Microbiology: Virus Structure

Question 1

Why can’t viruses replicate on their own?

Answer 1

*They are obligate parasites. They lack ribosomes, amino acids, nucleotides, E.R. or golgi to assemble proteins.

Question 2

^How do viruses interact with cell surfaces?

Answer 2

*Proteins on their surfaces determine what cellular receptors through which it will enter.

Question 3

^What are viruses made of?

Answer 3

*Proteins (capsids & enzymes), nucleic acids (RNA or DNA) and sometimes lipid envelopes.

Question 4

^What is the major viral protein and what is it used for?

Answer 4

*Capsid. Protein coat that surrounds the nucleic acid. These protein coats can self assemble in the rough E.R., initiating virus assembly.

Question 5

^How are viruses classified?

Answer 5

*

Question 6

^Viral protein syntesis

Answer 6

*

Question 7

^Why are +ssRNA viruses so infectious?

Answer 7

*DNA/RNA hybrid is incorporation into host DNA and infects the host for life.

Question 8

^What is the viral membrane made of?

Answer 8

*Mammalian cell membrane. Phospholipids bud off as the virus exits the cell.

Question 9

^What chemicals are enveloped viruses particularly sensitive to?

Answer 9

*Acids and detergents. They disrupt the phospholipid membrane.

Question 10

^GI disease viruses

Answer 10

*Non-envelope viruses. They can survive on door-knobs for long periods of time.

Question 11

^Where do RNA viruses replicate (copy its genome)?

Answer 11

*Cytoplasm. DNA viruses replicate in the nucleus.

Question 12

^What is an exception to RNA virus replication location?

Answer 12

*HIV. It is replicated in the nucleus and incorporated into the genome because it is a DNA/RNA hybrid.

Question 13

^What enzymes do most RNA viruses carry?

Answer 13

*RNA-dependent RNA polymerase.

Question 14

^What enzyme does HIV carry?

Answer 14

*RNA-dependent DNA polymerase. This reverse transcribes RNA to DNA.

Question 15

^What enzyme do most DNA viruses carry?

Answer 15

*DNA-dependent RNA polymerase

Question 16

^How do nonenvelope viruses leave the host cell?

Answer 16

*Lysis

Question 17

^How does the virus get into the cells cytoplasm?

Answer 17

*Penetration by cutting membrane and releasing virus, fusion with membrane and release of virus or endocytosis and degradation to release virus.

Question 18

^How are envelope viruses released from a host?

Answer 18

*Viral glycoproteins go to the membrane. The membrane closes around the glycoproteins. Enveloped virus exits.

Question 19

^What various morphological changes can be seen in a virus-infected cell?

Answer 19

*Ballooning, rounding, giant cell formation, inclusion bodies or lysis.

Question 20

^Inclusion bodies

Answer 20

*Misfolded viral proteins that aggregate within the cell. DNA viruses will have inclusion bodies in the nucleus. RNA viruses will have inclusion bodies in the cytoplasm.

Question 21

^Syncitium

Answer 21

*Giant cell formation

Question 22

^Viral latency

Answer 22

*Viruses stop producing proteins and “hibernate”.

Question 23

^Viral tropism

Answer 23

*The way viruses evolve to preferentially target specific cell types or tissues.

Question 24

^Where are viral receptors located? What do they receive?

Answer 24

*On the surface of the capsid. They help the virus attach to the host. They determine what cells the virus can infect. Usually each virus can only infect one type of cell.

Question 25

^What shapes do capsids come it?

Answer 25

*Icosahedral and helical.