3B1+Bio+DNA+Essay+by+Han+song(08)+Li+xi+chen(13)+Hu+yang+tao(09)+and+zhang+shuofei(XX)

Colour code: Han Song Li xichen Hu yang tao Zhang shuofei Deoxyribonucleic acid or DNA is a molecule that carries genetic information. Such information is crucial for all kinds of cellular functions, Such as cell division, protein synthesis and so on. A gene is a small segment of DNA that contains information used for constructing polypeptide chains to form proteins and enzymes. Each gene consists of two polynucleotide chains. Each DNA molecule is double-stranded, consisting of two parallel strands twisted around each other to form a double helix. These strands go in opposite directions and are joined together by hydrogen bonds at the bases. DNA molecule curls around proteins, forming a single chromatin strand, which will coil tightly into chromosomes when the cells divide. The basic structure of the DNA is helical, with the bases being stacked on top of each other.

DNA is made up of subunits called nucleotides; each nucleotide is made up of a sugar, a phosphate and a base. They consist of deoxyribose, a phosphate group and nitrogen containing base. There are four types of nitrogen-containing bases in DNA; they are known as adenine (A), cytosine(C), guanine (G) and thymine (T). Nucleotides can be joined to form polynucleotide. Each gene is made of a sequence of nucleotides. There are 4 to the power of n number of different combinations. Two chains of polynucleotides are bonded together according to the rule of base pairing; A bonds with T; C bonds with G. These pairings are known as complementary bases. This lets us know the sequence of the bases on the complementary strand just by knowing the sequence of bases along one strand. One of the chains, known as the template determines the type of protein made. These templates contained a sequence of nucleotides. Such nucleotide sequence store information as follows: three base code (codon) for one amino acids. Different sequence of codons make a different polypeptide consisting of different arrangement of amino acids. References: [] Textbook