Transcript Prokarya--They*re Everywhere!

VIRUSES AND OTHER NONCELLULAR INFECTIOUS
AGENTS
– Viruses exhibit some, but not all, characteristics of
living organisms. Viruses:
• Possess genetic material in the form of nucleic acids
• Are not cellular and cannot reproduce on their own.
Membranous
envelope
Protein spike
RNA
Protein coat
Figure 10.28
– Prions are responsible for neurodegenerative
diseases including:
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Mad cow disease
Scrapie in sheep and goats
Chronic wasting disease in deer and elk
Creutzfeldt-Jakob disease in humans
Figure 10.34
– Avian flu:
• Infects birds
• Infected 18 people in 1997
• Since has spread to Europe and Africa infecting 300 people
and killing 200 of them
Figure 10.35
Prokarya--They’re Everywhere!
– Prokaryotes
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Are found wherever there is life
Far outnumber eukaryotes
Can cause disease
Can be beneficial
– Compared to eukaryotes, prokaryotes are
• Much more abundant
• Typically much smaller
– Prokaryotic cells
• Lack true nuclei
• Lack other membrane-enclosed organelles
• Have cell walls exterior to their plasma membranes
– Prokaryotes come in several shapes:
• Spherical (coccus)
• Rod-shaped (bacillus)
• Spiral (spirillum)
Figure 15.7
Colorized SEM
Plasma membrane
(encloses cytoplasm)
Cell wall (provides
Rigidity)
Capsule (sticky
coating)
Colorized TEM
Prokaryotic
flagellum
(for propulsion)
Ribosomes
(synthesize
proteins)
Nucleoid
(contains DNA)
Pili (attachment structures)
Figure 4.4
SHAPES OF PROKARYOTIC CELLS
Colorized TEM
Spiral
Colorized SEM
Rod-shaped (bacilli)
Colorized SEM
Spherical (cocci)
Figure 15.8
Procaryotic Reproduction
– Most prokaryotes can reproduce by binary fission and at
very high rates if conditions are favorable.
– Some prokaryotes
• Form endospores, thick-coated, protective cells that are
produced within the cells when they are exposed to unfavorable
conditions
• Can survive very harsh conditions for extended periods, even
centuries
The Two Main Branches of Prokaryotic Evolution:
Bacteria and Archaea
– By comparing diverse prokaryotes at the molecular
level, biologists have identified two major branches
of prokaryotic evolution:
• Bacteria
• Archaea (more closely related to eukaryotes)
© 2010 Pearson Education, Inc.
– Some archaea are “extremophiles.”
• Halophiles thrive in salty environments.
• Thermophiles inhabit very hot water.
• Methanogens inhabit the bottoms of lakes and swamps
and aid digestion in cattle and deer.
(a) Salt-loving archaea
(b) Heat-loving archaea
Figure 15.13
– Lyme disease is
• Caused by bacteria carried by ticks
• Treated with antibiotics, if detected early
SEM
Tick that carries the
Lyme disease bacterium
“Bull’s-eye” rash
Spirochete that causes
Lyme disease
Figure 15.15
Bioterrorism
– Humans have a long and ugly history of using
organisms as weapons.
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During the Middle Ages, armies hurled the bodies of
plague victims into enemy ranks.
Early conquerors, settlers, and warring armies in South
and North America gave native peoples items purposely
contaminated with infectious bacteria.
In 1984, members of a cult in Oregon contaminated
restaurant salad bars with Salmonella bacteria.
In the fall of 2001, five Americans died from the disease
anthrax in a presumed terrorist attack.
Figure 15.16
PROTISTS
– Protists
• Are eukaryotic
• Evolved from prokaryotic ancestors
• Are ancestral to all other eukaryotes, which are
– Plants
– Fungi
– Animals
Photosynthetic
prokaryote
(Some cells)
Endosymbiosis
Aerobic
heterotrophic
prokaryote
Chloroplast
Mitochondrion
Photosynthetic
eukaryotic cell
(b) Origin of mitochondria and chloroplasts
Figure 15.20b
– The classification of protists remains a work in progress.
– The four major categories of protists, grouped by
lifestyle, are
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Protozoans
Slime molds
Unicellular algae
Seaweeds
Protozoans
– Protists that live primarily by ingesting food are called
protozoans.
– Protozoans with flagella are called flagellates and are
typically free-living, but sometimes are nasty parasites.
Colorized SEM
A flagellate: Giardia
Figure 15.21a
Colorized SEM
Another flagellate: trypanosomes
Figure 15.21b
– Amoebas are characterized by
• Great flexibility in their body shape
• The absence of permanent organelles for locomotion
– Most species move and feed by means of pseudopodia
(singular, pseudopodium), temporary extensions of the
cell.
LM
An amoeba
Figure 15.21c
LM
A foram
Figure 15.21d
– Apicomplexans are
• Named for a structure at their apex (tip) that is specialized
for penetrating host cells and tissues
• All parasitic, such as Plasmodium, which causes malaria
– Ciliates
• Are mostly free-living (nonparasitic), such as the
freshwater ciliate Paramecium
• Use structures called cilia to move and feed
LM
A ciliate
Figure 15.21f
LM
Colorized SEM
A flagellate: Giardia
An amoeba
Another flagellate: trypanosomes
Cilia
An apicomplexan
LM
Red
blood
cell
Oral
groove
TEM
LM
Apical complex
A foram
Pseudopodium
of amoeba
Colorized SEM
Food being
ingested
A ciliate
Figure 15.21
Slime Molds
– Slime molds resemble fungi in appearance and
lifestyle, but the similarities are due to convergence,
and slime molds are not at all closely related to
fungi.
– Plasmodial slime molds
• Can be large
• Are decomposers on forest floors
• Are named for the feeding stage in their life cycle, an
amoeboid mass called a plasmodium
Figure 15.22
– Cellular slime molds have an interesting and
complex life cycle that changes between a
• Feeding stage of solitary amoeboid cells
• Sluglike colony that moves and functions as a single unit
• Stalklike reproductive structure
LM
Slug-like colony
Amoeboid
cells
Reproductive
structure
Figure 15.23
Unicellular and Colonial Algae
– Algae are
• Photosynthetic protists
• Found in plankton, the communities of mostly microscopic
organisms that drift or swim weakly in aquatic environments
– Unicellular algae include
• Diatoms, which have glassy cell walls containing silica
• Dinoflagellates, with two beating flagella and external
plates made of cellulose
SEM
(a) A dinoflagellate, with its wall of protective plates
Figure 15.24a
LM
(b) A sample of diverse diatoms, which have glossy walls
Figure 15.24b
– Green algae are
• Unicellular
• Sometimes flagellated, such as Chlamydomonas
• Colonial, sometimes forming a hollow ball of flagellated
cells, as seen in Volvox
Colorized SEM
(c) Chlamydomonas, a unicellular green alga with a pair of flagella
Figure 15.24c
LM
(d) Volvox, a colonial green alga
Figure 15.24d
Seaweeds
– Seaweeds
• Are large, multicellular marine algae
• Grow on or near rocky shores
• Are often edible
– Seaweeds are classified into three different groups,
based partly on the types of pigments present in their
chloroplasts:
• Green algae
• Red algae
• Brown algae (including kelp)
Green algae
Red algae
Brown algae
Figure 15.25