VIRUS STRUCTURE

• Nature has found two basic ways of arranging the multiple capsid protein subunits and the viral genome into a nucleocapsid. The simpler structure is a protein helix with the RNA or DNA protected within. Tobacco mosaic virus (TMV) is a classic example of the helical nucleocapsid.

WHAT A VIRUS LOOKS LIKE

THE DISEASES VIRUSES CAUSE

• Viruses cause familiar infectious diseases such as the common cold, flu and warts. They also cause severe illnesses such as HIV/AIDS, smallpox and hemorrhagic fevers. Viruses are like hijackers. They invade living normal cells and use those cells to multiply and produce other viruses like themselves.

WHAT THEY ARE USED FOR BY HUMANS

• Virus's are used to make vaccines, Vaccines are made using the disease-causing virus or bacteria, but in a form that will not harm your child. Instead, the weakened, killed, or partial virus or bacteria prompts your baby's immune system to develop antibodies, or defenders, against the disease.

QUIZ ON VIRUS'S

• 1. A virus consists of: RNA or DNA and a cell membrane. RNA or DNA and a protein coat. RNA and DNA and a protein coat. proteins, cell membrane and RNA.
• 2. How do viruses reproduce? they divide by mitosis. sexually, by external fertilisation. replication outside the host. inserting DNA into the host cell.
• 3. Which of the following is smallest? eukaryote cell. bacteria. bacteriophage. cell membrane protein.
• 4. Retroviruses are different from viruses in that: they have RNA instead of DNA. they can become dormant. they are symmetrical all of these.
• Vaccines can be used to prevent viral infection by: creating an immune response in the host. destroying any viruses that enter the host. creating a blocking protein on the cell. preventing replication of the virus.
• Antiviral drugs that are used after infection often prevent: cell division. immune system degradation. reinfection by other viruses. uptake of the virus.
• Why do some viruses seem to go away and then return later, like a cold sore? host has been infected with a different strain. the immune system forgot the virus. the virus had entered the lysogenic cycle. the virus mutated.
• 8. Why is it difficult to develop vaccines for retroviruses? their small size evades the immune system. RNA mutates more frequently than DNA. the capsid of retroviruses is resistant. vaccines can only target blood-borne pathogens.
• Viruses are often named by: where they were first discovered the scientist who discovered it. the animal that carries it. all of these.
• What happens after the virus has been taken up by the cell? it begins making protein. it divides. it inserts into the host DNA. it switches to infectious mode.

QUIZ ANSWERS

• 1. RNA or DNA and a protein coat 2. inserting DNA into the host cell 3. bacteriophage 4. they have RNA instead of DNA 5. creating an immune response in the host 6. uptake of the virus 7. the virus had entered the lysogenic cycle 8. RNA mutates more frequently than DNA 9. all of these 10. it inserts into the host DNA