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- DNA is the molecule that stores genetic information.
- It is a chain (polymer) of smaller molecules (monomers) called
- Each nucleotide is formed by a sugar (deoxyribose), a nitrogenous
base (A, T, C, G), and phosphoric acid.
- There are four different types of nucleotides, depending on the base.
- DNA is a DOUBLE HELIX of two nucleotide chains.
- The two chains are linked thanks to the bonds
formed between the bases:
A is always paired to T
we say they are
G is always paired to C
James Watson and Francis Crick discovered the double helix
structure of the DNA in 1953, and won the Noble Prize in 1962.
Genetic information is stored in the SEQUENCE OF NUCLEOTIDES
of the DNA (that is, their order in the chain)
DNA REPLICATION: making two exact copies of a DNA molecule
1.- The helix uncoils and the two strands separate.
2.- The free nucleotides in the nucleus pair with the nucleotides of
each chain, according to the complementary rules (A-T, G-C).
3.- The new nucleotides join to form the new strands.
4.- In the end, two identical molecules of DNA are obtained: each
of them has an old strand and a newly-formed strand. That is why
we say that DNA replication is semi-conservative.
How is genetic information used in the cell?:
GENES AND PROTEINS: TRANSCRIPTION AND TRANSLATION
- Genes are fragments of DNA that have the information needed to produce a
protein. Genes are sequences of bases (ATTGCCTAG...) and they form a
- Proteins are the molecules that do the different jobs in the cells. They are
made of 20 different types of amino-acids joined in chains. Two proteins are
different depending on the composition and order of their amino-acids
(sequence of amino-acids) They are responsible of a person's phenotype.
- So, the sequence of bases of DNA will be used as a template to build
proteins (sequence of amino-acids).
Transcription: the genetic information stored in the DNA is copied to a
RNA molecule called mRNA (messenger RNA). This goes out of the
nucleus into the cytoplasm.
RNA is a single-strand molecule of polinucleotides. It has ribose instead of
deoxy-ribose, and U instead of T.
Translation: the genetic information that the RNA carries (in the
sequence of bases) is read in the cytoplasm by the ribosomes, which use it
as a template to synthesise proteins.
A group of 3 nucleotides (CODON or TRIPLET) codifies an amino-acid
- A 3 letters (codon) code.
- UNIVERSAL: shared by
all living beings.
- DEGENERATE: one
amino-acid is codified by
more than one codon (=
the genetic code is
- 3 stop codons mark the
end of protein synthesis.
MUTATIONS are changes in the DNA:
These changes happen RANDOMLY and naturally, although there are some
MUTAGENIC AGENTS or MUTAGENS that increase their frequency:
- RADIATIONS (X-rays, gamma-rays, UV-rays)
- some chemicals like mustard gas and many chemicals in tobacco
- pollutants in the environment
Mutations in somatic cells
cause alterations, diseases
(cancer...) but ONLY
MUTATIONS IN GERMINAL
CELLS (GAMETES) MAY BE
TRANSMITTED TO THE
Most mutations are harmful, or even deletereal for the individuals that carry them.
But some may be beneficial and give them an advantage to survive and reproduce.
Mutations increase genetic diversity, which allows the EVOLUTION of species.
TYPES OF MUTATIONS:
Point mutations (change in a
Silent mutations don't change the sequence
of amino-acids in the protein. This is possible
thanks to the degeneracy of the genetic code.
AN EXAMPLE OF MUTATION: SICKLE CELL ANAEMIA
A mutation in the gene of haemoglobin produces an abnormal protein that
makes red blood cells stiff and sickle-shaped instead of flexible and discshaped. This sickle cells can block the bloodflow in the capilaries.
Mutations can also happen with fragments of chromosomes. Or
even whole chromosomes or whole sets of chromosomes
Humans have 23 pairs of chromosomes, while
all the other apes have 24. Human
chromosome 2 is thought to have resulted from
the fusion of two ancestral chromosomes.
What is Biotechnology?
Biotechnology is the use of living organisms or
molecules obtained from them to develop products
that are useful for the people, the industry or the
Applied to HEALTHCARE
e.g. treating diseases,
designing organisms to
gene therapy, etc
Applied to MARINE and
e.g. increasing food supplies,
controlling proliferation, etc
Applied to INDUSTRIAL
e.g. producing enzymes and
Applied to AGRICULTURE
e.g. transgenic plants resistant to
pests and diseases, with increased
nutritional value, and other
BIOTECHNOLOGY IN HISTORY:
- For ten thousand years fermentation has been used
to produce wine, beer and bread.
