1. The Discovery of DNA Early 20th century
Ch.12 – Molecular Genetics
12.1 – DNA: The Genetic Material
The Discovery of DNA
Early 20th century
Thomas Hunt Morgan, working with the traits of fruit flies, discovered that the heritable factors Mendel discussed were located on the chromosomes of a cell.
It was known that chromosomes were made up of DNA and proteins, so scientists started working to figure out which was the heritable material
Greatest Discovery Vid (16: :30)

2. A chemical substance from one cell is able to transform another
Ch.12 – Molecular Genetics
12.1 – DNA: The Genetic Material
1928
Frederick Griffith
Conclusion:
A chemical substance from one cell is able to transform another
(some types of bacteria are able to go through transformation – absorbing and replicating outside DNA)

3. It is the DNA that causes transformation
Ch.12 – Molecular Genetics
12.1 – DNA: The Genetic Material
1944
Oswald Avery
Streptococcus Pneumoniae
Conclusion:
It is the DNA that causes transformation

4. Different organisms have differing amounts of the four bases
Ch.12 – Molecular Genetics
12.1 – DNA: The Genetic Material
1944
Erwin Chargaff
Conclusion:
Different organisms have differing amounts of the four bases
and
in DNA
Adenines = Thymines
Guanines = Cytosines

5. Measurements from her image revealed DNA to be a double helix shape
Ch.12 – Molecular Genetics
12.1 – DNA: The Genetic Material
1951
Rosalind Franklin
Conclusion:
Measurements from her image revealed DNA to be a double helix shape
Explanation of x-ray measurement

6. Ch.12 – Molecular Genetics
12.1 – DNA: The Genetic Material
1952
Hershey & Chase
Conclusion:
It is DNA that is injected into the bacteria that causes viral replication NOT proteins

7. 1953 Watson & Crick Ch.12 – Molecular Genetics
12.1 – DNA: The Genetic Material
1953
Watson & Crick
Armed with the research that…
DNA is most likely the hereditary molecule
2. In any given sample the amount of
adenines = thymines
and
guanines = cytosines
3. The shape is double stranded, helical and held together by base pairs in its interior

8. They proposed this little beauty:
Ch.12 – Molecular Genetics
12.1 – DNA: The Genetic Material
They proposed this little beauty:
DNA is made of two antiparallel strands held together by hydrogen bonds found between adenine and thymine and guanine and cytosine (referred to base pairing).

9. DNA is a nucleic acid (polymer)
Ch.12 – Molecular Genetics
12.1 – DNA: The Genetic Material
Remember…
DNA is a nucleic acid (polymer)
It is made up of many nucleotides (monomers)
Nucleotides consist of
 a 5 carbon sugar
 a phosphate group
 a nitrogenous base

10. Made of alternating deoxyribose molecules and phosphate groups
Ch.12 – Molecular Genetics
12.1 – DNA: The Genetic Material
5’ End
3’ End
DNA Backbone
Made of alternating deoxyribose molecules and phosphate groups
They are oriented in opposite directions (anti-parallel)
5’ End
3’ End

11. Nitrogenous bases 2 Categories Purines (double-ringed)
Ch.12 – Molecular Genetics
12.1 – DNA: The Genetic Material
5’ End
3’ End
Nitrogenous bases
2 Categories
Purines
(double-ringed)
Adenine & Guanine
Pyrimidines
(single-ringed)
Thymine & Cytosine
Base Pairing
A with T
C with G
EXCLUSIVELY
5’ End
3’ End

12. Ch.12 – Molecular Genetics
12.2 – The Replication of DNA
DNA Replication
Watson & Crick’s discovery of base pairing lead them to be able to explain how DNA can replicate.
This is referred to as the semiconservative model of replication because one parental strand is a part of each new strand

13. Ch.12 – Molecular Genetics
12.2 – The Replication of DNA
Replication starts at specific points called Origins of Replication. The separating strands create Replication Bubbles
Replication proceeds in both directions creating two y-shaped areas in each bubble called
Replication Forks

14. This creates a problem for one of the parental strands
Ch.12 – Molecular Genetics
12.2 – The Replication of DNA
New nucleotides can only be added to the 3’ end of the new strand, so that means it grows 5’ to 3’.
This creates a problem for one of the parental strands

15. Ch.12 – Molecular Genetics
12.2 – The Replication of DNA
The strand getting created in the opposite direction of the unwinding DNA is called the lagging strand
The strand getting created in the same direction of the unwinding DNA is called the leading strand

16. Helicase – unwinds & separates the DNA
Topoisomerase – Keeps the DNA from “overwinding” ahead of helicase by making breaks in the parental strands
Many enzymes and proteins are required for replication to occur

17. Binding Proteins - keep the separated strands from rejoining
Ch.12 – Molecular Genetics
12.2 – The Replication of DNA
DNA Polymerase - catalyzes the addition of nucleotides to the 3’ end of the new strand
Binding Proteins - keep the separated strands from rejoining

