Viruses+and+Bacteria

=  I.  VIRUSES  = ==  A.  What is a virus?- Viruses are made up of nucleic acids contained in a protein coat and are smaller than the smallest bacterium. It is widely considered that viruses are non-living because they don’t show all the criteria for life. They don’t grow, respirate, or develop. All they can do is replicate (make copies of themselves) They must have a living cell to do anything which is called the host cell. == ===  1.  Viral Structure- A virus has an inner core of nucleic acid, either RNA or DNA, and an outer protein called a   capsid. Larger viruses often have additional layers called an envelope surrounding their capsids. The nucleic acid core contains a virus’s genetic material. Viral nucleic acid is either DNA or RNA and holds blueprints for making copies of the virus. Some viruses have as little as four genes where as others have several hundred. The order of proteins in the capsid of a virus determines the virus’s shape. === ===  2.  Attachment to a host cell- A virus needs to attach to a host cell before it can replicate. To do this it attaches to a receptor site of the host cell. One of the virus’s proteins locks to the receptor. ===

1. Lytic Cycle- inside the cell viruses genes are expressed in the substances that are created take over the genetic material of the host cell
===  2.  Lysogenic Cycle- not all viruses kill the cells they infect, some viruses go through a lysogenic cycle. It’s a replication cycle in which the virus’s nucleic acids are put into the host cells chromosomes. Viral DNA that is integrated into the host cells chromosome is called a  provirus. Every time the host cell reproduces the provirus is replicated as well. === ===  3.  Disease Symptoms of Proviruses- the lysogenic process explains the recurrence of cold sores, which is caused by the herpes simplex I virus. Even though a cold sore heals the virus remains in your cells as a provirus. ===

5. Retroviruses- HIV and many other viruses are RNA viruses. The RNA virus with the most complex replication cycle is the  retrovirus.
===  6.  HIV: An infection of white blood cells- Once inside a human body HIV infects white blood cells. Newly made viruses are released into the blood stream, and infect other white blood cells. An HIV infected person can experience no AIDS symptoms for a long time. ===

C. Cancer and Viruses- Some viruses have been linked to certain cancers.
===  1.  Prions and viroids- scientists have found some particles that behave similar to viruses and cause infectious diseases. Prions are composed of proteins without nucleic acid. Viroids are made of a single circular strand of RNA with no protein code. === ===  2.  Plant viruses- there are more than 400 viruses that infect a variety of plants. These viruses cause as many as one thousand plant diseases. Not all viral plant diseases are fatal or even harmful. ===

D. Origins of Viruses- Viruses are not ancestral forms of life because they have probably originated from their host cells.
=  II. Archaebacteria and Eubacteria =

A. Diversity of Prokaryotes- Prokaryotes are unicellular organisms that are classified in two kingdoms, Archaebacteria and Eubacteria.
===  1.  Archaebacteria the extremists- three types of Archaebacteria that live mainly in extreme habitats. One type lives in oxygen free environments and produce methane gas. These Archaebacteria live in marches lake sediments, digestive tract of some animals. A second type lives only in water with high concentrations of salt. A third type lives in hot acidic waters of sulfur springs. ===

3. Eubacteria: Photosynthic Autotrophs- These eubacteria live in places with sunlight because they need the sun to make their food. They are composed of chains and independent cells.
===  4.  Eubacteria: Chemosynthetic Autotrophs- Like the photosynthetic autotrophs they make their own food, but instead of using the sun they break down and release the energy of inorganic compounds which is called   chemosynthesis. ===

B. What is a bacterium?- a bacterium consists of a very small cell, even though it is tiny it has all the structures necessary to sustain life
===  1.  The structure of bacteria- Prokaryotic cells have ribosomes but their smaller than those of the eukaryotes. They have genes that are located mainly in single circular chromosomes. Because bacteria live in hypotonic environments where there is a high concentration of water molecules, water is always trying to enter the cell. In 1928 Sir Alexander Fleming accidently discovered penicillin, the first antibiotic. Later biologists found that penicillin can interfere with the ability of some bacteria to create cell walls. === ===  2.  Identifying bacteria- Scientists have found ways to distinguish bacteria. One example is how they react to gram stain. This distinguishes two groups based on the difference of the composition of their cell walls. When staining gram positive are purple and gram negative are pink. Gram posititve are affected by different antibiotics than gram negative. Gram stains also give bacteria different shapes which is another way to categorize bacteria. === ===  3.  Reproduction by binary fission- bacteria arent able to reproduce by mitosis or meiosis because they have no nucleus. Also they do not have pairs of chromosomes but one circular chromosomes, with smaller pieces of DNA called plasmids. Bacteria reproduce asexually by a process called binary fission. To do this the chromosome is copied and is attached to the cells plasma membrane. It grows bigger and eventually the cell separates === ===  4.  Sexual Reproduction- some bacteria have a form of sexual reproduction called   conjugation. During this one bacterium transfers some or all of its chromosome to another cell through a bridge like structure called a pili. ===