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Transcript
AP Biology: Chapter 14
DNA Technologies
Recombinant DNA methods
– Restriction enzymes
• Enzymes from bacteria
• Used to cut DNA molecules in
specific places
• Enable researchers to cut DNA
into manageable segments
– Vector molecule
• Carrier of DNA fragment into cell
• Plasmids
• Engineered viruses
– Transformation
• Uptake of foreign DNA into cells
Splicing Foreign DNA into a Vector
• Foreign DNA and
plasmid DNA cut with
same restriction enzyme
• Produces linear
molecules with
complementary singlestranded ends
• Recombinant DNA
created by mixing so
sticky ends pair
• DNA ligase forms
covalent bonds, linking
the two fragments
Plasmid Vector Video
• Genetic probes
– Segments of single-stranded DNA that can
hybridize to complementary base sequences
in target gene
– Southern blot technique
• Genomic library
– Collection of DNA
fragments that represent
all the DNA in the
genome
• Chromosome
library
– All the DNA fragments in
that specific chromosome
• cDNA library
– Produced using reverse
transcriptase
– Makes DNA copies of
modified mRNA
• Amplifying DNA in vitro by PCR
•
•
•
•
Small amount of double-stranded DNA
DNA precursors
Specific nucleic acid primers
Taq DNA polymerase
– DNA is denatured
– Primers attach to primer-binding site on each DNA
strand
– Each strand acts as template for DNA synthesis
• DNA sequencing
– Based on chain termination method
– Yields information about
• Structure of gene
• Probable amino acid sequences of its encoded proteins
Comprehension Check
The gel at the right was produced from
four samples of single-stranded
DNA fragments that were incubated
with radioactively labeled primer,
DNA polymerase, the four
nucleotides, and a different one of
the four dideoxy nucleotides.
1. What is the sequence of nucleotides
shown in this gel?
GACTGAAGCTGTT
________________
2. What is the sequence of nucleotides
in the original single-stranded DNA
fragment?
CTGACTTCGACAA
_________________
• Applications of DNA technology
– Gene therapy
– Tissue engineering
– DNA typing
• Transgenic organisms
– Have a gene from some other organism inserted into their genome
– Gene targeting
• Adds precision to transgenic technology
• “Knocks out” or “knocks in” gene of interest at particular
chromosomal locus, where it trades places with an existing gene.
• By causing a specific gene to be inactive in the mouse, and
observing any differences from normal behavior or condition,
researchers can infer its probable function
Mouse on right
is normal; mouse
on left is transgenic
animal expressing
rat growth hormone
• Safety guidelines
– Safety concerns
• Introduction of transgenic organisms into the
environment
• Health effects on humans from consuming genetically
modified crops
– Safety measures
• Special facilities designed to hold pathogenic
organisms
• Science of risk assessment: the benefits must
outweigh the possible hazards