1. DNA STRUCTURE

2. Why Do We Study DNA? We study DNA for many reasons:
It’s 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.

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

4. Watson & Crick
Built their work off of x-ray crystallography performed by Rosalind Franklin
Created an accurate model of DNA structure
Awarded Nobel prize in 1967

5. 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.}

6. DNA Structure DNA is often called the blueprint of life.
In simple terms, DNA contains the instructions for making proteins within the cell.
A molecule of DNA is made up of millions of tiny subunits called Nucleotides
Each nucleotide consists of:
Phosphate group
Pentose sugar
Nitrogenous base

7. Nucleotide Structure
Phosphate
Nitrogenous
Base
Pentose
Sugar

8. The phosphate and sugar form the backbone of the DNA molecule, whereas the bases form the “rungs”
There are four types of nitrogenous bases.

9. 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.

10. Thymine and Cytosine are PYRIMIDINES
Thymine and cytosine each have one ring of carbon and nitrogen atoms. C N O
cytosine C N O
thymine

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

12. 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
The bonds between cytosine and guanine are shown to the right with dotted lines C N O

13. Hydrogen Bonds cont. C N O
When making hydrogen bonds, cytosine always pairs up with guanine
Adenine always pairs up with thymine (as shown to the right)

14. Nitrogenous Bases cont.
Each base will only bond with one other specific base.
Adenine (A)
Thymine (T)
Cytosine (C)
Guanine (G)
Form a base pair
Form a base pair

15. One Strand of DNA One strand of DNA is a polymer of nucleotides
One strand of DNA has many millions of nucleotides
{Point to the 3-D mode, if you have one, to show the parts as you discuss them.}

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

17. Two Stranded DNA
Remember, DNA has two strands that fit together something like a zipper
Complimentary base paring between the nitrogenous bases hold the strands together
{Point to the 3-D model to show the parts as you discuss them.}

18. Chargraff’s Rule: Adenine and Thymine always join together
A T
Cytosine and Guanine always join together
C G

19. Chargraff cont. Erwin Chargraff
Determined that the number of Thymine in a molecule of DNA has to equal the number of Adenine due to strict base pairing rules
Number of Cytosine is equal to the number of Guanine

20. Base Pairing
To crack the genetic code found in DNA we need to look at the sequence of bases.
The bases are arranged in triplets called codons
A G G - C T C - A A G - T C C - T A G
T C C - G A G - T T C - A G G - A T C

21. Central Dogma DNA  RNA  Protein
A gene is a section of DNA that codes for a protein
Each unique gene has a unique sequence of bases
This unique sequence of bases will code for the production of a unique protein
It is these proteins and combination of proteins that give us a unique phenotype (an organism’s physical appearance)

22. Central Dogma cont.
DNA is stored inside the nucleus of eukaryotic cells
Because it cannot leave the nucleus a messenger molecule, RNA, has to be made in order to send the genetic blueprint to the ribosomes in the cytoplasm that do the building
Proteins do the work of the genetic blueprints

23. DNA
Gene
Protein
Trait

24. Central Dogma cont.
Transcription = the process of using DNA to make complementary RNA
RNA uses the nitrogen base Uracil in place of Thymine to pair with Adenine
Translation = the process of using the RNA to make proteins

25. Your Task
Draw a flow chart to show how to get from: