Bacteria CHAPTER 27

You must know  The key ways in which prokaryotes differ from eukaryotes with respect to genome, membrane- bound organelles, size, and reproduction.  How horizontal acquisition of genetic information occurs in prokaryotes via transformation, conjugation, and transduction.  How these mechanisms plus mutation contribute to genetic diversity in prokaryotes.

Structure  Most bacterial cell walls contain peptidoglycan.  Cell wall is surrounded by a sticky layer of polysaccharide, called a capsule.  Hairlike appendages, fimbriae, is used to stick to their substrate.  Pili are appendages that pull two cells together prior to DNA transfer from one cell to another.  Majority are motile, because they possess whiplike flagella.

Replication  Binary fusion - a single prokaryotic cell divides into 2 cells, which can then divide into 4, 8, 16….  During harsh conditions, bacteria develop resistant cells called endospores.  The cell makes a copy of the genetic material and surrounds it with a tough multilayered structure, forming the endospore.  Short generation time, they are able to adapt rapidly to new conditions.

Genetic Recombination  Transformation: prokaryote takes up DNA from its surrounding, which is then integrated into the chromosome by the exchange of homologous DNA segments.  Transduction: bacteriophage (virus) transfers genes between one prokaryote and another. A random piece of DNA is accidently packaged into the head of the bacteriophage, which is then introduced to the next host during infection.  Conjugation : genes are directly transferred from one prokaryote to another when they are temporarily joined by a “mating bridge”. It is only one way, one donates, one receives.  F Factor: (a particular piece of DNA), the ability to form pili and donate DNA during conjugation. Can either be in plasmid form or as a segment of DNA within the bacterial chromosome.  F Plasmid: F Factor in the plasmid form. (F+ = DNA donor) (F- = DNA recipient)  Mutations: are rare, but they are the major source of genetic variation in prokaryotes due to the short generation time and large population sizes of bacteria.

R plasmids and Antibiotic Resistance  A bacterial plasmid carrying genes that confer resistance to certain antibiotics.  “Resistance genes” which code for enzymes that specifically destroy the effectiveness of certain antibiotics.  Exposing bacteria populations to antibiotics have developed resistant strains, making the treatment of certain bacterial infections more difficult.