Frederick Griffith discovered that something was transforming harmless bacteria into harmful bacteria in 1928. Alfred Hershey and Martha Chase showed in 1952 that DNA, not protein, was the genetic material using bacteriophages. James Watson and Francis Crick then proposed the double helix structure of DNA in 1953 based on Rosalind Franklin's X-ray crystallography photos.

1. Molecular Biology
of the Gene

2. Role of DNA as the Genetic Material
• Frederick Griffith (1928):
• Something was able to
transform harmless
bacteria into harmful
bacteria
• Transforming factor
• Transformation

3. Role of DNA as the Genetic Material
• Alfred Hershey and
Martha Chase (1952)
• Used Bacteriophages
• DNA (NOT PROTEIN) is the
genetic material

4. Role of DNA as the Genetic Material
• James Watson and Francis Crick (1953)
• Propose structural model for DNA based on
pictures from Rosalind Franklin
• Double Helix!

5. Discussion Prompt
Which experiment was the most important in
advancing our understanding of DNA/genetics?
a. Griffith
b. Hershey & Chase
c. Watson, Crick, & Franklin
Why?

6. DNA and RNA are polymers of nucleotides
• The monomer (building block) of DNA and RNA is the
Nucleotide
Nucleotides consist of:
1. Nitrogenous Base
2. 5-carbon sugar
3. Phosphate group
• DNA and RNA are
polymers (lots o’
building blocks) called
polynucleotides

7. DNA and RNA are polymers of nucleotides
• Covalent bonding between
the phosphate of one
nucleotide and the sugar of
the next nucleotide forms a
sugar-phosphate backbone
• Nitrogenous bases extend out
from backbone

9. DNA and RNA are polymers of nucleotides
Cytosine Adenine Guanine
Pyrimidines Purines

10. The Amazing (DNA) Race
•All models must include….
1.A distinguishable double helix shape
2.Sugar-phosphate backbone
3.Complimentary base-pairs
4.Nitrogenous bases
5.Noted directionality

11. Quick-Write
For the following, create a “guess definition” for each of the three words.
Example: Meningitis
Meninges Inflammation
Meningitis is an inflammation of
the meninges.
1.Replication
2.Transcription
3.Translation

12. Overview:
Process Product
1. Replication DNA
2. Transcription RNA
3. Translation Protein
Occurs in
nucleus
Occurs in
cytoplasm

13. 1. Replication
• Follows a semiconservative model
• Each DNA double helix has 1 parent strand and 1 shiny, new strand

14. 1. Replication
• Replication begins at origin
where it unwinds to form a
“bubble”
• Replication ends when these
”bubbles” merge
• Replication proceeds in two
directions simultaneously…
• 1. Continuous in 3’-5’ direction
• 2. Discontinuous (Fragmented) in
5’-3’ direction

15. 1. Replication (gets by with a little help from its friends)
• Helicase: Unwinds and unzips DNA
• Primase: Makes primer that DNA polymerase to synthesize (make) new DNA
• DNA Polymerase: Makes new DNA
• Ligase: Joins DNA fragments

16. 2. Transcription
• The Genetic Code: The set of rules giving the correspondence between
codons in RNA and amino acids in proteins.
• Protein construction requires a conversion of a nucleotide sequence to an
amino acid sequence
• Transcription rewrites the DNA code into RNA, using the same nucleotide
“language”
• Translation involves switching from the nucleotide “language” to amino
acid “language”

17. 2. Transcription
• The words of the “language” are codons…
• A codon consists of three nucleotides (A,C,G,U)
• Three nucleotides that specify one amino acid

19. 2. Transcription in a Nutshell
• The two DNA strands separate
• One strand is used as a pattern to produce an RNA chain
• For A in DNA, U is placed in RNA
• RNA polymerase catalyzes the reaction

20. 2. Transcription
•Three stages:
1. Initiation
2. Elongation
3. Termination

21. 2. Transcription (Types of RNA)
tRNA mRNA rRNA
• Transfer RNA
• Transfers an
amino acid to
growing protein
chain
• Messenger RNA
• Carries genetic
info from
nucleus to
ribosome
• Ribosomal RNA
• Makes up, you
guessed it,
ribosomes

22. 2. Transcription (Initiation)
• Brings together all the stuff needed to begin makin’ RNA
• RNA Polymerase binds at promoter region (start) and leads ribosome

23. 2. Transcription (Elongation)
• Addition of amino acids to the polypeptide chain
• Keeps on goin’ until a stop codon is reached

24. 2. Transcription (Termination)
• Completed polypeptide is released
• mRNA goes away (can be reused)

25. Quick-Write
• For each pair below, identify/explain the error in transcription:
DNA: TACGAAATCGCT….
RNA: AUACUUUAGCGA….
DNA: TACCCGATAGCA….
RNA: AUGGCUAUCGU….

26. 2. Transcription (Mutations)
•Mutation: Change in the nucleotide sequence of DNA
•Several types:
• Point Mutation  Change to one base (letter)
• Silent
• Nonsense
• Missense
• Frameshift Mutation  Insertion or deletion of bases

27. Mutations: Cystic Fibrosis
• Thick mucus in the lungs and
digestive track
• Constant lung infections and
impaired digestion
• (CFTR gene deleted) Occurs
because three base-pairs are
deleted

28. Mutations: Sickle Cell Anemia
• One amino acid changed
by substitution mutation
• Hemoglobin functions but
has a different shape…
causes cells to break
down easier

29. 3. Translation (the short & sweet version)
• A cell interprets a series
of codons along an mRNA
molecules
• tRNA transfers amino
acids from the cytoplasm
to a ribosome
• The ribosome adds each
amino acid carried by
tRNA to the growing end
of the polypeptide chain