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Viruses and Prokaryotes
Chapter 18
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Studying Viruses and Prokaryotes
Virus – an infectious agent made up of a core of nucleic acid and a protein coat. Pathogen – any living infectious disease causing agent Bacteria are actual cells Pathogens can be bacteria, viruses
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Studying Viruses and Prokaryotes
Only reproduce in host DNA/RNA Cannot Grow Cannot use energy Cannot respond to stimuli CAN change over time Bacteria Independent reproduction (sexual/asexual) DNA Grows and develops Uses energy for processes Responds to the environment Changes over time
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Studying Viruses and Prokaryotes
Viroids Infectious particles that cause disease in plants Single stranded RNA without protein coat Passed through seeds or pollen Major agricultural impact Prions Infectious particle made only of proteins Causes proteins not to fold properly Play a role in some diseases of the brain Ex. Mad Cow Disease Cruetzfeld-Jakob disease is caused by a prion and affects the brain Prions can incubate for long periods of time with no effect on the host-once they are seen however, the progress quickly and are always fatal
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Viral Structure and Reproduction
Discovery Dmitri Ivanovsky - small bacteria or poisons – virus Tobacco mosaic disease Martinus Beijerinck – later suggested the cause of the disease was from particles in the juice Showed the disease agent passed through gel Tiny particles in the substance caused the disease Virus – Latin for poison Mosaic disease was thought to have been caused by a bacterium Ivanovsky passed extracts of tobacco leaves through a filter small enough to remove bacteria and then sprinkled it on leaves
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Viral Structure and Reproduction
Simple structure Virion – single virus particle Shape determines infection Capsid – viruses protein coat Contains either DNA or RNA In some viruses, protein coat surrounded by lipids Can form spikes used for attachment Used for identification-Enveloped, Helical, Polyhedral Virus identifies host by the surface proteins of the host Enveloped – Have spikes with a lipid envelope - Ex. Influenza Helical – Long narrow coiled shape Ex. – Rabies Polyhedral – many sided Ex. Foot and mouth disease
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Viral Structure and Reproduction
Viruses can infect bacteria Bacteriophage Release enzymes that break down the bacterial cell wall Injects its DNA into the bacteria Viruses infecting eukaryotes My enter by endocytosis Also can enter if in envelope Ex. HIV Enveloped virus fuses with the plasma membrane and then capsid is released into the cell
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Viral Structure and Reproduction
Two main modes of infection by viruses Virus binds to cell Tricks cell into taking in DNA DNA either becomes copied or kills the cell Most viruses are very specific to the cell they attack
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Viral Structure and Reproduction
Lytic Cycle – the viral replication process that rapidly kills a host cell. Viral DNA enters cell and takes over Turns on genes to make more viruses Viral enzymes break down the host cell membrane and new viruses released Lyses means to break apart The virus enters the cell and makes copies of itself causing the cell to rupture Host cell cannot tell difference between its DNA and the viruses T4 enters a cell and causes mRNA to be made which goes back and chops up the host DNA Virus then uses the parts of the host cell to make new virus particles which are then releases by lyses which can go on to infect other cells
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Viral Structure and Reproduction
Lysogenic Cycle – type of replication in which a virus does not immediately kill a host cell Viral DNA combines with host DNA - prophage Prophage is copied during mitosis and passed on to daughter cell Two paths – remain a permanent part of the cell OR become lytic Virus incorporates its DNA into the host cell’s DNA and is replicated along with the host cell’s DNA Can remain dormant for a long period of time Prophage – viral DNA that is embedded in the host cell’s DNA
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Viral Diseases Defense against infectious disease First defense – Skin
Viruses can enter only through openings – nose, mouth, eyes, ears, etc. Once at the cell, the virus uses triggers to trick the cell in to allowing the virus in
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Viral Diseases Viral Diseases Common cold Influenza
200 different viruses Mutates easily Influenza Prominent in winter Easily spread – epidemic 3 subtypes infect humans Highly mutatable – new vaccine each year SARS – Severe Acute Respiratory Syndrome Recent viral infection Similar to influenza HIV Retrovirus – uses RNA instead of DNA Lysogenic infection Becomes a lytic infection when active Infects WBC which leads to AIDS Highly mutatable Many other influenza subtypes infect animals – avian flu or bird flu RNA makes double stranded DNA that then enters the cell and combines with host DNA When active it leaves cell by either buds or bursting through the cell membrane
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Viral Diseases Vaccine Preparation of a weakened or killed pathogen
Prompts the body to form immunity Ex. MMR, Chickenpox, Hepatitis, Menigitis When the virus returns again, the body is prepared
