pathogens and body defenses. part 1: comparing and contrasting: viruses and bacteria
TRANSCRIPT
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
Submicroscopic parasitic acellular
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
0.25 m
Virus
Animalcell
Bacterium
Animal cell nucleus
Bacteria
Two main “domains” or groups1. Bacteria
Cell walls with peptidoglycan
2. ArchaebacteriaCell walls lack peptidoglycanAdapted 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)
Asexual divisionDNA 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 unfavorableAn 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 nm 50 nm 50 nm 50 nm
(a) Tobacco mosaic virus (b) Adenoviruses (c) Influenza viruses (d) Bacteriophage T4
RNA
RNACapsomereof capsid
DNACapsomere
Glycoprotein Glycoprotein
Membranousenvelope
CapsidDNA
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 InfectionStep 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)
http://www.gla.ac.uk/immunology/education/nursing/images/cilia.gif
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 dilate2. Capillaries become more permeable3. 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
TonsilLymph 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