Viruses and Bacteria Lecture Notes
1. Compare the structure and functions of viruses to cells and describe the role of viruses in causingdiseases and conditions such as acquired immune deficiency syndrome, common cold, smallpox,influenza and warts.
2. Identify and describe the role of bacteria in maintaining health such as in digestion and causing
diseases such as in streptococcus infections and diphtheria
Piliare short, hair-like appendages that protrude through the capsule and serve in theattachment of bacteria to surfaces. The ability of the pili to attach to host cell receptorsdetermines the type of tissues that a bacterium can colonize. A specialized pilus known asthe sex pilus is involved in the transfer of DNAfrom one bacterium to another via aprocess known as conjugation. This ability to transfer DNA is an important factor in thespread of antibiotic resistance genes through a microbial community. Another difference between bacteria and viruses is motility. Viruses do not possess structures that enable them to move purposefully through the environment. Bacteria, on the other hand, are able to move through the environment using a structure known as the flagellum. Surrounding the bacterial plasma membrane is a cellwallcomposed of peptidoglycan. Peptidoglycan is composed of two glucose derivatives (N-acetylmuramic acid and N-acetylglucosamine) that are joined together into long chains. These long carbohydrate chains are then joined together by short amino acid chains, and the entire molecule is stabilized by additionalpeptidechains. The cell wall has a number of functions, including maintaining the shape of the cell, preventing the rupture of the cell in response to osmotic stress, and in some cases, contributing to the virulence of a bacterium. Antibiotics such as penicillin are effective because they disrupt the synthesis of peptidoglycan, thereby making the bacterium more susceptible to osmotic stress. Some bacteria, referred to as gram-negative bacteria, possess an additional outermembranethat surrounds the cell wall. A few groups of bacteria are able to produce structures referred to as endosporesin timesof nutritional stress. These endospores are difficult to kill and will remain dormant untilintroduced into an environment that is nutrient rich. Some examples of bacteria thatproduce these structures are Clostridium tetani (the causative agent of tetanus) andBacillus anthracis, the causative agent of anthrax.
Regardless of the type of host cell, all viruses follow the same basic steps in what is known as the lyticcycle(see figure above):
1. A virus particle attaches to a host cell. All viruses have some type of protein onthe outside
coat or envelope that "feels" or "recognizes" the proper host cell(s).
2. The particle releases its genetic instructions into the host cell.
3. The injected genetic material recruits the host cell's enzymes.
4. The enzymes make parts for more new virus particles.
5. The new particles assemble the parts into new viruses.
6. The new particles break free from the host cell
Your immune system responds to the infection, and in the process of fighting, it produces chemicals called pyrogensthat cause your body temperature to increase. This feveractually helps you to fight the infection by slowing down the rate of viral reproduction,because most of your body's chemical reactions have an optimal temperature of 98.6degrees Fahrenheit (37 degrees Celsius). If your temperature rises slightly above this, thereactions slow down. This immune response continues until the viruses are eliminatedfrom your body. However, if you sneeze, you can spread thousands of new viruses into
the environment to await another host.
Bacteria & Disease
The first thing the bacterium has to do isenter your system. We come into contact with millions of bacteria every day. They are in the air we breathe,in and on the food we eat and on the surfaces of most things we touch. Apart from ournormal flora, bacteria that come into contact with us have to pass our various defensemechanisms, our dry skin and our acid stomach. Physical actions such as the movementof matter through our alimentary canal, brushing our teeth and washing all help to makelife difficult for bacteria. Those bacteria which do colonize our system generally do so bybreaking through the mucus barrier that lines most of our alimentary canal (mouth toanus), or entering through damaged tissue, i.e. wounds and bites, etc.
Once a bacterium has entered the system it is free to grow and spread.
Infection simply means the bacterial or other agent entering the system. It does not equate with disease or damage. You can be infected by an organism that never makes you ill. Aninfectious agent is simply an organism that is capable of getting past your defenses andthen living/growing inside or you.
Bacteria rarely, if ever, cause disease merely by being present The pathogenicity ofinvasive bacteria, or their ability to cause disease is generally the result of toxins.
Substances produced by the bacterial cell, sometimes simply as a by-produce of its normal metabolism, which interact negatively with our body, by interfering with thenormal functioning. This is often done by simply damaging the specific cells, blockingthe transmission of some sort of internal signals or other or by overstimulating some sortsof cells so they malfunction. The ecological reasons for the production of these toxins isnot always understood. Also, because of the vagaries of bacterial genetic reproduction,
otherwise harmless species can acquire a gene which causes them to secrete a toxin, thus making them a pathogenic strain of a normally harmless species. A good example of thisis Escherichia coli which lives harmlessly in most people's intestines but whichoccasionally makes us sick.Toxins that are leaked or secreted out of the bacteria cell and into its host (you and me) iscalled an Exotoxin.. Cholera toxin works by disrupting the ionic balance of cells'membranes which results in the cells of the small intestine secreting large amounts ofwater into the intestine. This keeps happening and has two effects; all the water in thesmall intestine causes diarrhea and thus the body dehydrates. Eventually the small intestine loses water faster than the large intestine can reabsorb it and death follows fromdehydration. Clostridium botulinum produces toxins which are among the mostpoisonous or toxic substances known. One milligram of pure Botulinum toxin is enoughto kill 1 million guinea pigs.
Beneficial Bacteria:
• Help make essential soil mineral elements, available to the plant NitrogenFixation
• Decompose organic matter and improve physical properties of the soil
• Vast numbers of bacteria live in our bodies. One example is found in the intestine. This bacteria and humans have formed a symbiosis with each other. The bacteriahelp us with digestion and to produce vitamins. In exchange, they soak up a littleextra food for themselves
• Most dairy products are made by or with the help of bacteria. Some dairy foods are cheese, buttermilk, yogurt, and sour cream. Some other kinds of foods thatinvolve bacteria in their production are pickles and high fructose corn syrup.
• Bacteria help in the production of fuel in two major ways. Some bacteria decompose compost, garbage and sewage and help make methane. Methane is avaluable natural gas. It is used widely as a fuel. Also, over time, the earth'spressure has changed dead and decomposed animals and plants into coal, which isalso a widespread fuel.
• Bacteria also make, or help to make drugs, hormones, or antibodies.
• Bacteria can even help to break down oil to make clean-up after an oil spill easier.