LiroxtronIV (LiroxtronIV)H2 Biology 16 - Asexual reproduction in prokaryotes
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outline mechanism of asexual reproduction in prokaryotes
binary fission -> division of single parent bacterial cell into 2 genetically identical daughter cells
DR;
circular dsDNA replicates, begins @ ori, results in formation of repn bubble >
DNA double helix separates into 2 strands, each strand template for synthesis of daughter strand by SCDR >
from single ori, DNA synthesis progresses in both directions around circular chromosome until entire chromosome replicated >
CS;
newly formed & original ori move to opp poles of cell >
cell elongates by producing > cytoplasmic, CSM & cell wall components to prep for division into 2
Ck;
once DNA replication complete, bact reach 2x initial size, CSM starts to invaginate >
CSM invagination & new peptidoglycan cell wall deposition divides parent cell into 2 GI daughter cells >
parent bact cell contains plasmids, may not be segregated equally into daughter cells
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describe ways in which plasmid differs from bacterial chromosome
plasmids contain < genes than bact chr >
plasmids contain genes conferring selective advantages such as antibiotic/xenobiotic resistance absent from bact chr >
plasmids do not have genes needed for cell metabolism which are present in bact chr
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how transformation give rise to variation in prokaryotic genomes
bacterium takes up foreign naked DNA >
foreign DNA incorporated into bacterium DNA via homologous recombination by crossing over w/ homologous region found on bacterial chromosome >
results in recombinant cell, new allele expressed, new phenotype shown
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how generalised transduction give rise to variation in prokaryotic genomes
bacterial DNA/genes transferred from 1 bacterium to another via bacteriophage >
virulent bacteriophage undergoes lytic cycle, small piece of host bacterial degraded DNA packaged within capsid >
defective phage infects another bacterial cell, injects piece of host bacterial DNA into newly infected bacterial cell cytoplasm, host bacterial DNA incorporated into recipient bacterium DNA via homologous recombination
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how conjugation give rise to variation in prokaryotic genomes
F+ donor cell w/ F factor produces sex pilus, attaches to specific receptors on F- recipient cell >
TCMB formed b/w 2 bacterial cells, allows F+ donor cell to transfer (ss) F plasmid to F- recipient cell >
((after transfer of ss F plasmid DNA, complementary strands of F plasmid synthesised in F+(rolling circle mechanism) & F- cells >
transferred DNA circularises after SCDR)) F plasmid forms >
confers antibiotic/xenobiotic resistance for > survival
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how specialised transduction give rise to variation in prokaryotic genomes
bacterial DNA/genes transferred from 1 bacterium to another via bacteriophage >
temperate bacteriophage switches from lysogenic to lytic cycle, small region of host bacterial DNA adjacent to prophage excised, phage-host hybrid DNA packaged within capsid >
defective phage infects another bacterial cell, injects phage-host hybrid DNA into newly infected bacterial cell, phage-host hybrid DNA incorporated into recipient bacterium DNA via homologous recombination
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describe role of F factor
carries genes coding for production of sex pili >
contains genes coding for antibiotic, xenobiotic resistance
