Genetics 244
Molecular Genetics Week 1& 2
Written by Tegan Gibaud
Proving DNA Contains Genetic Material
Definitions Phages: (Bacteriophage) A virus that infects and replicates within
bacteria and archaea.
Transfection: The process of introducing nucleic acids (DNA or
RNA) into cells, utilizing means other than viral infection.
ssDNA: A DNA replication and repair intermediate generally induced
by stressed DNA replication forks and multiple DNA repair pathways.
Eukaryotic Cells: Cells that have a membrane-bound nucleus.
Translesion: The process in which cells copy DNA containing
unrepaired damage that blocks progression of the replication fork.
Properties of Genetic Properties
Material 1. Replication: The process of mitosis and meiosis.
2. Storage of information: Storing the complete DNA
component vs gene expression. Not all DNA information is
expressed phenotypically.
3. Expression of stored information: The “central dogma of
molecular genetics”. Transcription is the process in which
DNA is expressed.
4. Variation through mutations (gametes).
See below the process of DNA being expressed
Image: Source Unknown
1
,Proteins vs DNA Proteins were intiitally favoured as the genetic material in cells.
Proteins were studied more carefully at the time.
It was believed that DNA lacked the make up for genetic material as
it was so basic with phosphate, sugar and the nitrogenous four
bases: A, T, G and C.
Early Research on Tetranucleotide Hypothesis
DNA & Genetic ● Following the determined information that nucleic acids were
Material localized in the chromosomes, experiments were carried out
and suggested that the four base molecules A C G T occur in
approximately equal ratios.
● This was done by a chemist named Phoebus Levene.
Griffith’s Transformation of Bacteria
Image: Source Unknown
● Frederick Griffith worked with Stretococcus pneumoniae.
● Griffith concluded that R strain bacteria had been transformed
by S strain bacteria during the experiment. The R strain
inherited some “transforming principle” from the heat-killed S
strain bacteria which made them virulent.
● He assumed this “transforming principle” as genetic material.
● This was the first experiment suggesting that bacteria are
capable of transferring genetic information through a process
known as transformation.
Proof of DNA Avery et al Research
2
,Contains Genetic ● Avery & his team continued researching DNA and it’s
Material “transforming principle”.
● They experimented on cultures of virulent type 3S cells.
● They treated the extract from the experiment with:
- Protease: Proved that protein did not contain the
genetic material.
- Ribonuclease: Proved that the RNA did not contain
the genetic material.
- Dioxyribonuclease: Proved that DNA contained the
genetic material.
Image: Source Unknown
Hershey-Chase Research
● This research was conducted on bacteriophages, specifically
T2 which is 50% protein & 50% DNA.
● Hershey and Chase showed that when bacteriophages
(which are composed of DNA and protein) infect bacteria,
their DNA enters the host bacterial cell, but most of their
protein does not.
● Hershey and Chase therefore proved that DNA is the
hereditary material.
3
, Image:
https://chromoscience.com/2020/03/14/hershey-and-chases-proof-of-dna-as-genetic
-material/
Transfection of E.coli Protoplasts
● Research was carried out in which the transfection of E.coli
protoplasts with ssDNA of Bacertiophase ɸ174 resulted in the
production of complete phages.
● This proved that phage DNA alone contains all the
information needed to reproduce the virus.
Indirect Evidence In the 1950’s it was not allowed to use eukaryotic organisms for
research, therefore it was assumed that the fact that DNA carried
genetic material was the same for eukaryotic cells as all previous
research was done on prokaryotic cells.
There was circumstantial evidence to prove this to be true.
The initial indirect indications:
1. DNA distribution
Genetic material must be found where it acts (nucleus). Both
protein and DNA can be found in the nucleus, however,
protein can also be found in the cytoplasm. Chloroplasts and
mitochondria are also known to have genetic functions which
both contain DNA. This is consistent with the fact that genetic
material is only found in DNA.
2. UV mutagenesis
UV light induces specific mutations in the genome. The
mechanism of which this occurs has been thought to involve
translesion DNA synthesis over UV-induced DNA base
damage.
This proves that DNA contains genetic material.
