Chapter 19: Viruses

Question 1

Virus

Answer 1

• Infectious particle incapable of replicating outside of a cell
• Consists of an RNA or DNA genome surrounded by a protein coat (capside) and (for some) a membranous envelope

Question 2

Capsid

Answer 2

• Protein shell
• Encloses a viral genome
• May be rod-shaped, polyhedral, or more complex in shape

Question 3

Viral Envelope

Answer 3

• Membrane derived from membranes of the host cell

- Cloaks the capsid and therefore encloses a viral genome

Question 4

Bacteriophage (Phage)

Answer 4

Virus that infects bacteria

Question 5

Host Range

Answer 5

Limited number of species whose cells can be infected by a particular virus

Question 6

Lytic Cycle

Answer 6

• Type of phage replicative cycle

- Results in a release of new phages by lysis (and death) of the host cell

Question 7

Virulent Phage

Answer 7

Phage that replicates only by a lytic cycle

Question 8

Restriction Enzyme

Answer 8

• Endonuclease (type of enzyme)
• Recognizes and cuts DNA molecules foreign to a bacterium (such as phage genomes)
• Cuts at specific nucleotide sequences (restriction sites)

Question 9

Lysogenic Cycle

Answer 9

• Type of phage replicative cycle
• Viral genome becomes incorporated into the bacterial host chromosome as a prophage, replicated along with the chromosome, and doesn’t kill the host

Question 10

Temperate Phage

Answer 10

Phage that is capable of reproducing by either the lytic or lysogenic cycle

Question 11

Prophage

Answer 11

Phage genome that has been inserted into a specific site on the bacterial chromosome

Question 12

Retrovirus

Answer 12

• RNA virus
• Replicates by transcribing its RNA into DNA and then inserting the DNA into a cellular chromosome
• Important class of cancer-causing viruses
• High mutation rate

Question 13

Reverse Transcriptase

Answer 13

• Enzyme encoded by retroviruses

- Uses RNA as a template for DNA synthesis

Question 14

Human Immunodeficiency Virus (HIV)

Answer 14

• Infectious agent that causes AIDS

- A retrovirus

Question 15

AIDS (Acquired Immune Deficiency Syndrome)

Answer 15

• Symptoms and signs present during the late stages of HIV infection
• Defined by a specified reduction in the number of T cells and the appearance of characteristic secondary infections

Question 16

Provirus

Answer 16

Viral genome permanently inserted into a host genome

Question 17

Conjugation

Answer 17

• In prokaryotes, direct transfer of DNA between two cells that are temporarily joined
• When the two cells are members of different species, results in horizontal gene transfer

Question 18

Transformation

Answer 18

Change in genotype and phenotype due to the assimilation of external DNA by a cell