18. Ch.12 – Molecular Genetics
12.2 – The Replication of DNA
The Lagging Strand…
…has to be created in a series of sections called Okazaki Fragments, then bonded together with the aid of DNA Ligase
Replication Animation

19. Primase lays down a small RNA primer
Ch.12 – Molecular Genetics
12.2 – The Replication of DNA
Primase lays down a small RNA primer
DNA Polymerase III starts adding nucleotides after the primer.
Once reaching the next RNA Primer DNA Polymerase III detaches from the strand and starts at the newest RNA primer

20. DNA Polymerase I Then replaces the RNA primers with DNA nucleotides
Ch.12 – Molecular Genetics
12.2 – The Replication of DNA
DNA Polymerase I Then replaces the RNA primers with DNA nucleotides
DNA Ligase then joins all of the Okazaki Fragments and all of the breaks made by Topoisomerase
Replication Animation again?
The rate of elongation is about 500 nucleotides per second in bacteria and 50 per second in human cells

21. In 1972 James Watson discussed the “end replication problem”
Ch.12 – Molecular Genetics
12.2 – The Replication of DNA
In 1972 James Watson discussed the “end replication problem”
The 5’ end of new strands cannot be finished.
Telomeres – repetitive nucleotides at the end of the chromosomes provide protection to the genes found at either end of the chromosomes

22. RNA PROTEIN DNA Protein Synthesis
Ch.12 – Molecular Genetics
12.3 –DNA, RNA, & Protein
Protein Synthesis
Certain sequences of DNA are called genes
 Each gene codes for an enzyme (protein)
Proteins are assembled in the cytoplasm (at the ribosomes)
DNA cannot leave the nucleus
DNA’s code must be copied by RNA and taken to the ribosome in order for proteins to be synthesized
RNA
PROTEIN
DNA
Complete the “From DNA to Gene” PowerPoint Questions

23. RNA PROTEIN DNA Protein Synthesis
Ch.12 – Molecular Genetics
12.3 –DNA, RNA, & Protein
Protein Synthesis
Certain sequences of DNA are called genes
 Each gene codes for an enzyme (protein)
Proteins are assembled in the cytoplasm (at the ribosomes)
DNA cannot leave the nucleus
DNA’s code must be copied by RNA and taken to the ribosome in order for proteins to be synthesized
RNA
PROTEIN
DNA

24. Sugar is ribose not deoxyribose
Ch.12 – Molecular Genetics
12.3 –DNA, RNA, & Protein
RNA
Single Stranded
U replaces T
Sugar is ribose not deoxyribose
3 Types (to remember)
mRNA
tRNA
rRNA

25. Ch.12 – Molecular Genetics
12.3 –DNA, RNA, & Protein
RNA

26. Transcription Ch.12 – Molecular Genetics 12.3 –DNA, RNA, & Protein
Transcription Animation

27. Transcription RNA Processing Ch.12 – Molecular Genetics
12.3 –DNA, RNA, & Protein
Transcription
RNA Processing

28. Translation “Protein Synthesis”
Ch.12 – Molecular Genetics
12.3 –DNA, RNA, & Protein
Translation
“Protein Synthesis”
Translation Animation

29. Point Mutations SUBSTITUTION INSERTION DELETION
Ch.12 – Molecular Genetics
12.4 –
Point Mutations
Changes in the genetic material that occur in a single base pair
SUBSTITUTION
Change of one base in a sequence
Frame-Shift Mutations
INSERTION
Addition of base pairs in a sequence
DELETION
Removal of bases from a sequences

30. Why did the big fat guy eat one rat? Original
Ch.12 – Molecular Genetics
12.4 –
Why did the big fat guy eat one rat?
Original
Why did the bgf atg uye ato ner at?
Deletion
Who ydi dth ebi gfa tgu yea ton era t?
Insertion
Why did tho ebi gfa tgu yea ton era t?
Insertion
Why did the big fat guy eat one cat?
Substitution

31. Missense mutations: cause a change in the order of amino acids
Ch.12 – Molecular Genetics
12.4 –
Missense mutations: cause a change in the order of amino acids
Nonsense mutations: cause the polypeptide to stop early
mRNA 5¢ 3¢
Protein
Stop
Amino end
Carboxyl end
Base-pair substitution
No effect on amino acid sequence
Silent
U instead of C
Stop
Missense
A instead of G
Stop
Nonsense
U instead of A
Stop

32. Mutagens fall into two categories
Ch.12 – Molecular Genetics
12.4 –
Mutations can occur spontaneously or be caused by physical or chemical agents called mutagens
Most spontaneous changes in DNA are recognized and changed before replication. If it isn’t, that is when it is considered a mutation.
Mutagens fall into two categories
Chemical
May contain molecules that are very similar to the DNA bases, change the shape of the double helix or make chemical changes in the bases affecting base pairing
Physical
(high energy radiation such as x-rays or UV light)
Cause the DNA molecule to distort