Bacteria and viruses

1. Bacteria and viruses Biology 112

2. Prokaryotes • Smallest and most common microorganisms • Unicellular organisms that lack a nucleus • They can be divided into two separate groups • Eubacteria • Archaebacteria

3. Eubacteria • Live almost everywhere • Usually surrounded by a cell wall that protects it from injury as well as determines its shape • Cell wall contains peptidoglycan, a carbohydrate • Cell membrane inside the cell wall that surrounds the cytoplasm • Some have a second membrane which further protects it from damage

4. Archaebacteria • Have cell walls, lack nuclei and lack the peptidoglycan that is present in eubacteria • There are different lipids existing in their cell membranes • The DNA sequencing is more similar to eukaryotes than prokaryotes • May be the ancestors of eukaryotes • Most live in harsh environments, including mud, digestive tracts, volcanoes

5. Identifying prokaryotes • Shape • Rod-shaped (bacilli), spherical (cocci), spiral/corkscrew (spirilla) • Composition of Cell Walls • Thick peptidoglycan walls (gram positive) or thinner walls with a second outer lipid layer (gram negative) • Movement • Some do not move at all, others have flagella, which are whiplike structures while others still lash, snake, spiral and glide

6. Fourth identifying characteristic of prokaryotes (obtaining energy) Heterotrophs (ex. E coli) Autotrophs (ex. Cyanobacteria)

7. How prokaryotes obtain energy - heterotrophs • Heterotrophic Prokaryotes • Eat other organisms for energy as well as a supply of carbon • Called chemoheterotrophs • Others are autotrophs to obtain their energy but also eat other organisms for their necessity for carbon • Called photoheterotrophs

8. How prokaryotes obtain energy - autotrophs • Use light energy to convert carbon dioxide and water to carbon compounds and oxygen • Found where light is available • Photoautotrophs • Make organic carbon molecules from carbon dioxide but do not require light • Use energy from chemical reactions involving ammonia, hydrogen sulfide, nitrites, sulfur or iron • Present in harsh environments • Chemoautotrophs

9. How prokaryotes release their energy • They undergo cellular respiration, fermentation or both • Those that require a constant supply of oxygen are called obligate aerobes • Those that do not require it (or may even be killed by the presence of oxygen) are called obligate anaerobes • Those that can survive with or without oxygen are called facultative anaerobes • Do not require it but are not harmed by it either • As a result, they can survive almost anywhere

10. Growth and reproduction • How fast they grow and reproduce depends mostly on availability of food and the production/elimination of waste products • When a prokaryote has doubled in its size, it may divide in half through a process called binary fission (daughter cells are identical to single parent cell – asexual reproduction) • Conjugation occurs when a bridge forms between two cells and genetic material can be passed between the two • Spore formation, called endospores, may form within a prokaryote • A thick wall forms around the DNA and a portion of the cytoplasm • Spore may remain dormant until more favorable conditions occur

11. Importance of bacteria • Critical for maintaining the living world • Some are producers as well as decomposers • Others have uses in human survival • Decomposers • Bacteria recycles nutrients which maintains balance in the environment • Without them, sewage systems would not be able to eliminate all its waste and disease would spread

12. Importance of bacteria • Nitrogen fixers • Plants need nitrogen to make amino acids (building blocks of protein) • Nitrogen (N2) must be changed to ammonia (NH3) or other nitrogen compounds (nitrates) before it can be used by living things • This process is known as nitrogen fixation

13. Importance of bacteria – human uses • Human uses • Food industry • Lactobacillus is used for the preservation of dairy • Industry • Sulfate-reducing bacteria in the petroleum industry • Waste removal • Bacteria that converts waste into fuel • Mining • Bacteria that leaches copper from mines • Synthesize drugs and chemicals for improved health • Vaccines

14. Viruses • Viruses are composed of parts of nucleic acid, protein and lipids • Reproduction only occurs by infecting living cells • Great variety in their size and appearance • All viruses infect cells the same way – by entering healthy cells and once inside, use the organelles of the infected cell to produce more viruses • It is typically composed of DNA, RNA and a protein coat

15. Structure of a virus • Protein coat is also called a capsid • Contains proteins that enable the virus to enter the host cell • Binds to receptors on a healthy cell and “tricks” the cell into allowing it to enter • Once inside, viral genes are exposed to the cell • The healthy cell ‘reads’ the genetic information and then may, as a result, get destroyed in the process • The host cell may also make copies of the virus

16. Viruses attack different organisms • Viruses are highly specific to the host cell it is infecting • As a result, viruses which target plants may not contain the proteins in their capsids to gain entry to an animal cell • Viruses that attack bacteria are called bacteriophages

17. Viral infection • Some viruses replicate themselves immediately once inside the host cell and kill the cell • Others do not replicate in such a way that destroys the host cell immediately • Lytic Infection • Virus enters cell, replicates itself, and causes the cell to burst • Destroys the cells DNA, uses the cell to make viral proteins and viral DNA, then releases viral particles • Lysogenic Infection • Incorporation of the viruses DNA with the host cell DNA and replicates along with the host cell’s DNA • Viral DNA is called a prophagewhich may lay dormant for an indefinite amount of time