Viruses and Bacteria

1. Viruses and Bacteria Chapter 19

2. Viruses • Tobacco mosaic virus – 1st identified virus • Parts • Nucleic acid • DNA or RNA (retrovirus) • Capsid – protein coat • Has surface proteins that enable virus to enter host cell • Tend to be host specific • Bacteriophage – virus that infects bacteria • Envelope – found in some – protective covering

3. Viral reproduction – 2 processes • Lytic cycle – ex. T4 bacteriophage • Attachment • Entry • Replication – uses host cell’s organelles to produce new viral nucleic acids • Assembly • Lyses – bursting of cell – releases new viruses

4. Reprod. Cont. • Lysogenic cycle – Herpes Simplex I, HIV • Attachment • Entry • Prophage forms – viral DNA inserts itself into host DNA • Cell division • Prophage leaves – viral DNA leaves host DNA • Replication • Assembly • Lyses

5. Viral impact • Viruses are parasites – they depend entirely on the host. • Are not considered living because they are not made up of cells, do not grow/develop, do not obtain/use energy, or respond to their environment. • Diseases – disrupt the body’s equilibrium • Cause disease by attacking and killing certain cells or causing cells to change their growth/development. • Cannot be treated w/ antibiotics • Protection = prevention • Vaccines – only work if taken before contraction

6. Animals – may spread in a variety of ways – foot-and-mouth disease (cattle), cold, flu, smallpox, HIV, chickenpox, West Nile, polio • Plants – tend to be spread by insects – tobacco mosaic, potato yellow dwarf • Virus-like particles • Viroids – cause disease in plants • Single-stranded RNA, no capsid • Prions – protein infectious particles – cause disease in animals • Contain only proteins – no genetic material • Mad cow disease, Creutzfeldt-Jakob disease

7. Bacteria • Prokaryotes • Size = 1-5μm • Eubacteria – live everywhere • Cell walls of peptidoglycan • Archaebacteria – extreme environments • Cell walls do not have peptidoglycan • Great Salt Lake, Dead Sea, hot springs, methanogens - digestive tract of animals (oxygen free)

8. Bacteria identification • Shapes • Bacilli – rod shaped • Cocci – round • Spirilla – spiral • Cell walls • Gram + - have a lot of peptidoglycan – stain purple • Gram – - have little peptidoglycan; have an outer layer of lipopolysaccharides – stain pink • Movement varies – flagella, sliding

9. Bacterial energy • Obtaining energy • Chemoheterotrophs – must take in organic material for energy and carbon • Photoheterotrophs – use light for energy; use organic material for carbon • Chemoautotrophs – use carbon dioxide for carbon; use other chemicals for energy (ammonia, hydrogen sulfide, nitrites, sulfur, iron) • Photoautotrophs – use carbon dioxide for carbon; use light for energy

10. Energy cont. • Producing energy • Obligate aerobes – must have oxygen – use cellular respiration • Obligate anaerobes – must NOT have oxygen – oxygen will kill them – use fermentation • Facultative anaerobes – can survive with/without oxygen – switch btw cellular respiration and fermentation

11. Bacterial reproduction • Reproduction • Binary fission – asexual – replicates DNA & splits in ½ • Conjugation – sexual – sexual pili form btw cells to allow exchange of genes • May form an endospore for protection during harsh conditions (extreme heat, dryness, lack of nutrients).

12. Bacterial importance • Decomposers – break down organic matter and recycle it into the environment • Dead material, sewage • Nitrogen fixers – convert nitrogen gas into a form that plants can use (1 example - ammonia NH3) • Plants must have nitrogen – many live with nitrogen fixing bacteria in their roots • Ex. Soybeans • Human uses – antibiotics, food, bacteria in intestines produce vitamins we need

13. Bacterial Diseases • Pathogens – disease causing agents • Disrupt the body’s equilibrium by interfering with its normal activities • Pasteur – proved that bacteria may cause disease • Ex. Lyme disease, tetanus, strep throat, tooth decay • May cause disease in 2 ways • Break down cells to use as food • Ex. Mycobacterium tuberculosis – breaks down lung tissue • Release of toxins into blood stream • Ex. Streptococcus, Corynebacteriumdiptheriae

14. Diseases cont. • Prevention/treatment • Vaccines – weakened or killed pathogen • Prompts the body’s immune system • Antibiotics – compounds that stop the growth or reproduction of bacteria • Ex. Penicillin • Control • Sterilization – destroying bacteria with heat • Disinfectants – using chemicals to kill bacteria • Food storage/preparation • Colder temps – longer for bacteria to grow • Cooking at higher temps may kill bacteria – boiling, frying, steaming