Genetics 9
HC 1-2-3
9.1
Molecular genetics is the study of DNA structuring and its function at a molecular level, this
with the goal to understand how the bigger picture, our genetic material, works; where
does it consist out of? DNA and RNA form the basis of this understanding, of our genetic
material, though DNA is more stable than RNA, due to its double helix form. But how has
been shown DNA is genetic material?
First, one needs to grasp the four criteria that label something as genetic material:
1. Information: to construct the entire organism, like the blueprint for the inherited
traits. But it should be considered broad, since information is not only found in the
genes, not as necessarily gene expression, but as well in:
a. non-coding RNA can switch chromosomes on and off, thus influence the
information that is processed
b. proteins carry the message with them regarding the functioning of the body
c. promotors control the synthesis of many products by allowing access to read
the gene
d. factors such as centromeres and telomeres, which play an important role in
information sharing and processing.
2. Transmission: simply the fact that genetic material must be passed from the parent
to the offspring.
3. Replication: the prerequisite for transmission, since the information must be copied
in order to create a daughter cell from a mother cell which can then in turn be
passed on. However, the replicative process is not perfect and prone to mistakes,
resulting in a variety of differences arising in the offspring, giving form to the next
criterium.
4. Variation: as an inevitable outcome due to the replicative process, having a variety of
phenotypic differences within each species is a criterium of genetic material. The
accumulation of ‘so-called’ mistakes accounts for phenotypic variability, which in
turn adds to the evolutionary diversity, thus ought not to be regarded as a fault in
our system.
In one sentence: genetic material withholds the information needed to create a whole
organism in every aspect, provided to an individual by one’s procreator via a transmission of
this information, whilst prior and for the sake of this, a process of replication took place,
which due to its occasional inaccuracy delivers a variation of phenotypes within a species.
The first ideas of genetic material consisted out of the belief that a chemical substance is
responsible for the transmission of traits, the chromosomes, however simply naming it
chromosomes was not enough; since also DNA, RNA and proteins were on the scene.
One experiment used to show DNA being genetic material used mice and a bacterial strain,
of which one strain was able to produce capsules (the smooth strain, S) that could defy the
mouse’s immune system and the other could not produce the capsules (the rough strain, R).
The different strains have a variety in virulence, ability to cause disease. When injected, S
would kill the mouse and R would not. To verify S killed the mouse, its conductor Griffith
injected a mouse with a heat-killed S strain: the mouse lived. In the fourth experiment,
, Griffith mixed live R with heat-killed S and surprisingly the mouse died. Apparently,
something secreted by the dead S was taken in by live R, transforming it into live S enabling
itself to proliferate and kill the mouse. This transformation, as Griffith called it, was being
exercised by the so-called transformation principle. In our terminology, the transformed
bacteria acquired the necessary information to make a capsule, along with variations of the
outcome creating a capsule-secreting and deadly bacterial strain. This genetic information
from the specific variation must be replicated for it to be transmitted to new bacterial cells.
Griffith proved the existence of genetic material along all four criteria, but the actual
transforming substance was yet unknown. That’s where new scientists come to the picture.
They extracted type S bacteria and added in separate tubes all kinds of biochemical
purification substances. Namely the purified type S DNA was able to transform and when no
extract was added, no transformation took place. To even further verify it was DNA that did
the work, the scientists added enzymes that either digest DNA, RNA or proteins to the
samples; only the DNA enzyme, DNase, which digests DNA proved to prevent a
transformation with the logical explanation as follows. If all the DNA of the type S is
digested, in no way can R be transformed into S as the critical information was deleted.
RNase and protease cut away the respectively RNA and proteins, but still transformation
took place, so they are not the limiting factor. This proved DNA to be the transforming
principle.
Another promising experiment proved the same point. Hershey and Chase used a
bacteriophage, a virus that infects bacteria, and labelled its protein phage coat with a
radioactive chemical often found in proteins: 35S. Along with this, they as well labelled the
viral DNA with radioactive 32P. Hypothetically, after infecting the bacteria, the genetic
material transforming the victim (and causing lysis) ought to be found inside the cell. This
was indeed the case, the 32P was found inside the cell and the 35S merely outside.
9.2
Be notified though, not only DNA viruses exist, as do RNA ones. And not only do some carry
one strand, other are capable of carrying 7 RNA strands at once. They both are nucleic acids,
acidic due to their negative charge in neutral pH and their release of H +-ions. Its structures
are similar:
1. The repeating structural units of nucleic acid, nucleotides form the basis.
2. Nucleotides linked together linearly form a strand of DNA/RNA
3. Two strands form a double helix, mainly found in DNA
4. The folding of the double helix composes a 3D structure.
However, there are more ways to inherit, aside from the conventional genetic inheritance in
the form of DNA. There is as well epigenetic inheritance, with slightly tinkered DNA (due to
diet or stress) and proteins associated with DNA. There are many more proteins actually and
RNA that determine the epigenetic inheritance. They are found within the cytoplasm of
cells, which, upon division, pass on critical information to their daughter cells, which thus
now include mRNA and specific proteins in their system. Some proteins by the way have the
habit of aggregating, sticking together and so ending up in daughter cells with a more
prominent function of its genetic trait than even DNA.
9.3
So, DNA/RNA are genetically responsible, but how do they look?
