Molecular genetics is the field of biology and genetics that studies the
structure and function of genes at a molecular level. The study of
chromosomes and gene expression of an organism can give insight into heredity,
genetic variation, and mutations. This is useful in the study of developmental
biology and in understanding and treating genetic diseases.
Techniques in molecular genetics = Amplification =
Gene amplification is a procedure in which a certain gene or DNA sequence is
replicated many times in a process called DNA replication.
Polymerase chain reaction The main genetic components of the
polymerase chain reaction are DNA nucleotides, template DNA, primers and
Taq polymerase. DNA nucleotides make up the DNA template strand for the specific
sequence being amplified, primers are short strands of complementary
nucleotides where DNA replication starts, and Taq polymerase is a heat
stable enzyme that jump-starts the production of new DNA at the high
temperatures needed for reaction. Cloning DNA in bacteria
Cloning is the process of creating many identical copies of a sequence of DNA.
The target DNA sequence is inserted into a cloning vector. Because this vector
originates from a self-replicating virus, plasmid, or higher organism cell
when the appropriate size DNA is inserted the "target and vector DNA
fragments are then ligated" and create a recombinant DNA molecule.
The recombinant DNA molecules are then put into a bacteria strain which
produces several identical copies by transformation. Transformation is the
DNA uptake mechanism possessed by bacteria. However, only one recombinant
DNA molecule can be cloned within a single bacteria cell, so each clone is
of just one DNA insert. = Separation and detection =
In separation and detection DNA and mRNA are isolated from cells and then
detected simply by the isolation. Cell cultures are also grown to provide a
constant supply of cells ready for isolation.
Cell cultures A cell culture for molecular genetics is
a culture that is grown in artificial conditions. Some cell types grow well in
cultures such as skin cells, but other cells are not as productive in cultures.
There are different techniques for each type of cell, some only recently being
found to foster growth in stem and nerve cells. Cultures for molecular genetics
are frozen in order to preserve all copies of the gene specimen and thawed
only when needed. This allows for a steady supply of cells.
DNA isolation DNA isolation extracts DNA from a cell
in a pure form. First, the DNA is separated from cellular components such
as proteins, RNA, and lipids. This is done by placing the chosen cells in a
tube with a solution that mechanically, chemically, breaks the cells open. This
solution contains enzymes, chemicals, and salts that breaks down the cells
except for the DNA. It contains enzymes to dissolve proteins, chemicals to
destroy all RNA present, and salts to help pull DNA out of the solution. Next,
the DNA is separated from the solution by being spun in a centrifuge, which
allows the DNA to collect in the bottom of the tube. After this cycle in the
centrifuge the solution is poured off and the DNA is resuspended in a second
solution that makes the DNA easy to work with in the future. This results in a
concentrated DNA sample that contains thousands of copies of each gene. For
large scale projects such as sequencing the human genome, all this work is done
by robots. mRNA isolation
Expressed DNA that codes for the synthesis of a protein is the final goal
for scientists and this expressed DNA is obtained by isolating mRNA.
First, laboratories use a normal cellular modification of mRNA that adds
up to 200 adenine nucleotides to the end of the molecule tail). Once this has
been added, the cell is ruptured and its cell contents are exposed to synthetic
beads that are coated with thymine string nucleotides. Because Adenine and
Thymine pair together in DNA, the poly(A) tail and synthetic beads are
attracted to one another, and once they bind in this process the cell components
can be washed away without removing the mRNA. Once the mRNA has been isolated,
reverse transcriptase is employed to convert it to single-stranded DNA, from
which a stable double-stranded DNA is produced using DNA polymerase.
Complementary DNA is much more stable than mRNA and so, once the
double-stranded DNA has been produced it represents the expressed DNA sequence
scientists look for. Genetic Screens
Forward genetics This technique is used to identify which
genes or genetic mutations produce a certain phenotype. A mutagen is very
often used to accelerate this process. Once mutants have been isolated, the
mutated genes can be molecularly identified.
