Viruses and Prokaryotes

18.1- Studying Viruses and Prokaryotes A virus is an infectious particle made only of a strand of DNA or RNA surrounded by a protein coat A bacteria is a one-celled organism that can also cause infections

18.1- Studying Viruses and Prokaryotes Viruses and bacteria are pathogens. Pathogens are organisms or particles that cause diseases. However, this is where the similarities end.

18.1- Studying Viruses and Prokaryotes A virus is a problem for scientists because they don’t even believe it is a living organism. Living things have certain characteristics: They must show most notably reproducing on their own (VIRUSES CANNOT DO THIS) In fact, viruses are not anywhere in Linnaean classification.

18.1- Studying Viruses and Prokaryotes Other structures called viroids are even less like living things. Viroids cause diseases in plants. Finally, prions are the least likely to be living. These are just proteins that cause other proteins to act incorrectly.

18.1- Studying Viruses and Prokaryotes Viruses, Viroids, and Prions are all particles that cause infections but are not considered living things because they do not have all the characteristics of living organisms

18.2- Viral Structure and Reproduction Virus’ structure is very basic. It is made up of genetic material (DNA or RNA) surrounded by a protein shell called a capsid. Viruses have many different shapes and sizes. Their shape usually tells us something about how it infects a host cell

18.2- Viral Structure and Reproduction A virus can only reproduce with the help of a host cell. It has no mechanism to do it by itself: it has no organelles, membranes, no need for oxygen or ATP. It simply carries its genes to a cell and has that cell copy the genes for the virus

18.2- Viral Structure and Reproduction Viruses are specific. Certain viruses can only infect certain cells because of the viral shape. For example, the bacteriophage is a virus that ONLY infects bacteria. The bacteriophage has a specific shape that allows it to anchor to bacteria and inject its DNA. The whole bacteriophage does not enter the bacteria

18.2- Viral Structure and Reproduction Viruses that infect eukaryotes differ from bacteriophages in the way they enter cells. Generally, the whole virus enters the cell through endocytosis. Regardless of how viruses get into their host cells, all cause infection. Only two types of infection a virus causes LYTIC INFECTION LYSOGENIC INFECTION

18.2- Viral Structure and Reproduction A lytic infection causes the host cell to burst releasing new viral offspring into the host’s system and each new virus infects another cell. This type of infection happens very quickly.

18.2- Viral Structure and Reproduction A lysogenic infection merges together the host cell’s DNA and the viral DNA. The viral DNA combines with the host cell DNA to create a prophage. As the cell gets ready for mitosis, it copies it’s DNA and unknowingly copies the viral DNA as well. This viral DNA then gets passed on to two more cells. This can go on forever or at anytime the prophage can activate and burst all infected cells.

18.2- Viral Structure and Reproduction

18.4- Bacteria and Archaea Prokaryotes, which include bacteria and archaea are the most widespread organisms on earth. There are approximately (10^30) prokaryotes on Earth. These organisms live on about every square inch of Earth including rocks, soil, polar ice caps, deserts, and volcanoes. Scientists also acknowledge there may be as many as 1 billion different types of bacteria

18.4- Bacteria and Archaea Prokaryotes are grouped based upon their need for oxygen: Obligate Anaerobes- can not live in the presence of oxygen and are actually poisoned by it. These organisms live in the harshest enviornments on Earth Obligate Aerobes- Organisms that must have oxygen to survive Facultative Aerobes- these types of organisms can live with or without oxygen

18.4- Bacteria and Archaea

Domain Bacteria and Domain Archaea comprise all prokaryotes on Earth. Domain Bacteria are more diverse and are the ones you encounter of a daily basis. Domain Archaea are the prokaryotes that live in the harshest of environments. However, these two groups have some similarities.

18.4- Bacteria and Archaea Structural Comparisons- Under the microscope, Archaea and Bacteria look very similar. Both are single-celled, prokaryotic, and have cell walls Most all of Bacteria and Archaea come in generally 3 different shapes 1.Rod-Shaped (Bacilli) 2.Circle-Shaped (Coccus) 3.Spiral-Shaped (Spirilla)

18.4- Bacteria and Archaea Most all prokaryotes have no membrane- bound organelles. Their DNA is free-floating in the cytoplasm. They also have a structure called a plasmid, that is a small piece of genetic material that can replicate separately from regular chromosome.

