general dna

Category: Education

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full text about DNA funtion


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Watson and Crick Model of DNA The following are the features of the DNA molecule as described by Watson and Crick in 1953. 2 chains purine opposite a pyrimidine chains held together by H-bonds Guanine is paired with cytosine by three H-bonds Adenine is paired with thymine by two H-bonds anti-parallel orientation of the two chains 5'--------------->3' 3'<---------------5' the molecule is stabilized by: large # of H-bonds hydrophobic bonding between the stacked bases

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Deoxyribonucleic acid (DNA) is a NUCLEIC ACID that contains the GENETIC instructions used in the development and functioning of all known living ORGANISMS with the exception of some VIRUSES. The main role of DNA MOLECULES is the long-term storage of INFORMATION. DNA is often compared to a set of BLUEPRINTS, like a recipe or a code, since it contains the instructions needed to construct other components of CELLS, such as PROTEINS and RNA molecules. The DNA segments that carry this genetic information are called GENES, but other DNA sequences have structural purposes, or are involved in regulating the use of this genetic information.

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DNA is composed of two chains of repeating nucleotides. Each nucleotide consists of three components. These components are: Phosphate Group 2-deoxyribose sugar A nitrogen containing base Cytosine Adenine Guanine Thymine

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The DNA molecule that Watson and Crick described was in the B form. It is now known that DNA can exist in several other forms. The primary difference between the forms is the direction that the helix spirals. A, B, C = right-handed helix Z = left-handed helix (found in vitro under high salt) B is the major form that is found in the cell. Z-DNA was initially found only under high salt conditions, but the cellular environment is actually a low-salt environment.

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The question then is whether type Z exist under cellular conditions. Several features have been discovered that can stabilize Z-DNA under in a low salt environment. Alternating purine/pyrimidine tracts poly GC or poly AT stretches 5-methyl-cytosine Because both of these conditions can exists in the cell, it is suggested that stretches of Z-DNA may actually exists in the cell along with other stretches of B-DNA.

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