Transcript A View of Life - Websupport1

Lecture 2: Chapter 21
Viruses, Bacteria, and Archaea
Professor: Dr. Barjis
Room:
P313
Phone:
(718)2605285
Email:
[email protected]
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Alberts, Bray,
Sylvia S Mader
Hopkins,
Johnson
General Biology
Outline
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Viruses
– Structure
– Classification
– Reproduction
Prokaryotes
– Structure
– Reproduction
– Nutrition
Bacteria
Archaea
The Viruses
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Virus (poison) is chemical complexes of
RNA or DNA protected by protein.
They are noncellular and thus cannot be
classified with cellular organisms.
The Viruses
The Viruses
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Each type of virus has at least two parts.
– Capsid: Outer layer composed of protein
subunits.
– Nucleic acid core: the inner most portion
is made of DNA or RNA.
The Viruses
Viral Reproduction
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Viruses gain entry into host because
portions of capsid adhere to a specific
receptor on the host cell’s outer surface.
– Viral nucleic acid enters the cell and once
inside, the nucleic acid codes for the
protein units inside the capsid.
 Virus takes over metabolic machinery of
the host cell.
Lytic Cycle
Viral Infections
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Viruses are best known for causing infectious
diseases in plants and animals.
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Herpes, HIV, cancer (carrying oncogenes)
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Viruses lack enzymes; thus, antibiotics have
no effect.
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Retrovirus: may cause cancer or AIDS,
The Prokaryotes
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The prokaryotes include bacteria and
archaea, which are fully functioning cells.
They contain a single circular DNA
molecule as the genetic material.
Prokaryote Structure
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Lack a eukaryotic nucleus.
Have outer cell wall containing
peptidoglycan.
Lack membranous organelles.
Contain nucleoid.
May have accessory ring of DNA
(plasmid).
Move by flagella
Reproduction in Prokaryotes
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Prokaryotes reproduce asexually by means
of binary fission.
Variation in a strain of bacteria mainly
occurs from mutations, which are rapidly
replicated and selected in a haploid
Binary Fission
Reproduction in Prokaryotes
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Transformation occurs when bacterium
picks up free pieces of DNA from other
prokaryotes.
Transduction occurs when bacteriophages
carry portions of bacterial DNA from one cell
to another.
When faced with unfavorable conditions,
some bacteria form endospores.
Prokaryotic Nutrition
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Anaerobes -grow in the presence of oxygen.
Facultative anaerobes - grow in either the
presence or absence of oxygen.
Aerobics - grow only in the presence of
oxygen
Autotrophic Prokaryotes
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Photoautotrophs - use solar energy to
reduce carbon dioxide to organic
compounds.
Chemoautotrophs - oxidize inorganic
compounds to obtain the necessary energy
to reduce O2 to an organic compound.
Heterotrophic Prokaryotes
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Most prokaryotes are chemotrophs that take
in organic nutrients.
Chemotrophs – take in organic nutrients
The Bacteria
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Groups of bacteria are commonly
differentiated from one another using the
Gram stain procedure.
– Gram-positive bacteria retain dye and
appear purple.
– Gram-negative bacteria do not retain dye
and appear pink.
The Bacteria
Bacteria can be classified based on their
shape:
– Spiral (spirilli), Rod (bacilli), and Round
(cocci).
Cyanobacteria
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Cyanobacteria are Gram-negative bacteria
that photosynthesize.
Believed to be responsible for introducing
oxygen into the primitive atmosphere.
Cyanobacteria
Archaea Structure and Function
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Their plasma membranes contain unusual
lipids that allow them to function at high
temperatures.
Most are chemoautotrophs.
They are not photosynthetic.
Types of Archaea
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Methanogens
– Found in anaerobic environments.
Halophiles
– Require high salt concentrations for
growth.
Thermoacidophiles
– Reduce sulfides and survive best at
temperatures above 80oC.