1. Warm up
What is DNA?
Write down one thought.

2. The Structure of DNA
All life on earth uses a chemical called DNA to carry its genetic code or blueprint. In this lesson we be examining the structure of this unique molecule.

3. DNA DNA is often called the blueprint of life.
In simple terms, DNA contains the instructions for making proteins within the cell.
Where is DNA found in the cell?
Nucleus - brain or control center of the cell.
Proteins are used to build the cell and do the work in the cell.

4. Why do we study DNA? We study DNA for many reasons
its central importance to all life on Earth,
medical benefits such as cures for diseases,
better food crops.
About better food crops, this area is controversial. There is a Dr. Charles Arntzen who is working on bioengineering foods with vaccines in them. People in poor countries could be immunized against diseases just by eating a banana, for instance.

5. Chromosomes and DNA Our genes are on our chromosomes.
Chromosomes are made up of DNA.
DNA is located in the nucleus
{Ask students where the chromosomes are in this picture. Or ask them where the DNA is. Remind them that the mitochondria also have DNA.}

6. How do we know?
Rosalind Franklin took diffraction x-ray photographs of DNA crystals
In the 1950’s, Watson & Crick built the first model of DNA using Franklin’s x-rays

7. Rosalind Franklin

8. Deoxyribosenucleic Acid
A DNA nucleotide is made up of three parts
Sugar
Phosphate
Nitrogenous base

9. The Shape of the Molecule
DNA is a very long polymer.
The basic shape is like a twisted ladder or zipper.
This is called a double helix.
{Show students a model of the double helix. Explain what a spiral is and a helix is.}

10. The Double Helix Molecule
The DNA double helix has two strands twisted together.
We will take apart the DNA molecule to see how it is put together.
First, we will look at one strand.

11. One Strand of DNA
phosphate
The backbone of the molecule is alternating sugar and phosphate groups
Covalent bonds between nucleotides
The teeth are nitrogenous bases.
deoxyribose
{Point to the 3-D mode, if you have one, to show the parts as you discuss them.}
bases

12. Four nitrogenous bases
DNA has four different bases:
Cytosine C
Thymine T
Adenine A
Guanine G
These four bases are abbreviated by using their respective first letters.

13. Two Kinds of Bases in DNA
Pyrimidines are single ring bases.
Purines are double ring bases. N C O C C N C C N

14. Thymine and Cytosine are pyrimidines
Thymine and cytosine each have one ring of carbon and nitrogen atoms.

15. Adenine and Guanine are purines
Adenine and guanine each have two rings of carbon and nitrogen atoms. C N O
Guanine C N
Adenine

16. Double Stranded DNA
Remember, DNA has two strands that fit together something like a zipper.
{Point to the 3-D model to show the parts as you discuss them.}

17. Hydrogen Bonds The bases attract each other because of hydrogen bonds.
Hydrogen bonds are weak but there are millions and millions of them in a single molecule of DNA.

18. When hydrogen bonds form…C
Cytosine always pairs up with guanine
Adenine always pairs up with thymine T A
Complimentary base pairs

19. Chargaff’s Rule:
If A only bonds with T and G only bonds with C the ratio of
A to T
And
C to G
Equals
1:1

20. Question: If there is 30% Adenine, how much Thymine is present?
If the above is true how much Guanine is present in the DNA? 20

21. DNA by the Numbers Each cell has about 2 m of DNA.
The average human has 75 trillion cells.
The average human has enough DNA to go from the earth to the sun more than 400 times.
DNA has a diameter of only m.
The earth is 150 billion m
or 93 million miles from
the sun.
If you unravel all the DNA in the chromosomes of one of your cells, it would stretch out 2 meters. If you did this to the DNA in all your cells, it would stretch from here to sun more than 400 hundred times!

23. Write out the strand that is complimentary to:
A C G T T C G A G G C T A A C G T

24. Answer: A C G T T C G A G G C T A A C G T
T G C A A G C T C C G A T T G C T

25. Review What is the function of DNA? Where is DNA located?
What are the three pieces the make up a nucleotide?
What are the four bases?
DNA holds the genetic information of the cell and gives instructions for the creation of proteins. Proteins lead directly to all characteristics of an organism
DNA is located in the nucleus
Nucleotide is made of a sugar (deoxyribose), phosphate, and a nitrogenous base
Adenine, Guanine, cytosine, and thymine are the four nitrogenous bases