The Chemistry of DNA
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DNA is the inherited genetic material that controls gene expression through protein synthesis. This is a fancy way of saying that DNA is a chemical form of a genetic blueprint. The genetic instructions contained in DNA are housed in genes.
These smaller, individual segments connect together to comprise a molecule of DNA. The smallest component of a gene is a nucleotide monomer. Nucleotide monomers, also called nucleotides, are named after its nitrogenous base. The structure of DNA is a complex mix of chemistry and biology.
Nucleotides are made of three separate chemical units. The first unit is a pentose sugar made of five carbon atoms. The second unit is a phosphate group made of four oxygen atoms bonded to a central phosphate atom. The third unit is one of four nitrogenous bases, adenine, thymine, cytosine, or guanine.
The four bases, A, C, T, or G, are categorized into two types: Purines and pyrimidines. Purines are chemically a double-ringed structure, whereas pyrimidines form a single ring. Adenine and guanine are classified as purines, while cytosine and thymine are pyrimidines.
The structure of DNA is dependent upon the unique chemical interaction between a purine and a pyrimidine. This precise pairing of purines to pyrimidines essentially represents the mortar that bonds two strands of DNA. The result is a structure called a double helix.
The twisted shape of DNA is what led researches to coin the term double helix. A molecule of DNA is two single strands joined together by hydrogen bonds. A single strand of DNA is likened to a ladder that has been cut down the middle, resulting in two halves.
One strand complements the other in a way that is also related to chemical structure. The component nucleotides make the rungs of the ladder. The nucleotides in the first strand of DNA, the left side of the ladder, pair with nucleotides in the second DNA strand or the right side of the ladder. Together, the two DNA strands unite to form what looks like one single ladder.
For genes to properly function, the nucleotides must pair correctly. They do this by adhering to a strict set of base-pairing rules that were discovered by pioneers in the science of genetics, James Watson and Francis Crick. Base-pairing rules dictate that a purine always pairs with a pyrimidine. In other words, adenine always pairs with thymine and cytosine always pairs with guanine.
The hydrogen bonds formed between nucleotide pairs are important to the structure of DNA. These weak bonds, along with complex bonding among other molecular elements are what give DNA its twisted appearance. This particular shape is why DNA is aptly named a double helix.
Article Source: Articlelogy.com
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