- Nucleotide
HC 1-2-3
9.1
Molecular genetics is the study of DNA structuring and its function at a molecular level, this
with the goal to understand how the bigger picture, our genetic material, works; where
does it consist out of? DNA and RNA form the basis of this understanding, of our genetic
material, though DNA is more stable than RNA, due to its double helix form. But how has
been shown DNA is genetic material?
First, one needs to grasp the four criteria that label something as genetic material:
1. Information: to construct the entire organism, like the blueprint for the inherited
traits. But it should be considered broad, since information is not only found in the
genes, not as necessarily gene expression, but as well in:
a. non-coding RNA can switch chromosomes on and off, thus influence the
information that is processed
b. proteins carry the message with them regarding the functioning of the body
c. promotors control the synthesis of many products by allowing access to read
the gene
d. factors such as centromeres and telomeres, which play an important role in
information sharing and processing.
2. Transmission: simply the fact that genetic material must be passed from the parent
to the offspring.
3. Replication: the prerequisite for transmission, since the information must be copied
in order to create a daughter cell from a mother cell which can then in turn be
passed on. However, the replicative process is not perfect and prone to mistakes,
resulting in a variety of differences arising in the offspring, giving form to the next
criterium.
4. Variation: as an inevitable outcome due to the replicative process, having a variety of
phenotypic differences within each species is a criterium of genetic material. The
accumulation of ‘so-called’ mistakes accounts for phenotypic variability, which in
turn adds to the evolutionary diversity, thus ought not to be regarded as a fault in
our system.
In one sentence: genetic material withholds the information needed to create a whole
organism in every aspect, provided to an individual by one’s procreator via a transmission of
this information, whilst prior and for the sake of this, a process of replication took place,
which due to its occasional inaccuracy delivers a variation of phenotypes within a species.
The first ideas of genetic material consisted out of the belief that a chemical substance is
responsible for the transmission of traits, the chromosomes, however simply naming it
chromosomes was not enough; since also DNA, RNA and proteins were on the scene.
One experiment used to show DNA being genetic material used mice and a bacterial strain,
of which one strain was able to produce capsules (the smooth strain, S) that could defy the
mouse’s immune system and the other could not produce the capsules (the rough strain, R).
The different strains have a variety in virulence, ability to cause disease. When injected, S
would kill the mouse and R would not. To verify S killed the mouse, its conductor Griffith
injected a mouse with a heat-killed S strain: the mouse lived. In the fourth experiment,
, Griffith mixed live R with heat-killed S and surprisingly the mouse died. Apparently,
something secreted by the dead S was taken in by live R, transforming it into live S enabling
itself to proliferate and kill the mouse. This transformation, as Griffith called it, was being
exercised by the so-called transformation principle. In our terminology, the transformed
bacteria acquired the necessary information to make a capsule, along with variations of the
outcome creating a capsule-secreting and deadly bacterial strain. This genetic information
from the specific variation must be replicated for it to be transmitted to new bacterial cells.
Griffith proved the existence of genetic material along all four criteria, but the actual
transforming substance was yet unknown. That’s where new scientists come to the picture.
They extracted type S bacteria and added in separate tubes all kinds of biochemical
purification substances. Namely the purified type S DNA was able to transform and when no
extract was added, no transformation took place. To even further verify it was DNA that did
the work, the scientists added enzymes that either digest DNA, RNA or proteins to the
samples; only the DNA enzyme, DNase, which digests DNA proved to prevent a
transformation with the logical explanation as follows. If all the DNA of the type S is
digested, in no way can R be transformed into S as the critical information was deleted.
RNase and protease cut away the respectively RNA and proteins, but still transformation
took place, so they are not the limiting factor. This proved DNA to be the transforming
principle.
Another promising experiment proved the same point. Hershey and Chase used a
bacteriophage, a virus that infects bacteria, and labelled its protein phage coat with a
radioactive chemical often found in proteins: 35S. Along with this, they as well labelled the
viral DNA with radioactive 32P. Hypothetically, after infecting the bacteria, the genetic
material transforming the victim (and causing lysis) ought to be found inside the cell. This
was indeed the case, the 32P was found inside the cell and the 35S merely outside.
9.2
Be notified though, not only DNA viruses exist, as do RNA ones. And not only do some carry
one strand, other are capable of carrying 7 RNA strands at once. They both are nucleic acids,
acidic due to their negative charge in neutral pH and their release of H +-ions. Its structures
are similar:
1. The repeating structural units of nucleic acid, nucleotides form the basis.
2. Nucleotides linked together linearly form a strand of DNA/RNA
3. Two strands form a double helix, mainly found in DNA
4. The folding of the double helix composes a 3D structure.
However, there are more ways to inherit, aside from the conventional genetic inheritance in
the form of DNA. There is as well epigenetic inheritance, with slightly tinkered DNA (due to
diet or stress) and proteins associated with DNA. There are many more proteins actually and
RNA that determine the epigenetic inheritance. They are found within the cytoplasm of
cells, which, upon division, pass on critical information to their daughter cells, which thus
now include mRNA and specific proteins in their system. Some proteins by the way have the
habit of aggregating, sticking together and so ending up in daughter cells with a more
prominent function of its genetic trait than even DNA.
9.3
So, DNA/RNA are genetically responsible, but how do they look?
- Nucleotide
