Idit Exam 3 - Saviola - Viral Structure And Replication I

Front 1

Are viruses susceptible to antibiotics?

Back 1

No

Front 2

Can viruses synthesize their own proteins?

Back 2

No

Front 3

Do viruses generate their own metabolic energy

Back 3

No

Front 4

What is the mode of reproduction for viruses?

Back 4

Host cell synthesis of subunits then assemble them into iron

Front 5

Does virus compromise of DNA or RNA?

Back 5

Either but not both

Front 6

Virion

Back 6

Mature infectious virus particle

Front 7

Capsid

Back 7

Protein shell that encloses and protects the viral nucleic acid

Front 8

Capsomer

Back 8

Polymers of polypeptide chains

Morphological units of capsid

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Nucleocapsid

Back 9

Internal part of virus particle - consists of nucleic acid

Closely associated proteins

Used when this complex is a discrete substructure of a complex particle

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Envelope

Back 10

The viral membrane - consists of lipid bilayer, proteins, and glycoproteins

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+ssRNA

Back 11

Single stranded RNA of the same polarity as mRNA

Front 12

-ssRNA

Back 12

Single stranded RNA complementary to mRNA

Front 13

DNA dependent RNA polymerase

Back 13

Enzyme that uses DNA as a template for producing RNA

Front 14

RNA dependent RNA polymerase

Back 14

Enzyme that uses RNA as a template for producing RNA

Front 15

Are RNA dependent RNA polymerase found in host cells?

Back 15

No, viruses use this to make mRNA and RNA genomes

Front 16

DNA dependent DNA polymerase

Back 16

Enzyme that uses DNA as template for producing DNA (our cells use this to replicate)

Front 17

RNA dependent DNA polymerase

Back 17

Enzyme that uses RNA as the template for producing DNA

Front 18

What is an example of RNA dependent DNA polymerase?

Back 18

Reverse transcriptase in retroviruses and HepB

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cDNA

Back 19

Complementary DNA made from RNA by recombinant procedures

Can be cloned

Made by reverse transcriptase

Front 20

Transfection

Back 20

Infection of mammalian cells by bare viral nucleic acid

Front 21

Transformation

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Stable heritable change in genetic makeup and phenotype of a cell resulting from infection of that cell by a virus

Usually implies converting to a neoplastic phenotype

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Permissive cells

Back 22

Cells that supper the complete virus life cycle, with production of infectious virus particles

Front 23

Nonpermissive cells

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Cells which permit none of or only part of the virus life cycle

Front 24

How are non permissive cells usually transformed?

Back 24

By viruses (Applies esp. to DNA viruses)

Front 25

Defective Virus

Back 25

Virus that is not capable of going through its entire replication cycle unless the cell is infected with a complete virus (helper) particle as well

Front 26

Cytopathic effect (CPE)

Back 26

Observable damage to a cell resulting from virus infection

Front 27

Are animal viruses visible under light microscope? Electron microscope?

Back 27

Electron microscope only

Front 28

Can a virus have both DNA and RNA as its genetic material?

Back 28

No. Only either DNA OR RNA

Front 29

What is the structure of viral genomes?

Back 29

Can be segmented or a whole single piece

Front 30

What makes up the envelope of a virus?

Back 30

Host derived phospholipid bilayer

Virus derived proteins and glycoproteins for attachment and viral fusion

Front 31

Which is weaker- enveloped or naked viruses? Why?

Back 31

Enveloped viruses = Weaker

B/c envelopes can be inactivated by lipid solvents, and these viruses cannot function without their lipid components

Front 32

What are M proteins? Are they found on all viruses

Back 32

Matrix proteins - Aid in viral structure

Only in enveloped proteins

Front 33

What are F proteins? Are they found in all viruses?

Back 33

Fusion proteins - cause fusion between viral and cellular membranes

Only in enveloped proteins

Front 34

What are the 5 criteria to classify human viruses?

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1. Chemical structure of the nucleic acid
2. Symmetry of the nucleocapsid
3. Presence of an envelope
4. Dimensions of the virion and capsid
5. Nucleic acid sequence similarities

Front 35

What are the three types of capsids? Which is the least common

Back 35

1. Complex - least common
2. Icosahedral
3. Helical

Front 36

Were are complex capsids found? What's its shape?

Back 36

In Poxviruses.

Dumbell

Front 37

What is the shape of icosahedral capsid?

Back 37

20 triangular faces --> almost like a sphere

Front 38

What's special about a helical capsids?

Back 38

They always have an envelope

Front 39

What is the Penton on an Adenovirus?

Back 39

It mediates attachment of the adenovirus to the host cell

Front 40

What are the four steps for viral infection of a host cell?

Back 40

1. Attachment to the host cell
2. Entry of virus into the host celll
3. Synthesis of viral proteins and genome
4. Assembly and release

Front 41

What is the most important determinant of host specificity in viral attachment?

Back 41

Presence of specific viral receptors on host cells

Front 42

What cells do HIV infect? What is the receptor HIV recognizes on these cells?

Back 42

Macrophages and T cells

Receptor is CD4

Front 43

How does HIV induce a T cell response?

Back 43

By binding to MHCII

Front 44

What receptors does HIV bind to? Does it need to bind to all of these to enter the cell?

Back 44

Cxcr4 and Ccr5

No. It just needs to bind to either one

Front 45

What is Cxcr4 and Ccr5's normal function?

Back 45

Chemokine receptors on immune cells

Front 46

What other proteins does HIV use to bind to the host cell?

Back 46

SU and TM

Front 47

What are the two ways non-enveloped viruses can enter its host cell?

