December 4

Question 1

Viruses

Answer 1

Acellular genetic element

Cannot copy itself without a host cell

Classified by whether they have DNA or RNA

Linear genome, sometimes circular

Question 2

Viral Hosts

Answer 2

Bacterial virus (bacteriophage)

Animals

Plants (Tobacco Mosiac Virus)

Some only infect particular cells in particular organisms (HIV)

Question 3

Viral Structure

Answer 3

Capsid: protein covering viral genome composed of subunits called capsomeres

Viruses can also have an envelope around the capsid taken from the nuclear envelope

Question 4

Enveloped virus

Answer 4

Have an envelope around the capsid taken from nuclear envelope or cell membrane of host

Question 5

Viral Symmetry/Shape

Answer 5

Helical (rod shaped)

Icosahedral (20 sides)

Complex (other shapes including T4)

Question 6

Helical Virus

Answer 6

Tobacco Mosaic Virus

Question 7

Icosohedral Virus

Answer 7

Roughly spherical viruses

Question 8

Lysozymes

Answer 8

Make holes in cell walls common in phages

Question 9

Nucleic Acid Polymerase

Answer 9

To replicate genome

Question 10

Neuraminadases

Answer 10

Cleave glycosidic bonds, virus can leave host

Question 11

Complex shape

Answer 11

Other virus shapes including the shape of T4 bacteriophage

Question 12

Rabies

Answer 12

Broad virus, can infect most mammals

Complex shape (bullet), has no set size or shape

Question 13

Animal viruses

Answer 13

Can grow in tissue or cell culture

Don’t need whole animal to reproduce virus

Question 14

Bacteriophages

Answer 14

Easiest to grow

Model system for all viruses

Question 15

Plant viruses

Answer 15

Most difficult to study

The entire plant is needed to reproduce virus

Question 16

How are viruses quantified?

Answer 16

Plaque Assays: Analogues to bacterial colony, plaques are clear zones that develop on a lawn of bacteria, each plaque is a single virus particle

The number of plaques is usually lower than virus counts, inactive viruses

Plaque assay conditions are not always ideal

Question 17

Titer

Answer 17

Number of infectious units per volume

Question 18

Viral Replication

Answer 18

1. Attachment
2. Entry Phase
3. Synthesis
4. Assembly
5. Release

Question 19

T4 Entry Mechanism

Answer 19

Phage attaches via tail fibers, fibers interact with polysaccharides of outer membrane of E. coli

Lysozyme creates pore in peptidoglycan

Tail sheath contracts and inserts viral genome

Question 20

Restriction modification systems

Answer 20

Many bacteria have restriction modification systems to help evade infection. Restriction enzymes cleave DNA at specific sequences, only effective against double-stranded DNA viruses

Question 21

Attachment

Answer 21

The virus must first attach to a host cell (highly specific), complementary receptors on the host cell and its infecting virus, receptors on the host cell have a normal fuction (such as protein uptake), virus attaches to host cell, then it needs to get nucleic acids into the cell.

Question 22

Entry Phase

Answer 22

Nucleocapsid (nucleic acid and capsid) or viral genome enters host cell, entry of bacteriophage T4 (E. coli virus)

Question 23

Synthesis

Answer 23

Once a host cell has been infected, must make new copies of viral genome. First, mRNA must be generated, typically viral genome is a template for viral mRNA. In some viruses the viral RNA is the mRNA.

mRNA is either in the plus configuration, and its complement is the minus configuration

Positive RNA virus

Negative RNA virus

Retrovirus

Question 24

Positive Strand RNA Virus

Answer 24

Single-stranded RNA genome with same orientation as mRNA

Question 25

Negative Stranded RNA Virus

Answer 25

Singe-stranded RNA genome has complementary orientation as its mRNA

Question 26

Retrovirus

Answer 26

Usually animal viruses

HIV

Require a unique enzyme Reverse Transcriptase to go from RNA to DNA to RNA to proteins

Question 27

Viral Release

Answer 27

Viruses exist in host cell

Can result in lysis of cell–explode out occurs with phages

Or can bud off new host cell (virus factory)