§ Alteration of hereditary
traits by molecular biological techniques
§ One or more genes may be
§ Genes may be moved from
one organism to another
§ There is controversy
over genetic engineering surrounding ethics, use in food sources, and humans
Synthesis and Expression
§ In the early 1980s,
genetic engineers at Monsanto® Company began producing recombinant
bovine growth hormone (rBGH)
§ Made by genetically
§ The bacteria were given
DNA that carries instructions for making BGH
§ In cows, growth hormones
increase body size and milk production
Synthesis and Expression: From gene to protein
§ Protein synthesis – the process of using instructions
carried on a gene to create
§ Several steps are
involved and require both DNA and RNA.
§ Gene – a
sequence of DNA that encodes a protein
§ Protein – a large molecule composed of amino acids
§ Each nucleotide composed of deoxyribose, phosphate, and nitrogenous base
§ 4 bases: adenine (A),
thymine (T), guanine (G), cytosine (C)
§ Nucleotides comprised of
ribose, phosphate, and nitrogenous
§ 4 bases: A, C, G, and Uracil
§ The flow of genetic
information in a cell is DNA ® RNA ® protein
§ There are 2 steps in
going from gene to protein
§ Transcription (DNA ® RNA)
§ Translation (RNA ® Protein)
Synthesis and Expression: Trancription
§ Transcription occurs in
§ RNA polymerase binds to the promoter region of the gene.
§ RNA polymerase zips down the length of gene, matching RNA
nucleotides with complementary DNA nucleotides
§ The product of transcription is messenger RNA (mRNA).
Synthesis and Expression: Translation
§ Translation occurs in
the cytoplasm (outside the nucleus).
§ Translation requires:
mRNA (made during transcription), amino acids, energy (ATP), and some helper
§ Transfer RNA (tRNA)
§ The ribosome is composed
of rRNA and comprises a small and a large subunit.
§ Transfer RNA: tRNA carries amino acids and
matches its anticodon with codons on mRNA
§ A protein is put
together one amino acid at a time.
§ The ribosome attaches to
the mRNA at the promoter region.
§ Ribosome facilitates the
docking of tRNA anticodons to mRNA codons.
§ When two tRNAs are adjacent, a bond is
formed between their amino acids.
Synthesis and Expression: Genetic Code
§ The genetic code allows
a specific codon to code for a specific amino acid.
§ A codon is comprised of
three nucleotides = 64 possible combinations (43 combinations)
§ 61 codons code for amino
acids (& codon redundancy)
§ 3 others are stop
codons, which end protein synthesis
Synthesis and Expression: Mutations
§ Changes in genetic
sequence = mutations
§ Changes in genetic
sequence might affect the order of
amino acids in a protein.
§ Protein function is
dependent on the precise order of amino acids
§ Possible outcomes of
1 - no change
in protein (neutral mutation)
3 - different
§ Base-substitution mutation
– simple substitution of one base for another
§ Frameshift mutation – addition or deletion of a base, which
changes the reading frame
Synthesis and Expression: An Overview of Gene Expression
§ Each cell in your body
(except sperm and egg cells) has the same DNA.
§ But each cell only
expresses a small percentage of genes.
§ Example: Nerve and
muscle cells perform very different functions, thus they use different genes.
§ Turning a gene or a set
of genes on or off = regulating gene
§ Nerves and cells have
the same suite of genes, but express
Recombinant Proteins: Cloning a Gene Using Bacteria
§ rBGH is a protein, and is
coded by a specific gene.
§ Transfer of rBGH gene to bacteria allows for growth under ideal conditions.
§ Bacteria can serve as
“factories” for production of rBGH.
§ Restriction enzymes – Used by
bacteria as a form of defense. Restriction enzymes cut DNA at specific
sequences. They are important in biotechnology because they allow scientists to
make precise cuts in DNA.
§ Plasmid – Small, circular piece of bacterial DNA that exists
separate from the bacterial chromosome. Plasmids are important because they can
act as a ferry to carry a gene into a cell.
§ Step 1. Remove the gene
from the cow chromosome
§ Step 2. Insert the BGH
gene into the bacterial plasmid
§ Recombinant – Indicates material that has been
genetically engineered. A gene that has been removed from its
original genome and combined with another.
§ After step 2, the GBH is
now referred to as r (recombinant)
§ Step 3. Insert the
into a bacterial cell
§ The same principles
apply to other proteins.
§ Clotting proteins for hemophiliacs are produced using similar
§ Insulin for diabetics is also produced in this way.
§ About 1/3 of cows in the
US are injected with rBGH. rBGH increases milk volume from cows by about 20%.
§ Controversy over safety
to humans: USDA and Monsanto argue that milk from rBGH-treated
cows is indistinguishable from non-treated. Activists disagree.
Europe and Canada banned rBGH over concerns of
effects of rBGH on the health of cows.
Genetically Modified Foods
§ All agricultural
products are the result of genetic modification through selective breeding.
Artificial selection does not move genes from one organism to another, but does
drastically change the characteristics of a population.
Genetically Modified Foods: Why Genetically Modify Crop Plants?
§ Increase shelf life,
yield, or nutritional value
§ Golden rice has been
genetically engineered to produce beta-carotene, which increases the rice’s
Genetically Modified Foods: Modifying Plants with the Ti Plasmid and Gene Gun
§ Unlike rBGH, crop plants are directly modified. In order to do
this, the target gene must be inserted into the plant cell. Two methods to do
§ Ti plasmid
§ Gene gun
§ Transgenic organism – the result of the incorporation of a
gene from one organism to the genome of another. Also referred to as a Genetically Modified Organism (GMO).
Genetically Modified Foods: Effect of GM Crops and the Environment
§ Benefits: Crops can be
engineered for resistance to pests, thus farmers can spray fewer chemicals.
§ Concerns: Pests can
become resistant to chemicals. GM crops may actually lead to increased use of
pesticides and herbicides. GM crop plants may transfer genes to wild relatives.
Genetically Modified Humans: Stem Cells
§ Stem cells – undifferentiated cells, capable
of growing in to many different kinds of cells and tissues.
§ Stems cells might be
used to treat degenerative diseases such as Alzheimer’s or Parkinson’s,
multiple sclerosis, or liver, lung, or heart disease.
§ Stem cells could also be
used to grow specific tissues to treat burns, heart attack damage, or
replacement cartilage in joints.
Modified Humans: Human Genome Project
§ Human Genome Project – international
effort to map the sequence of the entire human genome (~20,000 – 25,000
§ For comparative
purposes, genomes of other model organisms (E.
coli, yeast, fruit flies, mice) were also mapped.
§ It was sequenced using
the technique of chromosome walking.
Genetically Modified Humans: Gene Therapy
§ Gene therapy –
replacement of defective genes with functional genes
§ Two approaches:
§ Germ line gene therapy
§ Somatic cell gene therapy
§ Germ line gene therapy
– embryonic treatment
§ Embryo supplied with a
functional version of the defective gene.
§ Embryo + cells produced
by cell division have a functional version of gene.
§ Somatic cell gene therapy – fix or replace the defective protein only in
§ Used as a treatment of SCID (severe combined immunodeficiency)
§ All somatic cells have
§ Therapy is not permanent
and requires several treatments per year.
Genetically Modified Humans: Cloning Humans
§ Human cloning occurs
naturally whenever identical twins are produced.
§ Cloning of offspring
from adults has already been done with cattle, goats, mice, cats, pigs, and
§ Cloning is achieved
through the process of nuclear transfer.