1. DNA: Structure and Function
Biology’s Biggest Moment
of the 20th Century!

2. DNA stands for: D: Deoxyribo (se) N: Nucleic A: Acid
Every living thing has DNA. That means you have something in common with every other living thing.

3. Intro to Viruses Genetic material, DNA or RNA enclosed within a capsid
Viruses are not considered to be living organisms, they are not made up of cells and can not reproduce on their own.
Genetic material, DNA or RNA
enclosed within a capsid

4. Intro to Bacteria Single circular chromosome
DNA found in the cytoplasm
Plasmids extra circular pieces of DNA that may code for
antibiotic resistance

5. DNA is made up of Nucleotides
3 components of a nucleotide:
Nitrogen Base
5-C sugar

6. 4 Bases of DNA Nucleotides
Purines(2 rings)
Adenine (A)
Guanine (G)
Pyrimidines(1 ring)
Thymine (T)
Cytosine (C)

7. Basic Nucleotide Pairings
What do you notice?
Pyrimidine
Purine
Pyrimidine = Purine

8. Chargaff’s Rule Base Pair Rule Amount of A = Amount of T
Amount of G = Amount of C
Base Pair Rule

9. Research of DNA Structure
Rosalind Franklin’s Photo 51
1952
DNA is a double helix,
2 complementary strands
twisted around each other

10. Watson & Crick’s Model 1953
Sequence on one chain is complementary to the sequence on the other (paired bases form rungs of a ladder)
Sugar-Phosphate forms a twisted ladder
Covalent bonds hold nucleotides together (formed by dehydration synthesis)
Hydrogen bonds hold bases together

12. Watson and Crick’s Model: Why it makes sense
Makes copies of itself - Replication
Encodes Information - Transcription
Controls Cells - Translation
Change by Mutation - Evolution

13. How is DNA packaged? Each cell has about 6 feet = 1.8m of DNA.
The average human has 75 trillion cells.
150 billion kilometers of DNA (250 billion miles)
Enough DNA to go from the earth to the sun more than 400 times.
DNA has a diameter of only m.

14. Chromosomes are made up of:
Histones (Proteins)
Nucleosomes
(DNA & Histones)

15. The most amazing molecule on the planet!!
Nobel Prize
awarded to
Watson, Crick and Wilkins
in 1962

16. Replication DNA is able to copy itself
Happens every time a cell divides
Occurs during the S phase of the cell cycle

17. Overview 1. Enzymes “unzip” the molecule
2.Each strand becomes a template for a new strand to be made from
3. DNA polymerase is the main enzyme but there are many others
4. DNA polymerase adds new bases to the opened up strands

18. Replication practice

20. Key to DNA Structure and Function
Lies Partly with the Carbons within Deoxyribose
The Carbons also are the key to antiparallelism

21. Orientation of DNA Model
Antiparallel
M.C. Escher captured antiparallelism

22. The Classic DNA Experiments
Griffith (1928)
Avery (1944)
Hershey/Chase (1950)
Is the Genetic Material DNA or Protein?

23. Griffith’s Experiment 1928
There is a transforming agent from the smooth strain that causes the rough strain to become virulent.

24. Step 2 - Treated the strains with Proteases
Avery Hypothesized that the transforming agent is a nucleic acid
Step 1 - Treated the Type R and Type S bacterial with DNASE
Result - Transformation did not occur
Step 2 - Treated the strains with Proteases
Result - DNA transformed the bacteria
+ DNAse
Rough Heat-killed
nonvirulent smooth virulent
(type R) (type S)
+ Protease

25. Doubting Griffith and Avery, Hershey & Chase set out in 1953 to prove them wrong using viruses.
Phage (virus) particles infecting a bacteria cell
Bacteriophage - virus that infects bacteria

26. The Classic Blender Experiment
1. Labelled phage particles in 2 batches:
a. radioactive sulfur (proteins)
b. radioactive phosphorus (nucleic acids)
2. Then allowed each batch to separately infect bacteria.
3. Used a blender to knock phage from bacteria then centrifuged.
4. Tube with sulfur found to have virus capsids labeled but bacteria were not.
5. The bacteria were labeled with phosphorus.
What was the conclusion?
The virus part that enters the cell is nucleic acid and not protein.