Chapter 19: Bacteria and Viruses

Viruses Means “poison” in Latin Nonliving Composed of nucleic acids enclosed in a protein coat Smaller than bacteria (can vary in structure and size) Can only replicate Make copies of itself Need a host/living cell to reproduce No cell respiration, growth, response to stimuli Not considered a living cell

1935: W. Stanley 1st to identify a virus Tobacco Mosaic Virus

Structure of a Virus Inner core of nucleic acid (DNA or RNA) Outer protein coat called a capsid Gives virus its shape Some viruses have a membrane (envelope) over the capsid Can have spikes, hooks, etc.

Bacteriophage Special group of viruses Infect bacteria Inject their nucleic acid into bacteria like a syringe

Viruses are classifies by the type of host they infect Plant viruses Animal viruses Bacterial viruses

Viruses are often species-specific Some are cell-type specific Ex: cold viruses affect respiratory cells Ex: Polio virus  affects nerve cells

2 Types of Reproduction Lytic cycle (short): takes about 30 minutes to produce 200 new viruses Virus enters cell  reproduces  exits cell Kills host cell: causes host cell to break open Steps: ex: cold virus attachment entry replication assembly lysis and release

Lysogenic Cycle (long) Virus has an inactive (dormant) period Steps: ex: herpes, HIV, and chickenpox attachment and entry provirus formation (prophage) viral DNA integrated into host’s chromosomes normal cell activity activation of the lytic cycle

Retrovirus RNA virus with the enzyme reverse transcriptase Makes viral DNA from host cell RNA Ex: HIV

Fighting Viruses Natural defenses Skin, mucus membranes, white blood cells, antibody production, interferon Vaccines Preparation of weakened or killed virus/viral proteins Some produce life-long specific antibodies Antibiotics do not kill viruses

How Viruses are Spread Air (measles, cold) Food and water (hepatitis) Animal/insect bites (rabies, encephalitis) Insects (flies can “carry” viruses) Sexual contact (HIV, Herpes) 1st line of defense  skin and membranes

Chapter 19 Review #1 A typical virus has a core composed of ___. a. capsid proteins c. membrane envelopes b. surface proteins d. DNA or RNA 2. The outer layer of a virus is composed of ____. a. RNA b. viral genes c. DNA d. proteins 3. A(an) _____ is a preparation of weakened or killed pathogens that can prompt the body to produce immunity to a disease.

Bacteria Prokaryotic: Unicellular organisms Have no nucleus No membrane-bound organelles

Divided into 2 Kingdoms Archaebacteria Live in extreme habitats (usually no oxygen present) Cell walls lack peptidoglycan (starch) 3 types: Methanogens Produce methane gas Live in marshes, lake sediments, and cow digestive tracts Found at sewage disposal plants to help break down sewage

Extreme Halophiles Lives only in places where there is a high salt concentration Found in Utah’s Great Salt Lakes and the Dead Sea

Thermoacidophiles Lives in hot, acidic waters of sulfur springs Found in volcanic vents

Eubacteria Live almost everywhere Cell walls made of peptidoglycan Divided up based on how they get their food Autotrophs Make their own food 2 types: Photosynthetic Need sunlight Ex: cyanobacteria (blue-green algae) Chemosynthetic Use sulfur and nitrogen to make food

Eubacteria Heterotrophs Use others/consumes to get food 2 ways: Parasitism, mutualism, commensalism Gets food from other living things Saprophytes Feed on dead organisms/wastes Decomposers

Structure of Bacteria Very small in size All have: Some have: DNA Pili Cell membrane Capsule Cell wall Flagella Ribosomes Genes are in a big circular chromosome (not paired chromosomes)

Cell wall keeps bacteria from bursting Most bacteria live in a hypotonic environment 1928: Alexander Fleming Accidentally discovered Penicillin 1st antibiotic Destroys bacteria by interfering with its ability to make a cell wall

Identifying Bacteria Gram Staining Based on differences in a bacterium’s cell wall Gram positive: will stain a blue/purple color Gram negative: will stain a pink color

Shapes of Bacteria Bacteria have 3 shapes: Cocci: sphere-shaped Bacilli: rod-shaped Spirilla: spiral-shaped

Bacteria can grow in patterns Diplo-: arranged in pairs Staphylo-: cells arranged like grapes Strepto-: arrangement of chains of cells

Asexual Reproduction Binary Fission Exponential growth: 12481632…etc Very fast (every 20 minutes) Cells produced are genetically identical

Sexual Reproduction Called conjugation DNA is exchanged through structures called pili that connect cells together

Metabolism Breaking down food to release energy 3 groups of bacteria based on way they metabolize: Obligate aerobes: require oxygen Ex: Mycobacterium tuberculosis

Facultative anaerobes: can live with or without oxygen Ex: E. coli

Obligate anaerobes: die in the presence of oxygen Ex: Clostridium, Treponema

Importance of Bacteria Help fertilize fields Recycles nutrients: breakdown dead materials/waste (called saprophytes) Produce foods and medicines/antibiotics Nitrogen fixation: makes a usable form of nitrogen

Harmful Bacteria: called pathogens Can cause disease in plants and animals Interferes with normal body function Affects homeostasis Can release a toxin that attacks the host (like a poison)

Survival Adaptations Produce endospores Contain bacterial DNA and cytoplasm Covered with a tough, outer case that resists temperature extremes, drying out, and harsh chemicals Dormant: resting state (can be as long as 1,000 years) Does not reproduce during this time Can germinate when environmental conditions improve Must be exposed to high heat under pressure to be killed Called sterilization

Chapter 19 Review #2 A ______ is a disease-causing agent. 2. List 4 ways to identify prokaryotes. 3. One way to control bacterial growth is by subjecting them to great heat, a process called _____. 4. Bacteria can also cause disease by releasing ______ that harm the body.