Bacteria

Ch. 19 - Bacteria and Viruses

Chapter 19

19-1 Bacteria• Common name for all prokaryotes

• unicellular organisms without a nucleus• Were all in Monera

• Eubacteria• live nearly everywhere• normally protected by cell wall containing

peptidoglycan - cell membrane inside of cell wall

• Archaebacteria• lack peptidoglycan• DNA similar to eukaryotic DNA• most are extremophiles – live in harsh

environments• methanogens; halophiles; extreme thermophiles

Prokaryotic Body Plan

DNA

ribosomes in cytoplasm

plasma membrane

capsule

bacterial flagellum

cytoplasmcell wall

pilus

Identifying Prokaryotes1. Shape

a. bacilli(us) – rod-shapedb. cocci(us) – sphericalc. spirilla(us) – spiral and corkscrew shaped

2. Cell Wallsa. Gram-positive – have thick peptidoglycan cell

walls that take and hold stainb. Gram-negative – thinner cell walls with lipids

on outside – does not hold stain

3. Movement Gram Positive Gram Negative

Metabolic Diversity1. Chemoheterotrophs – must

take in organic molecules for energy and a supply of carbon

2. Photoheterotrophs – use photosynthesis for energy, but take in organic compounds for carbon source

3. Photoautotrophs – use photosynthesis for both energy and carbon source

4. Chemoautotrophs – use chemosynthesis – get energy from chemical reactions and use carbon

dioxide as carbon source

Releasing Energy- bacteria release energy by cellular respiration

and fermentationA.Obligate Aerobes

- require a constant supply of oxygenB. Obligate Anaerobes

- must live in the absence of oxygenC. Facultative Anaerobes

- can survive with or without oxygen

Growth and Reproduction- under good conditions

bacteria can reproduce every 20 minutes

Binary Fission- normal asexual

reproduction of bacteria- replicate DNA and then

divideConjugation- exchange of genetic

material between bacterial cells

- increases genetic diversity

Spore Formation- allows survival of bad

conditions for a long time

Prokaryotic Fission - 1

DNA replication begins

Bacterium before DNA replication

Figure 21.7Page 350

bacterial chromosome

Prokaryotic Fission - 2

parent DNA molecule

DNA copy

DNA replication completed

Membrane growth moves DNA molecules

apart

Prokaryotic Fission - 3

New membrane and cell-wall material deposited

Cytoplasm divided in two

ConjugationTransfer of plasmid

nicked plasmidin donor cell

conjugation tubeto recipient cell

Importance of Bacteria- while we usually think of bacteria negatively they are actually

essential to correct functioning in ecosystemsA. Decomposers

- primary decomposers who make nutrients available to plants- used in sewage treatment plants also

B. Nitrogen Fixers- Rhizobium in nodules of legume roots fix nitrogen in a form the plants can use

C. Human Uses • in food production• in industry – can clean-up oil spills• to synthesize drugs and chemicals• genetic engineering now has them producing

human hormones• Mutualism with Eschecaria coli in our colon

where they help us make vitamins