| Microbial Genetics and Biotechnology |
Microbial Genetics and Biotechnology
| Topic Review on "Title":
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DNA
Replication
- DNA replication is semi conservative
process. DNA is copied from the 5� to the
3� direction.
- The process starts at the Origin (of
replication)
- Chromosomal proteins are released
exposing the DNA.
- DNA helicase unwinds or unzips a local
region of DNA breaking hydrogen bonds and
exposing the two separate strands.
- This opening is called the replication
fork (think of a fork in the road).
- DNA polymerase (an enzyme that matches a
complementary base to the one exposed) binds
to the open strand.
- Primase synthesizes a short
complementary RNA molecule. The RNA primer
provides a 3�hydroxyl group for the DNA
polymerase to bind.
- The polymerase moves along the strand in
the 5� to 3� direction.
- Because there are two strands that are
antiparellel cells synthesize new strand in
two ways.
- One strand is called the leading strand
is synthesized continuously as a single long
chain of nucleotides.
- Lagging strand is synthesized in short
segments that are later joined.
RNA
- Three kinds of RNA that are transcribed
from DNA: messenger RNA (mRNA), ribosomal
RNA (rRNA) and transfer RNA (rRNA).
- Initiation of transcription RNA
polymerase attaches nonspecifically to DNA
and slides along until it reaches a promoter
site.
- Upon recognition of the promoter RNA
polymerase unzips the DNA.
- RNA polymerase links the triphosphate
ribonucleotides with their DNA complement.
The high energy nucleotides produce the
energy for this reaction.
- Transcription terminated when the RNA
polymerase falls off the DNA as a result of
ether a stop code on the DNA or another
enzyme kicking it off.
Mutations
- DNA can be damaged from a variety of
mechanisms, including radiation, chemical
and mistakes made by the polymerase. This
damage can lead to mutation of the DNA.
Mutation is a change in the nucleotide base
sequence of a genome.
- Mutations are usually deleterious but
are sometimes neutral and rarely
improvements.
Biotechnology
- Horizontal gene transfer donor cell
contributes part of genome to a recipient
cell.
- Transduction a virus that has infected
one cell, can upon its lysing the host cell
take a part of the host genome with it.
When the virus then subsequently infects
another cell this DNA gets transferred.
- Bacterial conjugation can transfer
several traits that are carried on
plasmids. These may include the ability to
form pili, antibiotic resistance and other
metabolic advantageous traits.
- PCR, polymerase chain reaction is a
method for copying a specific DNA sequence.
A PCR reaction mixture includes: the DNA
template, excess amount of DNA primer,
polymerase and DNA nucleotides. A thermal
cycler mixes, heats and cools the reaction
mixture repeatedly allowing for multiple
successive DNA replication cycles.
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