Prokaryotic Cells - Before the nut
Dr. David E. Fulford, Ph.D.
Professor
Department of Biology and Health Services
Edinboro University of Pennsylvania
Edinboro, PA 16444
Prokaryotes vs. Eukaryotes
| Characteristic | Prokaryotes | Eukaryotes |
| Nucleus | nucleus absent | present w/envelope |
| Organelles | absent | present various types |
| DNA Structure | single closed loop naked w/ no protein | multiple chromosomes DNA ass/w/proteins |
| Chlorophyll | when present is in dissolved in cytoplasm | when present is in chloroplasts |
| Ribosomes |
|
|
| Cell walls | generally present chemically complex | may/may not be present chemically simple |
| Reproduction | binary fission | mitosis |
| typical prokaryotic cell | typical eukaryotic cell |
Characteristics of Living Organisms
All living organisms:
have complex structures - the cell
perceive and interact with their environment
grow and develop
reproduce
acquire and utilize energy
The Cell Theory
The cell is the basic unit of life
All living organisms are made up cells
All cells arise from pre-existing cells
The Central Dogma of Biology
DNA
RNA
Protein
Anatomy of Bacteria
bacillus ( bacilli) - rod shaped bacteria; may occur singly or in chains (streptobacilli)
coccus (cocci) - spherical bacteria; may occur singly, in pairs (diplococci) or in chains (streptococci). some grow in packets or cube like structures (sarcina) and others in grape like clusters (staphylococci)
vibrio - are curved rods
spirillum (spirilla) - are spiral shaped bacteria. These organisms have flagella external to their cell.
spirochete - are spiral shaped bacteria. These organisms have flagella that run the length of the cell inside the cell wall (endoflagella)
Flagella
long, rigid strands of flagellin
are a means of locomotion are anchored in the cell wall of the bacteria by a series of rings.
The inner ring rotates and turns the flagella and the outer ring remains still.
The flagella spins and acts like a propeller
they are only 0.2 mm in diameter and are too small to see unstained
there are different numbers and arrangements of flagella:
monotrichous - single flagella
lophotrichous - 2 or more flagella in bunches
amphitrichous - groups of flagella at both ends of the cell
peritrichous - the bacteria is covered in flagella the
flagella must be stained to be seen
Chemotaxis
the directed movement toward or away from source of a particular chemical along a gradient
when receptors on the surface of the bacteria bind to the chemical, the flagella begins to spin and cause the bacteria to move.
this is referred to as a run.
at intervals the flagella reverses the spin and cause the bacteria to tumble and change direction
when a bacteria is attracted to a compound, the runs are longer and the tumbles are less frequent.
when a bacteria is repelled by a compound, the runs are shorter and the tumbles are more frequent
Pili
are appendages that are similar to flagella, but are not involved in locomotion.
their main function is to anchor the bacteria to living tissue and as such are considered to be virulence factors.
Pili may also function in genetic recombination (sex pili). Click here
fimbrae is another term used for pili that are only involved in attachment
Bacterial Surfaces
Glycocalyx is the outer coating of molecules that surround the bacteria - capsules and slime layers
Capsule - a layer of usually polysaccharide and some small protein that is found external to the cell wall. the capsule is a buffer between the external environment and the cell wall the capsule may have anti-phagocytic properties the capsule
may enhance the attachment of the bacterial cells to objects
The Bacterial Cell Wall
the outer barrier of the cell that protects the cell membrane
there are several different types of bacterial cell walls. The three most common are:
Gram positive
Gram negative
Acid-fast
Components of Bacterial Cell Walls
peptidoglycan is made up of N-acetylglucosamine and N-acetylmuramic acid which are joined together by side chains of 4 or so amino acids. A bacterial cell usually has several layers of peptidoglycan which makes this a very large molecule.
It is assembled outside of the cell membrane.
The Bacterial Cell Wall
teichoic acid is a polysaccharide that is found in Gram-positive organisms, but not in Gram-negative.
Gram-positive organism have a thick cell wall (20-80 nm) made up primarily of peptidoglycan with about 10% teichoic acid.
It is a polymer of glycerol or ribitol joined by phosphate groups.
