10 - Transcription, translation and nucleic acid replication of DNA viruses

Question 1

What should be mentioned in the topic?

Answer 1

• Eclipse
  
  • Types
  • Viruses
• Baltimore system
  
  • Properties of virus multiplication
• Group I dsDNA
• Group II ssDNA

Question 2

Eclipse

Answer 2

• Central step of virus multiplication
• From the first mRNA until the first viron assembly
• Parts:
  
  • Early transcription, translation: enzymes
  • Replication: nucleic acid multiplication
  • Late transcription, translation: structural proteins
• Viruses - infectious genes
  
  • Multiplication depends on the host cell
  • Unique way of genetic information carry and expression

Question 3

Baltimore system

Answer 3

• Classification of viral families
• Types of nucleic acid - multiplication strategy:
  • I dsDNA
  • II ssDNA
  • III dsRNA
  • IV +ssRNA
  • V -ssRNA
  • VI viruses using reverse transcriptase

Properties of virus multiplication:

• Use of cellular enzymes, ribosomes, nucleotides, amino acids and energy
• For DNA virus: the nucleic acid is similar to the cellular genetic material
• For RNA virus: there are no information stored in the cell, so needs an enzyme of replication
  
  • RNA dependent RNA polymerase (RdRp)
    
    • Coded by the virus, sometimes carried in the virion
    • Mutations during replication – quick evolution
• II., III., V. group have a unique nucleic acid forms
• Coding system:
  
  • Cell: monocistronic → separate mRNAs for the proteins
  • Virus: lack of space – can be polycistronic

Question 4

dsDNA viruses

Answer 4

• Eg:
  
  • Papilloma
  • Polyoma
  • Adeno
  • Herpes
  • Pox
• Early transcription:
  
  • The viral DNA enters into the nucleus
  • Cellular transcriptase:→ mRNA
    
    • Except: Pox-, Asfarviridae
      
      • ​They have thier own viral transcriptase, multiplication in the cytoplasm
• Early translation:
  
  • On the surface of the ribosomes
  • Cellular translation → non-structural protein synthesis
• Replication:
  
  • _​_Viral replicase
    
    • Better than the cellular
    • High production
• Late transcription, translation:
  
  • The progeny DNAs serve as template → many structural proteins created

Question 5

ssDNA

Answer 5

• Eg:
  
  • Parvo
  • Circoviridae (circular genome)
• The DNA thread forms hairpins - self priming
  
  • Cellular polymerase synthesizes complementary thread
• Transcription:
  
  • _​_mRNA synthesis from the coding thread
• Translation:
  
  • _​_Cellular translation
  • Polycistronic mRNA: enxymatic clevage
• Replication:
  
  • _​_Small genome: no own polymerase
  • Cellular polymerase copies the dsDNA
  • Eventually one thread is removed
• Autonomous parvoviruses, Circoviridae:
  
  • Multiplication only in S-phase (dividing) cells!
  • Pathology: enterocyte, embryo, bone marrow cells…
• Dependovirus: use the replicase of adeno- or herpesvirus