free download PNG images :DNA

DNA (/ di?? Ksi? ra? bo? nj ?? kli ?? k,-? kle?。? K / (about this sound); DNA) is a linear nucleotide chain with genetic instructions for the growth, development, function and reproduction of all known living organisms and many viruses. DNA and RNA are nucleic acids; in addition to proteins, lipids and complex carbohydrates (polysaccharides), they are also one of the four major types of macromolecules essential to all known life forms. Most DNA molecules are made up of two biopolymer chains that intertwine to form a double helix.

These two strands of DNA are called polynucleotides because they consist of simpler monomer units called nucleotides. Each nucleotide consists of four nitrogen-containing nuclear bases (cytosine [C], guanine [g], adenine [a] or thymine [t]), one of the sugar and phosphate groups called deoxyribose. Nucleotides are linked in a chain by a covalent bond between the sugar of one nucleotide and the sugar of another, thus forming an alternate glycophosphate backbone. According to the base pairing rules (A and T, C and G, with bases), the nitrogen-containing bases of two separate polynucleotide chains are combined by hydrogen bonds to form double stranded DNA.

Complementary nitrogenous bases are divided into two groups, pyrimidine and purine. In a DNA molecule, pyrimidine is thymine and cytosine, and purine is adenine and guanine.

DNA stores biological information. The main strand of DNA has the ability of anti cutting, and the two strands of double strand structure store the same biological information. This information is copied when the two chains are separated. A large part of DNA (more than 98% for humans) is noncoding, which means that these parts cannot be used as patterns for protein sequences.

The two strands of DNA extend in opposite directions, so they are antiparallel. Linked to each sugar is one of four types of nuclear bases (informally, bases). The sequence of these four nuclear bases along the skeleton encodes biological information. RNA strand is created by DNA strand as template during transcription. Under the genetic code, these RNA chains are translated to specify the sequence of amino acids in the protein, which is called translation.