DNA, the information molecule of all living cells, is made up of nucleotide chains wound in a helix. It's structure and function are intertwined, and understanding these aspects of DNA helps biology students understand the basics of genetics.
The Structure of DNA – Nucleotides, Sugars and Phosphates
DNA, along with RNA, is a nucleic acid, a macromolecule made up of a strand of nucleotides. Nucleotide molecules are made of a nucleotide base, a five-carbon sugar and phosphate groups.
DNA, deoxyribonucleic acid, is made of two long strands of nucleotide bases with a sugar and phosphate backbone. The sugar-phosphate backbones are on the outside and the nucleotide bases are attached in the middle by hydrogen bonds and the strands are coiled around each other to create a helical ladder-like form. This double helix is then coiled and folded many times to fit inside a chromosome, which resides in the nucleus of the cell.
Nucleotide Bases Adenine, Thymine, Guanine and Cytosine Form Base Pairs
There are four nucleotide bases in DNA: adenine, thymine, guanine, and cytosine. They are often referred to by their first letters, A, T, G and C. These nucleotides pair up in the middle of DNA, but they can only match up with specific other bases, because they are two different types of nucleotide bases. Adenine and Guanine are both purines, while thymine and cytosine are pyrimidines. When joining together, adenine and thymine always pair up together and guanine and cytosine always make a pair.
The specific order of the nucleotide bases, read from the 5' end to the 3' end, makes up the genetic code, which directs the production of all of the components of a cell.
The Function of DNA – Storing the Genetic Code
DNA's function is to provide the code on which all life is based. This code is copied into RNA and then brought to different locations in the cell where proteins and RNA are made based on the information provided by the DNA. These proteins and RNA molecules carry out all of the functions in the body.
DNA also functions to pass along all of these important instructions to the next generation. This is why there are two copies of each chromosome, so that each parent can contribute one copy to the children, providing a blueprint for the development of the child and all of the functions it will need in the future.
The genetic code is the basis of all life on earth, and the structure and function of DNA support the cell's ability to create proteins and RNA to carry out all cellular functions. Understanding how DNA works is crucial to understanding modern biology, and students who learn the basics will be well prepared to further study DNA and the many effects it has on all life processes.
Sources:
Lodish et al., Molecular Cell Biology. W.H. Freeman and Company. 2004
Lewin, Benjamin. Genes IV. Oxford University Press., 1990
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