4
Molecular Genetics Week 1& 2
Written by Tegan Gibaud
Proving DNA Contains Genetic Material
Definitions Phages: (Bacteriophage) A virus that infects and replicates within
bacteria and archaea.
Transfection: The process of introducing nucleic acids (DNA or
RNA) into cells, utilizing means other than viral infection.
ssDNA: A DNA replication and repair intermediate generally induced
by stressed DNA replication forks and multiple DNA repair pathways.
Eukaryotic Cells: Cells that have a membrane-bound nucleus.
Translesion: The process in which cells copy DNA containing
unrepaired damage that blocks progression of the replication fork.
Properties of Genetic Properties
Material 1. Replication: The process of mitosis and meiosis.
2. Storage of information: Storing the complete DNA
component vs gene expression. Not all DNA information is
expressed phenotypically.
3. Expression of stored information: The “central dogma of
molecular genetics”. Transcription is the process in which
DNA is expressed.
4. Variation through mutations (gametes).
See below the process of DNA being expressed
Image: Source Unknown
1
,Proteins vs DNA Proteins were intiitally favoured as the genetic material in cells.
Proteins were studied more carefully at the time.
It was believed that DNA lacked the make up for genetic material as
it was so basic with phosphate, sugar and the nitrogenous four
bases: A, T, G and C.
Early Research on Tetranucleotide Hypothesis
DNA & Genetic ● Following the determined information that nucleic acids were
Material localized in the chromosomes, experiments were carried out
and suggested that the four base molecules A C G T occur in
approximately equal ratios.
● This was done by a chemist named Phoebus Levene.
Griffith’s Transformation of Bacteria
Image: Source Unknown
● Frederick Griffith worked with Stretococcus pneumoniae.
● Griffith concluded that R strain bacteria had been transformed
by S strain bacteria during the experiment. The R strain
inherited some “transforming principle” from the heat-killed S
strain bacteria which made them virulent.
● He assumed this “transforming principle” as genetic material.
● This was the first experiment suggesting that bacteria are
capable of transferring genetic information through a process
known as transformation.
Proof of DNA Avery et al Research
2
,Contains Genetic ● Avery & his team continued researching DNA and it’s
Material “transforming principle”.
● They experimented on cultures of virulent type 3S cells.
● They treated the extract from the experiment with:
- Protease: Proved that protein did not contain the
genetic material.
- Ribonuclease: Proved that the RNA did not contain
the genetic material.
- Dioxyribonuclease: Proved that DNA contained the
genetic material.
Image: Source Unknown
Hershey-Chase Research
● This research was conducted on bacteriophages, specifically
T2 which is 50% protein & 50% DNA.
● Hershey and Chase showed that when bacteriophages
(which are composed of DNA and protein) infect bacteria,
their DNA enters the host bacterial cell, but most of their
protein does not.
● Hershey and Chase therefore proved that DNA is the
hereditary material.
3
, Image:
https://chromoscience.com/2020/03/14/hershey-and-chases-proof-of-dna-as-genetic
-material/
Transfection of E.coli Protoplasts
● Research was carried out in which the transfection of E.coli
protoplasts with ssDNA of Bacertiophase ɸ174 resulted in the
production of complete phages.
● This proved that phage DNA alone contains all the
information needed to reproduce the virus.
Indirect Evidence In the 1950’s it was not allowed to use eukaryotic organisms for
research, therefore it was assumed that the fact that DNA carried
genetic material was the same for eukaryotic cells as all previous
research was done on prokaryotic cells.
There was circumstantial evidence to prove this to be true.
The initial indirect indications:
1. DNA distribution
Genetic material must be found where it acts (nucleus). Both
protein and DNA can be found in the nucleus, however,
protein can also be found in the cytoplasm. Chloroplasts and
mitochondria are also known to have genetic functions which
both contain DNA. This is consistent with the fact that genetic
material is only found in DNA.
2. UV mutagenesis
UV light induces specific mutations in the genome. The
mechanism of which this occurs has been thought to involve
translesion DNA synthesis over UV-induced DNA base
damage.
This proves that DNA contains genetic material.
4
