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DNA is obviously comprised of atoms, specifically N,C,H,O,and P. The cell needs not only these elements, but also other elements like Calcium, Magnesium, Manganese, Iron, Potassium, Sodium, Chloride. It also needs elements like Zinc, Cobalt, and Titanium in trace amounts.
DNA is built from nucleotides (adenine, thymine, cytosine, guanine). The basic structure consists of a sugar (deoxyribose) bonded to a base (A, T, G, C) at one position and bonded to a phosphate at a different position.
The bases protrude from the sugar-phosphate backbone and form hydrogen bonds with the bases on the complementary strand. These hydrogen bonds are important because they are not very strong so that the strands are easy to separate for duplication, yet they are strong enough to maintain the structure of the DNA.
Base Pairing: Adenine and thymine always bond with each other (A-T), while guanine and cytosine always bond to each other (G-C). Because of this relationship, one strand completely specifies the complementary strand and one strand is used to specify the other in replication. This complementary relationship provides a redundancy in the DNA which reduces the chance for error.
Directionality exists in DNA because the DNA strand has one 5' end and one 3' end. In a double stranded DNA the two strands run in opposite directions (they are antiparallel). The 3' end of one DNA strand lies at the same end of the double helix as the 5' end of the complementary strand. The directionality is the result of the DNA starting with a phosphate that is attached to the 5' position of the deoxyribose sugar of the first nucleotide. The second nucleotide in the chain is attached to the 3' position of that same sugar. The last nucleotide in the DNA has a free 3' end - nothing is attached to that (3') end.
The base pairs form a ladder and stack one on top of another along the inside of the helix, which serves to stabilize the structure.
The DNA structure is a right-handed double helix.Because the base pairs do not go directly through the middle of the helix, the sugar phosphate backbone on the outside of the helix are not symmetrical around the center of the helix. This results in either a smaller space between adjacent turns of the sugar-phosphate backbone around the outside of the helix, known as a minor groove, or a slightly larger space, known sensibly as a major groove.
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