1. Discovering the structure of DNA
DNA = Deoxyribose nucleic acid
Made out of sugars (deoxyribose), phosphates
and nitrogen bases

2. DNA Nucleotide O O=P-O N CH2 O C1 C4 C3 C2 Phosphate Group
Nitrogenous base
(A, G, C, or T)
CH2 O C1 C4 C3 C2 5
Sugar
(deoxyribose)

3. Discovering the structure of DNA
Structure was discovered in 1953 by James
Watson and Francis Crick

4. Discovering the structure of DNA
Rosalind Franklin’s DNA image
“Chargoff’s rule”
A = T & C = G

5. Cell division and DNA replication
Cells divide
Growth, Repair, Replacement
Before cells divide they have to double cell
structures, organelles and their genetic
information

6. Double helix unwinds DNA replication
Enzymes, called DNA helicase, breaks the H bonds
2 strands separate and form replication fork
Other enzymes and proteins hold them apart

7. DNA replication
Enzymes, called DNA polymerase, move along the separated strands and add nucleotides to the exposed bases by the base pairing rule
As DNA polymerase moves along the strands, 2 new double helixes are formed
Enzymes continue adding nucleotides until it reaches a signal for it to detach

8. Two complementary polynucleotide strands are joined by hydrogen bonds
DNA replication
Two complementary polynucleotide strands are joined by hydrogen bonds
To make a DNA molecule.

9. During replication the following steps are occurred.
DNA molecule unwind
The hydrogen bonds between complementary base pairs break
Two strands are separated from each other
Each single strand act as a template for a new complementary strand.
Complementary nucleotides are assembled alongside each strand.
Sugar-phosphate backbone is formed by phosphodiester bonds between adjacent nucleotides
Once this had occurred along the whole length of the each strand two identical molecules of DNA are formed.
W.B.K.HETTIARACHCHI

10. 1 2
Hydrogen bonds break
Two strands separate
W.B.K.HETTIARACHCHI

11. Let us animate the process of replication
DNA replication
Let us animate the process of replication

12. W.B.K.HETTIARACHCHI

13. H bonds break Two strands seperate
W.B.K.HETTIARACHCHI

14. Nucleotides with Complementary bases are assembled alongside each strands
Sugar phosphate backbone is made by joining the adjacent nucleotides ( DNA polymarase enzyme( ) )
W.B.K.HETTIARACHCHI

15. Two identical DNA molecules are formed
W.B.K.HETTIARACHCHI

16. Proof Reading
DNA polymerase cannot add a new nucleotide unless the previous nucleotide is correctly paired
The enzyme can also remove mismatched enzymes and add the correct ones
Semi-conservative Model of Replication- each new strand has one old strand from the parent and one newly synthesized strand.

17. Nucleotides as Language
We must start to think of the nucleotides – A, G, C and T as part of a special language – the language of genes that we will see translated to the language of amino acids in proteins

18. DNA Replication Video Clip

19. What would the complementary strand be?
T C G A T A C G C T T A

20. ATGCTA AUGCUA TACGAT CGTGGC
A strand of DNA that contains the bases TACGAT replicates. Which base sequence is in the new strand produced during replication?
ATGCTA
AUGCUA
TACGAT
CGTGGC

21. What preserves the genetic code from one generation to the next?
DNA replication
RNA translation
protein synthesis
enzyme activation

22. Let’s build our own DNA model and simulate DNA replication