Chapter 20 - Viruses and Bacteria

Chapter 20 - Viruses and Bacteria • Viruses: Structure, Replication, Viruses that infect bacteria • Bacteria: Common Characteristics, Differences from Viruses Size of Infectious particles • Viruses are smaller than bacteria • Bacteria are smaller than eukaryotic cells Bacteria shapes and structure Structure • Viruses are infectious particles made up of a genome of double- or single- stranded DNA or RNA • Genetic material is contained within a capsid or protein coat. • Viruses can have many shapes like polyhedral or rod-shaped. • Bacteriophage (viruses that infect bacteria) have a unique structure with a head and tail. Characteristics of Viruses • Viruses hijack the cell machinery after infection of a living cells. • Viruses are not living – do not have cells • Viruses can NOT reproduce unless inside another cell (host) • Viruses cannot use energy • Viruses cannot make proteins independently Virus replication • Lytic cycle – virus enters the host and releases genetic material - Virus replicates and re-assembles itself and the cell lyses to release the virus immediately • Lysogenic cycle – – virus enters host – Genetic material is incorporated into the host DNA – Virus copies with cellular DNA – Virus stays inactive (latent) – Virus becomes active based on environmental triggers. • Viruses may go back and forth between cycles Viral Illnesses • Viruses are carried by a vector (like animals or bacteria) • Examples of Viral Illnesses- – Chickenpox, Flu, Herpes, Mumps, Measles, Hepatitis, AIDS (HIV), H1N1 – Viruses may cause cancer (Human Papilloma Virus- Gardasil) • Medical treatment of viruses – Many viral illnesses are controlled by immunization or vaccination to prevent the virus from infecting the person. Lytic and Lysogenic Cycles – Antibiotics do NOT kill viruses. – Anti-viral drugs are available but must be taken soon after infection (Tamiflu) Eubacteria • Eubacteria have a cell wall made of peptidoglycan (different from cellulose in plants) • Bacteria replicate by binary fission • Bacteria replicate in 20-30 minutes (compared to 12-24 hrs for eukaryotic cells) • Bacteria can destroy body tissue directly • Bacteria can make toxins to cause disease Antibiotics • Antibiotics kill bacteria. – Penicillin was the first antibiotic developed by Sir Andrew Fleming – Mass produced around WWII to treat soldiers • Antibiotics may act in different ways – Disrupt production of cell wall – Disrupt protein synthesis – Disrupt nucleic acid synthesis Bacteria have three shapes • Rod-shaped bacteria are called bacilli (singular, bacillus). An example of bacilli is Escherichia coli. (E. coli) • Sphere-shaped bacteria are called cocci (singular, coccus). An example of cocci is Stapylococcus aureus which causes MRSA • Spiral shaped bacteria are called spirilla (singular, spirillum). An example of spirilla bacteria includes Borrelia burgdorferi that causes Lyme disease. Differences • Antibiotics kill bacteria not viruses • Viruses are not living • What causes common illnesses? – Is a cold caused by a virus or bacteria? – Is strep throat caused by a virus or bacteria? – What causes MRSA? – What shape is the MRSA bacteria? Lyme disease bacteria?