Prokaryotes_ Domains Archaea and Bacteria

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					Prokaryotes: Domains Archaea and Bacteria
I) Cellular Organization -smaller, simpler genome -no nucleus – instead, have a nucleoid region of concentrated DNA -some have plasmids (small, independently replicating rings of DNA) -has plasma membrane and cell wall -no membrane-bound organelles (not compartmentalized) II) Archaea: extreme conditions 1. methanogens – energy metabolism  uses H2 to reduce CO2 to CH4 -poisoned by O2  live in swamps, marshes 2. extreme halophiles – live in saline places 3. extreme thermophiles – live in hot environments III) Bacteria -most abundant prokaryotes -Reproduction: divide by binary fission: -have 1 double-stranded, circular DNA -1 origin of replication; DNA copying goes in both directions -asexual  most bacteria identical to parent -genetic variation arises from mutations -Genetic Recombination increases diversity within a bacterial population 1. Transformation: alteration of a bacterial cell’s genotype by taking DNA from surroundings -foreign allele incorporated into bacterial chromosome, and DNA segments cross over 2. Transduction: phages carry bacterial genes from 1 host cell to another -generalized transduction -at the end of a phage’s lytic cycle, viral nucleic acid is packed in a capsid -sometimes a small piece of the host cell’s DNA gets packed into capsid -when the phage is released from the host, it attaches to another bacterium and injects the contents of the capsid into the new host cell  bacterial DNA from the first cell crosses over with DNA from second cell -specialized transduction -in the lysogenic cycle of a temperate phage, phage’s genome integrates as a prophage into host bacterium’s chromosome -when the phage genome is excised from the chromosome, sometimes part of the bacterial DNA near the prophage is excised as well -when the phage infects another cell, it gives the DNA from the first bacterial cell to the second cell  crossing over, genetic recombination 3. Conjugation: direct transfer of genetic material between 2 bacteria -“male” donates DNA  uses sex pili to attach to recipient, or “female” -temporary cytoplasmic bridge formed

4. Transposons: a segment of DNA that is able to move from 1 location to another in a cell’s genome -“cut and paste” transposition – jumps from 1 genomic location to another - replicative transposition – transposon replicates at original site; a copy inserts itself elsewhere


				
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