Ch 17: Expression

Question 1

Structure of Viruses

Answer 1

• Viruses are not cells
• Viruses are very small infectious particles consisting of, nucleic acid enclosed, a protein coat, and a membranous envelope (in some cases)
• Viral genomes may consist of, Double- or single-stranded DNA, Double- or single-stranded RNA
• Depending on its type of nucleic acid, a virus is called a DNA virus or an RNA virus

Question 2

capsid

Answer 2

the protein shell that encloses the viral genome

Question 3

envelope

Answer 3

the membrane that surrounds the virus and helps them infect hosts, Called a Viral envelope, Both host and Viral molecules

Question 4

Bacteriophages (Phages)

Answer 4

• Viruses that infect bacteria
• Have complex capsids
• elongated capsid head that encloses their DNA
• A protein tailpiece attaches the phage to the host, injects the phage DNA inside

Question 5

Viruses are obligate intracellular parasites

Answer 5

can reproduce only within a host cell

Question 6

Each virus has a host range

Answer 6

a limited number of host cells that it can infect

Question 7

What are Viruses usually?

Answer 7

no cells, Viruses use enzymes, ribosomes, and small host molecules to synthesize progeny viruses

Question 8

Phages, 2 reproductive mechanisms

Answer 8

Phages are the best understood of all viruses, Phages have two reproductive mechanisms: the lytic cycle and the lysogenic cycle

Question 9

General Features of Viral Replicative Cycles

Answer 9

• Once a viral genome has entered a cell, the cell begins to manufacture viral proteins
• The virus makes use of host enzymes, ribosomes, tRNAs, amino acids, ATP, and other molecules
• Viral nucleic acid molecules and capsomeres spontaneously self-assemble into new viruses

Question 10

The Lytic Cycle

Answer 10

The lytic cycle is a phage reproductive cycle that ends in the death of the host cell

Produces new phages and ruptures the cell

Question 11

Virulent phage

Answer 11

A phage that reproduces only by the lytic cycle

Question 12

Bacteria have defenses against phages

Answer 12

restriction enzymes that recognize and cut up certain phage DNA

Question 13

The Lysogenic Cycle

Answer 13

The lysogenic cycle replicates the phage genome without destroying the host

The viral DNA is incorporated into the host cell’s chromosome(prophage)

Every time the host divides, it copies the viral DNA and passes the copies to daughter cells

An environmental signal can trigger the virus genome to exit the bacterial chromosome and switch to the lytic mode

Question 14

Temperate phages

Answer 14

use both the lytic and lysogenic cycles

Question 15

Retroviruses

Answer 15

use reverse transcriptase to copy their RNA genome into DNA, Viral RNA coded into DNA, Integrates into the host chromosome, Host transcribes Viral DNA into RNA, RNA used to make more viruses, HIV is the retrovirus that causes AIDS

The broadest variety of RNA genomes is found in viruses that infect animals

Question 16

Vaccines

Answer 16

harmless derivatives of pathogenic microbes that stimulate the immune system to mount defenses against the harmful pathogen. Vaccines can prevent certain viral illnesses, Viral infections cannot be treated by antibiotics, Antiviral drugs can help to treat, though not cure, viral infections

Question 17

Emerging Viruses

Answer 17

Emerging viruses are those that suddenly become apparent

Question 18

Viroids

Answer 18

small circular RNA molecules that infect plants and disrupt their growth

Question 19

Prions

Answer 19

slow-acting, virtually indestructible infectious proteins that cause brain diseases in mammals, propagate by converting normal proteins into the prion version, creates the aggregates as it progresses