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Module: BIOM 1009

Lecturer: Dr Bonab

Date: 15/11/16

Microbial Genetics
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Understanding the genetics of microbes is important for a number of reasons:
 Producing microbial strains with desirable characteristics
 Producing medicines to fight against resistant microorganisms

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Bacterial DNA, unlike human DNA, is circular and contains a much lower number of base pairs
...
coli for example contains ~4 million base pairs
 Human DNA contains ~3 billion base pairs

o

There are a few distinct differences between microbial DNA and human DNA:

Microbial
Small genome (Mbp)
Gene density is high (>90% are exons)
Exons are short (~1kbp)
Operons with promotors upstream of exon
Fewer non-coding RNA’s
Single circular chromosome
Chromosomes condensed in the nucleoid

Human
Very large genomes (Bbp)
Gene density is low (~25% are genes, only 1% are exons)
Genes can span >30kbp
Genes have ~3 transcripts
Promotor regions are distinct from the gene
Multiple linear chromosomes
Chromosomes condensed in nucleus via histones

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Microorganisms contain operons, clusters of genes
 Their mRNA is synthesised in one place and is under the control of a single promotor
 One example is the lac operon

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The size of bacterial chromosomes range from 0
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58Mbp
 This is not free living
 The largest currently belongs to Streptomyces coelicolor with 8
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Because microorganisms divide at a very fast rate, they must replicate their DNA very fast
 More will be spoken on DNA replication in BIOM 1006 – Dr Sherwood
 There are 2 components to control the initiation of replication:
 A replicator sequence
 This is a specific set of DNA that tells the initiator protein where to start
 The initiator protein
 This recognises the replicator sequence and start the unzipping of the DNA adjacent
to the sequence
 Another three components are needed during the reactions:
 A plentiful supply of nucleotides
 DNA helicase
 DNA polymerase
 When the DNA stops replicating, the two circular strands must be cut apart from each other
 This is done via the enzyme topoisomerase



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