1. 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.
{Point out the alligator’s eyes in the first picture.} By the way, can you make out what this is?
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[The goal of this presentation is to introduce high school biology students to the chemical structure of DNA. It is meant to be presented in the classroom while accompanying the teacher’s lecture, under the control of the teacher.]
Mr. Coleman
Biology

2. DNA DNA is often called the blueprint of life.
In simple terms, DNA contains the instructions for making proteins within the cell.
Why is DNA called the blueprint of life?

3. Why do we study DNA? We study DNA for many reasons, e.g.,
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.

4. 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.}

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. One Strand of DNA Nucleotides consist of:
1 sugar
1 phosphate
1 nitrogen base
One strand of DNA has many millions of nucleotides.
nucleotide
{Point to the 3-D mode, if you have one, to show the parts as you discuss them.}

7. One Strand of DNA
The backbone of the molecule is alternating phosphate 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

8. 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.

9. Important: Adenine and Thymine always join together A T
Cytosine and Guanine always join together
C G

10. 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

11. 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

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

13. Two Stranded DNA
Remember, DNA has two strands that fit together something like a zipper.
The teeth are the nitrogenous bases but why do they stick together?
{Point to the 3-D model to show the parts as you discuss them.}

14. 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.

15. 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!

16. I. DNA Replication
A. When a cell divides, it needs to make a copy of its DNA so that both of the new cells have the right amount of DNA
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!

17. I. DNA Replication B. The steps of DNA Replication
1. Separation of Strands- Enzyme unzips the DNA (breaks the hydrogen bonds)
2. Free Base Pairing- Free nucleotides pair up with the exposed nitrogen bases on the two half DNA strands
3. Base Bonding- Another enzymes zips the hydrogen bonds together
C. Two identical strands created!
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!

18. Genes & Proteins
Genes are where the ribosomes get the information to build different proteins
A gene is one section of the DNA strand
Different proteins make different traits
Eye color, height, hair color, etc
Proteins are made of amino acids
The gene tells the ribosome what order to put the amino acids
If they get out of order the wrong protein is produced.
{Ask students where the chromosomes are in this picture. Or ask them where the DNA is. Remind them that the mitochondria also have DNA.}

19. Protein Synthesis (Making Proteins)
Step 1: Transcription- Making a one sided copy of the DNA message called mRNA
Enzymes read the DNA in order to produce mRNA
RNA is made from ribose sugars and only has one side
RNA is small enough to leave the nucleus (DNA is not because it has two sides) This is why we call it messenger RNA—that’s what the m stands for!
In RNA uracil replaces thymine (U instead of T)
See anmation
{Ask students where the chromosomes are in this picture. Or ask them where the DNA is. Remind them that the mitochondria also have DNA.}

20. Protein Synthesis (Making Proteins)
Step 2: Translation-using mRNA and tRNA to link amino acids together to make proteins
Takes place in the ribosome
Ribosomes read mRNA and match it with the appropriate tRNA molecule
The tRNA carry the amino acids to the ribosome
See anmation
{Ask students where the chromosomes are in this picture. Or ask them where the DNA is. Remind them that the mitochondria also have DNA.}

21. I now give you the Protein Synthesis Rap…

22. Mutations
Mutation- Any permanent change in the order of nucleotides in the DNA
Causes different proteins to be made
Some mutations can be good, but many are harmful
Things that cause mutations:
UV Rays
Chemicals
Smoking, Drinking, poor eating, etc
Some happen naturally
Etc
{Ask students where the chromosomes are in this picture. Or ask them where the DNA is. Remind them that the mitochondria also have DNA.}