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Pathogens and Body Defenses Part 1: Comparing and Contrasting: 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 “plasmids” DNA that help code for genes to increase fitness (eg. 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 A Lytic Infection: 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 prophage 2. The host are “symptom-free” during dormancy 3. Infection is fast acting when the infection progresses to the lytic phase 4. Example: HIV, Herpes Part 2: Your Body's Defenses Your Body’s Defense • Nonspecific defense mechanisms – First Line & Second Line of Defense • Specific Defense mechanisms – Third Line of Defense (immune system) First-line Respiratory Defense • Mucus producing cells trap microbes before entering the lungs • Cilia expel trapped microbes and mucus into the pharynx (windpipe) Cross-section of cilia http://www.gla.ac.uk/immunology/education/nursing/images/cilia.gif Second-line of Defense • Anti-microbial proteins: Lysozymes – Digest the cell walls of many bacteria – Found in tears, saliva and mucous secretions This is the body’s own antibiotic! Alexander Fleming: Discovered penicillin and lysozyme Second-line of Defense • The Inflammatory Response Bacteria or other pathogen Blood clotting elements Chemicals released by damaged cells, like histamine Phagocytic Leukocyte Leukocyte Red Blood Cells Capillary Phagocytic cells engulf the bacteria In response to chemical signals, 1. Capillaries dilate 2. Capillaries become more permeable 3. Fluid & clotting elements move to the site Turn to your tablemates to figure this out: • What do you think would happen to a person if an inflammatory response happened to their entire body? – What would happen to their temperature? It would go up! – What would happen to their blood pressure? It would drop! This happens during conditions, like Sepsis (a systemic bacterial infection) Specific Players in the Second Line of Defense • White Blood Cells (Leukocytes): 1. 2. 3. 4. 5. • Monocytes Neutrophils Basophils Eosinophils Lymphocytes Phagocytes Develop into B and T Cells Collectively, their function is to fight infections. Third Line of Defense: The Lymphatic System Adenoid Tonsil Lymph nodes Peyer’s Patch (on small intestine) Lymphatic vessel Thymus Spleen Blood capillary Masses of lymphocytes and macrophages Appendix Bone Marrow Tissue cells Lymphatic vessel Pluripotent stem cell Differentiation of B and T Cells 1. 2. 3. 4. 5. A stem cell is produced in the bone marrow or in the fetal liver. That stem cell differentiates to become a lymphocyte stem cell. It can then become a B cell, or… Go to the thymus and become a T cell. Both B and T cells will go to the lymphoid tissue (lymph nodes, spleen, blood and lymph) to await their role in your immune response. Lymphocyte Stem Cell Thymus B cell To the lymphoid tissue T cell