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Viruses and Bacteria What is a Virus? • A virus is a tiny, nonliving particle that enters and reproduces inside a living cell. • A virus is considered nonliving because they do not have all the characteristics necessary for life. • What are the characteristics necessary for life? What is a Virus? • Viruses are not cells and do not have cells. • Viruses also do not use their own energy to grow or respond to their surroundings. • Viruses cannot make or eat food and do not produce waste. What is a Virus? • The only thing that makes a virus similar to an organism is that it can multiply. • Viruses multiply in a different way than organisms do. They can only multiply when they are inside a living cell. What is a Virus? • The organism that a virus enters and multiplies inside of is called a host. – The virus acts as a parasite, which is something that lives in or on a host and causes it harm. – Almost all viruses destroy the cells where they multiply. Virus Shape and Size • Viruses can come in all different types of shapes. • Viruses also come in different sizes, but all viruses are much, much smaller than even the smallest cells. – This makes viruses even smaller than bacteria. Virus Structure • Although viruses look different from each other, they all have a similar structure. • All viruses have two basic parts: – A protein that protects the virus – An inner core of genetic material Virus Structure • Each virus contains unique surface proteins which allow the virus to attach to a host cell. Active Viruses • After entering a cell, an active virus’s genetic material takes over cell functions. • The cell quickly begins to produce the virus’s proteins and genetic material. • These parts then assemble into new viruses. • When the cell is full, it bursts open, releasing hundreds of new viruses as it dies. Hidden Viruses • After a hidden virus enters a host cell, its genetic material becomes part of the cell’s genetic material. • Hidden viruses do not appear to affect the cell’s functions and may stay inactive for many years. Hidden Viruses • Each time the host cell with a hidden virus divides, the virus’s genetic material is copied along with the host’s genetic material. • Under certain conditions, the virus then becomes active. Viruses and Disease • Many diseases are caused by viral infections. • Some of these diseases, like colds, are gone after a short period of time, while others never go away. Gene Therapy • In gene therapy, scientists inject genetic material they want reproduced into a virus, and then as the virus enters a host cell, the cell reproduces that genetic material instead of the virus. Bacteria • Bacteria were discovered by a Dutch merchant named Anton van Leeuwenhoek. • He made this discovery in the late 1600s when he saw wormlike organisms in a sample he was looking at under a microscope. Bacteria Cells • Bacteria are single-celled organisms. • They are prokaryotes, which means that their genetic material is not held in a nucleus. Bacteria Cells • Bacteria cells have cell walls that protect them. • Beneath the cell walls is a cell membrane that controls what can go in or out of the cell. Bacteria Cells • Like plant and animal cells, bacteria have a gel-like cytoplasm filling the inside of the cell. • In the cytoplasm are ribosomes which produce proteins. • The genetic material can also be found in the cytoplasm. Bacteria Cells • Bacteria cells do not have any of the other organelles that plant and animal cells have. • Some bacteria also have flagellum coming off of the cell that help the cell move. • See page 49. Bacteria Cells • Bacteria cells come in three different shapes: – Spherical – Rodlike – Spiral Bacteria Cells • Bacteria can vary greatly in size, the largest being about the size of a period printed in a book. Most are much, much smaller and cannot be seen without the help of a microscope. Bacteria Food • Some bacteria are autotrophs, which means they make their own food. – Some use energy from the sun like plants. – Others use energy from chemical substances in their environment. Bacteria Food • Other bacteria are heterotrophs, which means they need to eat. – These organisms consume a variety of different food sources. Bacteria Reproduction • When bacteria have plenty of food, the right temperature, and other suitable conditions, they thrive and reproduce frequently. – However, these three things are often not all present. Bacteria Reproduction • Bacteria reproduce through binary fission. • Binary fission is when one cell divides to form two identical cells. Bacteria Reproduction • Binary fission is considered asexual reproduction because it only involves one parent. – Because only one parent is involved, the offspring is completely identical to the parent. Bacteria Reproduction • Some bacteria can undergo sexual reproduction, which involves two instead of one parent. – This happens through a process called conjugation, where one bacterium gives its genetic material to another. Bacteria Reproduction • Conjugation does not produce new bacteria, it just changes the genetic makeup of bacteria. Bacteria Reproduction • If the environment that a bacteria is living in is not suitable for reproduction, some bacteria can form endospores. – An endospore is a small, round, thick-walled cell that exists inside of the bacteria cell and contains some cytoplasm and genetic material. Bacteria Reproduction • Endospores can survive many years in harsh conditions. • Once the conditions are suitable for reproduction, endospores open up and the bacteria begins to grow and multiply. Bacteria in Nature • Most bacteria are actually harmless or helpful to people. – In fact, people depend on bacteria. Bacteria in Nature • Bacteria are involved in: – Oxygen production – Food production – Environmental recycling – Environmental cleanup – Health – Medicine Bacteria in Nature • Oxygen Production – Autotrophic bacteria which use the sun’s energy to make their own food produce oxygen, just like plants. – Since bacteria existed long before plants, and the atmosphere used to lack oxygen, scientists believe oxygen was first added to Earth’s atmosphere by these autotrophic bacteria. Bacteria in Nature • Food Production – Many foods would not exist if it weren’t for bacteria. • For example: – – – – – – – Cheese Pickles Vinegar Alcohol Yogurt Sour cream Many more Bacteria in Nature • Food Production – Some bacteria break down food chemicals, causing them to go bad. – This can be slowed or stopped by refrigeration, heating, or pasteurization. • Pasteurization is the heating of liquids so high that harmful bacteria is killed without changing the taste. Bacteria in Nature • Environmental Recycling – Some heterotrophic bacteria are decomposers, which means that they break down large chemicals in dead organisms into smaller chemicals. – By breaking down these chemicals, the chemicals can then be reused by living organisms. Bacteria in Nature • Environmental Cleanup – Some bacteria is used to help cleanup after oil spills, since they take in this oil as food. Bacteria in Nature • Health – Bacteria living in your body helps in all kinds of ways. • Some help you digest food. • Some make vitamins. • Some fight off disease-causing organisms. Bacteria in Nature • Medicine – Some bacteria either produce medicine or are used as medicine. • Penicillin • Insulin