Principles of
Genetic Engineering & Biotechnology
In Principle:
Genetic Engineering involves the laboratory
manipulation of DNA
What does a particular
region of DNA
do?
This may involve isolation & manipulation of a "gene of interest"
in vivo
or in vitro "cloning" of the gene
[Nobel
Prize 1980]
analysis of the cloned gene
gel electrophoresis
DNA
sequencing
mRNA expression
Restriction
enzymes
[Nobel
Prize 1978]
DNA
sequencing
[Nobel
Prize 1980]
Polymerase
Chain
Reaction (PCR)
[Nobel
Prize 1993]
Sources of DNA
fresh viral, prokaryotic, or eukaryotic (plant &
animal, etc.) material
DNA
separated from other molecules by selective binding
to beads
(CSHL animation
of DNA extraction)
Ancient DNA
museum specimens: 10s ~ 100s years
fossils: 1,000s ~ 1,000,000s years
Ex.: insects in amber
Ex.: ancient humans: Neanderthals
& relatives
Forensic DNA
Forensics:
data used as evidence
Ex.: blood / semen stains at crime scenes
Ex.: What species do
these fillets come from?
In vivo Molecular
Cloning of DNA
Type-II restriction endonucleases
cut DNA only at specific restriction
sites (list)
DNA
palindrome -
"Able was I ere I saw Elba"
"Madam, I'm Adam"
"Straw? No!
Too stupid a fad, I put soot on warts."
"A
man, a plan, a canal: Panama!"
''Doc, note
I dissent. A fast never prevents a fatness. I diet on cod."
"Saippuakivikauppias" - Finnish word for a soap
seller
restriction
site reads the same in 5'3' direction on both strands
Overhanging TTAA-5' are "sticky
ends"
Vector insertion
Vector - a means of moving DNA
from one place to another
Plasmids - a circular,
extrachromosomal DNA
"naked DNA", a "bacterial virus"
pUC18 - an artificial
plasmid with:
selectable markers that tell you when
plasmid is present
antibiotic
resistant (e.g., tetracycline or ampicillin)
lacZ
gene produces beta-galactosidase,
metabolizes Xgal sugar blue product
lacZ gene
includes polylinker
multiple, unique restriction sites
Recombinant DNA
molecules are formed when
linearization of vector
DNA by digestion with endonuclease
ligation of "sticky
ends" between source DNA & vector DNA
combines DNA from two
different sources
[online
animation]
In vivo cloning in E.
coli [IG1 02.18]
E. coli K12
strain
can't grow in presence
of antibiotics (antibiotic-sensitive)
can't metabolize X-galactose (Xgal)
sugars
Host transformation
integrates plasmid DNA into bacterial chromosome
Bacteria acquires genetic traits of plasmid
Colony
Selection Scheme: finding the rare bacterium with recombinant
DNA
Only E. coli cells with resistant plasmids grow on antibiotic medium;
only
plasmids with functional
lacZ gene can metabolize Xgal
lacZ(+)
blue
colonies
lacZ functional
polylinker intact nothing inserted, no clone
lacZ(-)
white
colonies
polylinker disrupted
successful
insertion & recombination
!
Bulk
bacterial culture of recombinant (white) colonies
Purify cloned plasmid DNA, cut cloned gene out with
endonucleases:
Gene is ready for Analysis
SUMMARY OF pUC CLONING
Polymerase
Chain Reaction
In vitro DNA "cloning": [IG1 ResBrief
10.2, pp. 198-199]
"DNA xeroxing": four components & a gadget
DNA template
anything with DNA in it
oligonucleotide primers ("oligos")
short (20 ~ 30 base) ssDNA complementary to
gene
some knowledge of gene is required :
"Universal primers" work across many species
Taq
DNA polymerase
heat-stable enzyme from hot-spring
bacteria (Thermus
aquaticus)
functional at 70 ~ 80oC, withstands
exposure to 95oC
dNTPs: four building-blocks for DNA
Thermal cycler: computer-controlled heating & cooling block
temperature change > 1oC / sec
PCR doubles gene copy
number each cycle
denature / anneal /
extend: 2 4 8 16 32 64 etc.:
10 cycles = 210
= 103 copies, 20 cycles 106 copies, 30 cycles
109 copies
[
of PCR] [online
MGA animation]
PCR process is completely automated
replicates specific gene
only
makes
sufficient
quantities
of
purified
genes
for
direct
analysis
Analysis of
cloned and (or) amplified DNA
Restriction mapping
Determining the order of & distances among restriction
sites in DNA fragment:
provides an "outline" of the DNA
sequence [IG1 21.22]
(much) finer scale than three-point test cross map
Gel electrophoresis
separates DNA fragments by molecular weight
( of agarose gel electrophoresis)
Fragment numbers & sizes compared in single & pairwise
restriction digestions:
order & distances among sites
determined as Restriction
map
(CSHL animation)
Restriction maps of overlapping
fragments assembled as contig map
DNA sequencing
in vitro DNA replication copies one
strand repeatedly
(cf PCR: both strands
replicated)
Provides complete order of bases
in a DNA fragment
DNA primer is
complementary to 3' end of gene of interest
dideoxynucleotide terminators (ddNTPs)
stop strand growth during replication
four separate reactions terminate at ddA, ddC,
ddG, or ddT [IG1
02.19]
Sequencing
gel shows series of partial DNA replications
Sequencing "ladder" autoradiogram read from
bottom to top
(
of dideoxy
DNA sequencing)
Automated DNA sequencers
uses laser fluorometry
ddNTPs
attached to fluorescent dyes in a single reaction
scanning laser activates & fluorometer "see" fluorescence
colours (A C G T) [HOMEWORK]
computer "calls
sequence" as a chromatogram
[IG1 02.21]
( of automated
DNA sequencing)
Next
Generation sequencing uses massively-parallel,
high-throughput methods [IG1 ResBrief
21.1, pp. 454-455]
NextGen sequencers use capillary
separation [IG1
02.20]
Southern Blot analysis
Useful when gene of interest rare: one locus / genome
DNA transferred ("blotted") to filter paper
Filter
exposed
to a DNA probe
Probe: instrument or method that measures
something (e.g., thermometer)
ssDNA complementary
to gene region of interest
~ same as primer /
oligo in PCR
experiment
Binds specifically to target DNA immobilized on
filter
Radioactive label with 32P-dNTPs exposes X-ray
film
Autoradiogram shows presence / absence
& size of
target DNA
RFLP differences
DNA animations on this page are available from Cold
Spring Harbor Laboratory
Click here to go to the download
site