Presentation on theme: "Viruses and Prokaryotes. What is a Virus? A virus is a noncellular particle made up of genetic material and protein that can invade living cells Structure."— Presentation transcript:
Viruses and Prokaryotes
What is a Virus? A virus is a noncellular particle made up of genetic material and protein that can invade living cells Structure –Core of nucleic acid surrounded by a protein coat called a capsid –Capsid can be DNA or RNA, but not both –Core can be several to several hundred genes
SO HOW BIG ARE VIRUSES??? Viruses are REALLY small. They are much smaller than bacteria. They can only be seen with an electron microscope.
Bacteriophage Bacteriophages are viruses that infect bacteria Bacteriophage –Head – capsid and DNA –Tail – with fibers to attach to bacteria
T group Most commonly studied are T group – T1, T2, T3, T4 etc... T4 has a DNA core within a protein coat, and tail with tail fibers to attach to bacteria.
Viral shapes Variety of shapes –Rod –Tadpole –Many sided, helical or cubelike
VIRUS SHAPES Round Rod-shaped Many sided (icosohedral)
SHAPES MAY DIFFER BUT… T4 Bacteriophage Tobacco Mosaic Virus Influenza Virus Head Tail sheath DNA Tail fiber RNA Capsid Surface proteins Membrane envelope RNA Capsid proteins All viruses have 1. Chromosome-like part that carries hereditary information – The Core 2. Protein coat: Protects hereditary information and provides the shape! The Capsid
ROUND VIRUSES Herpes virus –There are two types: Genital oral
ROD-SHAPED Tobacco mosaic virus
MANY SIDED bacteriophage E coli bacteria
Is this why viruses infect us? YES! Viruses need living organisms in order to reproduce and form more viruses! virusInjecting DNA
Virus Size Size – 20 to 400 nanometers (one nanometer is one billionth of a meter) Specificity – usually infect specific organisms –Cannot infect animals if it infects plants –Some can infect wider variety –Rabies – all mammals, some birds
VIRUSES ARE SPECIFIC IN THE CELLS THEY INFECT Rabies: only nervous system cells of mammals Common cold: infects cells on airway passage to lungs Tobacco mosaic virus: only tobacco plants…not wheat or corn
Lytic Infection Cause cells to lyse or burst 1.Infection – chance contact virus with right kind of bacterium. Virus attaches to bacterium and injects its DNA. Most times, complete virus particle does not enter. 2.Growth – Bacterium can’t tell difference between bacterial and viral DNA. RNA polymerase causes mRNA to be made from cell for virus. Viral DNA takes over and produces more DNA and viral proteins. 3.Replication – Virus uses bacterial material to make thousands of copies of the protein coat and DNA. Cell becomes filled with virus particles. (All three stages can happen with E. coli within 25 minutes!) 4.DNA serves as central point for virus particles to be assembled. Cells fill with virus and lyse (burst). New viruses can now infect new cells.
SO HOW DO VIRUSES CAUSE DISEASE? Bacteriophage enzyme lyses the bacterium’s cell wall, releasing new bacteriophage particles that can attack other cells. Bacteriophage proteins and nucleic acids assemble into complete bacteriophage particles Bacteriophage takes over bacterium’s metabolism, causing synthesis of new bacteriophage proteins and nucleic acids Bacteriophage injects DNA into bacterium Bacteriophage attaches to bacterium’s cell wall Bacteriophage Bacteriophage DNA Bacteriophage protein Bacteriophage protein coat Bacteriophage DNA Bacterial chromosome Lytic Cycle Section 19-3
Retroviruses RNA viruses When they infect a cell, they produce DNA copies of their RNA genes. Retroviruses have their genetic information copied backwards. RNA DNA One retrovirus is HIV. Others cause cancer in animals and humans. The theory is that viruses were not the first living things. They are dependent on living things to survive.