Amino acids are linked to the teichoic acid and the molecule is attached to the muramic acid in the peptidoglycan
Gram Positive Cell Wall - click here
Gram Negative Cell Wall - click here
Gram-negative organisms have a much thinner cell wall (3-11nm) made up of peptidoglycan and no teichoic acid.
This wall is surrounded by an outer membrane. The space between the outer membrane and the cell wall is referred to as the periplasmic space.
Gram-negative cell walls contain lipopolysaccharide
The Bacterial Cell Wall
cell walls hold the bacterial cell together.
without the cell wall the bacteria would lyse
lysozyme breaks down the cell wall by attacking the linkages between carbohydrates in the peptidoglycan penicillin prevents the construction of cell walls by preventing the cross linking of molecules of peptidoglycan
bacteria such as Mycoplasma lack a cell wall
bacteria such as Mycobacterium and Nocardia have cell walls with substances called mycolic acids which make the cell walls waxy and difficult to stain.
These organisms are acid-fast.
when bacteria loose their cell wall they become L forms or L-variants
Acid-fast Cell Wall - click here
The Bacterial Cell Membrane
Cell membrane - the plasma membrane: the boundary of the cell.
It is the outer limit of the cytoplasm (5-10 nm) aids in the transport of molecules into and out of the cell is a lipid bilayer made up of phospholipids and proteins.
The proteins move around in the phospholipids (the Fluid Mosaic model) (30-40% phospholipids; 60-70% proteins)
detergents dissolve the membrane as well as organism solvents such as ethyl alcohol.
Polymixin antibiotics function by breaking down membranes.
mesosomes are inwardly protruding portions of cell membrane
The Bacterial Cytoplasm
the cytoplasm - the cellular "stuff": is a mass of proteins, carbohydrates, lipids, nucleic acids, salts and inorganic ions.
ribosomes are found in the cytoplasm. they is made up of RNA and protein and function in protein synthesis
inclusion bodies - storage globules found in the cytoplasm. They often are polyphosphates
magnetosomes - magnetic structures in the cytoplasm that help some bacteria orient themselves in a magnetic field.
the chromosome - the DNA in a closed loop.
the region of the cytoplasm where the DNA is referred to as the nucleoid.
plasmids - extrachromosomal DNA (R or resistance factors)
Bacterial Spores - click here
spores (endosprores) are highly resistant structures that protect the cell during adverse conditions.
the spore basically is a small bit of cytoplasm with a copy of the cell's DNA covered by a thick wall of peptidoglycan
the spore is relatively inert and undergoes little biochemical activity.
the spore is stabilized by a protein called dipicolinic acid. spore formation is not a type of reproduction.
spores are resistant to heat - boiling for hours
then can survive in 70% ETOH for years
are highly resistant to radiation
are very resistant to drying
there are several clinically important spore forming bacteria - C. perfringens, C. botulinum, B. anthracis
Other Types of Bacteria
Rickettsiae,Chlamydia, and Mycoplasma:
all are considered to be small bacteria
all rely on living organisms
many cause serious disease RMSF, typhus, pneumonia
Cyanobacteria:
photosynthetic - may form filaments (phycocyanin)
are aquatic found in both freshwater and marine environments
may be important in water quality - algal blooms
Click here - algal bloom
Green and Purple Sulfur Bacteria:
are photosynthetic - different pigments than the
cyanobacteria (bacteriochlorophyll)
live in freshwater where anaerobic conditions develop
use hydrogen sulfide and sulfur in their metabolism and
lead to the depositing of sulfur or sulfite granules in
their cytoplasm
Gliding and Fruiting Bacteria:
the members of this group are Gram-negative bacteria
that lack flagella and glide over moist surfaces
these organisms can come together to form fruiting
bodies - slime bacteria (myxobacteria)
Appendaged Bacteria:
these bacteria produce structures that attach the
bacteria to structures
these bacteria reproduce by budding
the new bacteria swim away
Archaebacteria:
these bacteria live in extreme environments
methanogens convert carbon dioxide and hydrogen
into methane gas
some are extreme halophiles
some are extreme thermophiles
