Viruses 1 - Lecture 31

Question 1

One step viral growth cycle

Answer 1

The time required for a single cycle of virus reproduction and yield of infectious virus per cell or burst size

Question 2

What is the eclipse phase

Answer 2

This comes after the initial infection , and that’s when the viral particle’s disappear

Question 3

The latent period of viruses

Answer 3

Viral genome takes over the control of the host cell protein making machinery and directs the production towards viral components ,this happens until the new vision particles are assembled

Question 4

What are the stages of viral replication

Answer 4

1. Attachment
2. penetration
3. uncoating
4. Macromolecular synthesis
5. Postranslational modification
6. Assembly
7. Release (lysis of the cell )

Question 5

Describe the macromolecular synthesis in the stages in viral replication

Answer 5

a)early mRNA and protein synthesis : 
Proteins to shut off host cell 
Proteins to replicate viral genome 
b) Replication if the genome 
c) late mRNA and protein synthesis

Question 6

Virulent (lytic) phage:

Answer 6

kills the host following infection

Question 7

Lysogenic (temperate)

Answer 7

phage undergoes lysogeny wherein the host is not immediately killed and the phage genome becomes a prophage (provirus) either by integration into the host chromosome or exist as an independent entity but replicating with the rate equal to the host genome multiplication

Question 8

Attachment

Answer 8

• The interaction between a virus and its target cell
• Attachment is a critical step as a determinant of target selection by many viruses
• Requires viral attachment protein and cellular receptors

Question 9

Penetration and Uncoating-Enveloped viruses types

Answer 9

1. Fusion

2. Endocytosis and acidification

Question 10

1. Fusion

Answer 10

Virus glycoproteins attach to host cell receptors, envelope-membrane fusion
occurs, capsid enters, is uncoated and virus is released

Question 11

2. Endocytosis and acidification

Answer 11

Host cell cytoplasmic membrane wraps around virus and brings it
inside, the capsid is uncoated and the viral genome is released into the
host cell

Question 12

Penetration and Uncoating

Non-enveloped viruses types

Answer 12

1. Direct entry across plasma membrane

2. Endocytosis

Question 13

1. Direct entry across plasma membrane

Answer 13

Virus attaches to host cell receptors, sinks into cell membrane, and injects its
genome through a pore into the cell, e.g. poliovirus

Question 14

2. Endocytosis

Answer 14

Host cell cytoplasmic membrane wraps around virus and brings it
inside, the capsid is uncoated and the viral genome is released into the
host cell, e.g. parvovirus

Question 15

Early proteins

Answer 15

Play a role in viral replication

Question 16

Late proteins

Answer 16

participate in the formation of the viral capsomeres

Question 17

Exocytosis for viruses

Answer 17

causes the viral capsid to grab cellular membrane in a form
of an envelope which is laced with viral proteins. It is most commonly
observed for enveloped viruses

Question 18

Cell lyses for viruses

Answer 18

most commonly observed for non-enveloped viruses

Question 19

Positive (+ve) nucleic acid

Answer 19

gene coding strand (or

the actual gene sequence)

Question 20

Negative (-ve) nucleic acid

Answer 20

complementary strand to

the gene coding mRNA (the template strand)

Question 21

all viruses are haploid except :

Answer 21

retroviruses

Question 22

reverse

transcriptase

Answer 22

RNA dependent DNA

polymerase

Question 23

RNA

replicase

Answer 23

RNA dependent RNA

polymerase

Question 24

General Elements of Viral mRNA

Answer 24

➢ 5’-5’ N7
methylguanosinetriphosphate CAP
➢ poly A tail (100-200 adenosine
residues)

Question 25

When viruses replicate in the

cytoplasm they can either :

Answer 25

make
their own 5’ CAP (A) or possess a
3D RNA structure known as
internal ribosomal entry site
element (IRES) (B)

Question 26

Three ways of producing viral proteins with

single function:

Answer 26

➢ Transcription of individual
monocistronic mRNAmolecules from
the genome
➢ Segmented genome where each molecule
givessingle monocistronic mRNA
➢ Production of a single long polyprotein
that is later cleaved into individual
functional peptides

Question 27

Defective viruses (satellite )

Answer 27

• cannot replicate without a helper virus

e. g HDV needs hepatitis B virus

Question 28

Viroids

Answer 28

infectious agents that contain RNA
with some double stranded regions. They are
associated with certain plant diseases.

Question 29

Prions

Answer 29

infectious agents that are devoid of any
nucleic acids (DNA or RNA). They are composed solely
of proteins and are associated with diseases in
humans and animals
-hereditary and sponataneous

Question 30

Spontaneous Prions

Answer 30

• The normal, innocuous protein (PrPC) can change its
shape to a harmful, disease-causing form (PrPSc).
• The conversion from PrPC to PrPSc proceeds via a chainreaction.
• PrPSc proteins form long filamentous aggregates that
gradually damage neuronal tissue