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Bacteria
CHAPTER 27
You must know
The key ways in which prokaryotes differ from eukaryotes with respect to genome, membranebound 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.
