![]() ![]() The hydrophilic sugar-phosphate backbone is present on the outside while hydrophobic bases are present in the core.The distance between the base pair is 3.4Å. Each turn of the helix is 34Å consisting f 10 base pairs.The diameter of the double helix is 20Å (2 nm).One strand runs in 5 to 3 directions while the other in 3 to 5 directions. The two strands of DNA are anti-parallel.It consists of two strands that twist around each other. DNA is a right-handed helical structure.The double helical structure of DNA was discovered by James Watson and Francis Crick in 1953.The phosphodiester bond links the 5 carbon of one sugar to the 3 carbon of the second sugar.Ĭharacteristics of the double helix structure The monomeric units are linked by phosphodiester bonds. The monomeric units in DNA are deoxythymidylate (dTMP), deoxyadenylate (dAMP), deoxyguanylate (dGMP), deoxycytidylate (dCMP). The phosphate group consists of a phosphorus atom attached to four oxygen atoms.ĭNA is a polymer of deoxyribonucleotides. This is called complementary base pairing. Adenine always forms a bond with thymine while cytosine always forms a bond with guanine. Therefore, the guanine-cytosine pair is stronger than the adenine-thymine bond. Adenine links to thymine through two hydrogen bonds while guanine links to cytosine through three hydrogen bonds. Each nucleotide consists of three components a nitrogenous base, a pentose sugar, and a phosphate group.įour types of nitrogenous bases are present in the DNA adenine, thymine, guanine, and cytosine. Structure of DNAĭNA has a helix structure. Plastids also have their own DNA which play role in photosynthesis. Mitochondrial DNA has about 16,000 base pairs. It is also inherited from mothers to children. The DNA present in mitochondria is known as mitochondrial DNA. The DNA present in the nucleus of a cell (nuclear DNA) codes for the genome of the majority of organisms. Characteristics of the double helix structureĭNA is a nucleic acid that is a polymer of nucleotides and is responsible for the transmission of hereditary information from parent to offspring.ĭNA also plays an essential role in the synthesis of proteins.This pairing structure keeps the distance between the two backbones of phosphate-linked deoxyribose sugar molecules roughly equal. Specifically, Adenine (A), a purine base, always pairs with Thymine (T), a pyrimidine base, while Guanine (G), a purine base, always pairs with Cytosine (C), a pyrimidine base. Why is this important? Well 2-rings take up more room than 1-ring, so it helps us make sense of why the bases like to “pair” the way they do. The important difference between these two groups is that purine bases (A & G) have a 2-ring structure, while pyrimidine bases (C & T) have a 1-ring structure. These four bases can be further subdivided into groups of the purine bases (A & G) and the pyrimidine bases (C & T). Attached to each deoxyribose sugar molecule in the DNA backbone is one of four nitrogen-containing bases: Adenine (A), Thymine (T), Cytosine (C), and Guanine (G). These deoxyribose sugar molecules are linked to each other in long chains by their associated phosphate groups, creating the “backbone” of the DNA structure. ![]()
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