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Transcript
Bacteria & Viruses By the end of this class you should understand: • How life may have arisen from nonliving materials • Modern classifications of bacteria and familiar species we encounter every day • The life cycle of parasitic protists • How viruses work and whether they are alive • How to protect yourself from bacteria and viruses Early Life on Earth • Life first appeared around 3.8 billion years ago, soon after liquid water formed – Not recognizable as modern life • Fulfilled the basics of life – Reproduced – Took in energy – Probably didn’t maintain homeostasis very well yet Nonliving Synthesis • Life is formed from large assemblies of macromolecules – How could these have been assembled without life? • There are a number of hypotheses on how these molecules could have been assembled – Clay deposits that preferentially collect charged particles and then dried up – Hydrothermal vents at the ocean floor naturally produce carbon molecules Protocells • One way or another, these molecules eventually formed into protocells – Protocells have been studied as a likely mechanism for a precursor to life • Essentially, fatty acids collect into a simple membrane, and inside, enzymes made of RNA called ribozymes convert other molecules into RNA – Cell grows as more RNA is absorbed and splits naturally Evidence for Protocells • A lot of evidence exists that this mechanism is possible, but that’s not the same thing as evidence that it actually happened • The key evidence is protein synthesis – Common to all life – Uses RNA-based process (ribosomes and tRNA) Prokaryotes Revisited • Modern bacteria are nothing like early bacteria • Through natural selection, only the hardiest and fastestreproducing bacteria were represented in the next generation – Bacteria can ideally reproduce in 20 minutes – One bacterium in a soup of nutrients can make a colony of 100 million bacteria in 12 hours Three Modern Domains of Life Archaea Eubacteria Bacteria that resemble early life Live in unusual environments What we think of as bacteria All pathogens are eubacteria Eukarya All eukaryotes including humans Archaea Oldest and least changed bacteria Many live in hostile environments Extremely acidic Deep ocean vents Boiling hot springs (extreme thermophiles) Salt marshes (extreme halophiles) Oil wells Others live in more “normal” environments Eubacteria Most bacteria that we are familiar with Many are harmless or even helpful Bacteria that live on our skin and in our gut are called normal flora and they crowd out more dangerous bacteria Some are dangerous to our health Usually eat our tissues for nutrients Some release dangerous toxins instead Classifications of Eubacteria Gram staining Gram positive: turn purple in a Gram stain • Has a cell membrane and a crunchy cell wall Gram negative: stay pink in a Gram stain • Has two cell membranes with a wall between Another Classification Aerobic – Aerobic bacteria can survive in air – Many bacteria on the skin – Mitochondria are related to early aerobic bacteria Anaerobic bacteria – Die when exposed to air – Lack catalase and peroxidase enzymes – Many bacteria in your gut and that spoil food How do anaerobes get around? Solution: spores! Some bacteria create spores in harsh conditions These spores can survive almost anything Turn back into bacteria when the conditions have improved Bacteria shapes Coccus – sphere Bacillus – rod Spirillum – spiral Many other weirder shapes also exist Often in the bacteria name Staphylococcus Gram positive Common on human skin, usually harmless Some are harmful Infections Food poisoning Responsible for “Staph infection” Streptococcus Gram positive Many also found on human skin Dangerous strains responsible for “strep throat” Even more dangerous types cause Scarlet fever Most dangerous is “flesheating” bacteria Pictures not provided for the faint of stomach Escherichia coli “E. coli” Gram negative Common in human digestive tract Helpful for metabolism Some virulent strains exist “E. coli” outbreaks are really “Rare and dangerous strain of mutated E. coli outbreak” Often not the bacteria that is harmful but the toxins it produces Salmonella Gram negative Commonly found in humans and farm animals Can cause food poisoning in undercooked poultry products Other species cause typhoid fever Infect human cells using a capsule Potentially lethal Antibiotics Antibiotics are chemicals that selectively kill bacteria and not eukaryotic cells Ineffective against human, yeast, and protozoa Effective against certain types of bacteria only Penicillin was the first antibiotic that killed all Gram-positive bacteria Ampicillin and Streptomycin kill all bacteria Antibiotic resistance Bacteria constantly mutate and develop new genes Bacteria also pass genes to each other on plasmids, small rings of DNA As a result, bacteria may develop a resistance to an antibiotic, so taking antibiotics regularly is generally inadvisable Additionally, antibiotics kill the normal flora of your intestines and possibly your skin Better the devil you know... MRSA (methicillinresistant Staph aureus) is very dangerous Can have many resistance plasmids Becoming increasingly common in hospitals Best defense is a healthy immune system and normal flora This is a real problem… Protists • Protists are eukaryotic single-celled organisms – Amoebas, paramecium, etc. – Many probably resemble early eukaryotes • I will not be covering most of the protists since there are approximately a hojillion of them, but I will cover Plasmodium, the protist that causes malaria – Because I’m friendly like that! – Most protists are NOT infectious Malaria Life Cycle Virus A virus is a nonliving infectious particle that uses genetic information to reproduce All viruses reproduce by injecting their genetic molecules into a host cell The genetic molecules (DNA or RNA) force the cell to make more viruses Viruses have no metabolism of their own and do not maintain homeostasis or reproduce independently Parts of a Virus All viruses have: Protein coat Spikes that target host cell Genetic material Some viruses have a membrane called an envelope What about these weirdos? This is a bacteriophage Virus that infects bacteria Useful in scientific research Keeps its DNA in the capsule, injects it through the tube into the bacteria Bacteria have enzymes that try to chop up DNA that doesn’t belong, so it’s an ongoing arms race! What does the genetic info do? Sample: HIV in human cell Essentially the DNA or RNA causes the cell to make more viral proteins The viruses are exocytosed or bud off with envelope until the cell dies Host specificity The virus spikes can only latch onto certain receptors This keeps viruses from freely moving between different species of animals Crossover occurs due to mutation, e.g. “bird flu” Viruses can only infect certain cells in the host HIV only infects Helper T cells Rhinovirus infects epithelial cells Some viruses (e.g. herpes) infect nerve cells • These are generally incurable Antibiotics NOT for Viruses • Do NOT take antibiotics for viruses – Not only will it do nothing, it exposes you to potential bacterial infections to go with your viral infection! • Vaccines are available for some viruses – A vaccine is a piece of a bacterium or virus that your immune system “learns” to kill – Pre-training your immune system so you don’t get the same disease again • Many viruses and some bacteria mutate too quickly to have effective vaccines made! Protip: • VACCINES DO NOT CAUSE AUTISM • There was a time when vaccines were packaged with an antiseptic called thimerosal, which is a mercurycontaining compound – They are no longer packaged as such • The original study linking vaccines and autism was discredited, and many scientists have repeated the experiment but found no statistically significant difference • Autism is a developmental disorder and more prevalent in males, it cannot be caused by an injection at six months of age See you in lab!