1	VIRUSES Viruses can replicate only in a host (living cell). They require parts from their hosts for transcription and translation. Virus are, therefore, not considered to be organisms.
2	Reading Assignment Chapter 34 up to p. 796 plus ‘The SARS Outbreak’ essay on p. 799. Monday is the first BioS 101 exam. There will be a seating chart (according to your teaching assistant). Complete the scantron answer sheet information at the beginning of the exam. Do not wait until the end of the exam.
3	Why viruses don’t have scientific names Viruses can multiply only within the cells of host organism. Viruses don’t have any metabolism outside of a host cell. Viruses don’t have an independent ‘tree of life’ that links them all together, but viruses do evolve, as you will learn when we discuss new diseases.
4	Plasmids, simpler than virus Plasmids, usually circular DNA, can infect bacterial cells. Plasmids never form a capsid (protective cover). –that distinguishes them from viruses. Plasmids often carry genes for resistance to antibiotics. The R plasmid carries resistance to many antibiotics and spreads from benign bacteria to species that cause disease.
5	Viruses are smaller than cells Because they are small, the abundance of viruses is very high (large N). Small particles essentially float in air, but many viruses can not infect a new host via air. Viruses need a way to get into cells. Usually they use a particular protein on the cell surface and are therefore show high specificity, i.e. can only attack cells with that protein.
6	Viral diseases When a disease effects a large number of individuals at the same time, it is referred to as an epidemic. A virus or organisms that is able to kill the host after infection is called virulent. A virus or organisms that causes a human disease is called a pathogen.
7	Structure of Viruses All viruses store hereditary information in nucleic acids, but only a small proportion of viruses use double-stranded DNA. All viruses have a protein coat called a capsid. Enveloped viruses are surrounded by a lipid layer derived from the host. The others are said to be nonenveloped.
8	Reverse transcriptase Some viruses use RNA to store information. Many of these viruses, HIV included, make DNA complementary to the RNA. This is done with an enzyme call ‘reverse transcriptase’ (because it copies RNA into DNA -the opposite of transcription.) Reverse transcriptase has been a very important enzyme for research.
9	Entry of Viruses into cells Wounds, bites and air are ways viruses can initially get inside an individual, but this does not tell us how the virus spreads among cells of the body. Cells have proteins on their surface (doing many tasks). Most viruses attach to particular proteins and enter the cell thru that attachment.
10	How are viruses transmitted to new hosts? Public health involves protecting the human population from disease. For diseases that spread by intimate contact, developing a list of contacts is information that can be used to combat the spread.
11	Vaccination & Immune system The immune system defends the body against ‘exotic’ molecules. Self or native molecules were inventoried early in life. The immune system scrambles information so that essentially any type of molecule can be recognized (fit or match). When exotic molecules are detected, the cells that recognize them are stimulated to grow.
12	Vaccination Dead or damaged viral particles are injected into an individual. The material injected in a vaccination (antigens) stimulates the immune system to produce antibodies. The immune system ‘remembers’ the antigen and responds more quickly the next time it sees the antigen.
13	Vaccination Vaccination prepares the immune system to respond to a disease that it has not yet encountered. People who have been vaccinated will respond by quickly producing antibodies against the disease, if they are later exposed. Vaccinated individuals are said to be immune to the disease.
14	Population dynamics Contagious diseases typically can spread from individual to individual only a a particular stage or time period. If many individuals are immune to a disease, the rate of spread is reduced. If enough are immune, the disease dies out because it can find no never-infected individuals.
15	The Lytic Cycle of bacteriophage Nucleic acid injection Nucleic acid replication Translation into protein Capsid proteins surround nucleic acid. Host cell bursts open and the viral particles are released.
16	Lysogenic replication is alternative to lytic cycle Sometimes viral DNA integrates into the host DNA instead of replicating and making more viruses. In that state it causes no problems to host and does not produce viral proteins -until something causes it to ‘pop out’ of host DNA.
17	Emerging viruses emerging diseases Diseases are NOT permanent components of the human ‘landscape’. Most of the viral diseases that we are concerned with today did not exist as human diseases a few hundred years ago. A pathogen that jumps from animal into human populations is called a zoőnosis.
18	New Viral Diseases Hanta virus Ebola virus West Nile virus HIV SARS Severe acute respiratory syndrome Severe = serious, really sick Acute = rapid progression from onset to really sick
19	Origin of a new disease How does one figure out the probable source of a new viral disease? Identify the earliest cases. Look for common elements shared among the earliest cases. Use knowledge/experience of other epidemics to focus on likely common elements. Look for homologous nucleic acid sequences in the putative source(s).
20	The SARS outbreak Physicians familiar with the syndromes of diseases are the crucial link in recognizing new diseases. Syndrome is a name for the set of symptoms associated with a particular cause. Though many diseases effect a particular part of the body, good physicians recognize subtle symptom differences to classify the case as a particular known or new disease.
21	SARS continued The symptoms are described and other doctors are altered to look for the syndrome in their patients. By tracking the movements of people and getting information about the extent of contact among people, one learns how the disease is spread and identifies possible new victims. SARS has infected very few people because of effective tracking and rapid understanding.
22	Vocabulary Acute Antibody Antigen Epidemic Host Lysis Mutation Plasmid Public health Reverse transcriptase Severe Syndrome Vaccination Virulent