Week 3 - Viral Structure, Classification, and Replication - Ziegler

Question 1

What is a virion? What are its components?

Answer 1

the infectious virus particle
-Contains genetic material surrounded by a protein coat (capsid)
some viruses also have a lipid and glycoprotein envelope

Question 2

What does positive or negative polarity mean in reference to a viral genome?

Answer 2

+ polarity: Can immediately be translated into a protein as if it were mRNA

• polarity: Must make a complimentary strand of RNA from the original RNA genome in order to translate it

Question 3

Where do VAP’s attach on naked viruses and enveloped viruses?

Answer 3

Naked virus - on the capsid
Envloped - on the envelope itself

(becuz its gotta be on the outside)

Question 4

What is a viral peplomer?

Answer 4

Its a glycoprotein that acts as a VAP. IT sticks out of the viral membrane’s bilayer to interact with where it wants to attach.

Question 5

Virus infections that yield new infections?

Answer 5

productive

latent is non-productive

Question 6

Phases of virus multiplication:

Answer 6

1) attachment
2) penetration
3) uncoating
4) virus component synthesis
5) assembly
6) release

Question 7

Give an example of a cytopathic effect caused by a virus

Answer 7

One example is the Herpes virus. After infecting the host cell it causes it merge with neighbors creating a big multinucleated cells. These can easily be seen in a smear of the infected cells.

Question 8

What is the goal of an antiviral?

Answer 8

STOP mutliplication

Question 9

Why can viroporins really rain on a cell’s parade?

Answer 9

They are small virus-encoded proteins that can actually cause hydrophilic pore to open in the host cell’s membrane. This ruin’s the cell’s Ca and H+ gradients and the cell’s whole day in general.

Question 10

How do virion’s generally exit the host cell?

Answer 10

They usually form a bud and pinch off to form a free infectious virion.

Question 11

What’s the difference between the latent period and the eclipse period in the virus growth cycle?

Answer 11

Latent period = amount of time it takes before virions are released extracellularly

Eclipse Period = amount of time before virions are produced inside the cell

Question 12

RNA virus replication occurs where?

Answer 12

CYTOPLASM
except orthomyxoviruses (influenza)
and retroviruses (HIV) occur in the NUCLEUS

Question 13

Positive or negative sense RNA viruses have envelopes?

Answer 13

All negative-sense RNA viruses are enveloped

Question 14

Spontaneous mutations in RNA viruses are more common than in DNA viruses because:

Answer 14

their RNA polymerase are not as accurate in duplication

Question 15

How do RNA viruses produce individual peptides from polycistronic RNA since this is not a property of eukaryotic cells?

Answer 15

• Viral proteases can cleave larger proteins
• many initation and termination signals can lie within the viral RNA
• Orthomyxoviruses and retroviruses have segmented DNA, each segment cooding for 1 or 2 proteins

Question 16

DNA virus replication occurs where?

Answer 16

THE NUCLEUS

except poxviruses replicate in the CYTOPLASM

Question 17

For DNA virus replication to occur, what host functions must work properly?

Answer 17

The S Phase is needed to make things work

Question 18

Can DNA viruses transform cells?

Answer 18

YES. All of them can except for parvovirus

Question 19

Hepadnaviruses have a partially double-stranded DNA genome. Describe some specifics about this:

Answer 19

• replicate their DNA in the nucleus via a RNA intermediate
• involve a RNA-dependent DNA polymerase (reverse transcriptase) in their replication
• Can transform cells

REMEMBER: They can be treated with the same antiretrovirals as HIV, because of reverse transcriptase

Question 20

Parvoviruses have what kind of DNA genome?

Answer 20

Single-stranded

Question 21

What is the cytoplasmic DNA virus?

Answer 21

Poxviruses

They actually synthesize their own envelope, and provide their own mRNA and DNA synthetic machinery

Question 22

What does cellular transformation mean?

Answer 22

Some RNA and DNA viruses cause a stable, inheritable change result in poor or no control of cellular division

Question 23

Do DNA or RNA viruses transform permissive of non-permissive cells?

Answer 23

DNA tumor viruses lyse permissive cells and ONLY transform non-permissive cells

RNA tumor viruses transform both permissive cells & nonpermissive
(They can also carry the actual oncogenes responsible for transformation)

Question 24

What virus is responsible for human gentital tumors and squamous cell carcinoma?

Answer 24

Human papillomavirus

Question 25

EBV virus is responsible for what human cancers?

Answer 25

nasopharyngeal carcinoma
African BUrkitt’s Lymphoma
B-cell Lymphoma

Question 26

What virus causes cervical carcinoma?

Answer 26

herpes simplex type 2

Question 27

What cancer is caused by Hepatitis B virus?

Answer 27

Hepatocellular carcinoma

Question 28

HTL virus causes what human cancer?

Answer 28

Adult T cell leukemia

Question 29

The two important breaks in the cell cycle that cuase big problems with cancer when they get messed up:

Answer 29

P53 – when activated, turns on kinases which phosphorylate the master protein and stops cell cycle from going crazy

P-110
pRB protein, when it is phosphorylated it is the MASTER break in the cell cycle, keeps uncontrolled growth from occurring

Question 30

Cell oncogenes stem from?

Answer 30

Mutated form of normal cellular genes (proto-oncogenes. Its just the abnormal regulation or expression that cuases BIG problems

Question 31

Viral oncogenes

Answer 31

Copies of cellular oncogenes that have been acquired by viral genomes during replication, can be introduced to create cellular transformation

Question 32

Outline the:

tumor virus/host cell interaction.

Answer 32

DNA tumor viruses transform non-permissive cells; they kill permissive cells
DNA tumor virus rarely produce tumors in the natural host (human DNA tumor viruses are the exception)
RNA tumor viruses transform both permissive and nonpermissive cells and do produce tumors in the natural host

Question 33

Explain Hepadnaviruses’ link to cancer:

Answer 33

• 75-85% of liver cancers carry Hep B virus
• alcohol-associated cirrhosis and imparied immunity are cofactors
• X-protein interact with p53
• Can have LONG latency period

Question 34

Three mechanisms by which viruses can cause transformation:

Answer 34

-Introduction of oncogenes

-insertional activation or promoter insertion
(viral promoters on a cellular oncogene

-transcriptional activation
(transactivator proteins like TAX protein enhance transcription of viral and cellular genes)

Question 35

What sub-family of retrovirus can transform cells?

Answer 35

Onco viruses - Types B, C, and D

this means that lentiviruses like HIV cannot do this

Question 36

Viral genes involved in replication are called:

Cellular oncogenes that become part of the viral gemome:

Answer 36

Virogenes.

Viral Oncogenes

Question 37

Describe the differences between non-defective and defective viruses:

Answer 37

Non-defective

• retains virogenes along with an oncogene
• involved in chronic tumors

Defective

• Part or all of their virogenes have been replaced by oncogenes
• involved in acute tumors
• require helper virus for replication