DNA and RNA structure

DNA and RNA structure - C H A P T E R 4 DNA-RNA STRUCTURE...

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C H A P T E R 4 DNA-RNA STRUCTURE DNA Structure DNA Stability RNA Secondary Structure The two complementary strands of the DNA double helix run in antipar- allel directions (Fig. 4-1). The phosphodiester connection between indi- vidual deoxynucleotides is directional. It connects the 5 9 -hydroxyl group of one nucleotide with the 3 9 -hydroxyl group of the next nucleotide. Think of it as an arrow. If the top strand sequence is written with the 5 9 end on the left (this is the conventional way), the bottom strand will have a complementary sequence, and the phosphate backbone will run in the opposite direction; the 3 9 end will be on the left. The antiparallel direc- DNA STRUCTURE Double helix A 5 Adenine 5 purine T 5 Thymine 5 pyrimidine (DNA only) G 5 Guanine 5 purine C 5 Cytosine 5 pyrimidine U 5 Uracil 5 pyrimidine (RNA only) AT/GC base pairs Antiparallel strands Major groove–minor groove A-, B-, and Z-DNA 35
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tionality of DNA is an important concept (i.e., it always appears on exams). Either of the two strands could be written on top (just rotate the paper by 180°), but if the DNA codes for a protein, the top strand is usu- ally arranged so that it matches the sequence of the RNA that would be made from the DNA (see later). In Fig. 4-2, you’re looking at a base pair as it would be seen from above, looking down the helix axis. The DNA double helix has two grooves—the major and the minor. If the helix were flat, the major and minor grooves would correspond to the two different flat surfaces represented by the front and back of the flat sheet. The major and minor grooves are different size because the two strands come
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This note was uploaded on 04/09/2008 for the course BIO SCI 98 taught by Professor Goulding during the Spring '08 term at UC Irvine.

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DNA and RNA structure - C H A P T E R 4 DNA-RNA STRUCTURE...

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