Download HtoN

From Haystacks to Needles
AP Biology
Fall 2010
Isolating Genes

Gene library: a collection of bacteria
that house different cloned DNA
fragments, one of which is of interest
 May be the entire genome or of cDNA,
which is free of introns
Gene Library
Isolating Genes

A particular gene of interest can be
isolated from other genes by use of
probes
Isolating Genes

DNA probes: short DNA sequences
assembled from radioactive nucleotides
 Can pair with parts of the gene to be studied

This nucleic acid hybridization technique
can be used with other procedures to
select cells and their DNA
 May be of interest to a researcher
Isolating Genes
If researchers know the desired gene
sequence, they use it to construct a
primer by synthesizing the single
stranded DNA
 If the sequence is unknown, they use
DNA from the same gene of a closley
related species that has already been
isolated

Big Time Amplification – PCR

The polymerase chain reaction (PCR)
can be used to make millions of copies
of cDNA
Big Time Amplification – PCR

What is needed for the reaction?
 Primers are short nucleotide sequences
that are made in the laboratory
 They are recognized by DNA polymerases
as the START tags for building
complementary sequences of DNA dictated
by computer programs stored in the
machines
Big Time Amplification – PCR

What are the reaction steps?
1. Researchers mix primers, DNA
polymerase, cellular DNA from an
organism, and free nucleotides
Big Time Amplification – PCR
2. Precise temperature cycles cause the DNA
strands to separate, exposing the bases
Big Time Amplification – PCR
3. Primers become positioned on the
exposed nucleotides to form new copies of
the original DNA
Big Time Amplification – PCR
4.
Each round of reactions doubles the number
of DNA molecules to eventually produce
billions of molecules from very tiny amounts
of original DNA
http://www.youtube.com/watch?v=_YgXcJ4n-kQ