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

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

3. 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

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

5. 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

6. 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

7. 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

8. 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

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

10. 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

11. 5 A C T G 3 C G G T C A 3 5 A T
The two strands run anti-parallel

12. 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:
The two strands are twisted into a double helix
The helical shape and the H bonds help to keep DNA stable

13. 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:
Sugar–phosphate backbone
The two strands are joined by the bases

14. Messenger RNA Transfer RNA Ribosomal RNA
The structure of RNA
Messenger RNA
Transfer RNA
Ribosomal RNA

15. 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

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

17. 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

18. 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

19. 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