Nucleic Acids


DNA is the single most important molecule found within cells. It is a stable polynucleotide, which contains coded information for inherited characteristics. It is contained in chromosomes in the nucleus of an eukaryot cell. The essential features of the Watson-Crick model are summarised below.
1. The two helical polynucleotide chains are coiled around a common axis. The two chains have opposite polarity i.e. they are antiparrallel.
2. The regular repeating sugar phosphate backbone of each strand lies on the outside of the helix. The purine and pyrimidine bases project inwards at 900 to the axis of the helix.
3. The two strands are held together by hydrogen bonding between pairs of bases ...

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Sugar
The sugar will be one of two very similar pentose rings. Ribo contain the sugar ribose. Deoxyribo contain the sugar deoxyribose. The only difference between these two sugars is that deoxyribose contains one oxygen atom less than ribose. Pentose sugars are essential because they are involved in linking different nucleotides together by condensation reactions.
The Nitrogen-Containing Bases
There are two types of bases found in nucleic acids. The purine bases have two nitrogen containing rings, while the pyrimidines have only one. In DNA the purines are adenine (A) and guanine (G) and the pyrimidines are cytosine (C) and thymine (T). In RNA the purine bases are the same as in DNA, but the pyrimidines are cytosine and uracil (U). These rings have the chemical property of being bases because of the nitrogen atoms they contain.
Adenine always forms 2 hydrogen bonds with thymine.
Cytosine always forms 3 hydrogen bonds with guanine.
Phosphate Group
The phosphate group ...

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PAPER DETAILS
Added: 12/18/2003 12:17:23 PM
Category: Science & Nature
Type: Free Paper
Words: 425
Pages: 2

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