Viruses, Bacteria, and Archae
Viruses and Viroids
 Viruses consist of nucleic acid and protein coat. Its smaller than any
cell and has NO metabolic machinery of its own.
 Viruses are about 25-300 nanometers, only visible with electron
microscope
 Its genetic material may be RNA or DNA, single stranded or double
stranded
 Capsid consists of repeating protein subunits and may be helical or
polyhedral.
 The protein coat binds to the host cells membrane proteins and may
contain more than one viral enzyme
ANIMATION
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 Viruses attack more than animals
→ Plant viruses often enter through a wound from pruning, an insect,
or injury.
-Many have helical structure
- Move through body and even enter seeds 
 Viroids are a version of a plant virus that works a little different
→They are circular, single stranded RNA, tiny about 400 nucleotides,
doesn’t code for proteins, replicated in plants nucleus by its RNA
polymerase
-effects crops such as tomatoes, potatoes, citrus, apples, ect.
 Bacterial viruses are called Bacteriophaes carries the genetic material,
other protein components pierce bacterial cell wall to inject their DNA
into cell
Animal viruses are often Polyhedral.
-Adneovruses have a 20 sided capside with distinctive protein spikes at each
corner.
-They are considered “Naked” or Nonenveloped and often cause the common
cold.
-Most animal viruses have an enveloped around the capside made from the host
cell in which they were assembled.
-Mostly from its plasma membrane but sometimes from its nuclear
membrane.
?? Do you see the problem??
- Viruses are everywhere-effecting every form of life.
- -Viral infections often reduce the hosts ability to survive and reproduce,
which effects many ecological interactions.
- -Some viruses aid humans by killing insect pests or bacteria that make us
ill.
- -Viruses can economic problems when they infect agriculturally significant
plants and animals
VIRAL REPLICATION
 Viruses have no motility, so infection begins with a chance meeting.
 During attachment viral protein bind to host receptor protein.
 Viral genetic material enters host, takes over its genetic material, stop it.
Normal function, begins replicating and expressing the viral genome.
 Viral proteins and nucleic acids come together to self assemble as new
virion
 new viruses either bud on the surface of the host cell or escape when it
lyses
BACTERIOPHAGE REPLICATION
– two types.
 Lytic Pathway
o viral genes expressed immediately.
o First viral components are produced and self assembled
o next, viral encoded enzymes break down hosts cell wall causing lyses
 Lysogenic Pathway
o viral DNA is integrated into host genome BUT not expressed.
o When hosts cell reproduces viral DNA is passed along also.
o Viral DNA awaits a signal to enter the lytic pathway.
ANIMATION
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HIV [animal viruses] Replication
 viral protein binds to two proteins on the surface of a WBC
 viral RNA and enzymes into the cell.
 Viral reverse transcriptase creates double stranded viral DNA.
 DNA becomes integrated into host cells genome.
 Transcription produces viral RNA.
 Some RNA is translated into viral proteins.
 viral RNA and proteins self assemble at hosts cell membrane and bud from
host own plasma membrane
ANIMATION
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HUMAN PATHOGENS.
 An infection occurs when one organism enters another and replicates
inside it.
 Viruses, bacteria, fungi, and protists cause human disease.
 Most spread by contact with mucus, blood, or other body fluid.
 Other infectious diseases require a VECTOR, and animal that carries the
pathogen from host to host [often biting insects]
 most viral diseases cause mild symptoms, like the common cold, others
effect our digestive system.
 The minority of viruses are more persistent, such as herpes,
mononucleosis, or chickenpox. The initial infection causes symptoms that
subside, the virus remains in the body to strike again later on.
 Vaccines are a way to protect against common viruses such as measles,
mumps, rubella, and chickenpox.
THE FLU
 RNA viruses mutate very quickly, reverse transcriptase makes frequent
replication errors.
 Each year, scientists create a new flu shot, however, the virus may
mutate to dress rendering the vaccination useless.
 Flu subtypes are named after the structure of two proteins at the viral
surface. The glycoprotein hemagglutinin (H), and a the enzyme
neuraminidase (N)
 two important flu species, H1N1 and H5N1 are responsible for swine flu
and bird flu
 if VIRAL REASSORTMENT were to occur, the consequences could be
deadly and we would have a true pandemic on our hands. (pg 329
picture)
PROKARYOTES.
 As you have two distinct lineages referred to as domains – bacteria and
Archae
 Bacteria – well-known and widespread live in our environment.
 Archae – less studied and living extreme habitats
 → bacteria have three main shapes.
o Bacilli – rod shaped cells.
o Cocci – spherical cells.
o Spirilla – spiral shaped cells
 bacteria and Archae secrete a cell wall, including peptidoglycan [bacteria
only],
 bacteria may also have a slime later or capsule around the cell wall.
 They contain a single chromosome of circular double-stranded DNA
attached to the inner cell membrane [1 species has a membrane around its
nucleoid]
 many have a flagella that do not contain microtubules.
 Many have a pili, hair-like filaments that help it stick to surfaces, some pili
extend and contract to be in movement
 bacteria and arcade reproduce by binary fission and can divide every 20
minutes
.
o http://www.cengage.com/biology/book_content/9781111425692_sta
rr_udl13e/animations/PowerPoint_Lectures/chapter20/videos_anima
tions/prokaryotic_fission.html
 Several methods of gene transfer exist.
o Horizontal gene transfer – an individual acquires genes from another
individual may be from different species.
o Conjugation – transfer of genes on a plasmid [small circle of DNA
separate from the chromosome] using a special sex pilus.
 http://www.cengage.com/biology/book_content/978111142569
2_starr_udl13e/animations/PowerPoint_Lectures/chapter20/vi
deos_animations/bacterial_conjugation.html
o Transduction – bacteriophages move genes between cells.
o Transformation – take up of DNA from the surrounding environment.
[Griffith experiment]
o
BACTERIAL DIVERSITY
 there are a huge number and variety of bacteria occupy every possible
niche of the environment.
 Some produce oxygen for the environment . [Cyanobacteria] Some help
with the cycling of matter through the environment. [Nitrogen fixing
bacteria]
 Proteobacteria-a diverse group of photoautotrophs which do not release
O2 into the environment, chemoautotrophs, and chemoheterotrophs
including Rhizobium and E. coli
PATHOGENIC PROTISTS
 Eukaryotic
 No cell wall, have pellicle layer and can form cysts (seed like dormant
phase)
 Complex life cycle with large haploid phase
 Giardia (don’t drink the water), Malaria (mosquitos), and Toxoplasmosis
(cat litter)