together to form the protein.