Pathogens and Body Defenses

Part 1: Comparing and Contrasting: Viruses and Bacteria

The Difference in Definition BacteriaBacteria: Prokaryotic 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) VirusesViruses: 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 Prokaryo Submicroscopicparasiticacellular

The Difference in Size Bacteria can be measured in micrometers – m or Viruses are measured in nanometers – m or 10 -9

Comparing the size of a virus, a bacterium, and an animal cell 0.25  m Virus Animal cell Bacterium Animal cell nucleus

Bacteria Two main “domains” or groups 1.Bacteria Cell walls with peptidoglycan 2.Archaebacteria Cell walls lack peptidoglycan Adapted to extreme environments: - Extremely hot and cold, salty, without oxygen, etc. peptidoglycan Made up of types of peptide and sugar bonds

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

Gram-negative: Will not pick up the violet dye Infection by this type must be treated by a broad-spectrum antibiotic such as ciprofloxacin Bacterial Staining peptidoglycan

Bacterial Growth and Reproduction Binary Fission: (video)Binary Fission Asexual division DNA replicates and cytoplasm divides Conjugation (video)Conjugation “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 18  250 mm 70–90 nm (diameter) 80–200 nm (diameter) 80  225 nm 20 nm50 nm (a) Tobacco mosaic virus(b) Adenoviruses(c) Influenza viruses (d) Bacteriophage T4 RNA Capsomere of capsid DNA Capsomere Glycoprotein Membranous envelope Capsid DNA Head Tail fiber Tail sheath

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 1: Attachment of virus to host cell Step 2: Injection of viral DNA into cell Step 3: Replication of viral DNA and Synthesis of Protein Capsule using cellular “machinery” –DNA and RNA polymerases, ribosomes, etc. Step 4: Assembly of new viruses inside host cell Step 5: New viruses “lyse” the host cell and are released for further infection

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

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 Capillary Bacteria or other pathogen Chemicals released by damaged cells, like histamine Red Blood Cells Leukocyte In response to chemical signals, 1. Capillaries dilate 2. Capillaries become more permeable 3. Fluid & clotting elements move to the site Blood clotting elements Phagocytic Leukocyte Phagocytic cells engulf the bacteria

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? –What would happen to their blood pressure? It would go up! 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.Monocytes 2.Neutrophils 3.Basophils 4.Eosinophils 5.Lymphocytes Collectively, their function is to fight infections. Phagocytes Develop into B and T Cells

Third Line of Defense: The Lymphatic System Adenoid Tonsil Lymph nodes Thymus Spleen Peyer’s Patch (on small intestine) Appendix Bone Marrow Lymphatic vessel Tissue cells Blood capillary Lymphatic vessel Masses of lymphocytes and macrophages

Differentiation of B and T Cells 1.A stem cell is produced in the bone marrow or in the fetal liver. 2.That stem cell differentiates to become a lymphocyte stem cell. 3.It can then become a B cell, or… 4.Go to the thymus and become a T cell. 5.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. Pluripotent stem cell Lymphocyte Stem Cell B cell Thymus T cell To the lymphoid tissue