Genetics

Subtilisin Fermenters

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Subtilisin is a protein-breaking enzyme produced naturally by certain bacteria.

Genetically modified (GM) subtilisin that can work in hot, alkaline conditions is

used in detergents to break down protein-based stains, such as blood. GM

subtilisin is produced by the GM bacteria grown in fermenters.

Extracting a Gene

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Genetic engineering involves two processes. First, the gene is extracted and isolated and,

if necessary, modified. Then, it is inserted into an animal or plant cell (creating a "transgenic"

species) or a microbial cell. The protein encoded by the inserted gene is produced by the

animal or plant cell, or (if the gene was inserted into a microbe) by culturing microbial cells

in a fermenter.

Each gene is simply a set of chemical instructions, encoded as a sequence of four chemical

bases (abbreviated as A, C, G, and T) that make up a long double-stranded molecule called

DNA. A complete molecule of DNA called a chromosome, contains many distinct genes.

The first step in genetic engineering is to identify the gene of interest in the midst of a

chromosome. Scientist often do this by isolating the gene's messenger RNA (mRNA),

a molecule that carries instructions for protein manufacture from the gene in the cell nucleus

to protein-making units in the cytoplasm. mRNA is a complementary copy of one strand of the

section of DNA comprising a gene and can be use as a template for reconstructing the gene.

If desired, the gene can be modified to produce an improved protein.

Genetic Engineering in Animal Cells

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One method of incorporating a foreign or modified gene into an animal is

to inject copies of the gene into a newly fertilized egg. The gene then becomes

integrated into the chromosomes in the nucleus of the egg, which is then

implanted into a foster mother. As the cell starts dividing, the gene is copied

along with every other gene in the chromosomes. In this way, the gene is present

in every body cell of the "transgenic" animal.

Genetic Engineering in Micro-organisms and Plant Cells

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Some bacteria contain extra chromosomal loops of DNA called plasmids,

which replicate independently of the chromosome, both within the cell and

also when a bacterium divides. By inserting foreign genes into plasmids using

special "restriction" enzymes that cut the DNA at specific points, bacteria can

be used as protein factories on an industrial scale. Plasmid DNA can also be

inserted into plant cells in order to produce genetically modified crops.

Human Genome Project

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Most human body cells contain about 90,000 pairs of genes (units of hereditary data)

arranged on two sets of 23 chromosomes (structures of the molecule DNA). This

genetic information forms the genome. The Human Genome Project is an international

program launched in 1990 to map the sequence of nucleotide bases (the building

blocks of DNA) in the genome and determine the function of every gene.

The mapping of the human genome is a scientific achievement comparable with

putting people on the Moon. The genomes of some organisms, including a worm

and a fruit fly, have already been sequenced (mapped), but these genomes are

small compared to the human genome, which contains about 3 billion nucleotide

bases. By sequencing the human genome, scientists will better understand the

genes involved in body processes and diseases. The genes in each of an

individual's cells are identical, but the genome various slightly between individuals

(which, in part, makes them individuals), so the Human Genome Project maps

genes from a representative group of people. Although we now have the DNA

sequence of the human genome, it will take many years to identify the individual

genes and determine their function.

The Function of Genes

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A gene is a section of double-stranded DNA containing data that enables an

organism to function. Most genes contain instructions for making a protein.

These instructions are encoded within the sequence of nucleotide bases on

one of the gene's strands. An elaborate chemical machinery exists in body

cells to make proteins when they are needed, using the instructions encoded

by the genes. Proteins play many roles in the body, so genes ultimately affect

every aspect of an individual's development and function. For the same reason,

genetic defects can be cause of ill health and disease.

DNA Sequencing

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DNA is sequenced to work out the order of its four nucleotide bases ( T, A, C and G ) ,

which spell out the genetic information. By examining the sequence of a specific length

of DNA, scientists can see whether it contains a gene. Only about 10 percent of the

human genome contains genes (the remaining 90% is known as junk DNA). There are

several methods for sequencing . The one shown here is the Sanger Method, devised

by Frederick Sanger, a biochemist who used it to sequence the genome of a virus

during the 1970s. The Human Genome Project used new techniques , computers, and

robotic machinery that greatly increased the speed of DNA sequencing.

How a Protein is Made

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First, a section of DNA containing a gene seperates into two strands. A molecule called

messenger RNA (mRNA), consisting of a sequence of nucleotide bases that duplicate

the gene's protein-making instructions, forms on one strand. The mRNA then moves to

the cytoplasm, where the structures called ribosomes process the instructions.