Frontiers of Genetics

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Unit 9 Frontiers of Genetics
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I. Biologists have learned to manipulate DNA A.
The Beginnings of DNA Technology 1.
Biotechnology- the use of organisms to perform
practical tasks for humans 2. Recombinant
DNA technology- combines genes from
different sources into a single DNA molecule
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II. Biologists can engineer bacteria to make
useful products A. Engineering Bacteria An
Introduction 1. Plasmid- a small, circular DNA
molecule separate from the much larger
bacterial chromosome a) May carry a number of
genes and can make copies of itself.
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Figure 13-3In addition to their main chromosome,
many bacterial cells contain small, circular DNA
molecules called plasmids.
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b) When a plasmid replicates, one copy can pass
from one bacterial cell to another, resulting in
gene sharing among bacteria.
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2. Biologists use plasmids to move pieces of DNA
into bacteria. a) First, a plasmid is removed
from a bacterial cell and the desired gene is
inserted into the plasmid.
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b) The plasmid is now a combination of its
original DNA and the new DNA - it is called
recombinant DNA. c) Then, the recombinant DNA is
put back into a bacterial cell, where it can
replicate many times as the cell reproduces,
making many copies of the desired gene. This is
called gene cloning.
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Figure 13-4Plasmids can serve as carriers of
genetic information. This diagram shows the basic
technique for creating a genetically engineered
bacterial cell.
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B. Cutting and Pasting DNA 1. First, a piece
of DNA containing the desired gene must be cut
out of a much longer DNA molecule. a)
restriction enzyme- an enzyme that chops up
foreign DNA into small pieces at specific spots
in the DNA sequence
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2. Most restriction enzymes make staggered cuts.
These staggered cuts leave single-stranded DNA
hanging off the ends of the fragments. This is
called a sticky end because it is available to
stick to any sequence that is complementary to
it. a) DNA ligase (another enzyme) is used to
join the sticky ends together.
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Figure 13-5Restriction enzymes cut DNA molecules
at specific locations. Splicing together
fragments of DNA from two different sources
produces a recombinant DNA molecule.
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C. Cloning Recombinant DNA 1. Libraries of
Cloned Genes a) Genomic Library- the
complete collection of cloned DNA fragments
from an organism
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2. Identifying Specific Genes with Probes a) One
method requires knowing at least part of the
genes nucleotide sequence. 1) Knowing this, a
biologist can use nucleotides labeled with a
radioactive isotope to build a
complementary single strand of DNA. 2)
Nucleic acid probe- used to locate specific
genes
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b) Next, the biologist treats the DNA being
searched with chemicals or heat to separate the 2
DNA strands. The nucleic acid probe is mixed in
with these single strands. c) The probe tags the
correct DNA portion by pairing with the
complementary sequence in the protein-V gene.
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d) Once the biologist uses this radioactive
marker to identify the bacterial cells with the
desired gene, those cells are allowed to multiply
further, producing the desired gene in large
amounts.
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D. Useful Products from Genetically Engineered
Microorganisms 1. Genetically engineered
bacteria used to make medicine (ex
insulin) 2. Recombinant DNA technology is also
helping to develop effective vaccines (ex
hepatitis B)
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III. Biologists can genetically engineer plants
and animals A. Producing Genetically Modified
Plants 1. Genetically modified organism
(GMO)- any organism that has acquired one or
more genes by artificial means a)
Transgenic- a GMO whose source of new genetic
materials is from a different species
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Figure 13-11To genetically modify a plant,
researchers insert a plasmid containing the
desired gene into a plant cell. There, the gene
is incorporated into the plant cell's DNA. The
engineered plant cell then grows into a
genetically modified plant.
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B. Producing Genetically Modified Animals 1.
First step is to extract an egg cell from a
female. 2. Sperm from the same species is used
to fertilize the egg in a test-tube
environment. 3. Then the desired gene is
injected into the fertilized egg and the egg is
returned to a uterus where it can develop into
an embryo.
