find it mixed in our food on the shelves in the
supermarket--genetically engineered soybeans and
maize. We find it growing in a plot down the lane,
test field release sites with genetically engineered
rape seed, sugar beet, wheat, potato, strawberries
and more. There has been no warning and no consultation.
is variously known as genetic engineering, genetic
modification or genetic manipulation. All three
terms mean the same thing, the reshuffling of genes
usually from one species to another; existing examples
include: from fish to tomato or from human to pig.
Genetic engineering (GE) comes under the broad heading
how does it work? If you want to understand genetic
engineering it is best to start with some basic
is a cell? A cell is the smallest living unit, the
basic structural and functional unit of all living
matter, whether that is a plant, an animal or a
fungus.Some organisms such as amoebae, bacteria,
some algae and fungi are single-celled - the entire
organism is contained in just one cell. Humans are
quite different and are made up of approximately
3 million cells -(3,000,000,000,000 cells). Cells
can take many shapes depending on their function,
but commonly they will look like a brick with rounded
comers or an angular blob - a building block.Cells
are stacked together to make up tissues, organs
or structures (brain, liver, bones, skin, leaves,
an organism, cells depend on each other to perform
various functions and tasks; some cells will produce
enzymes, others will store sugars or fat; different
cells again will build the skeleton or be in charge
of communication like nerve cells; others are there
for defence, such as white blood cells or stinging
cells in jelly fish and plants. In order to be a
fully functional part of the whole, most cells have
got the same information and resources and the same
cell belonging to higher organisms (e.g. plant or
animal) is composed of:
· a cell MEMBRANE enclosing
the whole cell. (Plant cells have an additional
cell wall for structural reinforcement.)
· many ORGANELLES, which
are functional components equivalent to the organs
in the body of an animal e.g. for digestion, storage,
· a NUCLEUS, the command
centre of the cell. It contains all the vital information
needed by the cell or the whole organism to function,
grow and reproduce. This information is stored in
the form of a genetic code on the chromosomes, which
are situated inside the nucleus.
are the basic building materials of a cell, made
by the cell itself. Looking at them in close-up
they consist of a chain of amino-acids, small specific
building blocks that easily link up. Though the
basic structure of proteins is linear, they are
usually folded and folded again into complex structures.
Different proteins have different functions. They
can be transport molecules (e.g. oxygen binding
haemoglobin of the red blood cells); they can be
antibodies, messengers, enzymes (e.g. digestion
enzymes) or hormones (e.g. growth hormones or insulin).
Another group is the structural proteins that form
boundaries and provide movement, elasticity and
the ability to contract. Muscle fibres, for example,
are mainly made of proteins. Proteins are thus crucial
in the formation of cells and in giving cells the
capacity to function properly.
means "coloured bodies" (they can be seen under
the light microscope, using a particular stain).
They look like bundled up knots and loops of a long
thin thread. Chromosomes are the storage place for
all genetic - that is hereditary - information.
This information is written along the thin thread,
called DNA. "DNA" is an abbreviation for deoxyribo
nucleic acid, a specific acidic material that can
be found in the nucleus. The genetic information
is written in the form of a code, almost like a
music tape. To ensure the thread and the information
are stable and safe, a twisted double stranded thread
is used - the famous double helix. When a cell multiplies
it will also copy all the DNA and pass it on to
the daughter cell.
totality of the genetic information of an organism
is called genome. Cells of humans, for example,
possess two sets of 23 different chromosomes, one
set from the mother and the other from -the father.
The DNA of each human cell corresponds to 2 meters
of DNA if it is stretched out and it is thus crucial
to organise the DNA in chromosomes, so as to avoid
knots, tangles and breakages. The length of DNA
contained in the human body is approximately 60,000,000,000
kilometres. This is equivalent to the distance to
the moon and back 8000 times!
information contained on the chromo-somes in the
DNA is written and coded in such a way that it can
be understood by almost all living species on earth.
