VIRUSES AND PROCARYOTES
Viruses - (poisonous, noxious, venomous): non-cellular, infectious agents
Nucleic acid core and a
protective protein coat (capsid).
Very host specific (animal, plant, microorganisms), and in many higher host forms,
The nucleic acid, at least, must enter the host cell.
DNA viruses have a double strand, RNA (also called retroviruses) viruses have a
Varied morphology – regular polyhedron, rod or combination.
Generalized replication cycle:
1. Host recognition
2. Adhesion to host surface
3. Enter host cell
4. Take over host genetic function
5. Form new virus parts
6. Assemble new, intact viruses
7. Release from host cell
Cycle may be sequential and
repetitious (full lytic cycle) or it may be
interrupted at an
early stage (temporate cycle) leading to a latent, lysogenic state.
Bacteria - monerians,
2 subgroups: eubacteria and archeabacteria
metabolically very diverse
1. chemotrophs – chemical energy source
2. autotrophs – non-organic chemical energy source
3. heterotrophs – organic chemical energy source
4. phototroph – light as energy source
5. aerobes – require molecular oxygen
6. anaerobes – do not require molecular oxygen
7. thermophiles – heat loving
8. psychrophiles – cold loving
9. halophiles – salt loving
10. acidophiles – acid loving
structure - nuclear area, cytoplasm, ribosomes, cell
membrane, cell wall, and if
motile, by flagella.
Morphology - rods (bacilli), spheres (cocci), and curved or spiral (vibrios and spirilla)
Reproduction - binary fission:
simple duplication of the DNA and subdivision of the cell;
some bacteria possess an extra bit of DNA called a plasmid which is very small and
independent of the chromosome; often carries specialized genes, such as antibiotic resistance.
- vast array of infectious diseases caused by bacteria; most are treatable
with antibiotics; recent cause for concern about effectiveness of antibiotics.
Photosynthetic monerans - cyanobacteria (blue-green algae)
In the 1970s and 1980s scientists discovered that some bacteria had rRNA quite different from other bacteria.
This group comprised a distinct category of bacteria, found also to have other differences:
Cell wall composition
Different membrane composition
Proteins associated with the DNA
Thus, this group of bacteria was more related to eukaryotes and it was suggested that the group should comprise a distinct kingdom.