1. THE NUCLEIC ACIDS. STRUCTURE
RNA
DNA

2. Friedrich Miescher in 1869
isolated what he called nuclein from the nuclei of pus cells
Nuclein was shown to have acidic properties, hence it became called nucleic acid

3. Two types of nucleic acid are found
Deoxyribonucleic acid (DNA)
Ribonucleic acid (RNA)

4. The distribution of nucleic acids in the eukaryotic cell
DNA is found in the nucleus of eukaryotic cells (with small amounts in mitochondria and chloroplasts)
RNA is found throughout the cell

5. DNA as genetic material: The circumstantial evidence
Present in all cells and virtually restricted to the nucleus
The amount of DNA in somatic cells (body cells) of any given species is constant (like the number of chromosomes)
The DNA content of gametes (sex cells) is half that of somatic cells. In cases of polyploidy (multiple sets of chromosomes) the DNA content increases by a proportional factor
The mutagenic effect of UV light peaks at 253.7nm - the peak for the absorption of UV light by DNA

6. NUCLEIC ACID STRUCTURE
Nucleic acids are polynucleotides
Their building blocks (monomers) are nucleotides

7. NUCLEOTIDE STRUCTURE NUCLEOTIDE PHOSPATE SUGAR Ribose or Deoxyribose
BASE
PURINES
PYRIMIDINES
Adenine (A)
Guanine(G)
Cytocine (C)
Thymine (T)
Uracil (U)
NUCLEOTIDE

8. Ribose is a pentose (5 C sugar)
Note how the Carbons are numbered

9. Spot the difference

10. THE SUGAR-PHOSPHATE BACKBONE
The nucleotides are all orientated in the same direction
The phosphate group joins the 3rd Carbon of one sugar to the 5th Carbon of the next in line. (HL)
Bonding between a ribose sugar and a phosphate is covalent.

11. P G C A T
ADDING IN THE BASES
The bases are attached to the 1st Carbon of the ribose sugar
The order of the bases is important. This determines the genetic information of the molecule

12. DNA IS MADE OF TWO STRANDS OF POLYNUCLEOTIDEG T A
Hydrogen bonds
DNA IS MADE OF TWO STRANDS OF POLYNUCLEOTIDE

13. DNA IS MADE OF TWO STRANDS OF POLYNUCLEOTIDE
The sister strands of the DNA molecule run in opposite directions (antiparallel double helix) (HL)
They are joined by the hydrogen bonds between bases
Each base is paired with a specific partner:
A is always paired with T
G is always paired with C
Purine with Pyrimidine (HL)
Thus the sister strands are complementary but not identical
The bases are joined by hydrogen bonds, individually weak but collectively strong

14. THE BASES CAN ONLY PAIR T-A & C-G

15. WEAK HYDROGEN BONDS LINK THE BASES AND THEREFORE THE TWO STRANDS
WEAK HYDROGEN BONDS LINK THE BASES AND THEREFORE THE TWO STRANDS. THE H BONDS CAN ZIP UNDONE EASILY.

16. Purines & Pyrimidines (HL)
Adenine
Thymine
Guanine
Cytosine

17. Wilkins & Franklin (1952): X-ray crystallography
© Norman Collection on the History of Molecular Biology in Novato, CA

18. Watson & Crick: Base pairing

19. The Double Helix (1953) Public Domain image
© Dr Kalju Kahn USBC Chemistry and Biochemistry

20. More about the bases (HL)
Hydrogen bonds
Pyrimidines & Purines
3′ end & 5′ end

21. 3′ and 5′ Ribose (HL)
The 3′ and 5′ bonding to the phosphate, and the 1′ bonding to the base are important to understand for DNA replication and later, transcription.

22. A DNA problem! Human genome (in diploid cells) = 6 x 109 bp
6 x 109 bp X 0.34 nm/bp = 2.04 x 109 nm = 2 m/cell
Very thin (2.0 nm), extremely fragile
Diameter of nucleus = 5-10 mm
So …. DNA must be packaged to protect it, but must still be accessible to allow gene expression and cellular responsiveness

23. How is it all held together? (HL)

24. Histone proteins support the DNA (HL)
The nucleosome is an 8-protein core, wrapped around a single protein strand.
The DNA is wrapped around these proteins.

26. Genes and Bases (HL)

27. Exons and Introns (HL)

28. Single copy genes
&
Highly repetitive sequences (HL)

29. Highly Repetitive Sequences (HL)
The 'gene coding region' (about 1.5 % of our DNA) codes for a polypeptide (around 25, 000 proteins).
Around 3% of the human genome is regulatory coding for genetic switches which control development.
The non-coding region function remains unclear but can be as much as 5-45% of the total genome.
These regions are often made of highly repetitive sequences of bases each some bases long. These are referred to as satellite regions.
Due to the combination of bases in the repeating regions they tend to create dense and less dense DNA regions. These show as bands of DNA, which are used in finger print technologies.