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Exam 4 notes - Final Exam 4 May 2 4:15 Lecture 24 Bacteria...

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Final Exam 4 May 2 4:15 Lecture 24 Bacteria and Viruses Bacteria are prokaryotes - No nucleus or other membrane bound organelles - Reproduce by binary fission (asexual) - Cell wall, cell membrane, nucleoid, capsule, ribosomes, and flagellum Bacterial Genome - Most bacteria contain a single circular DNA ‘chromosomes’ (naked DNA) - The DNA replicates prior to cell division - There is a single replication origin (ori site) - There are no histone proteins - Most bacterial genomes contain 1-4 million bp of DNA. Many have been completely sequenced - E.coli have 4,639,221 bp and 4,403 genes (sequenced 1995) - In contrast humans have about 3 billion bp and ~25,000 genes - Why do bacteria have relatively small genomes? - They are relatively simple organisms - Selection for rapid replication keeps the genome small The bacterial Chromosome - is a circle of DNA - Doesn’t contain histones - Other proteins help compact it - Nucleoid - clump of DNA confined to a region of the cytoplasm - Bacteria are always haploid - They have twisted loops of DNA on other proteins Binary fission - The parent cell grows and the ori site starts replication - Once the replication is complete it start a primitive form of telophase Growing bacteria - Liquid medium - Estimate density (cells per mL) by Optic Density (spectrophotometer) - Agar plates Media - Minimal medium contains only inorganic salts and a carbon source - cells can grow on a minimal medium only if they can synthesize all the organic mo- lecules they need (eg - amino acids, nucleotides, vitamins, enzymes, etc)
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Nutritional mutants - Phototroph - can synthesize all of its organic molecules on minimal media - Auxotrouph - can’t synthesize an essential chemical (eg - amino acid) and can only grow on a medium that provides the required chemical Plasmids - A plasmid is a circular NA molecule, capable of replicating independently of the bac- terial chromosome (.05% to 10% of the size of the bacterial chromosomes) - They have their own ori sites - Plasmids may or may not be present in bacteria and are not essential - Plasmids are big enough to carry genes (eg - r plasmids carry antibiotic resistance genes) - Plasmids can be single or multiple copy (they can have one or more copies per cell) Genetic Recombination in bacteria - In bacteria reproduction is asexual (binary fission) - Genetic recombination occurs through a number of different processes, none of which involve reproduction - Either 2 new cells or the same cell with more genetic diversity, never both Sexual Conjugation - Two bacterial cells will come together - A single conjugation tube (modified pili) connects them - Genetic material is exchanged through the tube - Genetic exchange is always a one way street. One cell is the donor of genes tha other is the recipient. - The donor has pili - The donor-ship and recipient-ship is a genetically determined trait F + and F - - F + cells are donors: F - cells are recipients - After conjugation between f - and F + cells - the F - cell is changed to a F + What's the difference - F + cells have a plasmid called the sex factor or fertility factor (f) - F -
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