10) Bacteria Summary_9744_2018

The Cell & Biomolecules of Life | Genetics & Inheritance (9744) Bacteria 2018 Prepared by: Mr Low Chor Meng and Mrs Selvamani Nair 1 Structure of Bacterial Cell Binary Fission – asexual reproduction produces genetically identical/clonal bacteria 1. DNA replication begins at the origin of replication (ori) where DNA is unzipped by breaking hydrogen bonds between bases of the 2 strands to form a replication bubble 2. DNA replicates by semi-conservative replication where each original strand serves as template for synthesis of daughter strands by complementary base pairing 3. 2 newly formed ori move to opposite poles of the cell and attach to the plasma membrane 4. Cell elongates to prepare for division. 5. DNA is circular with no free ends, and the 2 daughter DNA molecules will be interlocked with the completion of replication. 6. Enzyme topoisomerase cut, separate and reseal the two DNA molecules 7. Invagination of the plasma membrane and the deposition of new cell wall (division septum) eventually divide the parent cell into two daughter cells  each inherits a complete genome (genetically identical) Compare Binary Fission & Mitosis  Produces genetically identical offspring: selective advantage in a stable, favourable environment as it allows successful genotypes to rapidly colonise a habitat Point of Comparison Binary Fission Mitosis End Product 2 genetically identical cells 2 genetically identical cells Amount of DNA Same in each daughter cell as compared to parent cell Daughter cells have the same amount of DNA as parent cells DNA Replication DNA replication occurs during binary fission DNA replication occurs during S phase of interphase before mitosis Behaviour of Chromosomes Attachment of chromosomes to plasma membrane No attachment of chromosomes to plasma membrane Formation of entangled rings made up of 2 DNA molecules to be separated DNA molecules are not entangled No chromosome condensation into sister chromatids Chromosome condensation into sister chromatids No specific positioning of chromosomes in the cell that characterizes the different stages Specific positioning of chromosomes in the cell characterize the different stages Spindle Fibres No spindle fibres involved Spindle fibres involved Chromosome: > circular DNA which contains essential genes for survival Peptidoglycan cell wall: > protects the cell from osmotic lysis Fimbria: > for attachment to surfaces 70S ribosome: > site of protein synthesis Flagellum: > for motility Capsule (distinct layer) / Slime layer (diffused): > protects against phagocytosis Storage granule Plasmid: > extrachromosomal circular D