Virus Replication

Question 1

What are the 6 steps of virus multiplication

Answer 1

Attachment, penetration, uncoating, biosynthesis, assembly and release

Question 2

What is entry to host cell dependent on

Answer 2

Interaction between between viral surface protein and host cell surface protein

Question 3

What is required for viral biosynthesis

Answer 3

Host ribosomes, enzymes and precursors for biosynthesis

Question 4

What is biosynthesis

Answer 4

Genome replication, mRNA synthesis and translation

Question 5

What are the 4 stages of attachment

Answer 5

Diffusion- low affinity receptors- primary receptors -coreceptor(s)

Question 6

What are receptors composed of

Answer 6

Most commonly plasma membrane proteins, sometimes carbohydrates and lipids

Question 7

What else are receptors used for apart from attachment

Answer 7

Have important cellular function

Question 8

What is the function of the CCR5 receptor and which virus hijacks it

Answer 8

Chemokine receptor, hijacked by HIV

Question 9

What is the function of the ICAM-1 receptor and which virus hijacks it

Answer 9

Intracellular adhesion molecule, hijacked by rhinovirus

Question 10

What is the function of the acetylcholine receptor and which virus hijacks it

Answer 10

Neuronal signal transduction, hijacked by. Rabies virus

Question 11

What is the function of the angiotensin converting enzyme 2 (ACE2) receptor and which virus hijacks it

Answer 11

Maturation of angiotensin (vasoconstriction and blood pressure), hijacked by SARS-CoV-2 (COVID 19 virus)

Question 12

What is the function of the DDW150 (SLAM) receptor and which virus hijacks it

Answer 12

Lymphocyte activation, hijacked by measles virus

Question 13

What is internalization

Answer 13

Attachment, fusion of enveloped virus with cell membrane, genome released into cytoplasm

Question 14

What is receptor mediated endocytosis

Answer 14

Attachment, virus fuses with endosome, pH drops in vesicle/endosome and genome is released into cytoplasm

Question 15

Why does the mechanism of genome replication and transcription vary dependent upon the nature of the genome

Answer 15

Virus genome can be DS, SS, DNA, RNA, linear or circular (variable genome)

Question 16

What is the +ve sense strand in double stranded DNA

Answer 16

Coding strand

Question 17

What is the -ve sense strand in double stranded DNA

Answer 17

Complementary
/ non-coding strand

Question 18

What are DNA viruses replicated and transcribed by

Answer 18

Host polymerases

Question 19

Why can RNA viruses not be replicated and transcribed by host polymerases

Answer 19

As host cell DNA and RNA polymerases can only use DNA as a template

Question 20

What is the role of RNA transcriptase

Answer 20

Converts RNA to DNA

Question 21

How do RNA viruses overcome not being able to use host polymerases

Answer 21

Encode their own polymerases that can use RNA as template (RNA dependent RNA polymerases)

Question 22

What is the function of the proteins encoded for by the virus genome

Answer 22

replication of the genome
package the genome into virus particles
alter the metabolism of the infected cell

Question 23

What are structural proteins

Answer 23

Form part of virus particle

Question 24

What are non-structural proteins

Answer 24

Not incorporated into virus particle E.g. enzymes for transcription

Question 25

Do viruses carry their own ribosomes

Answer 25

No, must compete for host ribosomes

Question 26

What is translation of most viral mRNA dependent on

Answer 26

5’ terminal cap

Question 27

What are Eukaryotic initiation factors (eIFs)

Answer 27

Bind to 5’ cap and 40s ribosomal subunit

Question 28

What is the cap-independent mechanism

Answer 28

virus evolved mechanisms to ensure viral mRNA is translated more efficiently than host cell mRNA eg. Some viral RNAs can be translated via cap-independent mechanism (internal ribosome entry site: IRES)

Question 29

Describe viral post translational modification

Answer 29

Viral proteins undergo the same range of post translational modifications as the host cell proteins eg. glycosylation, acylation, lipoylation

Question 30

How are long, single viral polyproteins modified post translation

Answer 30

must be post-translationally cleaved to release individual viral proteins (eg poliovirus, rhinovirus, hepatitis C virus)

Question 31

How do enveloped viruses acquire membrane and surface glycoproteins

Answer 31

Most enveloped viruses acquire envelope by budding through plasma membrane (may also bud from nucleus eg herpes virus and into ER eg coronavirus )

Question 32

Describe viral release

Answer 32

Release by cell lysis (naked virus), eg poliovirus, Release by budding (enveloped virus), from plasma membrane (eg influenza) into lumen of endoplasmic reticulum (eg rotavirus). Virus can also spread from cell to cell via pores between cells (eg herpesvirus), by inducing fusion of their membranes (eg RSV) Release may be preceded by or followed by a maturation step

Question 33

Summarise primary site replication of viruses

Answer 33

Virus binds to cell-surface receptor and enters cell by fusion from without or receptor mediated endocytosis Viral genome must be replicated and transcribed into mRNA Viral proteins are translated and modified using host cell machinery (ribosomes, Golgi, enzymes etc) Virions are released from cell by budding, cell lysis, or cell-to-cell spread

Question 34

What are bacteriophages

Answer 34

Viruses which infect bacteria

Question 35

What are the three main categories of phage

Answer 35

ssDNA, dsDNA, ssRNA

Question 36

Describe the M13 filamentous bacteriophage

Answer 36

-Circular ssDNA -Cloning and DNA-sequencing -Released without lysing host cell -(Wouldn’t see plaques in an assay)-don’t break open cell they are infecting -‘budding’ makes own channel

Question 37

Why are bacteriophages important

Answer 37

Can turn bacteria virulent (phenotypic change) Alternative to antibiotics – phage therap Great tool in the lab – recombinant DNA technology (but also can be bad when they kill your precious cultures!)