1. Section 1: The Structure of DNA
Preview
Bellringer
Key Ideas
DNA: The Genetic Material
Searching for the Genetic Material
The Shape of DNA
The Information in DNA
Discovering DNA’s Structure
Summary
Section 1: The Structure of DNA

2. DR 13.1. Section: The Structure of DNA
Read each question, and answer based upon what you learn in the section. 1. With what kinds of bacteria did Griffith inject mice? 2. What was different about the S bacteria and the R bacteria? 3. Why were the heat-killed S bacteria harmless? 4. Why was the mixture of heat-killed S bacteria and R bacteria virulent? 5. What did Griffith discover as a result of his experiments? 6. How did Avery discover that the material responsible for transformation in bacteria was DNA? 7. Viruses that infect bacteria are called [bacteriophages / rough]. 8. A virus is made of DNA and [proteins / cell walls]. 9. Radioactive sulfur was used to label the [DNA / protein] in the viruses. 10. Radioactive phosphorus was used to label the [DNA / protein] in the viruses. 11. Hershey and Chase discovered that after the 32P-labeled phages infected the bacteria, most of the radioactive phosphorus was found in the layer containing [bacteria / phage]. Match the letter of the phrase with the appropriate term _____ 12. double helix _____ 13. nucleotides _____ 14. deoxyribose _____ 15. hydrogen bond _____ 16. nitrogenous bases _____ 17. adenine _____ 18. cytosine _____ 19. Chargaff Explain how the terms in each pair are related to each other. 20. base-pairing rules, complementary 21.Wilkins and Franklin, DNA structure
a. a five-carbon sugar
b. type of weak bond between base pairs that holds the double helix together
c. four kinds and they form specific pairs
d. subunits that make up DNA
e. one of two pyrimidines used as a nitrogenous base in nucleotides
f. one of two purines used as a nitrogenous base in nucleotides
g. discovered that the amount of adenine always equaled the amount of cytosine and that guanine always equaled cytosine
h. two strands of nucleotides twisted around each other

3. DNA This is DNA. What do you know about it?
What is its job & why is it important?
How was it discovered?
What is its structure?
How does it get created/duplicated?
How does the information contained therein get accessed?

4. Properties of Life: Linking to Current Content
Heredity is one of the 7 properties of life.
What is this?
How is the passing of traits from parents to offspring achieved?
Properties of Life: Linking to Current Content

5. DNA: The Genetic Material
In the 1800’s, Austrian monk Gregor Mendel discovered how traits (the physical things you can see on the outside of an organism) are passed on from parent to offspring.
The information Mendel lacked was what these traits were transported in or on.
Physically, how did the trait exist in an organism?
We now know that traits are transferred from parents to offspring through the transfer and sharing of genes contained in DNA.
But it took 50 years of research in studies performed by important scientists.
DNA: The Genetic Material

6. Objectives: DNA Structure
Today you are going to learn all about the basic structure of the molecule that holds our heredity… DNA.
By the end of this lesson you will be able to…
Identify the substance that makes up genetic material.
Name the experiments that identified the role of DNA as the genetic material.
Name the studies that led to the discovery of DNA’s structure.
Relate the structure of DNA to the function of DNA as a carrier of information.
Build a model of a DNA molecule.
Objectives: DNA Structure

7. Gene
DNA
Nucleotide
Purine
Pyrimidine
Vocabulary

8. Part I: DNA History

9. DNA, the Genetic Material
So, Mendel knew what happens with traits but not how they were stored and transferred.
Traits are contained as directions in DNA (deoxyribonucleic acid): the primary genetic material that contains genes.
It causes recognizable, inheritable characteristics in related groups of organisms.
Traits are “written” into specific areas, called genes, within the large, continuous DNA molecules called chromosomes.
A gene is the most basic physical unit of heredity
A gene contains the instructions for to make a trait, just like a recipe contains the instructions for a meal.
DNA, the Genetic Material

10. Searching for the Genetic Material
Three major experiments led to the conclusion that DNA is the genetic material in cells.
These experiments were performed by:
Discovering DNA as the genetic material
Scientist (s)
Contribution
Griffith
Avery
Hershey and Chase

11. Searching for the Genetic Material
Griffith worked with two related strains of bacteria which cause pneumonia in mice.
One strain was deadly… it made the mice sick and killed them.
The other strain did little to nothing to the mice.
Griffith discovered that when harmless live bacteria were mixed with heat-killed disease-causing bacteria and then injected into mice, the mice died.
These results led Griffith to discover transformation. Transformation is a change in genotype that is caused when cells take up foreign genetic material.
Griffith’s experiments led to the conclusion that genetic material could be transferred between cells.

