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2. Beskrive hvordan nukleotider er opbygget og forbundet i et RNA molekyle
Devlin, s.78

RNA is an unbranched linear polymer of ribonucleoside monophospahtes – ribonucleotides, joined together by a 3´-5´- phosphodiester bond.

Each ribonucleotide consists of the following components: 

• Ribose sugar – contains 2`-OH group which makes RNA more susceptible to hydrolysis.
    

• Phosphate-groups: monophosphat, diphsophat and triphosphat.

The RNA molecule is built in the way that there is phosphodiester bond of a monophosphat is formed between the 3´-OH end of one ribose to the 5`-OH group to the next ribose. The standard direction of RNA, as in DNA is 5´-3´, because the first base in the linear polynucleotide has a 5`-free end and it’s 3`-OH group is linked with a phosphodiester bond to the 5`-OH of the next nucleotide, which is what happens in the last nucleotide.

• Heterocyclic bases: purines – adenine and guanine linked to the sugar by at glycosidic bond though N-9 and pyrimidines – cytosine and uracil linked to the sugar thru N-1. These bases extend away from the axis of the backbone and can pair with complementary bases by intramolecular base pairing to form double-helical base paired regions called hairpins. They are the secondary structure of RNA.

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