1. (2) Structure and Replication of DNA
(A) DNA Structure
(C) DNA Replication
(B) Chromosome Structure

2. Structure and Replication of DNA (a+b)
Describe the structure of DNA in terms of nucleotides, backbone and complementary base pairing
State how 2 DNA strands are held together
Describe the antiparallel structure of the DNA strands
State where genetic information is stored
Define the term ‘genotype’
State what the genotype is determined by
State what the molecule of inheritance is
Describe the structure of a chromosome

3. 1= Nucleotides 2= DNA double helix 3=Genes 4=Chromosomes
5= Nucleus of cell 6=You!

4. What is DNA & why is it important?
Deoxyribonucleic acid
All cells store their genetic information in the base sequence of DNA, which is found inside the nucleus.
DNA is the molecule of inheritance and within the structure of DNA, there are many instructions to make specific proteins.
The sequence of DNA determines the genotype
The genotype is the term given to the genes that are present in an organisms.
The genotype determines the order of amino acids
The order of the amino acids determines the type of protein that is to be made.

5. Structure of DNA DNA is made up repeating units called nucleotides
Each nucleotide contains:
A phosphate molecule
A deoxyribose sugar
A base
Sugar-Phosphate Bond

6. The Deoxyribose Sugar

7. Carbon 5
Carbon 1
Carbon 4
Carbon 2
Carbon 3

8. The SUGAR-PHOSPHATE Backbone
The deoxyribose Sugar contains 5 carbons
The base is attached to carbon 1
The phosphate is attached to carbon 5
The phosphate of the NEXT nucleotide is attached to carbon 3 by a SUGAR-PHOSPHATE BOND

9. DNA Bases In DNA, there are 4 different bases:
Therefore, DNA has 4 different bases.
Base

10. Complementary Base pairs
What do you notice about the 2 strands?
Complementary Base pairs
ADENINE
THYMINE
CYTOSINE
GUANINE
WEAK HYDROGEN BOND

11. Anti-Parallel Strands
DNA is double stranded with the two strands running in opposite directions. This is known as an antiparallel arrangement. 5’ 3’ 3’ 5’

12. Double Helix

13. Structure of DNA (Summary)
DNA is made up repeating units called nucleotides
Each nucleotide contains:
A phosphate molecule
A deoxyribose sugar
A base
There are 4 bases. Adenine pairs with Thymine and Guanine pairs with Cytosine. This is known as complementary base pairing.
The two DNA strands are held together by weak hydrogen bonds (between each of the bases)
The DNA strands have an antiparallel structure because the strands run in opposite directions to each other
The DNA strand has 2 distinct ends: a phosphate group is at the 5’ end whereas the 3’ end is on the deoxyribose sugar
DNA has a sugar–phosphate backbone
The deoxyribose sugar of the 1st nucleotide is joined onto the phosphate molecule of the next nucleotide
They are joined together by a strong sugar-phosphate bond

14. 5’ C-G-T-T-T-T-A-A-G-C-C-C-T-G-A 3’
Problem Solve!
What is the correct sequence of bases to the single DNA strand below?
If a DNA molecule contained a total of bases and 400 were ADENINE bases, how many bases of CYTOSINE would it contain?
5’ C-G-T-T-T-T-A-A-G-C-C-C-T-G-A 3’
3’ G-C-A-A-A-A-T-T-C-G-G-G-A-C-T 5’
400 Adenine = 400 Thymine
= 200
200/2 = 100 guanine & 100 cytosine

15. How was all this discovered?
Your Task:
Your task is to research one of the individuals or groups of scientists below whose work contributed to the discovery of DNA structure and produce a report on them:
Griffiths
Avery et al.
Hershey and Chase
Chargaff
Franklin and Wilkins
Watson and Crick
WHAT TO INCLUDE:
Who the scientist(s) is, where they worked and when
The aims of the experiments
What the experiments were, including a diagram
What the conclusions were
other interesting information that you have gathered that lends interest to the story.
You could do this OR your could do the next slide

16. How was all this discovered?
Avery and Griffiths used bacterial transformation experiments to change one form of bacteria to another using the isolated DNA (they were not sure what the mystery molecule was that had this effect) – See animation here
Hershey and Chase used viruses called phage to demonstrate that the molecule changing the bacteria was DNA – See animation here
Erwin Chargaff worked out the base pair rule - See animation here
Wilkins and Franklin used X ray crystallography to investigate the structure of DNA – See animation here
Watson and Crick were the first to work the structure of the double helix – See animation here
You could do this OR your could do the previous slide

17. What happens when the DNA strands have been formed?
Video: zoom in on the structure of chromosomes and DNA
Video: How DNA is packaged

18. DNA is tightly coiled up around 8 proteins
These proteins are called Histones
The DNA/protein ‘bundle’ is called a nucleosome
Many nucleosomes make up a chromosome

19. Chromosome Structure
Chromosomes consist of tightly coiled DNA and are packaged with associated proteins

20. Questions
What is the name given to the molecule inside cells that controls inheritance of all features ?
What feature of the molecule contains the code controlling inheritance of features?
Draw a single nucleotide and label the three component parts
Draw a second nucleotide and show how the two nucleotides are joined to form part of the backbone and label the bond.
Explain the base pair rule
What type of bond holds the bases between opposite strands together?
What name is given to the final shape of DNA?
The two strands of DNA run in opposite directions. What name is given to this arrangement?
What special molecules are DNA packaged around?
What structures contain the all of the final DNA/protein complexes?
Could do show me boards or get pupils to write them in their jotters

21. Structure and Replication of DNA (a+b)
Describe the structure of DNA in terms of nucleotides, backbone and complementary base pairing
State how 2 DNA strands are held together
Describe the antiparallel structure of the DNA strands
State where genetic information is stored
Define the term ‘genotype’
State what the genotype is determined by
State what the molecule of inheritance is
Describe the structure of a chromosome