Forward saturation genetics is a method for treating organisms with a mutagen,
then screens the organism's offspring for particular phenotypes. This type of
genetic screening is used to find and identify all the genes involved in a
trait. Reverse genetics
Reverse genetics determines the phenotype that results from a
specifically engineered gene. In some organisms, such as yeast and mice, it is
possible to induce the deletion of a particular gene, creating what's known
as a gene "knockout" - the laboratory origin of so-called "knockout mice" for
further study. In other words this process involves the creation of
transgenic organisms that do not express a gene of interest. Alternative methods
of reverse genetic research include the random induction of DNA deletions and
subsequent selection for deletions in a gene of interest, as well as the
application of RNA interference. Gene therapy
A mutation in a gene can cause encoded proteins and the cells that rely on
those proteins to malfunction. Conditions related to gene mutations are
called genetic disorders. However, altering a patient's genes can sometimes
be used to treat or cure a disease as well. Gene therapy can be used to
replace a mutated gene with the correct copy of the gene, to inactivate or
knockout the expression of a malfunctioning gene, or to introduce a
foreign gene to the body to help fight disease. Major diseases that can be
treated with gene therapy include viral infections, cancers, and inherited
disorders, including immune system disorders.
Gene therapy delivers a copy of the missing, mutated, or desired gene via a
modified virus or vector to the patient's target cells so that a
functional form of the protein can then be produced and incorporated into the
body. These vectors are often siRNA. Treatment can be either in vivo or ex
vivo. The therapy has to be repeated several times for the infected patient
to continually be relieved, as repeated cell division and cell death slowly
randomizes the body's ratio of functional-to-mutant genes. Gene therapy
is an appealing alternative to some drug-based approaches, because gene
therapy repairs the underlying genetic defect using the patients own cells with
minimal side effects. Gene therapies are still in development and mostly used in
research settings. All experiments and products are controlled by the U.S. FDA
and the NIH. Classical gene therapies usually require
efficient transfer of cloned genes into the disease cells so that the introduced
genes are expressed at sufficiently high levels to change the patient's
physiology. There are several different physicochemical and biological methods
that can be used to transfer genes into human cells. The size of the DNA
fragments that can be transferred is very limited, and often the transferred
gene is not a conventional gene. Horizontal gene transfer is the transfer
of genetic material from one cell to another that is not its offspring.
Artificial horizontal gene transfer is a form of genetic engineering.
The Human Genome Project The Human Genome Project is a molecular
genetics project that began in the 1990s and was projected to take fifteen years
to complete. However, because of technological advances the progress of
the project was advanced and the project finished in 2003, taking only thirteen
years. The project was started by the U.S. Department of Energy and the
National Institutes of Health in an effort to reach six set goals. These
goals included: identifying 20,000 to 25,000 genes in
human DNA, determining sequences of chemical base
pairs in human DNA, storing all found information into
databases, improving the tools used for data
analysis, transferring technologies to private
sectors, and addressing the ethical, legal, and
social issues that may arise from the projects.
The project was worked on by eighteen different countries including the United
States, Japan, France, Germany, and the United Kingdom. The collaborative effort
resulted in the discovery of the many benefits of molecular genetics.
Discoveries such as molecular medicine, new energy sources and environmental
applications, DNA forensics, and livestock breeding, are only a few of
the benefits that molecular genetics can provide.
See also Bacteriophage
Complementation Differential Susceptibility
DNA damage DNA damage theory of aging
DNA repair DNA repair-deficiency disorder
DNA replication Epigenetics
Gene mapping Genetic code
Genetic recombination Genomic imprinting
History of genetics Homologous recombination
Mutagenesis Mutation
Nucleic acid sequence Phage group
Regulation of gene expression Semiconservative replication
Timeline of the history of genetics Transformation
Sources and notes External links
NCBI: lm.nih.govprimer/genetics_molecular.html
Further reading Sites and databases related to genetics,
cytogenetics and oncology, at Atlas of Genetics and Cytogenetics in Oncology
and Haematology Jeremy W. Dale and Simon F. Park. 2010.
Molecular Genetics of Bacteria, 5th Edition ISBN 978-0470741849