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Bacteria and Archaea Microorgansims are everywhere
Smallest are prokaryotes Range in size 1 – 5 micrometers There are roughly 1 billion types of bacteria and 1030 individual prokaryotes above, on, and in the earth’s surface Epulopiscium fishelsoni lives in the intestines of surgeonfish in the tropical Pacific – 500 micrometers long
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Bacteria and Archaea Identification of Prokaryotes Shape
Chemical nature of cell wall Movement Obtaining of energy
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Bacteria and Archaea Respiration Obligate aerobes - breathes oxygen
Obligate anaerobes - does not breathe oxygen Facultative anaerobes – don’t need oxygen, but are not harmed by it Mycobacterium tuberculosis – obligate aerobe
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Bacteria and Archaea Structural Comparisons
Archaea and bacteria appear very similiar Cell walls, single celled DNA is in the form of a plasmid Some are non-motile Others: Whiplike movement with a flagellum or cillia
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Bacteria and Archaea Cell shape Cocci – spheres Bacilli – rods
Spirilla – spirals Strepto – chains Staphylo – clusters
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Bacteria and Archaea Cell shape Cocci – spheres Bacilli – rods
Spirilla – spirals Strepto – chains Staphylo – clusters
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Bacteria and Archaea Cell Shape Cocci – spheres Bacilli – rods
Spirilla – spirals Strepto – chains Staphylo – clusters
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Bacteria and Archaea Cell shape Cocci – spheres Bacilli – rods
Spirilla – spirals Strepto – chains Staphylo – clusters
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Bacteria and Archaea Cell shape Staphylo – clusters Cocci – spheres
Bacilli – rods Spirilla – spirals Strepto – chains Staphylo – clusters
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Bacteria and Archaea Cell wall composition
Gram positive – retain initial stain easily (violet) Gram negative – much thinner cell wall; doesn’t retain initial stain (pink) Gram staining is a method of identifying the bacteria based upon its cell wall structure Violet stain is applied first and stains peptidoglycan walls – alcohol treatment follows which washes out the stain and in Gram negative bacteria removes the thinner cell wall – pink counter-stain follows and makes the Gram negative appear light red or pink
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Bacteria and Archaea Nutrition Heterotrophs - eat to obtain energy
Chemoheterotrophs – must take in carbon Autotrophs - make their own food Most prokaryotes are heterotrophs Carbon is used as a source of energy and also for a supply of carbon – we are chemoheterotrophs so we compete directly with these bacteria for food Staph aureus – likes to eat the same things we do and if food is not handled properly then we eat the bacteria and get lovely food poisoning Photoheterotrophs can perfrom photosynthesis, but still need to take in carbon Chemoautotrophs – make organic molecules from carbon dioxide
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Bacteria and Archaea Growth Binary Fission – replicate DNA and divide
Conjugation – exchange of genetic information through a pilli Endospores – thick portion of cytoplasm enclosing the DNA Conjugation involves a bridge forming and the information between the bacteria is exchanged When conditons are less than favorable the bacteria will form spores that can remain dormant until ready
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Beneficial Roles of Prokaryotes
Prokayotes provide nutrients Key part of the digestive system of animals Decomposers Symbiosis - both members benefit (Ex. Plants and bacteria for nitrogen) Fermentation Diseases Lyme disease Cholera Tetanus Toxic Strep Prokaryote Roles in Ecosystems Cyanobacteria Produce much of the oxygen we breath Bioremediation Using bacteria to remove pollutants Ex. Oil spills, biodegradeable materials Symbiosis with plants for nitrogen fixation - Rhizobium
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Bacterial Diseases and Antibiotics
Two ways bacteria infect Damage cells and tissue Release toxins throughout body Damaged cells and tissue are used for food Released toxins interfere with normal activity of the host
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Bacterial Diseases and Antibiotics
Mycobacterium Tuberculosis Destroys cells in the lungs Streptococcus and Clostiridium botulinum Strep throat Food poisoning Corynebacterium diptheriae Diptheria Common to have a rash (possibly associated with scarlet fever) Staph normally lives in the nasal lining – transferred when food handlers do not wash their hands after blowing nose Clostiridium can cause death when food not properly canned – spores remain inactive in the food, then become active Diptheria releases toxins into the bloodstream where they destroy tissues and lead to breathing problems, heart failure, paralysis, and death
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Bacterial Diseases and Antibiotics
Block growth and reproduction of bacteria Major reason for increase in human expectancy Also prime example of evolution MRSA Evolution results from overuse, underuse, and misuse Overuse – taking antibiotic when no bacteria present Underuse – not finishing the course of antibiotic Misuse – antibiotics given to livestock to promote growth can allow the bacteria in livestock to evolve
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