Viruses and Viruses and BacteriaBacteria

VirusesVirusesLiving or Non-Living?

•Infectious particles of nucleic acid and proteins •Cannot “live” (reproduce) outside a host

History/Discovery 1883 Adolf Mayer sought cause of

Tobacco Mosaic Disease 1935- Wendell Stanley crystallized

the infectious particle—determined it was NONLIVING (can’t crystallize cells)

1st virus discovered-Tobacco Mosaic Virus (TMV)

Virus StructureVirus Structure Very small and simple (smaller than Very small and simple (smaller than

a ribosome ~20nm in diameter)a ribosome ~20nm in diameter) Made of DNA or RNA surrounded by a Made of DNA or RNA surrounded by a

protein coat (capsid) protein coat (capsid)

Characteristics Host specific—identify host cells by Host specific—identify host cells by

“lock and key” fit between proteins “lock and key” fit between proteins on virus and host cell receptorson virus and host cell receptors

*Presumed that receptors first *Presumed that receptors first evolved because they carried out evolved because they carried out some functions that benefited the some functions that benefited the organismorganism

Naming Viruses International Committee on

Taxonomy of Viruses names them based on three characteristics: Type of nucleic acid (DNA or RNA) Is the nucleic acid double or single

stranded Presence or absence of nuclear

envelope

Viral InfectionViral InfectionLytic Infection-Lytic Infection- virus enters the cell, virus enters the cell,

makes copies of itself, and causes makes copies of itself, and causes the cell to burstthe cell to burst

Lysogenic Infection-Lysogenic Infection- virus integrates it virus integrates it DNA into the DNA of the host. Viral DNA into the DNA of the host. Viral DNA replicates with host DNADNA replicates with host DNA

Viral Reproduction Steps of Lytic Cycle

Attachment Entry Replication Assembly Lysis/Release (lyses the cell)

RetrovirusesRetroviruses Contain RNA instead of DNA Contain RNA instead of DNA Copy their RNA into DNA instead of Copy their RNA into DNA instead of

DNA to RNADNA to RNA

Examples: AIDS, some cancersExamples: AIDS, some cancers

BacteriaBacteria

Most numerous and widespread Most numerous and widespread organismsorganisms

““Discovered” with the invention of Discovered” with the invention of the microscope by Robert Hooke and the microscope by Robert Hooke and Anton van Leeuwenhoek (1676)Anton van Leeuwenhoek (1676)

ClassificationClassification Two kingdoms of Two kingdoms of Prokaryotes Prokaryotes

(Prokaryotes (Prokaryotes are organisms that lack are organisms that lack nuclei or membrane-bound organelles)nuclei or membrane-bound organelles)

Kingdom EubacteriaKingdom Eubacteria: “true bacteria” , : “true bacteria” , variety, 3 shapes, no phylavariety, 3 shapes, no phyla

Kingdom Archaebacteria: Kingdom Archaebacteria: “ancient”, “ancient”, lives in extreme environmentslives in extreme environments

ArchaebacteriaArchaebacteria Methanogens–live in large intestines of Methanogens–live in large intestines of

animals, decompose dead organisms, animals, decompose dead organisms, produce methane gas (CHproduce methane gas (CH44))

Halophiles--live in salty environmentsHalophiles--live in salty environments Thermoacidophiles—live in hot, acidic Thermoacidophiles—live in hot, acidic

environmentsenvironments

Size and StructureSize and Structure

1-5 micrometers (much smaller than eukaryotic 1-5 micrometers (much smaller than eukaryotic cells– 10-100 micrometers)cells– 10-100 micrometers)

Unicellular (although grow in colonies)Unicellular (although grow in colonies) Prokaryotic- no nucleus, no membrane-bound Prokaryotic- no nucleus, no membrane-bound

organellesorganelles * CAN IDENTIFY BACTERIA BASED ON:* CAN IDENTIFY BACTERIA BASED ON:

Shape, Cell Wall, and MovementShape, Cell Wall, and Movement

Method of Obtaining Energy Most are heterotrophic (mostly

decomposers) Some are autotrophic—chemotrophs

and photoautotrophs

Ex: cyanobacteria

ShapeShape Coccus (spherical)*Coccus (spherical)* Bacillus (rod-shaped)*Bacillus (rod-shaped)* Spirillum (spiral-shaped)*Spirillum (spiral-shaped)* *Arranged in chains, groups, or pairs*Arranged in chains, groups, or pairs

Pair– Diplo-Pair– Diplo- Chains– Strepto-Chains– Strepto- Groups– Staphylo—Groups– Staphylo— **Example: Spherical shaped bacteria arranged in **Example: Spherical shaped bacteria arranged in

chains would be named, “Streptococcus”chains would be named, “Streptococcus”

Cell Wall For Eubacteria only!

Gram negative- thin cell wall consisting of a few layers of peptidoglycan

Gram positive- thick cell wall consisting of many layers of peptidoglycan

Typical Bacterial CellTypical Bacterial Cell Cell wallCell wall Cell membranesCell membranes DNA (floating freely)-circular DNA (floating freely)-circular

chromosomechromosome RibosomesRibosomes Some can move (flagella, others glide)Some can move (flagella, others glide)

ReproductionReproduction

Most bacteria reproduce by Most bacteria reproduce by Binary FissionBinary Fission Produces 2 identical “daughter” cellsProduces 2 identical “daughter” cells Can grow and divide every 20 minutesCan grow and divide every 20 minutes Asexual (no exchange or recombination of genetic Asexual (no exchange or recombination of genetic

information)information)

Image of E. coli going through Binary fission

Ways bacteria can accomplish genetic recombination

(variation) Conjugation- exchange of genes from 1 bacterial cell

to another

Transformation-bacteria take up pieces of free DNA from another bacterial cell

Transduction- bacteriophage transfer portions of bacterial DNA from one cell to another.

E.coli undergoing conjugation

““BAD” BacteriaBAD” Bacteria Food Spoilage—Food Spoilage—smells, makes you sicksmells, makes you sick Bacterial DiseasesBacterial Diseases

Only 3% of all bacteria cause human diseasesOnly 3% of all bacteria cause human diseases Can be treated with antibiotics and prevented Can be treated with antibiotics and prevented

through vaccinationthrough vaccination 11stst antibiotic discovered/source antibiotic discovered/source Examples: pneumonia, bubonic plague, Strep. Examples: pneumonia, bubonic plague, Strep.

Throat, Syphilis, gonorrhea, anthrax, botulismThroat, Syphilis, gonorrhea, anthrax, botulism

E. coli

““GOOD” Bacteria: The GOOD” Bacteria: The Importance of BacteriaImportance of Bacteria

DecomposersDecomposers Help ecosystem recycle nutrientsHelp ecosystem recycle nutrients Breakdown complex compounds into Breakdown complex compounds into

usable materialsusable materials Nitrogen fixersNitrogen fixers

Bacteria perform nitrogen fixationBacteria perform nitrogen fixation

Importance of Bacteria Importance of Bacteria (Cont.)(Cont.)

Human UsesHuman Uses Production of food and beveragesProduction of food and beverages Medicine and chemical industryMedicine and chemical industry Genetic engineeringGenetic engineering Bioremediation: Cleaning up the Bioremediation: Cleaning up the

environmentenvironment