The structure of DNA and RNA Nucleic Acid The structure of DNA and RNA

P Organic base 5C sugar The structure of a nucleotide DNA and RNA are polymers of nucleotides

The bases in nucleotides can differ There are two types of bases Purines and pyrimidines Purines are double ring structures A or G Adenine and Guanine are both purines

Pyrimidines are single ring structures More simply shown CTU Cytosine, thymine and uracil are pyrimidines

G The phosphate group of one nucleotide joins to the pentose sugar of the next C The bases stick out to the side A The nucleotides can be in any order T Nucleotides join together to form a polymer

The structure of DNA DNA nucleotides contain deoxyribose sugar DNA is made up of four types of DNA nucleotides The DNA nucleotides contain the bases C A adenine cytosine thymine T guanine G DNA has two chains of nucleotides

The two chains are joined by the bases Purines always join with pyrimidines This makes the molecule the same width along its length The base pairing is specific and complementary Adenine always joins with thymine Guanine always joins with cytosine Bases are joined by H bonds

The two backbone strands of sugar phosphate are the same distance apart If two pyrimidines pair the molecule would be thinner If two purines pair the molecule would be thicker

A Complementary base pairing T A T G C G C The bases are joined by hydrogen bonds

To pair one of the nucleotides must flip over 2 H bonds between adenine and thymine G C 3 H bonds between guanine and cytosine

5 A C T G 3 C G G T C A 3 5 A T The two strands run anti-parallel

The two strands are twisted into a double helix Subject to copyright clearance a suitable image showing a double helix could be inserted here. e.g. one similar to that found at: http://library.thinkquest.org/3659/orgchem/dna.gif The two strands are twisted into a double helix The helical shape and the H bonds help to keep DNA stable

Sugar–phosphate backbone The double helix Subject to copyright clearance a suitable image showing a double helix could be inserted here. e.g. one similar to that found at: http://library.thinkquest.org/3659/orgchem/dna.gif Sugar–phosphate backbone The two strands are joined by the bases

Messenger RNA Transfer RNA Ribosomal RNA The structure of RNA Messenger RNA Transfer RNA Ribosomal RNA

Structure of RNA RNA nucleotides form single strand polymers Contain ribose sugar contain the bases C A adenine cytosine uracil U guanine G The thymine in DNA is replaced by uracil in RNA

Messenger RNA (mRNA) is made in the nucleus from RNA nucleotides is involved in protein synthesis is relatively short lived

Transfer RNA (tRNA) Is a single strand folded into a cloverleaf shape Has a specific site to which specific amino acids can attach There is a different type of tRNA for each type of amino acid Each type of tRNA has three bases which are specific to the type of amino acid which will attach These three bases are called the anticodon

Specific amino acid attaches tRNA Specific amino acid attaches More simply drawn GCA Anticodon – specific to the amino acid which attaches to this tRNA molecule

Activities Draw up a table of differences between DNA and RNA Click here to go to AS Guru and build a molecule of DNA End