Viruses and Bacteria

Viruses Living 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 Structure Very small and simple (smaller than a ribosome ~20nm in diameter) Made of DNA or RNA surrounded by a protein coat (capsid)

Characteristics Host specific—identify host cells by “lock and key” fit between proteins on virus and host cell receptors *Presumed that receptors first evolved because they carried out some functions that benefited the organism

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 Infection Lytic Infection- virus enters the cell, makes copies of itself, and causes the cell to burst Lysogenic Infection- virus integrates it DNA into the DNA of the host. Viral DNA replicates with host DNA

Viral Reproduction Steps of Lytic Cycle Attachment Entry Replication Assembly Lysis/Release (lyses the cell)

Retroviruses Contain RNA instead of DNA Copy their RNA into DNA instead of DNA to RNA Examples: AIDS, some cancers

Bacteria Most numerous and widespread organisms “Discovered” with the invention of the microscope by Robert Hooke and Anton van Leeuwenhoek (1676)

Classification Two kingdoms of Prokaryotes (Prokaryotes are organisms that lack nuclei or membrane-bound organelles) Kingdom Eubacteria: “true bacteria” , variety, 3 shapes, no phyla Kingdom Archaebacteria: “ancient”, lives in extreme environments

Archaebacteria Methanogens–live in large intestines of animals, decompose dead organisms, produce methane gas (CH4) Halophiles--live in salty environments Thermoacidophiles—live in hot, acidic environments

Size and Structure 1-5 micrometers (much smaller than eukaryotic cells– 10-100 micrometers) Unicellular (although grow in colonies) Prokaryotic- no nucleus, no membrane-bound organelles * CAN IDENTIFY BACTERIA BASED ON: Shape, Cell Wall, and Movement

Method of Obtaining Energy Most are heterotrophic (mostly decomposers) Some are autotrophic—chemotrophs and photoautotrophs Ex: cyanobacteria

Shape Coccus (spherical)* Bacillus (rod-shaped)* Spirillum (spiral-shaped)* *Arranged in chains, groups, or pairs Pair– Diplo- Chains– Strepto- Groups– Staphylo— **Example: Spherical shaped bacteria arranged in 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 Cell Cell wall Cell membranes DNA (floating freely)-circular chromosome Ribosomes Some can move (flagella, others glide)

Reproduction Most bacteria reproduce by Binary Fission Produces 2 identical “daughter” cells Can grow and divide every 20 minutes Asexual (no exchange or recombination of genetic 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” Bacteria Food Spoilage—smells, makes you sick Bacterial Diseases Only 3% of all bacteria cause human diseases Can be treated with antibiotics and prevented through vaccination 1st antibiotic discovered/source Examples: pneumonia, bubonic plague, Strep. Throat, Syphilis, gonorrhea, anthrax, botulism

E. coli

“GOOD” Bacteria: The Importance of Bacteria Decomposers Help ecosystem recycle nutrients Breakdown complex compounds into usable materials Nitrogen fixers Bacteria perform nitrogen fixation

Importance of Bacteria (Cont.) Human Uses Production of food and beverages Medicine and chemical industry Genetic engineering Bioremediation: Cleaning up the environment