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C. Animal Cloning 1. The first successful clone
was the sheep named Dolly. 2. The procedure
for cloning is the same as producing a GM
animal, except that instead of inserting a gene
into an egg, an entire foreign nucleus replaces
the eggs own nucleus.
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D. The GMO Controversy 1. Can GM crops pass
their new genes to closely related plants in the
nearby wild areas? 2. Another concern is the GM
plants and animals could have unknown risks to
human consumers.
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IV. DNA technologies have many applications A.
Mass-Producing DNA in a Test Tube 1.
Polymerase chain reaction (PCR)- a technique
that makes many copies of a certain segment of
DNA without using living cells
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Figure 13-15PCR produces multiple copies of a
segment of DNA.
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B. Comparing DNA 1. Gel electrophoresis- a
technique for sorting molecules or fragments of
molecules by length a) First, each DNA sample
is cut up into fragments by a group of
restriction enzymes.
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b) Next, a few drops of each sample are placed in
a small pocket or well at one end of a gel. The
other end of the gel has a positive charge. All
DNA molecules are negatively charged, so they
move through pores in the gel toward the positive
pole.
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c) The shorter DNA fragments slip more easily
through the pores of the gel. Therefore, the
shorter DNA fragments will travel faster through
the gel and be closer to the positive end of the
gel than the longer fragments.
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d) Lastly, the gel is treated with a stain that
makes the DNA visible under ultraviolet light.
The fragments show up as a series of bands in
each lane of the gel.
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Figure 13-16The gel electrophoresis technique
shown above can be used to compare DNA of
individuals or species.
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2. Genetic markers- particular stretches of DNA
that are variable among individuals (easy way to
tell if an individual is a carrier of a
disease) 3. DNA fingerprints- an individuals
unique banding pattern
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V. Control mechanisms switch genes on and
off A. Regulation of Genes in Prokaryotes 1.
Operon- cluster of genes and their controlled
sequences 2. Promoter- control sequence on an
operon where RNA polymerase attaches to the
DNA
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Figure 13-18E. coli bacteria, natural
inhabitants of your intestine, break down the
sugar lactose. The genes that code for
lactose-processing enzymes are located next to
control sequences. Altogether, this stretch of
DNA is called the lac operon.
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3. Operator- a control sequence that acts like a
switch, determining whether or not RNA polymerase
can attach to the promoter 4. Repressor- a
protein that functions by binding to the operator
and blocking the attachment of RNA polymerase to
the promoter turns off transcription
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Figure 13-19The lac operon is inactive in the
absence of lactose (top) because a repressor
blocks attachment of RNA polymerase to the
promoter. With lactose present (bottom), the
repressor is inactivated, and transcription of
lactose-processing genes proceeds.
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B. Regulation of Genes in Eukaryotes 1.
Transcription factors- proteins that regulate
transcription by binding to those promoters or
to RNA polymerases are activated and
deactivated by chemical signals in the cell 2.
Gene expression- the transcription and
translation of genes into proteins
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C. From Egg to Organism 1. Cellular
differentiation- when cells become increasingly
specialized in structure and function
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Figure 13-21Though all the genes of the genome
are present in every type of cell, only a small,
specific fraction of these genes are actually
expressed in each type of cell. The yellow color
indicates a gene that is "turned on" (expressed).
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D. Stem Cells 1. Cells that remain
undifferentiated they have the potential to
differentiate into various types of cells may
be able to help people with disabling diseases
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Figure 13-22Present at a very early stage of
human development, stem cells have the potential
to develop into any type of human cell.
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E. Homeotic Genes 1. Master control genes that
direct development of body parts in specific
locations in many organisms
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Figure 13-24The highlighted portions of the
fruit fly and mouse chromosomes carry very
similar homeotic genes. The color coding
identifies the parts of the embryo and adult
animals that are affected by these genes.