1. DNA
Lesson 11

2. Success Criteria State the structure of DNA
Explain how twisting of DNA molecule produces the double helix shape
Outline how DNA replicates

3. Starter
In pairs draw and label the structure of DNA

4. Task http://www.youtube.com/watch?v=8kK2zw jRV0M
Watch the video and answer the questions

5. DNA Structure: Nucleotides

6. Antiparallel DNA Strands

7. Bases bond with Hydrogen Bonds
Two types of bases
Pyrimidine base
Purine base
A pyrimidine base (Thymine or Cytosine) always binds to a purine base (A or G)
Bases are complementary to each other
G & C bind with 3 H bonds
A & T bind with 2 H bonds

8. DNA DNA molecules consist of 2 polynucleotide strands linked together
The sequence of bases enables the DNA to store information
Introns (junk DNA) are regions of DNA that enable several different proteins that share some sections in common to be produced from a single gene
At some loci there are multiple repeats of certain triple letters
e.g. CAGCAGCAG

9. Task
Make a plasticene model of DNA in pairs and label

10. Task
Ensure your homework is improved. Check you have included comparisons between RNA and DNA

11. Structure and Function
What is the function of DNA?
Information storage – in the form of codes to build proteins
How does the structure ensure this function is performed?
Long –
Base-pairing rules –
Double helix –
Hydrogen bonds –
large amount of information
replication possible
stability
easy unzipping

12. DNA Replication

13. Semi Conservative DNA Replication
DNA helix untwists
Hydrogen bonds between bases break and the DNA ‘unzips’
Free nucleotides hydrogen bond to exposed bases
Covalent bonds form between phosphate of one nucleotide and the sugar of the next
Ends up with 2 identical DNA molecules

14. Semi conservative replication

15. Dna helicase Dna polymerase
Breaks the hydrogen bonds connecting the bases
Attaches free nucleotides to the exposed bases on each strand
Dna polymerase
Watch first 3 min of video: Chromosomes & Replication

16. A T C G G C C G A T C G
this shows a double stranded length of DNA A T T A

17. helicase causes the 2 strands of DNA to separateG T G T C A
helicase causes the 2 strands of DNA to separate
And the separation of the strands

18. A C G T G T C A
helicase causes the 2 strands of DNA to separate

19. A C G T G T C A

20. A C G T G T C A
Free nucleotides bind to the exposed strands T A C G

21. A C G T G T C A
free nucleotides are attracted to their complementary base pairs T A C G

22. A C G T G T C A
free nucleotides are attracted to their complementary base pairs G A T A T C

23. A C G T G T C A G C T A G
And the formation of the new strands C A T A T

24. A C G T G T C A T A G C C G G C A T G C A T A T

25. A C G T G T C A G T C A A C G T

26. A C G T G T C A G T C A A C G T
finally condensation reactions join the nucleotides together…catalysed
by DNA Polymerase

27. A C G T G T C A G T C A A C G T
…forming 2 identical strands of DNA….

28. A C G T G T C A G T C A A C G T
…because the strands each contain half of the original material…

29. …it is called the semi-conservative method.G T G T C A G T C A A C G T
(The free nucleotides could be shown in a different colour to explain how radioactive markers were used to determine the semi-conservative method of replication)
…it is called the semi-conservative method.

30. Task
Draw a cartoon of DNA replication

31. Experimental work: Meselson and StaHl

32. Experimental work: Meselson and StaHl
Grew bacteria in a medium containing heavy nitrogen (isotope 15N)
Then put the bacteria in a growth medium containing light nitrogen (14N)
The first generation of bacteria had DNA made from 15N, when the bacteria replicated the new half of the DNA strand was made from 14N

33. Copy and Complete

34. Answers

35. Evidence for semi conservative replication of dna

36. answers

37. Success Criteria State the structure of DNA
Explain how twisting of DNA molecule produces the double helix shape
Outline how DNA replicates

38. Plenary: Quick Quiz Define the term antiparallel
A DNA strand have the base sequence ATTAGGCTAT, write the complementary strand
A DNA molecule is 20% Thymine, what %age of each of the other types of bases would it contain?
What type of diseases can result from DNA copying going wrong?

39. Plenary Answers
Parallel, but with chains running in opposite directions
TAATCCGATA
20% A, 30% C and 30% G
Cancers may occur (when a mutation happens in a forming gamete genetic diseases can occur e.g. sickle cell anaemia)