Most proteins are in the range of 100 to 1000 amino acids in length (since amino acids are ≈ 100 Da on average, this corresponds to masses from 10 4 to 10 5 Da), and since each amino acid is about a cubic nanometer in volume, folded proteins are from a few to a few tens of nm in size.ĭNAs in cells are covered with proteins, some of which interact rather specifically with short (< 20 bp) specific base-pair sequences, and some of which are less discriminating, interacting with DNA of essentially any sequence. Proteins are the workhorse molecules of the cell, and are themselves polymers of amino acids, folded into specific shapes by the action of relatively complex amino-acid-amino-acid interactions. However, the functions of DNA in vivo cannot be realized without the action of a huge number of protein molecules. The presence of the two complementary copies along the two polynucleotide chains in the double helix provides redundant storage of genetic information and also facilitates DNA replication, via the use of each chain as a template for assembly of a new complementary polynucleotide chain.ĭNA molecules by themselves are already quite interesting objects for biophysical study. Each base pair has a chemical weight of about 600 Daltons (Da). These rules follow from the chemical structures of the bases, which permit two hydrogen bonds to form between A and T (indicated by =), versus three that form between G and C (indicated by ≡). Corresponding bases on the two chains in a double helix bind one another according to the complementary base-pairing rules A=T and G≡C. The double helix encodes genetic information through the sequence of chemical groups - the “bases” adenine, thymine, guanine and cytosine (A,T,G and C). DNA molecules in cells are found in double helix form, consisting of two long polymer chains wrapped around one another, with complementary chemical structures.
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