1. Viruses – composed of nucleic acids enclosed in a protein coat; incredibly small!
a. Non-living – no growth and development!
b. Replicates inside a Host Cell (cell in which a virus replicates)
c. Typically identified by disease they cause followed by genus name “virus”
d. Viruses that infect bacterium are bacteriophages
2. Viral Structure
a. Nucleic Acid – either DNA or RNA; codes for proteins!!
b. Capsid – outer protein coat surrounding nucleic acid; protects genetic material
c. Envelope – larger viruses; envelope consists of lipids, carbs, and proteins!!
d. Tail/Tail Fibers – binding to receptor fibers in the cell
3. Viral Replication Cycles
a. Lysogenic Cycle – replication cycle in which the virus’s nucleic acid is integrated into the
host cell’s chromosome
i. Attachment and Entry
1. Attachment to host cells is SPECIFIC as a result of proteins in the
envelope/capsid of the virus – they bind to specific receptors on the
outside of the host [think LOCK (host cell) and KEY (viral protein)]
2. After attachment, virus inserts genetic material into host (receptor
mediated endocytosis or membrane fusion)
a. Uncoating: removal of the viral capsid (typically by viral or host
enzymes or simple degradation); exposure of viral “DNA”
ii. Provirus Formation
1. Viral “DNA” incorporates itself into DNA of host cell (via crossing over),
resulting in a “provirus”
2. Lysogeny – dormant provirus as a result of a repressor protein made by
the virus itself; protein not allosteric and must be destroyed!
iii. Replication
1. Although the provirus is inactive, it reproduces as a part of the host
cell’s genetic material
b. Lytic Cycle – replication cycle in which a virus takes over a host cell’s genetic material
and uses the host cell’s structures and energy to replicate until the host cell bursts.
i. Attachment and Entry (see lysogenic cycle)
ii. Replication – the host’s metabolic machinery makes viral nucleic acid and
proteins
iii. Assembly – viral N.A. and proteins are “put together” to form new viruses
iv. Lysis – the host cell breaks open and releases new virus particles
4. RNA Viruses
a. Most complex RNA virus = retrovirus: type of viral replication where a virus uses reverse
transcriptase to make DNA from viral RNA
i. Attachment and Entry of RNA and reverse transcriptase (enzyme that produces
double stranded DNA from viral RNA)
ii. Viral DNA binds to host chromosome and creates viral mRNA, which creates
new viruses that are released into the extracellular space
5. Other Virus-Like Particles
a. Prions – composed of proteins but have no nucleic acid to carry genetic information;
harm caused by incorrect folding of proteins (ex. Mad Cow Disease)
b. Viroids – composed of single, circular strand of RNA with no protein coat
Bacteria!
1. Archaebacteria – prokaryotes that live in extreme, typically oxygen-free environments
2. Eubacteria
a. Heterotrophic prokaryotes
i. Vary in nutritional needs
ii. Live almost everywhere
iii. Use organic molecules as food source
b. Photosynthetic autotrophs
c. Chemosynthetic autotrophs
3. Bacterial Structure
a. Capsule – gelatinous outer covering
b. Cell wall – provides structure and protection
c. Plasma membrane – SPM
d. Pilus – hairlike extension of the PM; also acts as a bridge between bacterium
e. Flagellum – long, whiplike protrusion; used for movement
f. Plasmid – small, circular chromosome containing a small amount of genes
g. Chromosome – not enclosed in a nucleus; majority of genetic information
4. Bacterial Shape and Identification
a. Spheres – coccus
b. Rods – bacillus
c. Sprials – spirillum
d. Gram Stain – positive = purple; negative = pink
5. Bacterial Reproduction
a. Binary Fission - Asexual reproduction in which a bacterium will copy its chromosome,
attach to the PM while the cell grows, migrate to opposite ends of the cell, and divide
with the formation of a partition
i. Creates two, genetically identical cells!
ii. Can occur every 20 minutes!
b. Conjugation – sexual reproduction in which one bacterium transfers its genetic
information to a new bacterium that can then undergo binary fission
6. Bacterial Adaptations
a. Metabolism
i. Obligate Aerobes – require oxygen for respiration
ii. Obligate anaerobes – killed by oxygen
b. Survival Mechanisms
i. Endospore: small structure that contains a bacterium’s DNA and a small amount
of cytoplasm
1. Resists drying out, extremes in temperature, and harsh chemicals
2. As an endospore, bacterial cell does not reproduce
3. Once environmental conditions change, will germinate to create a cell
that will reproduce!
7. Importance of Bacteria
a. Nitrogen fixation
b. Recycling of Nutrients
c. Food
d. Medicine
e. Disease