It is thus termed the universal code of life. In
this coding system, cells need only four symbols
(called nucleotides) to spell out all the instructions
of how to make any protein. Nucleotides are the
units DNA is composed of and their individual names
are commonly abbreviated to the letters A, C G and
T These letters are arranged in 3-letter words which
in turn code for a particular amino acid - as shown
in the flow diagram 1. The information for how any
cell is structured or how it functions is all encoded
in single and distinct genes. A Gene is a certain
segment (length) of DNA with specific instructions
for the production of commonly one specific protein.
The coding sequence of a gene is, on average about
1000 letters long. Genes code for example for insulin,
digestive enzymes, blood clotting proteins, or pigments.
does a cell know when to produce which protein and
how much of it? In front of each gene there is a
stretch of DNA that contains the regulatory elements
for that specific gene, most of which is known as
the promoter. It functions like a "control tower,"
constantly holding a "flag" up for the gene it controls.
Take insulin production (which we produce to enable
the burning of the blood sugar). When a message
arrives in the form of a molecule that says, 'more
insulin", the insulin control tower will signal
the location of the insulin gene and say "over here".
The message molecule will "dock in" and thus activate
a "switch" to start the whole process of gene expression.
does the information contained in the DNA get turned
into a protein at the right time? As shown in picture
2, each gene consists of 3 main components: a "control
tower" (promoter), an information block and a polyA
signal element. If there is not enough of a specific
protein present in the cell, a message will be sent
into the nucleus to find the relevant gene. If the
control tower recognises the message as valid it
will open the "gate" to the information block. Immediately
the information is copied - or transcribed - into
a threadlike molecule, called RNA. RNA is very similar
to DNA, except it is single stranded. After the
copy is made, a string of up to 200 "A"-type nucleotides
- a polyA tail - is added to its end (picture 2).
This process is called poly-adenylation and is initiated
by a polyA signal located towards the end of the
gene. A polyA tail is thought to stabilise the RNA
message against degradation for a limited time.
Now the RNA copies of the gene leave the nucleus
and get distributed within the cell to little work
units that translate the information into proteins.
cell will ever make use of all the information coded
in its DNA. Cells divide the work up amongst one
other - they specialise. Brain cells will not produce
insulin, liver cells will not produce saliva, nor
will skin cells start producing bone. If they did,
our bodies could be chaos!
same is true for plants: root cells will not produce
the green chlorophyll, nor will the leaves produce
pollen or nectar. Furthermore, expression is age
dependent: young shoots will not express any genes
to do with fruit ripening, while old people will
not usually start developing another set of teeth
(exceptions have been known).
in all, gene regulation is very specific to the
environment in which the cell finds itself and is
also linked to the developmental stages of an organism.
So f I want the leaves of poppy plants to produce
the red colour of the flower petals I will not be
able to do so by traditional breeding methods, despite
the fact that leaf ells will have all the genetic
information necessary. There is a block that prevents
he leaves from going red. This block may be caused
by two things:
· The "red" gene has been permanently
shut down and bundled up thoroughly in all leaf
cells. Thus the information cannot be accessed any
· The leaf cells do not need
the colour red and thus do not request RNA copies
of this information. Therefore no message molecule
is docking at the "red" control tower to activate
course - you might have guessed - there is a trick
to fool the plant and make it turn red against its
own will. We can bring the red gene in like a Trojan
horse, hidden behind the control tower of a different
gene. But for this we need to cut the genes up and
glue them together in a different form. This is
where breeding ends and genetic engineering begins.
is the natural process of sexual reproduction within
the same species. The hereditary information of
both parents is combined and passed on to the offspring.
In this process the same sections of DNA can be
exchanged between the same chromosomes, but genes
will always remain at their very own and precise
position and order on the chromosomes. A gene will
thus always be surrounded by the same DNA unless
mutations or accidents occur. Species that are closely
related might be able to interbreed, like a donkey
and a horse, but their offspring will usually be
infertile (e.g. mule). This is a natural safety
devise, preventing the mixing of genes that might
not be compatible and to secure the survival of