Week 5: Bacteria
Week 5: Bacteria Bio 107
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This 6 page Class Notes was uploaded by Rachel Johnson on Friday September 25, 2015. The Class Notes belongs to Bio 107 at Washington State University taught by William Davis in Summer 2015. Since its upload, it has received 19 views. For similar materials see Biology in Biology at Washington State University.
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Date Created: 09/25/15
Bacteria I Bacteria and Archaea 339 Excellent at adapting to their environment Sets them apart from eukaryotes Examples salt tolerant Halobacterium Can live in a variety of habitats Two of the three domains of life 0 O 90 90 Archaea are more closely related to eukaryotes that bacteria are v Both are prokaryotes Prokaryotes 339 No membrane bound organelles ex nucleus v Possess a cell wall in addition to the cell membrane Helps protect the cell from the environment v 05 5 mm in diameter 339 Unicellular Can live in colonies v Common cell shapes Spherical Contains cocci in the name Rod Contains bacillus in the name Spiral Usually contains some form of spiro in the name Cell Walls Protective layer of polysaccharide complex sugar Bacteria contain peptidoglycan sugar protein complex Archaea do not contain peptidoglycan Features 0 O O 90 90 90 0 Capsules also referred to as halos Found on some prokaryotes but not all Sticky layer of polysaccharide or protein Used for adherence and protection Located outside of outer membrane provides additional protection from the environment Example Streptococcus uses it to stick to the respiratory track Fimbriae attachment pili Long rods extending out from the cell Used for attachment and for bringing cells together Example Neisseria gonorrhoeae uses it to attach to mucous membranes Motility Taxis Directional movement towards an area of advantage Often involved agella Example chemotaxis an attraction towards a chemical signal Flagella Allow cells to swim Can push or pull Motor turns hook and filament Powered by a chemical gradient of protons H across the cell membrane and cell wall Gram Staining 339 Useful for quick classification 339 Involves the use of crystal violet dye 339 Can be used to distinguish between two types of bacteria Gram positive bacteria Thicker layer of peptidoglycan outside of plasma membrane made of phospholipids Traps the dye causing a purple stain Examples Staphylococcus and Streptococcus Gram negative bacteria Thinner layer of peptidoglycan in between plasma membrane and outer membrane Very little dye enters the cell and the rest of the dye washes away staining the cell red Examples E coli and Salmonella Possess toxic lipopolysaccharides Can cause a fever and if major infection shock that may lead to death of the host Possess an outer membrane May protect them from the immune system May make them more antibiotic resistant Cell Organization 339 DNA in nucleoid region not a membrane bound nucleus One large circular chromosome Smaller circular plasmids Kept inside the cell Carries a small number of genes Can be acquired readily by other cells 339 Infolded plasma region Provides a surface for metabolic pathways 339 Endospores Resistant cells formed around chromosomes in periods of stress Allows the cell to survive for thousands of years in right conditions Thick coat of polysaccharides form around DNA Protective mechanism Bacteria II Prokaryotes Reproduce Rapidly 0 v Every 12 24 hours in average conditions 6 8 hours in a lab the cell will divide into daughter cells 339 Allows them to rapidly adapt to their environment New mutations may be introduced each DNA replication Mutations can occur every 12 24 hours Evolution 0 v Rapid rate of mutation can give rise to new genes 0 v Experiments in the Lenski Lab at Michigan State Serial dilutions for 20000 days straight and counting Place E coli in lactose Selected for survival on lactose instead of glucose Found evolution occurs on a daily basis Sources of Genetic Diversity 0 90 Bacteria divide rapidly Errors in DNA replication can lead to spontaneous mutations v Bacteria are capable of genetic transfer Allows them to exchange portions of their genome Bacteria are constantly trading genes 39 Significance O Antibiotic resistance Resistant genes can be transferred between species not just among one population 0 90 Allows for genetic recombination 339 Three major types Conjugation physical contact Transduction bacteriophage Transformation absorption of DNA Conjugation 339 Transfer of DNA from one cell to another Requires physical contact 339 Involves transfer of an F Fertility factor Contains genes required for conjugation Can t initiate conjugation Without it Cell Without F factor is called F Can be on a plasmid F Can be in a chromosome Hfr 339 F cell donor conjugation General steps Sex pilus attaches cells and mating bridge forms One strand of F plasmid moves across the bridge DNA is replicated and may recombine The other cell a F becomes a F cell No transfers between F and F Protective measure on the membrane that prevents future invasions 339 Hfr cell donor conjugation One strand of chromosome moves across the bridge Not all of the chromosomal DNA is transferred May stay as a F cell Hfr segment of the chromosome has to be transferred in order to convert the cell to Hfr DNA is replicated and may recombine Remainder of donor DNA is degraded
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