Chapter 19

Question 1

unique features of viruses

Answer 1

Smaller and simpler than bacteria
No organelles
No cell membrane
No metabolic machinery
Cannot reproduce on its own
Need specific host cells
Living or non living?

Question 2

structure of viruses

Answer 2

Genes packaged in a protein coat
Protein shell – capsid
Genetic material – DNA, RNA 
Tail  
Tail fibers

Question 3

capsid

Answer 3

Made up of protein subunits- capsomeres

Glycoproteins

Question 4

helical capsids

Answer 4

identical capsomeres in rotational symmetry

Question 5

isometric capsids

Answer 5

capsomeres arranged in a hollow quasi-spherical shape

Question 6

enveloped viruses

Answer 6

phospholipid and protein membrane covering over the capsid

Question 7

isometric shape

Answer 7

Composed of 20 facets, each an equilateral triangle,

and 12 vertices

Question 8

bacteriophages

Answer 8

Viruses that attack bacteria

Capsids have long isometeric heads
Tail with sheath
Tail fibers

Question 9

intracellular obligate parasites

Answer 9

Uses HOST cell’s ribosomes, enzymes and much of the cellular machinery to reproduce.

Viral reproduction produces progeny

leave the host cell to infect other cells in the organism.

Question 10

1st step of infection adsorption

Answer 10

Viruses’reactive sites interact with specific receptors on host cells

Specificity defines and limits the host species as well as the type of cell that is infected

Damage to virus binding sites – can make viruses non-infectious.

Question 11

2nd step of infection uptake

Answer 11

Virus’ envelope may fuse with host cell membrane and release the viral capsid into the host cytoplasm.
OR enter the cell by endocytosis

Question 12

3rd step of infection uncoating

Answer 12

release of the viral genome from its protective capsid

nucleic acid will be transported within the cell and transcribed to form new progeny virions.

Question 13

4th step of infection activation

Answer 13

mRNA is transcribed from viral DNA

OR formed directly from some viral RNA

codes for viral proteins are translated by the host cell.

Nucleic acid replication produces new viral genomes for progeny virions.

DNA viruses replicate mainly in the nucleus

RNA viruses mainly in the cytoplasm

Question 14

5th step of infection activation assembly

Answer 14

Assembly of viral nucleocapsids may take place in the nucleus (ex. herpes virus)

OR in the cytoplasm (ex. polio virus)

OR at the cell surface, ex. “budding” viruses such as influenza.

Question 15

6th step of infection release

Answer 15

Release of new infectious viruses is the final stage of reproduction.

Question 16

lytic cycle of bacteriophage

Answer 16

Virus attaches to bacteria cell

Viral enzyme digests part of cell wall and its viral DNA enters the host cell.

Host DNA disintegrates.

Viral DNA is transcribed and translated, producing protein coats and enzymes.

The viral DNA is replicated.

Protein coats and DNA are assembled into new viral particles.

Lysozyme causes the host cell to rupture.

New viruses are released and seek out new host cell.

Question 17

lysogenic cycle

Answer 17

Viral DNA becomes integrated into the bacterial DNA after infection.

It is replicated along with the host DNA when the host reproduces.

The viral DNA is referred to as a prophage.

Environmental factors will trigger the prophage to begin a lytic cycle.

Question 18

Effects of viral infection

Answer 18

release of hydrolytic enzymes from lysosomes of host cells

infected cells produce toxins

toxic envelope proteins

Question 19

HIV(retrovirus)

Answer 19

stores its genetic information as RNA

HIV enters a human cell, releases its RNA, and an enzyme called Reverse Transcriptase

Reverse Transcriptase makes a DNA copy of the HIV RNA
this DNA is integrated into the infected cell’s DNA

Question 20

HIV DNA copy (inactive /latent)

Answer 20

The virus is present but does no damage.

Question 21

HIV DNA copy is activated

Answer 21

The virus takes over the functions of the cell, causing it to produce new HIV copies, which then invade other cells.

Question 22

How is HIV transmitted

Answer 22

HIV is transmitted through contact with body fluid that contains the virus.

HIV targets various types of white blood cells

This weakens the body’s defenses against infections and cancers

Question 23

First symptoms of HIV

Answer 23

• fever, rashes, swollen lymph nodes, and fatigue may last a few days to several weeks.

Within 10 years, about half of all HIV patience become seriously ill and develop AIDS (WBC count dangerously low.)

With a compromised immune system, AIDS patience can become ill from unusual pathogens and rare types of cancer.

Question 24

viroids

Answer 24

circular RNA molecules (only nucleic acid)
capable of replication in the host cells
do not code for any proteins

Question 25

Prions

Answer 25

infectious misfolded proteins (only protein, no nucleic acid)

transmitted through food

indestructible – cannot be destroyed by heating

interferes with normal cellular functions

How does it replicate?
triggers normal proteins to misfold

Question 26

Endemic

Answer 26

a disease that exists permanently in a particular region or population.

Question 27

Epidemic

Answer 27

An outbreak of disease that attacks many people at about the same time and may spread through one or several communities (Ex. Influenza or Ebola)

Question 28

Pandemic

Answer 28

: When an epidemic spreads

throughout the world (1918 “Spanish” Influenza)

Question 29

Syndemic

Answer 29

A set of linked health problems involving
two or more infections, interacting, and
contributing to excess burden of disease in a population.
(Ex. HIV and ______)