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Prokaryotic Cells

Lecture #2 - Summer 2012 Micro Series

Irina Mavrodi

on 14 June 2013

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Transcript of Prokaryotic Cells

Prokaryotic Cells
A quick introduction to the prokaryotic cells of the microbial world
Binomial System of Nomenclature: two word naming system
Genus species
(always italicized or underlined; genus can be abbreviated to first letter)


follow (if applicable)
Genus species
strain designation
(for example:

E. coli
strain B
E. coli
strain K12
These organisms are not alive
Consist of only a few molecules that are typically in cells
Viruses, Viroids, and Prions
Simpler than viruses
Consist of a single, short piece of nucleic acid (RNA) without a protective coat
Can reproduce only inside of cells
Cause a number of plant diseases
May cause diseases in humans (?)
Unusual agents
Responsible for 7 degenerative diseases
Always fatal
Consist of only protein
A piece of nucleic acid surrounded by a protein coat
Variety of shapes
Reproduction leads to copies
Can only multiply inside living host cells
Borrow their machinery
Outside hosts, they are inactive
Obligate intracellular parasites
All forms of life are susceptible to viruses
Microbes cover a tremendous range in their sizes
Smallest viruses are about 1 million times smaller than the largest eukaryotic cells
The small size and broad range of microbes require the use of measurements not commonly used in everyday life
Use of logarithms is helpful in designating sizes of prokaryotes and viruses
Size in the Microbial World
Prokaryotic cells come in a variety of simple shapes
Some form characteristic groupings and some aggregate living as multicellular associations
Morphology of Prokaryotic Cells
Most common bacteria are one of two shapes
-Spherical - coccus
-Cylindrical (rod) - bacillus
Cells have a variety of other shapes
-Short, rod-shaped - coccobacillus
-Short, curved rod - vibrio
-Spiral - spirillum
Greatest variety is found in aquatic environments
Most prokaryotes divide by binary fission
Cocci that divide in one plane form chains
Pairs are called diplococci (i.e., Neisseria gonorrhoeae)
Cocci that divide in two or three planes perpendicular to one another form cubical packets
Cocci that divide in several planes at random form grape-like clusters
For example:
Myxobacteria glide over moist surfaces
Form a swarm of cells that move as a pack
Release enzymes that degrade organic material
When nutrients are depleted, cells aggregate to form fruiting bodies (visible to the naked eye)
Live on surfaces in associations called biofilms
Multicellular Associations
Deceptively simple
Cytoplasmic membrane surrounds the cell (i.e., barrier)
Cytoplasmic membrane enclosed by cell wall (i.e., rigid barrier)
Cloaking the wall may be additional layers and appendages
Structure of Prokaryotic Cells
Capsule (if present), cell wall, and cytoplasmic membrane make up the cell envelope
Encloses the contents of the cell
Cytoplasm and Nucleoid
Cytoplasm holds a variety of substances
Nucleoid holds chromosomes
-enable cell to survive and multiply
-some essential, some optional
-can be targeted for selective toxicity
-important in identifying bacteria
-Filamentous appendages:
-Flagella (motility)
-Pili (adherence, motility, DNA transfer)
-Surface layers
-Capsule (sometimes), slime layer, cell wall
Extracellular Components
-Cytoplasmic Membrane
-Functions as a boundary
-Discriminating conduit
Cell Boundary
-Gas Vesicles
Intracellular Components
-Can be found growing in the harshest environments
-Important for microbiologists to identify, isolate, and cultivate many species
Dynamics of Prokaryotic Growth
-Binary Fission: One cell dividing into two
-Microbial Growth: An increase in the # of cells in a population
-Generation/ Doubling time: time it takes a population to double
Principles of Prokaryotic Growth
-Growth is different in nature compared to the growth in a laboratory setting
Bacterial Growth in Nature
-Polysaccharide-encased communities of bacteria
-Very difficult to destroy
-Cooperative relationships exist
-Competitive relationships exist, as well
Interaction of Microbial Mixed Communities
Full transcript