18.4- Bacteria and Archaea Most all prokaryotes move on their own- Most use a flagella, which is a whip-like tail at the end of the organism. While looking the same, the flagella of Bacteria and Archaea are differently structurally. Some also have pili, which are shorter extensions all around the cell.

18.4- Bacteria and Archaea Molecular Comparisons- Molecular analysis techniques finally allowed scientists to see the many differences between Bacteria and Archaea. Actually, most scientists believe archaea are more closely related to Eukaryotes rather than Bacteria. Archaea contain lipids in their cell membranes and walls

18.4- Bacteria and Archaea Molecular Comparisons (cont.) Bacteria, however, contain a substance called peptidoglycan, a polymer only found in Bacteria. The amount of peptidoglycan in the cell walls is an important characteristic of Bacteria. This polymer is detected by a process called Gram-Staining.

18.4- Bacteria and Archaea Gram-Staining- Bacteria are placed in 2 groups based on this test: Gram tests are used to detect the amount of peptidoglycon in a cell wall. Gram-Negative: Stains red and means there is only a thin layer of peptidoglycan Gram-Positive: Stains purple and means there is a very thick layer of peptidoglycan

18.4- Bacteria and Archaea

Prokaryotes have found numerous ways to survive and pass on genes: They are very quick at adapting to a new environment. Most prokaryotes reproduce asexually and binary fission the chromosome copies itself and the cell doubles in size and then splits in half. Prokaryotes can sexually reproduce through conjugation the pili of each prokaryote connect and this connection is used to exchange genes

18.4- Bacteria and Archaea Prokaryotes can also survive unfavorable conditions by certain an endospore. This is a specialized cell with a thick wall to protect the prokaryotes from harsh conditions

18.5- Beneficial Roles of Prokaryotes Prokaryotes, such as bacteria, are a key part of animal digestion of foods. If we didn’t have these bacteria, it would take up to 7 days to digest food. They (bacteria) also make vitamins and other compounds and keep other microbes away. The bacteria gets a place to live and food.

18.5- Beneficial Roles of Prokaryotes Prokaryotes benefit us in other ways too. Many of the foods we enjoy are fermented by bacteria. Yogurt, cheese, pickles, soy, sauerkraut, and vinegar depending of prokaryotes to be made.

18.5- Beneficial Roles of Prokaryotes Prokaryotes also help balance the ecosystem: Some, like cyanobacteria, produce oxygen while others recycle carbon and other gases Other bacteria fix nitrogen so plants can use it: Plants need nitrogen, but can’t use it in it’s atmosphere gas form. Bacteria takes atmospheric nitrogen and converts it to ammonia for plants to use. Soybeans would not survive without this benefit

18.5- Beneficial Roles and Prokaryotes Some prokaryotes can even be used to clean the environment. So bacteria digests oil, helping in oil spills. Bacteria also breaks down decaying organic matter.

18.6- Bacterial Diseases and Antibiotics Bacteria can cause sickness for a host organism in two ways: 1.Invading Tissues 2.Releasing Toxins EXAMPLES: 1. Tuberculosis- invading lung tissues and kill white bloods cells 2. Botulism (Food Poisoning)- caused by toxins released by a bacteria called clostyidium botulinum.

18.6- Bacterial Diseases and Antibiotics Antibiotics- These are medications that fight bacterial infection. THEY DO NOT FIGHT VIRAL INFECTIONS LIKE COLDS AND FLUS!!!

18.6- Beneficial Diseases and Antibiotics Antibiotics work by not allowing bacteria to create cell walls so they cannot reproduce. Some organisms, such as some fungus, create antibiotics normally. Antibiotics, however, should not be the 1 st line of defense against infections, prevention should be…………WASH YOUR HANDS!!

18.6- Bacterial Diseases and Antibiotics Finally, when given an antibiotic, do not abuse it, but instead, follow the directions. When mis-used, bacteria can build-up a resistance to antibiotics. Mis-using involves using too much or not taking all of antibiotics of a given course of treatment. Both of these cases create “superbugs” that are bacteria that can resist almost any antibiotic.