Chapter 13: Viruses - Essential structure

Question 1

What are viruses?

Answer 1

• Acellular particles capable of infecting host cells and causing disease

Question 2

What does it mean by viruses are not free-living?

Answer 2

• they require a host cell in which to multiply

Question 3

Obligate intracellular parasites are a type of virus. What do they do?

Answer 3

• use host metabolic systems and usually disrupt normal host cell function

Question 4

What are characteristics of viruses? (5)

Answer 4

1. Acellular
2. do not have a plasma membrane
3. contains a single type of nucleic acid (DNA or RNA)
4. surrounded by a protein coat
5. May or may not have additional envelope of lipids

Question 5

Do viruses have enzymes?

Answer 5

have very few of their own, but they take enzymes of their host

Question 6

In lecture, what type of viruses are more prone to degradation?

Answer 6

• envelope viruses

Question 7

What kind of organisms can viruses effect? (5)

Answer 7

• animals
• plants
• fungi
• protozoa
• bacteria

Question 8

Most viruses are specific for a single host species. What does this mean?

Answer 8

• To infect a cell, the virus must recognize features on the host cell surface
  ex. some viruses recognize the fimbriae of a certain bacterial species

Question 9

What type of microscope must be used to view viruses?

Answer 9

• electron microscopes
• range from 20-1000 nm in length

Question 10

What three parts do viruses have?

Answer 10

• nucleic acid
• capsid
• envelope
  note that viruses need at least 2 of these

Question 11

Can viruses have both DNA and RNA?

Answer 11

no

Question 12

What can the nucleic acid in viruses be?

Answer 12

• single stranded or double stranded
• linear or circular
• can be in several pieces - segmented

Question 13

What is the total amount of nucleic acid in a virus

Answer 13

• a few thousand to 250 000 base pairs

Question 14

How many base pairs does the E. coli chromosome have?

Answer 14

4.6 million

Question 15

What is a capsid? (2)

Answer 15

• protein coat surrounding the nucleic acid
• made up of individual proteins called capsomeres

Question 16

What is a nucleocapsid?

Answer 16

• nucleic acid and capsid
• minimum required structure for a virus

Question 17

What is an envelope?

Answer 17

• lipid bilayer (membrane) acquired from the host cell
• external coating around the nucleocapsid

Question 18

Are envelopes present in all viruses?

Answer 18

no

Question 19

What are spikes in an envelope?

Answer 19

additional viral proteins inserted into envelope