12. Griffith’s Discovery of Transformation
Harmless bacteria
Deadly bacteria
Deadly bacteria that was made harmless because it was boiled to death.
Harmless bacteria mixed with killed deadly bacteria…
Conclusion… Whatever made the deadly bacteria deadly was being transferred into the harmless bacteria. This process of exchanging information between organisms is called TRANSFORMATION…

13. So first, genetic material is known to exist and it can be transferred in a process called transformation.

14. Searching for the Genetic Material
Griffith proved hereditary information can be transferred but what was it?
Avery wanted to determine whether the transforming agent in Griffith’s experiments was protein, RNA, or DNA.
Avery used enzymes to destroy each of these molecules in heat-killed bacteria.
Avery’s experiments led to the conclusion that DNA is responsible for transformation in bacteria.

15. So first genetic material is known to exist and it can be transferred in a process called transformation.
Then we knew that DNA was the genetic material being passed on…but was it the only genetic material?

16. Searching for the Genetic Material
Hershey and Chase studied bacteriophages.
Bacteriophages are viruses that infects bacteria.
By using radioactive isotopes (chemical that emit light when charged with UV radiation) painted in the virus’s DNA and proteins, Hershey and Chase showed that DNA, not protein, is the genetic material in viruses.

17. – Griffith
So first genetic material was known to exist and it can be transferred.
– Avery
Then we knew that DNA was the genetic material being passed on…but was it the only genetic material?
– Hershey & Chase
Next a discovery lead to the realization that DNA, not anything else, was responsible for containing the genetic information that is passed between organisms.
The next question…What is the structure?...

18. Discovering DNA’s Structure
The search for DNA’s structure was headed by several scientists that each contributed a little at a time:
Discovering DNA Structure
Scientist (s)
Contribution
Watson & Crick
Chargaff
Franklin & Wilkins

19. Discovering DNA’s Structure
The discovery of the structure of DNA was credited to Watson & Crick
but they borrowed information from several other scientists.
Chargaff:
Showed that the amount of adenine always equaled the amount of thymine
& the amount of guanine always equaled the amount of cytosine.
Franklin and Wilkins:
Developed X-ray diffraction images of strands of DNA that suggested the DNA molecule resembled a tightly coiled helix.
Discovering DNA’s Structure

20. Discovering DNA’s Structure, continued
Watson and Crick used both Chargaff’s data and the X-ray diffraction studies to create a complete three-dimensional model of DNA.
Their model showed a “spiral staircase” in which two strands of nucleotides twisted around a central axis.
These pictures are looking straight down the staircase.
Discovering DNA’s Structure, continued

22. What were the three experiments that lead to the discovering what the genetic material in humans was?
What is the name of the molecule that contains genetic information?
Who is credited for discovering the structure of DNA?
Name two other contributing scientists and what they discovered.
Concept Check:

23. Part II: DNA Structure

24. DNA is often compared to a ladder or a spiral staircase
DNA is often compared to a ladder or a spiral staircase. Look at picture to the right and answer the following questions.
How is the structure of DNA similar to that of a ladder or spiral staircase?
How is it different from that of a ladder or spiral staircase?

25. The Shape of DNA The spiral shape of DNA is known as a double helix.
Double = two strands
Helix = spiraled around itself.

26. The Structure of DNA
DNA is made up of individual nucleotides bonded to each other.

27. The Structure of DNA
A nucleotide is a DNA subunit made up of three parts: a phosphate group, a 5-carbon sugar group, and a nitrogen-containing base.
The five-carbon sugar in DNA is called deoxyribose, from which DNA gets its full name, deoxyribonucleic acid.
“de” means removed = it lacks one hydroxide group present in RNA

28. The Shape of DNA The blue ribbon area is known as the BACKBONE
These are always the same.
PhosphateRibosePhosphateRibosePhosphate… R P R

29. Phosphate
Deoxyribose
Phosphate
DNA Backbone

30. The Shape of DNA The two strands are antiparallel.
The backbones are equidistant but going in opposite directions.

31. The Structure of DNA
The term “anti-parallel” refers to the fact that whereas DNA backbones are equidistant from each other, they go in opposite directions.
One strand goes in the 3’5’ direction
The other goes in the 5”  3’ direction
The 3’ or 5’ refers the carbons in the ribose sugar.

