1. N UCLEIC A CIDS AS Biology BY1

2. N UCLEIC A CIDS - M ADE IN THE NUCLEUS AND SLIGHTLY ACIDIC Long molecules (polymers) made up of nucleotides Linked by condensation reactions 2 main types: DNA = deoxyribonucleic acid RNA = ribonucleic acid

3. N UCLEOTIDES Nucleotides consist of a: Pentose sugar Phosphate group Nitrogen-containing base (purine or pyrimidine)

4. I NTRODUCTION TO NUCLEOTIDES All nucleotides contain the following three groups: In DNA the sugar is deoxyribose, whereas in RNA the sugar is ribose. a phosphate group a pentose sugar a nitrogen- containing base

5. F ORMATION OF NUCLEOTIDES

6. DNA Has deoxyribose as the sugar Exists as a double helix of 2 chains linked by H bonds between complementary bases Contains the nucleotides: Adenine Thymine Cytosine Guanine Figure 2.16

7. COMPLEMENTARY BASE PAIRING : A bonds with T C bonds with G

8. B ASES There are five bases, split into two types: adenine (A) and guanine (G) are purine bases. AG TU thymine (T), cytosine (C) and uracil (U) are pyrimidine bases. DNA contains A, G, T and C, whereas RNA contains A, G, U and C. C

9. I DENTIFYING BASES

10. B ASE PAIRING RULES

11. F ORMATION OF POLYNUCLEOTIDES

12. DNA S TRUCTURE Held by covalent bonds

13. DNA 2 major functions: 1. replication, in dividing cells 2. carrying the information for protein synthesis in all cells Replication allows accurate copying of DNA for cell division

14. D ETERMINING THE STRUCTURE OF DNA The double-stranded structure of DNA was determined in 1953 by the American biologist James Watson and the British physicist Francis Crick. X-ray diffraction studies by British biophysicist Rosalind Franklin strongly suggested that DNA was a helical structure. The Austrian chemist Erwin Chargraff had earlier showed that DNA contained a 1:1 ratio of pyrimidine:purine bases.

15. S TRUCTURE OF DNA

16. H OW IS DNA PACKAGED ? In eukaryotic cells: DNA is packaged as chromosomes in the nucleus In prokaryotic cells: DNA is loose in the cytoplasm – there are no histones or chromosomes. It is tightly coiled and folded so that all 2m can fit in the nucleus It is wrapped around proteins called histones DNA + Histones = chromatin

17. S TRUCTURE OF EUKARYOTIC CHROMOSOMES

18. RNA Has ribose as the sugar Is single-stranded Uracil replaces Adenine A can hydrogen bond with U C can hydrogen bond with G

19. RNA 3 types: Ribosomal (rRNA) Messenger (mRNA) Transfer (tRNA)

20. RNA is made by making a complementary copy of a section of the DNA DNA RNA

21. R IBOSOMAL RNA Makes up part of the ribosome – made in the nucleolus mRNA strand ribosome

22. T RANSFER RNA nucleotides amino acid attachment site anticodon Found in the cytoplasm Used to carry amino acids to the ribosome during protein synthesis 3’ end 5’ end hydrogen bond

23. M ESSENGER RNA Is a mobile copy of a gene that codes for a protein It moves out of the nucleus to the ribosome to act as a template for protein synthesis mRNA strand ribosome mRNA DNA

24. ATP – ADENOSINE TRIPHOSPHATE Has ribose sugar, adenine, and 3 phosphate groups (Has 2 extra phosphates on the adenine containing nucleotide

25. ATP Is made by condensation reactions (dehydration synthesis) Is broken by hydrolysis reaction to liberate useful energy for the cell

26. DNA R EPLICATION

27. Watson and Crick provided evidence that complementary base pairing was key to DNA’s ability to replicate The DNA ‘unzips’ as hydrogen bonds between base pairs are broken

28. DNA R EPLICATION New polynucleotide strands can then be synthesized using the originals as a template Replication allows accurate copying of the DNA for cell division ( mitosis and meiosis )

29. DNA REPLICATION

30. W HAT ’ S THE KEYWORD ?

31. M ULTIPLE - CHOICE QUIZ