Bacteria and Viruses

1. Bacteria and Viruses

2. Viruses Viral Characteristics and Structure • From the Latin meaning poison • Not living organisms; noncellular; referred to as phages • Deadly viruses are said to be virulent viruses • Are extremely small; couldn't be seen until electron microscope invented

3. Consist of a nucleic acid core (DNA or RNA) and a protein coat called the capsid • Cannot grow or replicate on their own (inactive particles) • Can only reproduce inside of a living host cell using its raw materials & enzymes

4. Some can cause disease (smallpox, measles, mononucleosis, influenza, colds, AIDS, Ebola) • Some may also cause cancers such as leukemias • Highly host specific (only infect certain cells) • Viruses are classified into 2 main groups by their nucleic acid --- DNA or RNA Viruses

5. Bacteriophages or T-Phages • Among the most complex viruses • Attack bacterial cells • Composed of a head, tail, base plate, & tail fibers • Long DNA molecule is inside the head  • Tail helps inject the viral DNA into host cell • Tail fibers used to attach to host

6. Retroviruses • Contains RNA • Have an enzyme called reverse transcriptase which helps use the RNA to make DNA • Use the host cell's ribosomes & raw materials to make viral proteins • Cause some cancers & AIDS

7. The LyticVirus • Viral replication that rapidly (no inactive time) kills the host cell causing it to lyse or burst • Virus attaches to the cell • Nucleic acid injected into the cell • Viral DNA takes control of cell (replication of virus parts) • Assembly of viral parts into new virus • The cell is broken open (lysis) releasing new viruses

9. The LysogenicVirus • Replication in which the virus stays inactive inside of the host cell & doesn't immediately kill it • Consists of two phases a lysogenic phase (incorporates its DNA into the host creating a prophage) and lytic phase (reproduction of virus parts and lysis of host cell) • The prophage survives as a permanent part of the organism’s DNA until an external stimulus causes the cell to produce new viruses

11. Viral Control • Interferon are proteins made by cells to fight viruses • Two types of viral vaccines exist --- inactivated & attenuated – given before infection (antibiotics don’t work on viruses) • Inactivated virus vaccines don't replicate in the host's system • Attenuated viral vaccines have been genetically altered so they can't cause disease • Antiviral drugs (AZT, acyclovir, & azidothymidine) interfere with viral DNA synthesis • Protease Inhibitors interfere with viral capsid production • New viruses emerge as rain forests are cleared (Ebola virus) with no known treatment (vaccine)

12. Bacteria • Most numerous organisms on earth; usually found in moist habitats • Once grouped together in the kingdom Monera but now grouped into 2 kingdoms --- • Eubacteria (true bacteria) • Archaebacteria (ancient bacteria)

13. Basic Characteristics: • Microscopic prokaryotes; contain ribosomes • Surrounded by protective cell wall containing peptidoglycan • Many are surrounded by a sticky, protective coating of sugars called the capsule • Have small rings of DNA called plasmids • May have short, hairlike projections called pili on cell wall to attach to host or another bacteria when transferring genetic material • Move by flagella, gliding over slime they secrete

14. Some can form protective endosporesaround the DNA when conditions become unfavorable; may stay inactive several years & then re-activate when conditions favorable

15. Importance: • The main decomposers of dead organisms (recycle nutrients) • Some convert nitrogen gas to nitrogen compounds that cells can use (nitrogen fixation)

16. Some help in the manufacture of food and medicine (cheese, yogurt, antibiotic) • Some bacteria breakdown chemical & oil spills

17. Some cause disease  (known as pathogens) and can produce poisonous toxins • Antibiotics interfere with cellular functions such as osmosis • Bacteria can mutate and become antibiotic resistant (often results from overuse of antibiotics)

18. Kingdom Archaebacteria(ancient bacteria) • Found in harsh environments (undersea volcanic vents, acidic hot springs, salty water)

19. Kingdom Eubacteria(true bacteria) • Most bacteria in this kingdom • Classified by their • structure • motility (ability to move) • molecular composition • reaction to stains (Gram stain)

20. Come in 3 basic shapes --- cocci (spheres), bacilli (rod shaped), spirilla (corkscrew shape) • Bacteria can occur in pairs ( diplo- bacilli or cocci) • Bacteria occurring in chains have prefix - strepto- (bacilli or cocci) • Bacteria in grapelike clusters have prefix - staphylo (staphylococci)

21. Most are heterotrophic • Can be aerobic or anaerobic • Some feed on dead organic matter; some are parasites • Can be identified by Gram staining (gram positive or gram negative)  

22. Gram Staining • Developed in 1884 by Danish microbiologist, Hans Gram • Bacteria are stained with two dyes • Bacterial cell walls either stain purple or reddish-pink  

23. Gram-positive bacteria (Gram +) have a thick layer of peptidoglycan in the cell walls & single layer of lipids and will stain purple • Gram-positive bacteria can be treated with penicillin (antibiotics) & sulfa drugs • Gram-negative bacteria (Gram -) have a thin layer of peptidoglycan & an extra layer of lipids on the outside and stain pink or reddish  • Lipid layer prevents the purple stain & antibiotics from entering Gram-negative bacteria • Gram-negative bacteria are antibiotic resistant

24. Methods of Respiration • Obligate aerobic bacteria can’t live without oxygen • Obligate anaerobes die if oxygen is present • Facultative anaerobes do not need oxygen, but don’t die if oxygen is present

25. Bacterial Reproduction & Genetic Recombination • Most bacteria reproduce asexually by binary fission (mitosis)   • Some bacteria can replicate (double in number) every 20 minutes under ideal conditions   • Bacterial plasmids are used in genetic engineering to carry new genes into other organisms

26. Bacteria can recombine genetic material using conjugation where two bacteria form a bridge or tube between them and DNA is transferred from one bacteria to the other