Although nucleic acids are not generally important components of foods, they are perhaps (and ironically) the most important biomolecule class of all for the simple reason that everything we eat was at some point alive, and every process and structure in those organisms were determined via enzymes encoded for by DNA. Indeed, the entire purpose of breeding programs is to control the propagation of DNA between successive generations.
Understanding the basics of DNA (deoxyribonucleic acid) and its biochemical forms is important for food scientists to gain an appreciation of the basis for genetic manipulations of food-related proteins as well as DNA-based food authentication techniques. DNA is composed of three main chemical components: a nitrogenous base, a sugar and a phosphate. There are four bases: Adenine (A) and guanine (G) are purines, while thymine (T) and cytosine (C) are pyrimidines.
The bases bound to both the sugar and phosphate moieties make up nucleotides and the four building blocks of DNA are deoxyadenosine triphosphate, deoxyguanosine triphosphate, deoxythymidine triphosphate and deoxycytidine triphosphate (dATP, dGTP, dTTP and dCTP, respectively). These building blocks are typically referred to as ‘bases’ or simply A, T, G and C; however, common usage of these terms are meant to imply nucleotides as opposed to bases alone. The nucleotides covalently bond together forming a DNA strand that is synthesised by DNA polymerase.
Additionally, each nucleotide’s base moiety can bond via hydrogen bonds to other bases; A–T and G–C, termed base pairs and are said to be complementary. In fact, DNA exists in two-stranded form, consisting of two complementary strands. For example, a strand ATCG would be paired to its complement TAGC. 5’-ATCG-3’ 3’-TAGC-5’ Two-stranded DNA spontaneously forms a helix, hence the term double helix, which can contain many thousands of base pairs with molecular weights in the millions, or billions, of Daltons. By comparison, the largest known protein is a mere 3 million Daltons. Genes are stretches of DNA that encode for the synthesis of proteins; DNA is transcribed, yielding messenger RNA (mRNA), which is then translated at ribosomes, yielding specific sequences of amino acids (proteins).
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