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Viruses and ProkaryotesChapter 20.1-20.3
Difference between Bacteria and Viruses
A virus is a strand of DNA or RNA surrounded by a protein coat (CAPSID)
Viruses are not considered to be alive!!
Bacteria are one-celled microorganisms
BOTH ARE INFECTIOUS!
Any disease-causing agent is known as a PATHOGEN
Viral Structure
Structure: genetic material surrounded by a capsid (protein shell).
Different shapes and sizes
Capsids surrounded by lipid envelope or protective outer coat
Why aren’t Viruses Alive?
CAN ONLY REPRODUCE BY INFECTING OTHER
LIVING CELLS
How do viruses enter cells?
Viruses enter host cells in various ways
Eukaryotic viruses fuse with host cell membrane
Eukaryotic viruses enter through endocytosis
When virus is taken in through endocytosis, the virus is now able to reproduce.
Lytic Infection
Viruses cause two types of infections:
First Type:
LYTIC: causes host cell to burst, or lyse
host bacterium
The bacterophage attachesand injects it DNA into a host bacterium.
The host bacterium breaks apart, or lyses. Bacteriophages are ableto infect new host cells.
The viral DNA directs the hostcell to produce new viral parts.The parts assemble into newbacteriophages.
The viral DNA forms a circle.
Lysogenic InfectionSecond Type:
LYSOGENIC: does no immediate harm
Prophage: phage DNA that is inserted into host cell DNA
The viral DNA is called a prophagewhen it combines withthe host cell’s DNA.
Although the prophage is notactive, it replicates along withthe host cell’s DNA.
Many cell divisions produce acolony of bacteria infectedwith prophage.
The prophage may leave thehost’s DNA and enter thelytic cycle.
Bacteriophages
Viruses that infect bacteria
ex: T-bacteriophage, which infects E. coli bacteria
Pierce host cells and inject their DNA into viral hosts
capsid
DNA
tail sheath
tail fiber
Prokaryotes
• Unicellular organisms that lack a nucleus
• DNA not membrane bound and is located in cytoplasm
• Either ARCHAEA or BACTERIA
Bacteria
• Wall protection
• Flagella
• Peptidoglyclan cell wall (polymer of sugars and amino acids)
Archaea
• Walls lack peptidoglycan
• More like eukaryotes than bacteria genetically
• Live in extreme environments (salty, hot, methane-rich)
Great Salt Lake
Prokaryote Structure and Function
• Prokaryotes vary in:
• Size
• Shape
• Mode of movement
• Way obtain and release energy
Size, Shape, and Movement
• Shapes: Bacilli, cocci, spirilla
• Bacilli: rod shape
• Cocci: spherical
• Spirilla: spiral, coiled
Energy Used by Prokaryotes: Nutrition &
Metabolism• Heterotroph: take in nutrients
• Photoheterotroph: use light energy and take in nutrients
• Photoautotroph: use light energy to convert carbon dioxide into carbon compounds
• Chemoautotroph: use energy released by chemical reactions to make food
Energy Released by Prokaryotes
Growth and Reproduction in
Prokaryotes• Reproduce by BINARY
FISSION (asexual)
• When growth conditions are unfavorable, prokaryotic cells form an ENDOSPORE (thick, internal wall that encloses the DNA)
Recombination in Prokaryotes
• Mutations: cause prokaryotes to evolve
• Conjugation: exchange of genetic information when a hollow bridge forms between 2 bacterial cells and genetic material (plasmid) moves from one cell to the other.
Importance of Prokaryotes
• Decomposers
• Producers
• Nitrogen fixers
• Food production
• Drugs and antibiotics
What is a Pathogen?
Microorganisms (viruses and bacteria) that cause disease
Bacterial Pathogens
• Bacteria cause disease by destroying living cells or by releasing chemicals that upset homeostasis
• Damage host tissue
• Release toxins
Methods for controlling bacteria: removal, disinfectants, food storage and
processing, sterilization by heat, vaccines, and antibiotics!
What is the Benefit of a Vaccine?
Vaccines are made from weakened pathogens and stimulates the body’s OWN immune response
Immune system gets MEMORY of pathogen
Made from killed or weakened microbes or certain parts of microbes
Viral Diseases• Viruses cause disease by directly destroying
living cells or by affecting cellular processes in ways that upset homeostasis
Viral DiseasesSome can be prevented with vaccines
Examples of Viral Infections:
Cold
Influenza
SARS
HIV
Mono
Rabies
Smallpox
Common Cold
> 200 different viruses cause cold symptoms each season
High mutation rate
Symptoms last between 5-7 days
InfluenzaWhy is the spread difficult to control?
FLU virus
Spreads quickly, causes local epidemics
20% of American population infected with flu virus per year
Different types of flu viruses affect different species
H1N1 (Swine Flu/Spanish Flu of 1918)
Others infect pigs, birds, horses, etc.
SARS
Severe Acute Respiratory Syndrome
Coronavirus: cause respiratory or enteric infections
8096 infected and 774 deaths from 11/2002-7/2003
Symptoms: Fever, GI problems, cough, sore throat, shortness of breath
HIV/AIDSHuman Immunodeficiency Virus
Lysogenic and Lytic Infection
Retrovirus: contain RNA and uses reverse transcriptase enzyme to make DNA (RNADNA)
Viral DNA enters host nucleus and incorporates itself into host DNA strand and remains dormant for years
When active, however, new viral parts are made, viruses bud or lyse through host cell and infect other host cells.
Mononucleosis
Caused by Epstein-Barr Virus (EBV)
Same family as the Herpes Virus
Has a lytic and a latent cycle
Increases WBCs in bloodstream
Symptoms: severe fatigue, sore throat
In US, 95% of adults 30-40 years old have antibodies against EBV
RabiesCauses acute encephalitis (swelling of the brain)
Most commonly transmitted through bites from animals infected with the virus
Virus travels to the brain via peripheral nerves
Once symptoms begin to show (usually after a few months), the disease is usually fatal.
IF BITTEN BY RABID ANIMAL: need 4 doses of Rabies Vaccine and 1 dose of Human Rabies Immunoglobulin
SmallpoxUnique to humans
Found in blood vessels of skin, throat, and mouth
In 18th century, virus killed 400,000 Europeans; During 20th century, virus killed 300-500 million people throughout the world
Vaccine available
As of NOW, Smallpox is the only infectious disease to be completely eradicated.
What is a Viroid?
Infectious particle
Cause disease in plants
Passed through seeds or pollen
Made only of single-stranded RNA
What is a Prion?
ALSO Infectious
Proteins that can cause other proteins to fold incorrectly
Infections BUT contain NO GENETIC MATERIAL!
Mad Cow Disease
degeneration in the brain and spinal cord