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Mader: Biology 8th Ed.
Viruses, Bacteria, and Archaea
Chapter 21
Mader: Biology 8th Ed.
Outline
• Viruses– Structure– Classification– Reproduction
• Prokaryotes– Structure– Reproduction– Nutrition
• Bacteria• Archaea
Mader: Biology 8th Ed.
The Viruses
• Viruses are noncellular and thus cannot be classified with cellular organisms.
• Generally smaller than 200 nm in diameter.
– Each type has at least two parts.
!Capsid: Outer layer composed of protein subunits.
!Nucleic acid core: DNA or RNA.
Mader: Biology 8th Ed.
The Viruses
Fig. 21.1baFig. 21.1bb
Mader: Biology 8th Ed.
The Viruses
• Classification is based on:
– Type of nucleic acid.
– Size and shape.
– Presence / absence of outer envelope.
Mader: Biology 8th Ed.
The Viruses
Fig. 21.1c Fig. 21.1d
Fig. 21.1p363ba
Mader: Biology 8th Ed.
Parasitic Nature
• Viruses are obligate inrtracellular parasites (cannot reproduce outside a living cell).
– Can infect a wide variety of cells, but are very specific.
!Bacteriophages - Infect bacterial cells.
Mader: Biology 8th Ed.
Viral Reproduction
• 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.
Mader: Biology 8th Ed.
Lytic Cycle
• Lytic cycle may be divided into five stages:
– Attachment
– Penetration
– Biosynthesis
– Maturation
– Release
Mader: Biology 8th Ed.
Virus Lytic Cycle
15
Fig. 21.3
Mader: Biology 8th Ed.
Lysogenic Cycle
• Phage becomes a prophage that is integrated into the host genome.
– Becomes latent, and later may reenter the lytic cycle.
Fig. 21.3a
Mader: Biology 8th Ed.
Reproduction of Animal Viruses
• After animal viruses enter the host cell, uncoating releases viral DNA or RNA and reproduction occurs.
– If viral release occurs by budding, the viral particle acquires a membranous envelope.
– Retroviruses
!Contain reverse transcriptase which carries out RNA " cDNA transcription.
Mader: Biology 8th Ed.
Reproduction of HIV-1
Mader: Biology 8th Ed.
Viral Infections
• Viruses are best known for causing infectious diseases in plants and animals.
– Herpes, HIV, cancer
! Viruses lack enzymes; thus, antibiotics have no effect.
– Many crop diseases have been attributed to viroids (naked strands of RNA).
– Some human and other animal diseases have been attributed to prions (protein molecules).
! Mad cow disease
TA p362
Mader: Biology 8th Ed.
The Prokaryotes
• The prokaryotes include bacteria and archaea, which are fully functioning cells.
– A single spoonful of earth can contain 1010 prokaryotes.
– Range in size from 1-10!m in length and .7-1.5!m in width.
TA p368
Fig. 21.5
Mader: Biology 8th Ed.
Prokaryote Structure
– Lack a eukaryotic nucleus.
– Have outer cell wall containing peptidoglycan.
– Some move by means of flagella.
– Lack membranous organelles.
– Contain nucleoid.
– May have accessory ring of DNA (plasmid).
Mader: Biology 8th Ed.
Flagella
Mader: Biology 8th Ed.
Bacterial Diversity
28
Mader: Biology 8th Ed.
Reproduction in Prokaryotes
• Prokaryotes reproduce asexually by means of binary fission.
– Conjugation occurs between bacteria when the donor cell passes DNA to recipient cell by way of sex pilus.
Mader: Biology 8th Ed.
Binary Fission
TA p369
Mader: Biology 8th Ed.
Reproduction in Prokaryotes
• 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.
Fig. 21.9
Mader: Biology 8th Ed.
Prokaryotic Nutrition
• Obligate anaerobes are unable to grow in the presence of free oxygen.
• Facultative anaerobes are able to grow in either the presence or absence of gaseous oxygen.
Mader: Biology 8th Ed.
Autotrophic Prokaryotes
• Photoautotrophs use solar energy to reduce carbon dioxide to organic compounds.
– Photosynthetic
• Chemoautotrophs oxidize inorganic compounds to obtain the necessary energy to reduce CO2 to an organic compound.
– Chemosynthetic
Mader: Biology 8th Ed.
Heterotrophic Prokaryotes
• Most prokaryotes are chemotrophs that take in organic nutrients.
– Aerobic saprotrophs decompose most large organic molecules to smaller molecules.
• May be free-living or symbiotic.
– Nitrogen fixation
– Commensalism
Mader: Biology 8th Ed.
The Bacteria
• 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.
Mader: Biology 8th Ed.
The Bacteria
• Bacteria can also be classified in terms of their three basic shapes.
– Spiral (spirilli), Rod (bacilli), and Round (cocci).
Mader: Biology 8th Ed.
Cyanobacteria
• Cyanobacteria are Gram-negative bacteria that photosynthesize.
– Believed to be responsible for introducing oxygen into the primitive atmosphere.
!Lack visible means of locomotion.
!Can live in extreme environments.
!In association with fungi, form lichens.
Mader: Biology 8th Ed.
Cyanobacteria
Fig. 21.12c
Mader: Biology 8th Ed.
The Archaea
• Archaea were considered bacteria until Carl Woese discovered their rRNA has a different sequence of bases than rRNA of bacteria.
– Eukarya are believed to be more closely related to archaea than to bacteria.
Mader: Biology 8th Ed.
Archaea Structure and Function
• Plasma membranes of archaea contain unusual lipids that allow them to function at high temperatures.
• Some are methanogenic.
• Most are chemoautotrophs.
– None are photosynthetic.
• Sometimes mutualistic or commensalistic, but none are parasitic.
Mader: Biology 8th Ed.
Types of Archaea
• Methanogens– Found in anaerobic environments.
!Produce methane from hydrogen gas and carbon dioxide.
• Halophiles– Require high salt concentrations for
growth.• Thermoacidophiles
– Reduce sulfides and survive best at temperatures above 80oC.
Mader: Biology 8th Ed.
Review
• Viruses– Structure– Classification– Reproduction
• Prokaryotes– Structure– Reproduction– Nutrition
• Bacteria• Archaea
Mader: Biology 8th Ed.
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