Mader: Biology 8 th Ed. Viruses, Bacteria, and Archaea Chapter 21.

Mader: Biology 8th Ed.

Viruses, Bacteria, and Archaea

Chapter 21


Outline• Viruses

– Structure– Classification– Reproduction

• Prokaryotes– Structure– Reproduction– Nutrition

• Bacteria• Archaea


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.


The Viruses


The Viruses

• Classification is based on:– Type of nucleic acid.– Size and shape.– Presence / absence of outer envelope.


The Viruses


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.


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.


Lytic Cycle

• Lytic cycle may be divided into five stages:– Attachment– Penetration– Biosynthesis– Maturation– Release


Lysogenic Cycle

• Phage becomes a prophage that is integrated into the host genome.– Becomes latent, and later may reenter the

lytic cycle.


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.

– RetrovirusesContain reverse transcriptase which

carries out RNA cDNA transcription.


Reproduction of HIV-1


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


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 1-10µm in length

and .7-1.5µm in width.


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).


Flagella


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.


Binary Fission


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.


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.


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 O2 to an organic compound.

– Chemosynthetic


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


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.


The Bacteria

• Bacteria can also be classified in terms of their three basic shapes.– Spiral (spirilli), Rod (bacilli), and Round

(cocci).


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.


Cyanobacteria


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.


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.


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.


Review• Viruses

– Structure– Classification– Reproduction

• Prokaryotes– Structure– Reproduction– Nutrition

• Bacteria• Archaea

Mader: Biology 8 th Ed. Viruses, Bacteria, and Archaea Chapter 21.

Documents

Transcript of Mader: Biology 8 th Ed. Viruses, Bacteria, and Archaea Chapter 21.