Chapter 13- Viruses and Prions

Question 1

When a virus particle is located _______ (outside a cell) it is comprised of 2 basic components: a protein coat called a _____ which surrounds a ______ _____ core. There may be a third component, a phospholipid membrane called an ______, surrounding the capsid.

Answer 1

When a virus particle is located extracellularly (outside a cell) it is comprised of 2 basic components: a protein coat called a CAPSID which surrounds a nucleic acid core. There may be a third component, a phospholipid membrane called an ENVELOPE, surrounding the capsid.

Question 2

Capsid

Answer 2

A protein coat

Question 3

Envelope

Answer 3

a phospholipid membrane that surrounds the capsid (only some viruses have them)

Question 4

The _____ ____ core contains the genetic material of the virus. This can be either _____ __ ____ (part of the _________ structure)

Answer 4

The nucleic acid core contains the genetic material of the virus. This can be either DNA or RNA (part of the intracellular structure)

Question 5

The capsid is composed of protein subunits called ______. The capsomeres are arranged in different ways creating three basic viral shapes. These are:

Answer 5

The capsid is composed of protein subunits called CAPSOMERES. The capsomeres are arranged in different ways creating three basic viral shapes. These are:

1. Helical
2. Polyhedral
3. Complex

Question 6

Virus characteristics:
- _____
- no ____ _____, no _______, no ______
- cannot carry out any ____ _____
- neither grow nor respond to ______
- cannot _____ _____

Answer 6

• acellular
• no cell membrane, no cytoplasm, no organelles
• cannot carry out any metabolic pathways
• neither grow nor responds to environment
• cannot reproduce independently

Question 7

Genetic material of viruses:
- May be DNA or RNA but ___ ___
- Can be ____, _____, ____, or ____
- May be _____ or _____
- Much smaller than genomes of cells
- Composed of same nucleotides as cells (A,T,C,G,U)

Answer 7

• May be DNA or RNA but never both
• Can be dsDNA, ssDNA, dsRNA, or ssRNA
• May be linear or circular
• Much smaller than genomes of cells
• Composed of same nucleotides as cells (A,T,C,G,U)

Question 8

The viral envelope is acquired from____ ____ during _____ _____ and ____ and is called _____

Answer 8

The viral envelope is acquired from host cell during viral replication and release and is called budding

Question 9

If an envelope is present it is composed of a _____ _____ and is located exterior to the capsid. The membrane is obtained from the host cell which it infects and ultimately helps in attachment as well as helps in evading the immune response of the host. The main disadvantage to a virus having an envelope is that it is susceptible to detergents, alcohol, and desiccation. Basically, enveloped viruses are ____ ____ than ____ ____.

Answer 9

If an envelope is present it is composed of a phospholipid bilayer and is located exterior to the capsid. The membrane is obtained from the host cell which it infects and ultimately helps in attachment as well as helps in evading the immune response of the host. The main disadvantage to a virus having an envelope is that it is susceptible to detergents, alcohol, and desiccation. Basically, enveloped viruses are more fragile than naked viruses.

Question 10

The capsid proteins or ______ within the envelope have _____ for not only the species they will attack but more directly, the _____ ____ in the body that they will attach to and infect. Entry of the virus into animal cells then occurs via one of 3 ways:
1.
2.
3.

Answer 10

The capsid proteins or glycoproteins within the envelope have specificity for not only the species they will attack but more directly, the specific cells in the body that they will attach to and infect. Entry of the virus into animal cells then occurs via one of 3 ways:
1. Direct penetration through cell membrane
2. Fusion of cell membrane
3. Endocytosis

Question 11

Most viruses infect a

Answer 11

specific species

Question 12

General pattern of a typical virus life cycle:

Answer 12

1. Attachment
2. Entry of nucleic acids/enzymes
3. Synthesis of new nucleic acids and capsids
4. Assembly
5. Release

Question 13

The general pattern is called ____ _____

Answer 13

Lytic replication

Question 14

In many viruses, lysis doesn’t always occur. Instead, newly assembled viruses can be released via _____

Answer 14

exocytosis

Question 15

Naked vs Enveloped virus

Answer 15

Naked virus is nucleic material surrounded by a protein molecule

Enveloped virus is nucleic material surrounded by a protein molecule, surrounded by a cell membrane

Question 16

What primarily happens with naked viruses? ____. The same process happens with envelopes, but what differs is..

Answer 16

What primarily happens with naked viruses? lysis

What differs is mode of entry (could do membrane fusion or endocytosis, and when it exits, it doesn’t have to lysis the cell. It can just push its way out and take some of the cell membrane with it.)

Question 17

Some viruses, once intracellular, go into a period of ____ where they remain ____ only to surface at a later date.

Answer 17

Some viruses, once intracellular, go into a period of LATENCY where they remain DORMANT only to surface at a later date.

Question 18

Where does the life cycle get altered with latency?

Answer 18

A pause occurs between entry and synthesis
1. Attaches
2. Enters
3. Pauses
4. Synsthesis
5. Assembly
6. Release

Question 19

Latency is often represented by the ______ _____

Answer 19

Lysogenic replication

Question 20

Most antivirals are not broad spectrum but rather are ______ to the ____ that’s causing disease in the individual. Most antivirals do not actually kill the virus but instead ____ the replication. Since the virus uses the host cell, it is difficult to develop antivirals that will specifically target the virus without _____ ____ to the ____ ____. Basically, ______ ____ doesn’t apply to viruses because it’s guaranteed to harm the host. The vast majority of the time, the virus is eventually eliminated by a functioning immune system.

Answer 20

Most antivirals are not broad spectrum but rather are specific to the virus that’s causing disease in the individual. Most antivirals do not actually kill the virus but instead inhibit the replication. Since the virus uses the host cell it is difficult to develop antivirals that will specifically target the virus without risking harm to the human host. Basically, selective toxicity doesn’t apply to viruses because it’s guaranteed to harm the host. The vast majority of the time, the virus is eventually eliminated by a functioning immune system.

Question 21

What is the significance of glycoproteins?

Answer 21

Recognition and attachment

Question 22

Prions are a _______ agent and are considered _____ ____ that cause neurologic lesions in ____ ____

Answer 22

Prions are a proteinaceous agent and are considered infectious proteins that cause neurologic lesions in multiple species

Question 23

Example of prion diseases

Answer 23

BSE
scrapie
CWD
kuru
vCJD

Question 24

Prions:
- ___ _______
- Can only be destroyed by ______
- Cause for disease development:
- Any pattern to age?
- Any pattern to symptoms?

Answer 24

• No treatment
• Can only be destroyed by incineration
• Cause for disease development: inheritance or ingestion
• Any pattern to age? age-related, 50
• Any pattern to symptoms? amyloid plaques/ death

Question 25

Cellular PrP

Answer 25

Normal protein that has an alpha-helices structure

Question 26

Prion PrP

Answer 26

Disease-causing form that has beta-pleated sheets

Question 27

The prion converts normal ___ cellular PrP into __ (bad). Ultimately, prions ____ _____

Answer 27

The prion converts normal alpha cellular PrP into beta (bad). Ultimately, prions don’t replicate

Question 28

T/F- Prions replicate very slowly

Answer 28

False, they don’t replicate!