Upcoming… Today: intro to viruses, project assigned, MiN 1/5/14: FINAL MiN! due 1/6/14 & 1/8/14: work on projects in class 1/10/14: sub- virus activity & study guide 1/14/14: project presentations 1/16/14: finish presentations; assessment on projects, viruses, antibiotic resistance 1/21/14: Review 1/23/14: FINAL! Last class before switch

Warm-Up (full sentences in NB) Do viruses contain genetic information? If so, is it DNA, RNA, both, or depends on the virus? How are viruses transmitted between organisms? Are all viruses harmful?

VIRUSES

GENERAL CHARACTERISTICS Obligatory Intracellular Parasites Protein coated fragments of DNA or RNA. Because they cannot replicate on their own, they are not organisms. Viruses are generally host-specific. They reproduce only within a certain host.

VIRUS

Viruses and Harm Not all viruses cause disease Not all viruses are harmful to humans Some are harmful because the virus enters a host cell, forces the host cell to make copies of the virus, and then the viruses are released from the host cell

VIRUS-HOST RANGE The host range of a virus is the spectrum of host cells the virus can infect. Some viruses have broad host ranges which may include several species(e.g. swine flu and rabies).

VIRUS-HOST RANGE (cont) Some viruses have host ranges so narrow that they can: –Infect only one species(e.g. phages of E.coli) –Infect only a single tissue type of one species(e.g. AIDS virus binds only to specific receptors on certain white blood cells.)

VIRAL SIZE Smallest = 17 nanometers in diameter. Largest = 1000 nanometers(1 micrometer) in greatest dimension. Few are barely visible at light microscope level. Most are visible only via Electron Microscope.

VIRAL STRUCTURE The virus is just nucleic acid enclosed by a protein coat. Viruses are classified by differences in the structures of these coats. Viruses can contain DNA or RNA

NUCLEIC ACID- VIRAL GENOMES Depending on the virus, viral genomes: –May be double-stranded DNA, single-stranded DNA, double-stranded RNA or single-stranded RNA.

CAPSID AND ENVELOPE Capsid: Protein coat that encloses the viral genome. It’s structure may be rod-shaped, polyhedral or complex.

ENVELOPE Membrane that cloaks SOME viral capsid Helps viruses infect their host. Derived from host cell membrane

GENERAL MORPHOLOGY. Helical viruses (Ebola and Rabies) Polyhedral viruses. (Adenovirus, and poliovirus) Enveloped viruses (Influenza and Herpes) Complex viruses(bacteria phages)

Break- Reading Read the handout (double-sided) and answer the questions that go along with it –Many of these questions can be answered without the reading, but a couple do require assistance from the reading Turn the answer sheet in when you are done

TAXONOMY OF VIRUSES Viruses are not organisms and are not classified in the kingdoms of life. In comparison to living things, viruses are acellular (not cells and do not consist of cells), do not metabolize energy, no photosynthesis, cell respiration or ferment. Viruses are cell parasites as they infect organisms at all taxonomic levels.

VIRAL MULTIPLICATION Viruses are nonliving particles that reproduce only inside specific host cells. There are two main viral cycles: –Lytic –Lysogenic

LYTIC AND LYSOGENIC CYCLES Lytic cycle: Results in the death or lysis of the host cell. Virus takes over the machinery of the cell, so viral replication and release occur. Virulent viruses reproduce by a lytic replication cycle= that lyse their host cells. Lysogenic cycle: Involves the incorporation of the viral genome into the host cell genome. Virus becomes a prophage ( genome integrated into the host genome) Later, the virus may reenter the lytic cycle and replicate itself. Temperate viruses= integrate and remain latent.

THE LYTIC CYCE Attachment- attached to the host cell Penetration-injects genetic material into host Biosynthesis- forces host cell to make new viral parts Maturation- assembly of the new viral parts into mature viruses Release- lysis of the cell and release of new mature virus

THE LYTIC CYCLE.

THE LYSOGENIC CYCLE Attachment Penetration Integration Prophage-viral genetic material incorporates into the host cells genetic material. The host will carry the viral genetic material without symptoms. –May be activated at a later time to become Lytic Replication- the integrated material replicates with the cell so that all new cells contain the viral genetic material

THE LYSOGENIC CYCLE.

Chain of Infection & Project Partners PPT on chain of infection Choose one other person to work with Sign up for a virus on the list at the front of the room If you have internet on your phone, you may find your own MiN article and work on it. If not, pick up a copy of the article I have up front and complete this month’s MiN!