- Selective breeding of animals such as horses and
dogs has been going on for centuries.
- Selective breeding of essential foods such as rice,
corn and wheat have created thousands of local
varieties with improved yield compared to their wild
Nowadays, biotechnology uses GENETIC ENGINEERING techniques to transfer
genes from one organism to another, in order to improve its properties or
produce useful products. Genetic engineering has some important advantages:
- Genetic engineering allows us to transfer only the
precise isolated gene we are interested in, and not
the whole genome.
- Also, it allows us to transfer genes between
organisms of different species.
The gene that is transferred from one organism to the
other is called a TRANSGENE. The organism that are
obtained with this technique are GENETICALLY
MODIFIED ORGANISMS (GMO), and the DNA that
contains fragments of different origins is
Cloning a Gene: isolating a gene and producing many copies of it in another
A plasmid from a bacterium can be used to clone a gene of interest from another
After cloning it in a host cell,
multiple copies of a gene of interest
can be harvested.
The cloned genes are useful for
basic research, and their proteins
can be applied to many uses.
- Pest resistance in plants.
- Cleaning up toxic waste.
- Proteins that dissolve blood clots.
- Human growth hormone (HGH).
APPLICATIONS OF BIOTECHNOLOGY:
1.- DRUG PRODUCTION
- HUMAN INSULIN
- GROWTH FACTOR
- COAGULATION FACTOR VIII
- VACCINES (Hepatitis A, B)
2.- GENE THERAPY
Analytical devices that give us information about our organism with a
The enzymatic oxidation of glucose produces
hydrogen peroxide, which in turn generates
electrons by electrode reaction. The current
density is used as a measure of glucose in
4.- AGRICULTURE AND FOOD PRODUCTION:
Genetic Engineering allows us to introduce one or a few
known genes into a plant, giving it the desired qualities
that traditionally we would obtain by random crossing.
Through these techniques we can obtain new crops (ie. rice, cotton, corn, soy,
tobacco, tomatoes, sugar beet) with new features such as:
- plague or herbicide resistances
- higher tolerance to adverse conditions (droughts,
- faster growth, higher efficiency
- new industrial applications: biodegradable
plastics, bioplastics – plastics made of
vegetables-, edible vaccines; Euro notes are made
of transgenic cotton.
Bt corn incorporates a gene of a soil bacterium called Bacillus thuringiensis and
so it is able to produce a protein “Bt toxin” that kills Lepidoptera larvae, in particular,
European corn borer.
Growers use Bt corn as an alternative to spraying insecticides for control of this
Biotechnology may be applied to any of the steps in the food production chain:
- improvements in the foods: golden rice (genetically modified to contain betacarotene, a source of vitamin A that may prevent blindness caused by malnutrition)
- new products with new scents and additives
- enriched foods (in vitamins, fibre...)
- detection of pathogens
- detection of alimentary frauds
5.- BIOTECHNOLOGY IN VETERINARY
- Transgenic animals are more difficult
to develop than plants.
- To obtain GM animals, we inject the
desired genes in the ovule, so alll the
cells in the animal will inherit it.
- We can produce drugs (ie. Factor IX
in sheep milk) or animal models to
study human diseases.
- We can also clone a whole animal by injecting the nucleus of a cell from an
individual in the previously enucleated zygote of another. Dolly the sheep was the
first animal that was clonned in this way (1996-2003)
6.- ENVIRONMENTAL BIOTECHNOLOGY
- treatment of waste waters
- degrading the hydrocarbons in black tides /oil spills
- removal of heavy metals (As, Pb, Hg) from the soil
- fuels obtained from living beings or organic matter that help
reduce the use of fossil fuels
- BIODIESEL: from oily seeds. It is used mixed with normal diesel.
- BIOETANOL: an alcohol obtained from the fermentation of sugars
(sugar cane, sugar beet, corn...)
- BIOGAS: mixture of methane and carbon dioxide obtained from
the bacterial decomposition of organic wastes.
- EFFECTS ON GENETIC BIODIVERSITY
- POSSIBLE GENE TRANSFER FROM TRANSGENIC TO WILD
- EFFECTS ON HUMAN HEALTH ??