EUBACTERIA AND ARCHAEBACTERIA: The two bacterial kingdoms Bacteria on a pin head
Eubacteria “True” bacteria largest Kindgom of prokaryotes generally surrounded by cell wall composed of complex carbohydrates have a cell membrane (some have 2 cell membranes) Some have flagella for movement Found everywhere Some produce disease Some photosynthetic some very useful – cheese is just one example
PROKARYOTIC CELLS Prokaryote – what does that mean? Classification of Prokaryotes All prokaryotes were in kingdom Monera. Now – 2 kingdoms –Eubacteria and archaebacteria
Archaebacteria Archaebacteria includes organisms that live in very harsh environments Methanogens – live in oxygen free environments – mud, digestive tracts of animals Extremely salty environments Hot springs
Cell Wall Chemical nature – Gram staining Hans Christian Gram 2 dyes – crystal violet (purple) and safranine (red) –bacteria either take one or the other –If only one thick layer of carbohydrate and protein molecules outside the cell membrane – picked up crystal violet – appeared purple – GRAM POSITIVE –If cell had 2nd, outer layer of lipid and carbohydrate – picked up safranine – appeared red GRAM NEGATIVE
Bacterial movement propelled by flagella lash, snake, or spiral forward no movement
Bacterial Respiration Obligate aerobes – require oxygen Obligate anaerobes – must live in absence of oxygen –example is Clostridium botulinum Facultative anaerobes – can live with or without oxygen
Reproduction Some can reproduce every 20 minutes Held in check by food and production of wastes Types: Binary Fission Replication of DNA and division in half Asexual Conjugation Sexual – involves the exchange of genetic material Long bridge of protein forms between the cells Donor genetic information transferred to recipient through bridge Recipient cell has different genes at the end than it did to begin with
Importance of Bacteria Used in production of products we use every day Yogurt Cheese Buttermilk Sour cream Pickles Sauerkraut Vinegar Wine Industry digest petroleum remove wastes and poisons from water synthesizing drugs – through genetic engineering
Symbiotic Relationships (mutuallism) E. coli in humans – help us digest food – make vitamins we can’t, we give them a home, food, and transportation Bacteria in the intestines of cattle allow them to break down cellulose (in grass and hay)
Bacteria in the Environment Bacteria are like the stage hands that allow the show to go on without being seen (or always given the credit) Bacteria recycle and decompose dead material Saprophytes – organisms that use the complex molecules of a once living organism as their food source
Sewage decomposition Sewage treatment – bacteria is added directly to the raw sewage How does a septic tank work?
Nitrogen Fixation All organisms are TOTALLY dependent on monerans for Nitrogen All Plants need nitrogen to make amino acids (- NH2) Because animals eat plants, they get their proteins from plants What percentage of the air is Nitrogen? Plants, and most other organisms cannot use this directly Need Nitrogen to be “FIXED” chemically as ammonia
Nitrogen Fixation Scientists can make synthetic nitrogen containing fertilizers by mixing Nitrogen and Hydrogen gases, heating to 500 degrees C and compressing it to 300 X normal atmospheric pressure – dangerous, expensive, time consuming Many cyanobacteria can take nitrogen from the air and convert it to a useable form – this is called Nitrogen Fixation Bacteria are the only organisms that can do this. Some plants have a symbiotic relationship with nitrogen fixing bacteria soybean – Rhizobium grows in nodules around roots
Diseases caused by Viruses and Monerans only a small number of viruses and bacteria can cause disease Pathogens – organisms that cause disease All viruses infect living cells Disease occurs when infection causes damage to the cells
Vaccine The body’s own defenses must be used Vaccine – dead or weakened viruses that stimulate the bodies defense system Symptoms can be treated sometimes, but once someone is infected by a virus, there is not much science can do
2 ways bacteria cause disease 1.Damage cells and tissues of infected organisms directly by breaking down cells 2.Releasing toxins (poisons) Many bacteria can live without a host organism (on a petri dish) Rickettsiae cannot live outside a host cell. They have leaky cell walls Rickettsiae cause Rocky Mountain Spotted Fever, typhus, and Legionnaire’s disease
Measures to fight bacterial infection include: –Antibiotics – drugs and natural compounds that attack and destroy bacteria in the body –NOT Effective against viruses