Viruses (Ch.27)

Question 1

What is unique about the origin of viruses?

Answer 1

no common evolutionary origin

Question 2

Why are viruses considered non-living?

Answer 2

1. cannot reproduce on their own
2. lack the metabolic system to provide energy for their life cycle ( they depend on host cells they infect for these functions)

Question 3

Viruses are classified more as _____ than organisms

Answer 3

infectious biological particles

Question 4

What is the structure of viruses?

Answer 4

• one or more nucleic acid molecule surrounded by a protein capsid or coat
• nucleic acid genome may be DNA or RNA and it can be either single or double stranded

Question 5

what is a feature about some of the capsids on a virus?

Answer 5

maybe be enclosed within a membrane or an envelope derived from the cell’s membrane
- Viruses have no cytoplasm enclosed with the cell membrane

Question 6

What must viruses ALWAYS code for?

Answer 6

1. coat proteins

2. proteins involved in regulation of transcript

Question 7

Genomes of Enveloped Viruses

Answer 7

include genes required for the synthesis of envelope proteins (some viral genomes include virus-specific enzymes for nucleic replication)

Question 8

What 2 basic structural forms can viruses take on?

Answer 8

1. Helical - protein subunits assemble in a rod-like spiral around the genome (ie. mostly infect plants)
2. Polyhedral - coat protein form triangular units that fit together like a soccer ball. Protein spikes that provide cell recognition would extend from the corners where the facet fits (ie. infect plants, animals and bacteria)

Question 9

How do some viruses protect humans from pathogenic viruses?

Answer 9

they interfere with their replication

Question 10

Bacteriophages (phages)

Answer 10

reason why bacteria do not overrun earth

Question 11

How do viruses impact prokaryotes?

Answer 11

impact the nutrient cycling through their effect on prokaryotic organisms