AP Biology: Chapter 14DNA 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 single-stranded 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 CheckThe 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?

________________

2. What is the sequence of nucleotides in the original single-stranded DNA fragment?

_________________

GACTGAAGCTGTT

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 rightis normal; mouseon left is transgenicanimal expressingrat 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