It is a technique used for amplifying DNA
allowing you to increase the amount of
DNA from a small sample.
How does it work? - Artificial replication of
DNA. There are 3 stages: Denaturing - Heat
DNA sample to 94-96 to break hydrogen
bonds. Annealing - Cool to 68 degrees. This
allows the primer to hydrogen bond
creating the first bit of the new
double-stranded. Extending - Heat to 72,
DNA polymerase binds to end and
catalyses addition of nucleotides.
Uses of PCR: Tissue typing, detection of oncogenes,
detecting mutations, identifying viral infections and
monitoring spread of infectious diseases.
Electrophoresis
Separates
different size
fragments of
DNA using an
electric current.
Firstly DNA is cut into pieces. The gel is placed
into the tank and the tank is filled with buffer.
Loading dye is mixed with DNA and placed into
the wells in the jelly. An electric current is passed
through the gel. DNA carries a negative charged.
Fragments migrate to the anode with the lightest
moving the furthest.
DNA Profiling
A DNA profile is made up of the patterns of VNTR and
STR.
Minisatellites are called VNTRS. These
are 20-50 base pairs long. In every intron.
They are repeated 50 to several 100
times in.
Microsatellites are called STRs. These are 2-4 base
pairs long and are repeated 5-15 times.
Satellites appear in the same places on chromosomes. The number of repeats
vary between individuals. Different lengths are inherited from both parents. An
image of these patterns is known as a DNA profile.
How it works: DNA is cut with restriction enzymes. The fragments are
separated by gel electrophoresis. Cut at defined points in introns so leave
some repeats and satellites intact. Then the fragments are stained to reveal a
pattern.
Used for forensics and
paternity tests.
Genetic Engineering
4 stages: obtaining the gene, gene placed in
a vector, vector carries a gene into the cell
and the cell is expressed in the novel gene.
Obtaining the gene: mRNA obtained from the
cells where the gene is expressed. Reverse
transcriptase forms a single strand of cDNA
from mRNA.
Gene placed in a vector: Plasmids are mixed
with restriction enzymes. The plasmids are cut
at specific sites by the enzymes. This leaves
exposed sticky ends. Free complementary
nucleotides are added. DNA ligase then
anneals the gene. Or the gene is sealed in a
weakened virus to carry the DNA into the cell.
Getting the vector into the
recipient cell: Heat shock,
electrofusion, electroporation
and T1 plasmids.
An example is
golden rice. It is a
precursor for
vitamin A.
DNA Sequencing
Fred Sanger came up with an early method.
1. DNA mixed with primer made up
of DNA polymerase, nucleotides and
terminators.
2. Placed in a thermal cycler which alternates between two
cycles. One at 96 degrees separating the DNA strands. And
one at 50 degrees which anneals the primers to the
bases.
3. At 60 degrees the DNA polymerase
begins to build new DNA strands.
4. Terminators are added.
This stops synthesis and
different length fragments.
5. Fragments are separated by capillary
sequencing. There are markers on the
terminators meaning the last base is
detected.
6. The order is fed to a computer. It assembles a
genome by looking at the overlapping.
Flow cell
Allows millions of fragments to be replicated without
having to move them from one medium to another. This
produces clusters of fragments. It is a very efficient
process. Often called high throughput sequencing.
Allows large amounts of NDA to be processed.
Genomes
It is an organisms
complete set of
DNA. This
includes all of its
genes.
DNA
Made up of two antiparallel
chains.
A nucleotide is the monomer of
a polynucleotide which is one of
the chains. This consists of a
pentose sugar, phosphate group
and a nitrogenous base.
Two condensation reactions
are required to produce a
polynucleotide.