Questions for Chapter 10:

1
Questions for Chapter 10 3, 4, 6, 12, 15, and
20
2
Characteristics of Genetic Material
Able to be replicated Able to store
information Able to express information as
traits Able to be changed (by mutation)
3
Characteristics of Genetic Material
Protein vs. DNA as Genetic Material Why was
protein favored over DNA as the genetic material
prior to 1944? Abundant variety in cells
DNA too simple (4 bases vs 20 AA) Lack
of interest in understanding
Levene observed DNA comprised of 4 nucleotides in
relatively equal amounts Tetranucleotide
Hypothesis
Miescher isolated Nuclein 1868
4
Griffiths Observations with the Transforming
Principle of D. pneumoniae
Used two strians of D. pneumoniae, one virulent
(S) and one non-virulent (R) to inject mice.
5
Griffiths Observations with the Transforming
Principle of D. pneumoniae
When he treated the virulent strain with heat
(S-), he observed a loss of virulence.
However, when he combined the heat treated with
the rough, he observed regained virulence.
Why?
bacteria isolated from these mice was S type
6
Griffiths Conclusion
Frederick Griffith concluded from his experiment
that some substance moved from the dead S cell to
the live R cell and allowed the growth of
capsule. With a capsule the non-pathogenic R type
cell would now become pathogenic. However, he
failed to recognize the the substance was DNA.
Enter O.T. Avery and his colleagues
7
Avery, MacLeod and McCarty Experiments
8
Avery, MacLeod and McCarty Experiments

• This was the first published demonstration that
  DNA is the hereditary material by showing that
  the substance that transformed the non-virulent
  bacteria to become virulent was "a
  deoxyribose-containing nucleic acid."
• Despite the paper's novel conclusions and
  technical strength, it was not widely appreciated
  or accepted and many biologists claimed that the
  discovery (like Mendel's discovery of the gene in
  1865) was "premature."

9
Hershey-Chase Experiments Support DNA as the
Genetic Material

• Transfection of E.coli with Bacteriophage T2
  
• Viruses are composed of 50 protein and 50
  DNA
• Protein high in Sulphur (35S)
• DNA high in Phosphorus (32P)
• As easy as 1-2-3!
• 1. Label the phage
• 2. Infect the bacteria
• 3. See what happens!

Why were 35S and 32P used?
10
Labeling the Phage
11
Follow the Label
12
Follow the Label
DNA is passed on to the next generation of phage
13
A Closer Look at Nucleotide Composition

• Chargaffs Observations
• The amount of Adenine residues is
  proportional to the amount of Thymine residues.
• The amount of Guanine residues is
  proportional to the amount of Cytosine residues
• The sum of the purines (AG) equals the sum
  of the pyrimidines (TC)
• The sum of CG does not equal the sum of AT

14
What is DNA?
Deoxyribonucleic Acid
Biopolymer
15

• Things you should know for the test on Wednesday
• Statistics of normal distribution
• Additive inheritance
• Quantitative inheritance
• Heritibility (broad and narrow sense)
• Linkage
• Effect of linkage on Mendelian ratios
• Mapping (physical and linkage)
• How to calculate map distances and gene order
• Coefficients of coincidence and chromosomal
  interference
• Evidence for chromosomal basis for inheritance
• The different types of ploidy
• Diseases due to chromosomal abnormalities
• Types of chromosomal rearrangements
• Experiments demonstrating DNA is genetic material
• Physical characteristics of DNA
• How nucleotides pair
• Chemistry of nucleic acids

16
Watson-Crick Model of DNA
1. Based on X-Ray data from Rosliand Franklin,
recognized that the 3.4 Angstrom period suggested
a double helix.
2. Based on Chargaffs rule (AT and
CG), recognized that the two strands must be
held together by H-bonds between purine and
pyrimidine pairs.
3. Accepted the assumption that nucleotides were
held together by phosphodiester bonds with
phosphate as the chain backbone.
17
The Journal Article that Won the Nobel Prize
18
Watson-Crick Model of DNA

• Chains were in an antiparallel orientation
• Bases stacked perpendicular to helix axis
  and associate through hydrogen bonds
• Each turn is 34 Angstroms 10 bases/turn
• Major and minor grooves within the helix
• Double helix has a 20 Angstrom diameter

19
Deoxyribonucleotides
Nucleotides are the basic units that comprise DNA
20
Nucleotide Base Pairing
Nucleotides pair by forming H-bonds between
bases. The pairing is the basis for the
antiparallel strands associating with each other.
21
Phosphodiester Bond

• Nucleotides are joined 5-3 by a phosphodiester
  bond
• The linkage is between the phosphate and two
  sugars
• Addition to a chain of nucleic acid is
  usually 5-3
• Chains lt 20 nucleotides are called
  oligonucleotides
• Chains gt 20 nucleotides are called
  polynucleotides

22
Phosphodiester Bond Formation
dGTP
DNA Polymerase
dGTP
23
Phosphodiester Bond
24
Single Stranded DNA
Sugar and phosphate provide backbone and bases
hang free.
25
Single Stranded DNA
Double Stranded DNA
5
3
5
3
26
DNA Double Helix
27
RNA Versus DNA

• RNA is Similar to DNA
• RNA like DNA is polymerized 5-3
• RNA is single stranded (usually)
• Major forms
• -ribosomal RNA (rRNA)
• -transfer RNA (tRNA)
• -messenger RNA (mRNA)
• -heterogeneous nuclear RNA (hnRNA)
• -small nuclear RNA (snRNA)

28
RNA Versus DNA
29
Notice the Difference
30
RNA serves as the genetic material in some
viruses

• Two types
• Type I utilizes RNA replicase
• -example - phage Q
• Type II utilizes Reverse Transcriptase
• -examples - HIV, polio

31

• Things you should know for the test on Wednesday
• Statistics of normal distribution
• Additive inheritance
• Quantitative inheritance
• Heritibility (broad and narrow sense)
• Linkage
• Effect of linkage on Mendelian ratios
• Mapping (physical and linkage)
• How to calculate map distances and gene order
• Coefficients of coincidence and chromosomal
  interference
• Evidence for chromosomal basis for inheritance
• The different types of ploidy
• Diseases due to chromosomal abnormalities
• Types of chromosomal rearrangements
• Experiments demonstrating DNA is genetic material
• Physical characteristics of DNA
• How nucleotides pair
• Chemistry of nucleic acids