32. Anti-Parallel C#5 C#3 Ribose is a 5- carbon sugar.
5’ refers to the end of the nucleotide closest to the #5 carbon.
3’ refers to the end of the nucleotide closest to the #3 carbon.
C#5
C#4
Carbon#1
Ribose
C#3
C#2
Anti-Parallel

33. Compliments… not mirror images
The Shape of DNA
The two strands are complimentary.
One strand contains bases that are complimentary to the other strand’s bases.
Compliments… not mirror images

34. DNA: Hydrogen Bonding DNA is held together by hydrogen bonds.
They are represented by dashed lines.
Notice the # of H-bonds. They change depending on the bases involved.
Hydrogen Bonds
Hydrogen Bonds
Hydrogen Bonds
Hydrogen Bonds
DNA: Hydrogen Bonding

35. The Bases
The four kinds of bases are adenine (A), guanine (G), thymine (T), and cytosine (C).
Bases A and G have a double-ring structure and are classified as purines.
Bases T and C have a single-ring structure and are classified as pyrimidines.
A purine on one strand of a DNA molecule is always paired with a pyrimidine on the other strand.
Specifically, adenine always pairs with thymine, and guanine always pairs with cytosine.
Hydrogen Bond
Hydrogen Bond
Hydrogen Bond
Hydrogen Bond
Hydrogen Bond

36. Base-pairing rules (as given to us by Chargaff) are dictated by the chemical structure of the bases.
It has to do with the category (purine/pyrimidine) as well as their hydrogen bonding characteristics.
A double bonds with T
G triple bonds with C
The bonds are HYDROGEN BONDS
Whereas hydrogen bonds are weak individually, the billions of bonds between bases keep the two long strands of DNA together.
Base-Pairing

37. The “puzzle piece” refers to the hydrogen bonding between the paired bases.
Guanine and cytosine have 3 hydrogen bonds
whereas thymine and adenine have 2 hydrogen bonds.
Complimentary Bases

38. How The Bases Fit Into Larger Molecules

39. What to Know at This Point
The three experiments that lead to the discovery of DNA as the genetic material.
Who contributed to the discovery of the structure of DNA?
The structure of DNA
What a nucleotide is composed of.
How the nucleotides are arranged to create strands of DNA.
What holds the bases together…Hydrogen Bonds (H- bonds)
The base-paring rules
A – T, C – G, pyrimidine, purine.
How many hydrogen bonds between the bases
HW: Complete the half-sheet. Fill in all shapes with abbreviations for the part that goes there. Label the hydrogen bonds too.

40. Look at the number of rings then the number of bonds…
Summary: Complete the Illustration in your notes. Using the rules of complementary bases and h-bonding, determine what each shape is.
To solve:
Look at the number of rings then the number of bonds…

41. Phosphate
Ribose
Nitrogenous base
Adenine
Cytosine
Tyrosine
Guanine

42. Day 2 Take out your homework We’ll discuss in 5 minutes.
The half sheet you had from yesterday.
We’ll discuss in 5 minutes.
Make sure you check with neighbors and get clarification on anything you couldn’t get.
Day 2

43. The Information in DNA
The information in DNA is contained in the order of the bases.
The order of how the bases are arranged determines the trait that will result.
This order is called the “sequence”
Different sequences, called “spellings”, give different genes.
AATGCTAGC would be spelling of one the sequence in one gene
TGCATACCG would be part of another
It’s the same stuff, just a different arrangement

44. Paired bases on opposite sides of a double helix are said to be complementary because they fit together like puzzle pieces.
Because of base-pairing rules, if the sequence (the order) of bases is known for one strand of DNA, then the sequence of bases for the complementary strand (the other) can be quickly identified or predicted.
Ex. CTGAA BONDS WITH…. This is the TEMPLATE strand
GACTT This is the COMPLEMENTARY strand
What is the complementary strand for.
CCGTATACCGATTG?
GGCATATGGCTAAC
(Template Strand)
(Complimentary Strand)
The Information in DNA

45. It’s due tomorrow if not.
Pick up an assignment sheet from the back.
This is HOMEWORK and is due by tomorrow.
Scissors and tape are up front.
Check in when complete.
It’s due tomorrow if not.
Homework

46. DNA is the primary material that causes inheritable characteristics in related groups of organisms.
Three major experiments led to the conclusion that DNA is the genetic material in cells. These experiments were performed by Griffith, Avery, and Hershey and Chase.
A DNA molecule is shaped like a spiral staircase and is composed of two parallel strands of linked subunits.
The information in DNA is contained in the order of the bases, while the base-pairing structure allows the information to be copied.
Watson and Crick used information from experiments by Chargaff, Wilkins, and Franklin to determine the three-dimensional structure of DNA.
Summary

47. Nitrogenous Bases: Categories, pairing
Number of rings
Makes it a
Hydrogen bonds with
Structure
Adenine 2
Purine
Thymine
Guanine
Cytosine 1
Pyrimidine