Transcript Prokaryotes, Viruses, and Protistans

Prokaryotes, Viruses, and
Protistans
Chapter 20
Microorganisms
• Single-celled organisms that are too
small to be seen without a microscope
• Bacteria are the smallest living
organisms
• Viruses are smaller but are not alive
The Prokaryotes
• Only two groups
• Archaebacteria and Eubacteria
• Arose before the eukaryotes
Prokaryotic Characteristics
• No membrane-bound nucleus
• Single chromosome
• Cell wall in most species
• Prokaryotic fission
• Metabolic diversity
Prokaryotic Body Plan
pilus
bacterial
flagellum
DNA
plasma
capsule
cell wall membrane
ribosomes
in
cytoplasm
Bacterial Shapes
coccus
bacillus
spirillum
Archaebacteria
Methanogens
Extreme halophiles
Extreme thermophiles
Eubacteria
• Includes most familiar bacteria
• Have fatty acids in plasma membrane
• Most have cell wall; always includes
peptidoglycan
• Classification based largely on
metabolism
Bacterial Genes
• Bacteria have a single chromosome
– Circular molecule of DNA
• Many bacteria also have plasmids
– Self-replicating circle of DNA that has a
few genes
– Can be passed from one cell to
another
Prokaryotic Fission
nicked plasmid
in donor cell
Conjugation
conjugation tube
to recipient cell
Virus
• Noncellular infectious agent
• Consists of protein wrapped
around a nucleic acid core
• Cannot reproduce itself; can
only be reproduced using a host
cell
Viral Body Plans
• Genetic material is
DNA or RNA
• Coat is protein
Helical virus
Polyhedral virus
Complex virus
(bacteriophage)
Enveloped Virus (HIV)
lipid envelope; proteins span
the envelope, line its inner
surface, spike out above it
viral coat
(proteins)
Viral Multiplication - Basic Steps
• Virus attaches to host cell
• Whole virus or genetic material enters host
• Viral DNA or RNA directs host to make viral
genetic material and protein
• Viral nucleic acids and proteins are
assembled
• New viral particles are released from cell
Lytic Pathway
Lysis
Assembly
Assembly
Virus injects
genetic material
Production of
viral components
Lysogenic
Pathway
Stimulus may cause cell
to enter lytic pathway
Latent period
extends the
cycle
Viral DNA
becomes
part of host
chromosome
for a time
Viral material
integrated
Viral material
passed on
Replication
of an
Enveloped
Virus
Transcription
of viral genes
DNA replication
Assembly
Translation
Proteins
Viroids
• Smaller than viruses
• Strands or circles of RNA
• No protein-coding genes
• No protein coat
• Cause many plant diseases
Prions
• Small proteins
• Linked to human diseases
– Kuru
– Creutzfeldt-Jakob disease (CJD)
• Animal diseases
– Scrapie in sheep
– Bovine spongiform encephalopathy
(mad cow disease)
Protistans Differ
from Prokaryotes
• Have a nucleus and organelles
• Have proteins associated with DNA
• Use microtubules in a cytoskeleton,
spindle apparatus, and cilia and
flagella
• May contain chloroplasts
• May divide by mitosis and meiosis
Sporozoans
• Parasitic
• Complete part of the life cycle inside
specific cells of a host organism
• Many have elaborate life cycles that
require different hosts
• Many cause serious human disease
Cryptosporidium
(Giardia)
• Motile infective stage (sporozoite)
invades intestinal epithelium
• Causes cramps, watery diarrhea
• Commonly transmitted by water
contaminated with cysts
Toxoplasma
• Cysts may be ingested with raw or
undercooked meat
• Exposure to cysts from cat feces
• Symptoms are usually mild in people
with normal immune function
• Infection during pregnancy can kill or
damage the embryo
Malaria
• Symptoms have been known for more than
2,000 years
• Most prevalent in tropical and subtropical
parts of Africa
• Kills a million Africans each year
• Caused by four species of Plasmodium
• Transmitted by Anopheles mosquitoes
Plasmodium Life Cycle
sporozites
sporozites
Gametes form
in mosquito gut,
combine to form
zygotes
merozoite
Male and female
gametocytes
in blood
Offspring enter
blood, cause
malarial
symptoms