BIOL 0510 Lecture Notes - Lecture 5: The Double Helix, Dna Supercoil, Dnainfo.Com
7 Nov 2016
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But rna can also be reverse transcribed into dna. Strands held together by h bonds between a+t (2 bonds) and g+c (3 bonds) H bonds are weak because easier to open it and pull it apart for replication. Strands wind around each other to form a double helix. Dna in a living organism typically exists in a right-handed helix. Introducing or removing additional twists imparts strain --> supercoiling. Subtraction of twists (underwinding) leads to negative supercoiling. Most dna in living organisms is negatively supercoiled. Allows lots of linear dna to be packed into a bacterial cell. E coli nucleoid contains more than 1 mm of linear dna (400x the length of the cell!) Dna gyrase: class ii topoisomerase only found in prokaryotes. Means you can mess with dna gyrase without affecting eukaryotes. Moderates supercoiling, introducing negative supercoils into the dna. The dna molecule is broken (double-sided break) and resealed on the opposite side of the strand.
