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DNA virus Flashcards

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Biology 101 flashcards
1
Q

what are the Characteristics of viruses

A

1) Extracellular state
- Called virion
- Protein coat (capsid) surrounding nucleic acid
- Nucleic acid and capsid also called nucleocapsid
- Some have a phospholipid envelope
- outermost (envelope and capsid) provides protection and recognition sites for host cells
2) Intracellular state
- Capsid removed
- Virus exists as nucleic acid

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2
Q

Explain the EXTRACELLULAR STATE OF VIRUS?

A
  • Called virion
  • Protein coat (capsid) surrounding nucleic acid
  • Nucleic acid and capsid also called nucleocapsid
  • Some have a phospholipid envelope
  • outermost (envelope and capsid) provides protection and recognition sites for host cells
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3
Q

Explain the INTRACELLULAR STATE OF VIRUS

A
  • Capsid removed

- Virus exists as nucleic acid

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4
Q

What is the VIRAL ENVELOPE?

A
  • Acquired from host cell during viral replication or release
    + Envelope is portion of membrane system of host
  • Composed of PHOSPHOLIPID BILAYER and PROTEINS
    + Some proteins are virally coded glycoproteins (SPIKES)
  • Envelope proteins and glycoproteins often play role in host recognition
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5
Q

What are the ENTRY OF ANIMAL VIRUSES?

A

1- Direct penetration
-The viral capsid attaches and sinks into the cytoplasmic membrane, creating pore through which the genome alone enters the cell. Poliovirus.
2- Membrane fusion
- Viral envelope and host cell membrane fuse and the capsid is released inside the cell. Measle virus
3- Endocytosis
- Of naked or enveloped viruses. Adenoviruses, Herpesviruses

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6
Q

Explain DIRECT PENETRATION of animal virus entry

A

1- Direct penetration
-The viral capsid attaches and sinks into the cytoplasmic membrane, creating pore through which the genome alone enters the cell. Poliovirus.

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7
Q

Explain MEMBRANE FUSION of animal virus entry

A

2- Membrane fusion

- Viral envelope and host cell membrane fuse and the capsid is released inside the cell. Measle virus

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8
Q

Explain ENDOCYTOSIS of animal virus entry

A

3- Endocytosis

- Of naked or enveloped viruses. Adenoviruses, Herpesviruses

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9
Q

Explain VIRAL REPLICATION

A

1) Dependent on host organelles and enzymes to produce new virions
2) Lytic replication
1- Viral replication usually results in death and lysis of host cell
2- Five stages of ytic replication cycle:
1. Attachment to the host cell
2. Entry of virion or its genome into the host cell
3. Synthesis of new viral nucleic acid and proteins by the host cell enzymes and ribosomes
4. Assembly of new virion swithi host cell
5. Release of new virions from the host cell

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10
Q

Explain the 5 STAGES OF LYTIC REPLICATION.

A

Five stages of ytic replication cycle:

  1. Attachment to the host cell
  2. Entry of virion or its genome into the host cell
  3. Synthesis of new viral nucleic acid and proteins by the host cell enzymes and ribosomes
  4. Assembly of new virion swithi host cell
  5. Release of new virions from the host cell
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11
Q

Explain LYSOGENIC REPLICATION

A

1) in bacteriphages
2) Modified replication cycel
3) Infected host cells grow and reproduce normally for generations before they lyse
4) Temperate phages or lysogenic phages
+ Prophages - inactive phages. reglated by a repressor protein. Prophages are inserted in bacterual chromosomes
5) Lysogenic conversion
+ Results when phages carry genes that alter the phenotype of a bacterium: e,g, toxins, disease-evoking proteins.
6) Induction: The prophage is excised from the chromosome by recombination or other genetic events ( x-rays, UV light, mutagenic chemicals) and it reenters the lytic phase

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12
Q

Explain the SYNTHESIS OF DNA VIRUSES OF ANIMALS

A

1) dsDNA
- similar to replication of cellular DNA
+ viral genome is replicated in the nucleus using each strand of virsal DNA as a template
+Viral proteins are made in the cytoplasm, then they enter the nucleus where new virions assemble
- Some exceptions
+ Poxvirus replication occurs within the cytoplasm
+ Hepatitis B viruses replicate DNA from an RNA intermediary which is used as a template by viral reverse transcriptase
2) ssDNA viruses
- cells do not use ssDNA
- Parvoviruses have ssDNA genomes
+ Host enzymes produce DNA strand complementary to viral genome to form dsDNA molecule
+ dsDNA used for viral replication and transcritption

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13
Q

SYNTHESIS OF DNA VIRUSES OF ANIMALS

dsDNA

A

1) dsDNA
- similar to replication of cellular DNA
+ viral genome is replicated in the nucleus using each strand of virsal DNA as a template
+Viral proteins are made in the cytoplasm, then they enter the nucleus where new virions assemble
- Some exceptions
+ Poxvirus replication occurs within the cytoplasm
+ Hepatitis B viruses replicate DNA from an RNA intermediary which is used as a template by viral reverse transcriptase

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14
Q

SYNTHESIS OF DNA VIRUSES OF ANIMALS

ssDNA

A

2) ssDNA viruses
- cells do not use ssDNA
- Parvoviruses have ssDNA genomes
+ Host enzymes produce DNA strand complementary to viral genome to form dsDNA molecule
+ dsDNA used for viral replication and transcritption

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15
Q

Explian the process of budding in enveloped viruses

A

1) Virions are extruded through one of the cell membranes:

Nucleus, ER, Cytoplasmic membrane. Viral glycoproteins are inserted into cell membranes.

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16
Q

What is the correlation between viruses and cancer?

A

1) Viruses causes 20-25% of human cancers
2) Some carry copies of oncogenes as part of their genomes
3) Some promote oncogenes already present in host
4) Some interfere with tumor repression
5) Specific viruses are knwon to cause 15% of human cancers:
• Burkitt’s lymphoma (Human Herpesvirus 4, Epstein-­Barr virus ­‐ EBV)
• Hodgkin’s disease (HHV-­‐4)
• Kaposi’s sarcoma (HHV-­‐8)
• Cervical cancer (Papillomavirus)
• Adenoviridae
• Hepadnaviridae
• Retroviridae

17
Q

Classification of DNA viruses

A

1) 7 families
2) Based on several factors
1- Type of DNA
2- Presence of envelope
3- Size
4- Mode of attack

18
Q

`Types of DNA viruses based on their type of DNA

A 
dsDNA:
Poxviridae
Herpesviridae
Papillomaviridae
Polyomaviridae
Adenoviridae

ssDNA:
Parvoviridae

both dsDNA and ssDNA:
Hepadnaviridae

Microbiology (20 decks)

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