Back 47

1. Binds to host cell surface and rearranges capsid protein

2. Receptor mediated endocytosis of virus --> breakup of capsid --> migration into cytoplasm

Front 48

What are the two ways enveloped viruses can enter its host cell?

Back 48

1. Fusion of viral membrane and host cell membrane by F protein

2. Phagocytosis and fusion of viral membrane and phagosome membrane by F protein

Front 49

Is F protein required for enveloped virus function?

Back 49

YES

Without it, virus cannot enter cell

Front 50

How does poliovirus (naked) enter host cells?

Back 50

Binds to receptors --> endocytosed --> creates a pore --> injects its RNA into cytoplasm

Front 51

How does Adenovirus enter the cell?

Back 51

Penton base interacts with integrin receptor --> endocytosis --> pentons disassemble --> capsid enters cytoplasm and docks on nuclear pore --> viral DNA enters nucleus

Front 52

How does Paramyxoviridae (enveloped) enter the cell?

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Envelope fuses with cell membrane --> capsid enters cell

Front 53

How does Influenza (DNA) virus enter the cell

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Hemmaglutinin binds sialic acid receptors --> endocytosis --> low pH in endosome --> conformational change --> fusion peptides bring endosome and nuclear membrane close

Front 54

How does Semliki Forest virus (RNA) enter the cell?

Back 54

Clathrin dependent endocytosis --> acidification -> membrane fuses --> Viral RNA enters cytoplasm --> goes to ribosome for translation

Front 55

Which domain of the F protein inserts into the host cell membrane?

Back 55

hydrophobic domain

Front 56

How does HIV enter cells?

Back 56

SU binds CD4 --> Cxcr4 and Ccr5 binding site is exposed --> SU binds Cxcr4 OR Ccr5 --> conformational change --> fusion peptide enters membrane

Front 57

Is Cxcr4 or Ccr5 the coreceptor for T-cell-tropic strains?

Back 57

Cxcr4

Front 58

Is Cxcr4 or Ccr5 the coreceptor for macrophage-tropic strains?

Back 58

Ccr5

Front 59

Can an individual be resistant to HIV infection?

Back 59

YES

If they are homozygous for deletion for Ccr5

Front 60

How is a syncytium formed?

Back 60

F protein mediates fusion of membranes of adjacent cells --> multinuclate giant cells --> syncytium

Front 61

What occurs during the eclipse period of the growth curve of Adenovirus?

Back 61

Nucleic acid has entered the cell BUT the cell is not making any new viruses

Front 62

What occurs during the latent period of the Adenovirus growth curve?

Back 62

Infectious viruses are being made but they are still INSIDE the host cell.

There are no infectious viruses outside the host cell yet.

Front 63

Do viruses typically bring their own enzymes or use host cell enzymes in replication?

Back 63

Host cell enzymes

Front 64

What is the sequence of events in DNA virus's synthesis of macromolecules

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1. Synthesis of early proteins (enzymes for nucleic acid replication
2. Viral genome synthesis
3. Late protein synthesis (structural proteins)

Front 65

Where do DNA viruses replicate?

Back 65

Nucleus

Front 66

What is an enzyme that DNA viruses need?

Back 66

Host cell RNA polymerase II

Front 67

Before a DNA virus does protein synthesis, what must happen?

Back 67

Synthesis of viral mRNA

Front 68

How does retroviruses (RNA virus) synthesize proteins?

Back 68

1. Viral RNA is reverse transcribed into DNA
2. DNA --> mRNA through RNA pol II

Front 69

What is an example of a DNA virus that uses reverse transcriptase?

Back 69

Hep B

Front 70

Why are Poxviruses an exception to the general rule for protein synthesis of DNA viruses? Why do they do this?

Back 70

It brings its own Viral DNA dependent RNA polymerase and viral accessory proteins.

Because it replicates in the CYTOPLASM, not nucleus

Front 71

Can +ssRNA, -ssRNA, and dsRNA initiate viral replication and growth?

Back 71

Only +ssRNA b/c it can act as mRNA

-ssRNA and dsRNA have to be converted to +ssRNA

Front 72

Are -ssRNA and dsRNA infectious by themselves?

Back 72

NO

Front 73

Do -ssRNa and dsRNA have to carry enzymes to produce +ssRNA to become infectious?

Back 73

YES

only +ssRNA can act as mRNA

Front 74

Is +ssRNA infectious by itself?

Back 74

Yes

Front 75

Do all RNA viruses have to encode its own RNA dependent RNA polymerase?

Back 75

No,

Retroviruses and +ssRNA viruses do not

Front 76

What do retroviruses have instead?

Back 76

RNA directed DNA polymerase

Converts viral RNA into dsDNA

Front 77

What has a higher mutation rate - DNA or RNA? Why?

Back 77

RNA -- probably because DNA replication has proofreading function while RNA replication does not

RNA dependent DNA polymerase - even higher mutation rate

Front 78

Where does mRNA synthesis typically occur?

Back 78

Cytoplasm

May occur in nucleus (Influenza)

Front 79

How do RNA viruses have more heterogeneity in the order of their genes transcribed and proteins produced?

Back 79

They can have segmented genomes that can "shuffle" in an infected host cell

Front 80

What are the 3 things virion protein shells can be produced from?

Back 80

1. Individual polypeptides
2. Polyprotein precurosor then cleaved into smaller functional viral proteins
3. Chaperone mediated

Front 81

What are the two mechanisms of assembly and release of viruses?

Back 81

1. Bursting of cell - more common for naked viruses

2. Slow release of virus - with an envelope as the nucleocapsid buds through a virus modified cellular membrane (Ex: HepB)