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Viruses

Viruses. Doesn’t belong to any kingdom -It’s not a plant or an animal. -It’s not a fungi, protist, or bacteria. WHAT IS A VIRUS?. A virus is an infectious agent made up of nucleic acid ( DNA or RNA ) wrapped in a protein coat called a capsid .

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Viruses

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  1. Viruses Doesn’t belong to any kingdom -It’s not a plant or an animal. -It’s not a fungi, protist, or bacteria. WHAT IS A VIRUS?

  2. A virus is an infectious agent made up of nucleic acid (DNA or RNA) wrapped in a protein coat called a capsid. Viruses have no nucleus, no organelles, no cytoplasm or cell membrane—Non-cellular This is why it does NOT belong to any kingdom. vs

  3. Viruses have either DNA or RNA but NOT both. Viruses with RNA that transcribe into DNA are called retroviruses. • Viruses are parasites—an organism that depends entirely upon another living organism (a host) for its existence in such a way that it harms that organism. HIV Infected Cell (This is the reason why HIV is so incurable.) A flea is a parasite to a dog and is harmful to the dog.

  4. Bacteriophage—viruses that infect bacteria Capsid(protein coat) • inside contains either • RNA or DNA 2. Flu (influenza), HIV DNA or RNA Surface Marker Capsid(protein coat)

  5. Capsid Nucleic Acid Bacteriophage—a virus that infects bacteria (bacteria is the host)

  6. Characteristics of Retroviruses • Contain RNA, not DNA • Family Retroviridae • Contain an enzyme called ReverseTranscriptase • When a retroviurs infects a cell, it injects its RNA and reverse transcriptase enzyme into the cytoplasm of that cell. • Examples: • HIV, the AIDS virus, is a retrovirus • Feline Leukemia Virus is also a retrovirus

  7. C. Replication (reproduction): is how a virus spreads. A virus CANNOT reproduce by itself—it must invade a host cell and take over the cell activities, eventually causingdestruction of the cell and killing it. (The virus enters a cell, makes copiesof itself and causes the cell to burst releasing more viruses.) DNA/RNA is copied. DNA/RNA injected into cell. Virus attaches to cell. Step 3 Step 2 Step 1 Virus copies itself. Cell bursts (lyses) and releases new viruses. Step 4 Step 5

  8. Certain viruses can only attack certain cell types. They are said to be specific. Example: The rabies virus only attacks brain or nervous cells. Surface Markers Virus Receptor Sites It’s like the pieces of a puzzle. The ends have to match up so only certain pieces fit. Cell

  9. A virus recognizes cells it can infect by matching its surface marker with a receptor site on a cell. Virus Surface Markers Cell Receptor Sites

  10. Cell Cycle • Attachment Phage attaches by tail fibers to host cell • Penetration Injection of viral DNA or RNA • Replication (Biosynthesis) Production of new viral proteins and nucleic acid • Maturation (Assembly) Assembly of a new virus • Release of the new virus into the environment (cell lyses)

  11. Viral Lysogenic • Some viruses have the ability to become dormant inside the cell called latent viruses • They may remain inactive for long periods of time (years) • Later, they activate to produce new viruses in response to some external signal HIV and Herpes viruses are examples.

  12. Vaccines • An attenuated virus is a weakened, less vigorous virus • “Attenuate” refers to procedures that weaken an agent of disease (heating) • A vaccine against a viral disease can be made from an attenuated, less virulent strain of the virus • Attenuated virus is capable of stimulating an immune response and creating immunity, but not causing illness

  13. Virus Living Cell RNA or DNA core (center), protein coat (capsid) Cell membrane, cytoplasm, genetic material, organelles Structure Copies itself only inside host cell--REPLICATION Asexual or Sexual Reproduction DNA and RNA Genetic Material DNA or RNA Growth and Development NO YES—Multicellular Organisms Obtain and Use Energy NO YES Response to Environment YES NO Change over time NO YES

  14. Think back to the 8 characteristics of life. How many characteristics of life do viruses possess? ONE *Genetic Material DNA/RNA Are viruses living? NO

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