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Viruses and Bacteria The Difference in Definition • Bacteria: Pro Prokaryotic karyo Organisms – Pro: Primitive or “prior to” – Karyon: Nucleus or “kernel” – Single-celled organisms – Has circular DNA; often has “plasmid” DNA that helps codes for genes to increase fitness (ex. Antibiotic resistance) Submicroscopic parasitic • Viruses: Submicroscopic, parasitic, acellular entity composed of a nucleic acid core surrounded by a protein coat. – Below the resolution of a microscope – Relies on a host – Does not have the properties of cellular life The Difference in Size • Bacteria can be measured in micrometers – 0.000001m or 10-6 • Viruses are measured in nanometers – 0.000000001m or 10-9 Comparing the size of a virus, a bacterium, and an animal cell Virus Bacterium Animal cell Animal cell nucleus 0.25 m Bacteria Two main “domains” or groups 1. Bacteria Cell walls with peptidoglycan Made up of types of peptide and sugar bonds 2. Archaebacteria Cell walls lack peptidoglycan Adapted to extreme environments: - Extremely hot and cold, salty, without oxygen, etc. Bacteria: Shapes • Three basic shapes: – Rod-shaped (Bacilli) Bacillus anthracis (Anthrax), Yersinia pestis (Bubonic plague) - Comma-shaped (Vibrios) Vibrio cholerae – Spherical (Cocci) Streptococcus, Staphylococcus – Spiral (Spirilla) Treponema pallidum (Syphillis) Bacterial Staining • Gram-positive: Retains the crystals of violet dye in the peptidoglycan layer • Infection by this type can be treated by antibiotics such as penicillin Bacterial Staining • Gram-negative: Will not pick up the violet dye • Infection by this type must be treated by a broad-spectrum antibiotic such as ciprofloxacin peptidoglycan Bacterial Growth and Reproduction • Binary Fission: (video) Asexual division DNA replicates and cytoplasm divides • Conjugation (video) “Sexual” reproduction Sex Pilus extends between bacteria plasmid DNA is transferred from one bacterium to another • Spore Formation: occurs when growth conditions are unfavorable An endospore is a “spore” with a thick internal wall of membrane that encloses and protects its DNA Viral Shapes and structure Capsomere of capsid RNA Capsomere Membranous envelope DNA Head Capsid Tail sheath RNA DNA Tail fiber Glycoprotein 18 250 mm 20 nm (a) Tobacco mosaic virus Glycoprotein 70–90 nm (diameter) 80–200 nm (diameter) 50 nm 50 nm (b) Adenoviruses (c) Influenza viruses 80 225 nm 50 nm (d) Bacteriophage T4 Viruses Reproduction Viruses reproduce by infecting other cells. Two types of viral infections: 1. Lytic Infection 2. Lysogenic Infection Figure 18.1 T4 bacteriophage infecting an E. coli cell 0.5 m The Lytic Infection Step Step 1:3:Attachment 5:Replication New viruses of virus to thehost host cell cell Step of “lyse” viral DNA and and areof released furtherusing infection Synthesis Proteinfor Capsule cellular “machinery” –DNA and RNA polymerases, ribosomes, etc. Step of viral new DNA virusesinto inside Step 4:2: Assembly Injection of cell host cell Characteristics of Lytic Infections 1. Fast acting 2. Symptoms emerge within 24 – 48 hours 3. Examples – influenza, west-nile The Lysogenic Infection Step 1: Virus attaches and inserts its DNA inside host Step 2: Viral DNA attaches to the host DNA (prophage) Step 3: The viral DNA lies “dormant” and only replicates each time the cell replicates Step 4: Stress or other “factors” causes the infection to progress to the “lytic” phase Characteristics of Lysogenic Infections 1. Slow Acting - Viral DNA can lie “dormant” for many years as proghage 2. The host are “symptom-free” during dormancy 3. Infection is fast acting when the infection progresses to the lytic phase 4. Example: HIV