It is also right-handed, but there are 11 bases per turn and the helix is broader. When the DNA becomes dehydrated, the A-form can be observed. The above information described the B-form of DNA. They found that the sugar-phosphate backbone was on the outside and the bases are positioned on the inside of the helix. The X-ray diffraction photographs obtained from DNA fibres, displayed a unique X-shape, which illustrates a helical stucture, although they indicated a repeating structure of 3.4 Å apart per turn of the helix, each base is rotated 36 degrees from the next one. This was solved as a result of 'stick-and-ball' models they created, along with utilising the work of fellow scientists Rosalind Franklin and Maurice Wilkins on X-ray crystallography. In 1953, despite many other theories, James Watson and Francis Crick discovered the true structure of a double stranded DNA molecule to be a 'Double Helix'. DNA is much more stable then RNA since RNA is only single-stranded - the nitrogenous bases are left exposed to attack by nucleophiles on one side. This makes DNA less vulnerable to nucleophilic attack, thus DNA is considered to be a very stable molecule. The negative charge from the phosphate groups gives the sugar-phosphate backbone of DNA a negative charge, which repels nucleophiles, including water. ĭue to the double helical structure of DNA, the nitrogenous bases are found on the inside of the structure, forming a hydrophobic interior. The specific nucleotides that face into the major groove are the N7 and C6 groups of purines and the C4 and C5 groups of pyrimidines, which accept hydrogen ions from the amino acids in the protein to form hydrogen bonds. The major groove is much wider than the minor groove and this means that specific DNA-protein interactions can take place on the major groove due to the backbone not being in the way. This leads to the formation of major and minor grooves. In the DNA double helix the strands of the backbone are closer together on one side of the helix than they are on the other. The transcribed mRNA is then translated to a polypeptide in a process called translation by tRNA. The process of DNA being copied into mRNA is termed transcription. DNA is copied into mRNA (messenger RNA) which carries the information from the original DNA template strand to be involved in protein synthesis. Each strand acts as a template for the other one in DNA replication. These interactions form bridges between two DNA chains, thus creating a double-stranded 'ladder' shaped structure. In between these bases are hydrophobic interactions known as van der Waal forces. The complementary base pairs in DNA interact with one another via hydrogen bonds: A-T interactions consist of 2 intermolecular hydrogen bonds, whereas G-C interactions consist of 3 intermolecular hydrogen bonds. In order to produce a double-stranded DNA structure, interactions occur between complementary bases. The deoxyribose sugar/ phosphate group region is regarded as the 'backbone' of DNA strands due to its structural purpose and the sequence of bases carries the gentic information. Its chemical formula is C 5H 10O 4), a phosphate group (which forms a phosphodiester bond: connecting 2 deoxyribose sugars together) and a nitrogenous base (one from A (Adenine), C ( Cytosine), G ( Guanine) or T (Thymine), which forms a side chain branching from the 1' carbon of the 2` deoxyribose sugar). A nucleotide consists of: a 2` deoxyribose sugar (A five-carbon pentose similar to that of ribose sugar found in RNA.
Humans have 99.5% similarities with other humans in their DNA.ĭNA ( deoxyribonucleic acid) is a chain of monomers (repeating units) called " nucleotides". The phosphate group is attached to the sugar through a phosphodiester bond. DNA also contains a phosphate group connected to a deoxyribose sugar. These form complementary base pairs of A-T and G-C.
DNA is composed of 4 bases: the purines, adenine (A) and guanine (G) and pyrimidines, thymine (T) and cytosine (C). The structure of DNA was first identified as having a 'double-helix' structure by Watson and Crick in 1953. It is arranged into structures called chromosomes. DNA ( deoxyribonucleic acid) is the genetic information found in the nuclei of most organisms.
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