BMSC207 Lecture Notes - Lecture 3: Polymerase Chain Reaction, Methicillin, Guanine
Molecular bacteriology:
Bacterial cell division:
A bacterial cell must duplicate its genomic DNA before it can divide
•
All bacterial genomes are circular, and their replication begins at a single site known as the origin
replication (termed OriC).
•
A multienzyme repli cation complex binds to the origin and initiates unwinding and separation of the
DNA strands, using enzymes called helicases and topoisomerases (eg. DNA gyrase)
•
The separated DNA strands each serve as a template for DNA polymerase
•
Polymerization reaction invol ves incorporation of deoxyribonucleotides, which correctly base pair
the template DNA
•
Two characteristic replication forks are formed, which proceed in opposite directions around the
chromosome.
•
The two copies of the total genetic information (genome) produced during replication each comprise
one parental strand and one newly synthesized strand of DNA
•
Accurate replication is essential because DNA carries the information that defines the properties
processes of a cell
•
It is achieved because DNA polymerase is capable of proofreading newly incorporated
deoxyribonucleotides and excising those that are incorrect.
•
Mutations occur more frequently in bacteria as the time a cell splits is shorter than us
○
This reduces the frequency of errors to approximately one mistake (an incorrect base pair) per 10^
nucleotides copied
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Segregation of the replicated genomes
○
Formation of a septum in the middle of the cell
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Division of the cell to give separate daughter cells
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The process of cell division (or septation)
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In some bacteria this can occur every 20
-
40 minutes
•
Bacteria growth and divisions are important targets for antimicrobial agents
•
Gene expression:
Gene expression describes the processes involved in decoding the ‘genetic information’ contai ned
within a gene to produce a functional protein or RNA molecule
•
Most genes are transcri bed into mRNA, which is translated into proteins
•
Some genes are transcri bed to produce ribosomal RNA species (5S, 16S, 23S)
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Others are transcribed into transfer RNA (tRNA) molecules which decode mRNA into functional•
proteins
Bacterial genes are present on DNA as separate discrete units (si ngle genes) or as operons •
(multigenes), which are transcribed from promoters to give messenger RNA (mRNA) molecules;
mRNA is then translated into protein
Many of the proteins responsible for the pathogenic properties of medically important
•
microorganisms are encoded by operons
Transcription
and translation are important targets for antimicrobial agents
•
Regulation of gene expression:
Eg. Aerobic/anaerobic○
Salt concentration○
Expression of genes in bacteria is highly regulated, enabling them to switch genes on or off in
to change sin available nutrients or other changes in their environments
•
The expression of many virulence determinants by pathogenic bacteria is highly regulated
•
Genes and operons control led by the same regulator constitute a regulon•
The most common way of altering gene expressi on is to change the amount of RNA transcription•
Most instances of transcriptional regulation are mediated by regulatory proteins, which bind
to the DNA adj acent to or overlapping the promoter site and alter RNA polymerase bindi ng and
transcription
•
The regions of DNA at which regulatory proteins bind are known as operators or operator sites
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Those that increase the rate of transcription initiation (activators)
○
Those that inhibit transcription (repressors)
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Regulatory proteins fall into two distinct classes:
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Lecture 2.1
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8/8/16
Sunday, 7 August 2016
10:41 PM
Lectures Page 1
Document Summary
A bacterial cell must duplicate its genomic dna before it can divide. All bacterial genomes are circular, and their repli cation begins at a single site known as the origin replication (termed oric). A multienzyme repli cation complex binds to the origin and initiates unwinding and separation of the. Dna strands, using enzymes called helicases and topoisomerases (eg. dna gyrase) The separated dna strands each serve as a template for dna polymerase. Polymerization reaction involves incorporation of deoxyribonucleotides, which correctly base pair the template dna. Two characteristic repli cation forks are formed, which proceed in opposite directions around the chromosome. The two copies of the total genetic information (genome) produced during replication each comprise one parental strand and one newly synthesized strand of dna. Accurate replication is essential because dna carries the information that defines the properties processes of a cell. It is achieved because dna polymerase is capable of proofreading newly incorporated deoxyribonucleotides and excising those that are incorrect.
