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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.] 1 1

2. New Question/restated question -
Virus Lab
#4. Is it possible for two people to exchange fluids and at the conlcusion of the exercise one person be “infected” while the other remains “healthy”? Explain.
New Question/restated question -
Were you able to tell who the 1st infected person was before I had told you it was #3? Or can you only get down to the last 2 people? Explain

4. DNA fun facts - true or false?
Your DNA is 99.9% similar to your classmates
Identical twins have the same fingerprints
Identical twins have the same DNA
You share 50% of your DNA with a banana
DNA is only found in some of your cells
DNA and RNA are structurally the same
A mutation in your DNA can turn you into a zombie
You eat DNA everyday
DNA lab techniques are used to solve crime
The first cloned mammal was a cat.

6. 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? 6 6

7. Watson & Crick’s Model 7 7

8. Watson & Crick Determined DNA was a double helix in 1953
Looked at an X-ray diffraction image of DNA to make the model
Nobel Prize in Watson, Crick, & Wilkins

9. Franklin’s and Wilkin’s Photo

11. Why do we study DNA? 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. 11 11

12. Deoxyribonucleic Acid
DNA stands for...
Deoxyribonucleic Acid

13. Chromosomes are made up of a chemical called DNA.
Chromosomes and DNA
Chromosomes: a threadlike structure of nucleic acids and protein found in the nucleus of most living cells.
Carries genetic information in the form of genes.
Genes: segments 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.} 13 13

14. DNA is found in all our cells!
In the nucleus within our chromosomes

16. 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.} 16 16

17. 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. 17 17

18. One Strand of DNA
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 18 18

19. Nucleotides
One deoxyribose together with its phosphate and base make a nucleotide.
{Ask students where they have seen a similar molecule before in this class.
Answer: ATP Emphasize that nucleotides are the basic building blocks or units of a DNA molecule and that a single molecule has many millions of nucleotides.} 19 19

20. One Strand of DNA One strand of DNA is a polymer of nucleotides.
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.} 20 20

21. DNA has four different nitrogenous bases:
Cytosine C
Thymine T
Adenine A
Guanine G
These four bases are abbreviated by using their respective first letters. 21 21

23. Two Kinds of Bases in DNA
Pyrimidines are single ring bases. C & T
Purines are double ring bases. A & G N N C O C C N C C N 23 23

24. 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 24 24

25. Adenine and Guanine are purines
Adenine and guanine each have two rings of carbon and nitrogen atoms. C N O
Guanine C N
Adenine 25 25

26. Two Stranded DNA - discussion
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.} 26 26

27. Hydrogen Bonds
C - G
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. C N O 27 27

28. Hydrogen Bonds, cont. When making hydrogen bonds:
- cytosine always pairs up with guanine
-Adenine always pairs up with thymine 28 28

29. Chargaff’s Rule: Adenine and Thymine always join together A T
Cytosine and Guanine always join together
C G 29 29

31. 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! 31 31

32. 32 32

33. DO NOW: research and compare RNA vs. DNA

36. Log onto a laptop and sign into your google drive
Do now -
Log onto a laptop and sign into your google drive

37. DNA Replication

38. DNA Replication Process: Two strands of DNA unwind (like twizzlers)
Replication: Before a cell divides, all of the DNA is copied.
Process:
Two strands of DNA unwind (like twizzlers)
Nucleotides (A-T & G-C) pair up with each of the strands
Now there are two identical DNA molecules
Each molecule has a strand of old and new DNA

39. Original DNA strand on each used as a template!

41. Proteins involved in DNA replication
DNA polymerase adds nucleotides to a growing chain
DNA ligase joins small fragments into a continuous chain
Helicase unwinds the DNA strand
Primase tells DNA polymerase where to start; “primer”

43. Types of RNA Messenger RNA (mRNA)- (like a secretary!)
Located in both the nucleus and the cytoplasm
Brings genetic code from DNA to the ribosome to make protein

44. Types of RNA Ribosomal (rRNA) Located within the ribosome
Helps make the structure of the ribosome

45. Types of RNA Transfer (tRNA) Located in the cytoplasm
Brings amino acids to ribosome to build proteins.