Slide 1

Genetics and Evolution

Molecular Basis of Inheritance - The Genetic Material in Viruses

• Viruses are unique infectious agents
• They have a protein coat (capsid) and a nucleic acid core
• Genetic material in viruses can be either DNA or RNA

Slide 2

Discovery of Genetic Material in Viruses

• Frederick Griffith’s experiments in 1928

  • He experimented with Streptococcus pneumoniae and its two strains - S (smooth) and R (rough)
  • Concluded that R strain can be transformed into S strain through a process called transformation

• Oswald Avery’s experiments in 1944

  • Identified DNA as the transforming principle in Griffith’s experiments
  • DNA was responsible for transferring genetic information

Slide 3

Types of Genetic Material in Viruses

1. DNA Viruses

   • Examples: Herpesviruses, Adenoviruses, Poxviruses
   • Genetic information is stored in the form of DNA

2. RNA Viruses

   • Examples: Influenza virus, HIV, Measles virus
   • Genetic information is stored in the form of RNA

Slide 4

Structure of Viral Genetic Material - DNA Viruses

• DNA in viruses can be either single-stranded or double-stranded
• Single-stranded DNA viruses:
  • Example: Parvovirus
  • Genetic information stored in a single strand of DNA
• Double-stranded DNA viruses:
  • Example: Herpesvirus
  • Genetic information stored in two complementary strands of DNA

Slide 5

Structure of Viral Genetic Material - RNA Viruses

• RNA in viruses can be either single-stranded or double-stranded
• Single-stranded RNA viruses:
  • Example: Poliovirus
  • Genetic information stored in a single strand of RNA
• Double-stranded RNA viruses:
  • Example: Reovirus
  • Genetic information stored in two complementary strands of RNA

Slide 6

Replication of Viral Genetic Material

• Replication process varies between DNA and RNA viruses
• DNA viral replication:
  1. Attachment of viral DNA to host cell receptor
  2. Entry of viral DNA into the host cell
  3. Replication of viral DNA using host cell enzymes
  4. Assembly of new viral particles
  5. Release of newly formed viruses

Slide 7

Replication of Viral Genetic Material (contd.)

• RNA viral replication:
  1. Attachment of viral RNA to host cell receptor
  2. Entry of viral RNA into the host cell
  3. Conversion of viral RNA to viral DNA by reverse transcriptase enzyme (in retroviruses)
  4. Integration of viral DNA into the host genome
  5. Transcription and translation of viral genes
  6. Assembly of new viral particles
  7. Release of newly formed viruses

Slide 8

Recombination in Viral Genetic Material

• Recombination refers to the exchange of genetic material between two viral strains
• Can occur through:
  • Genetic reassortment (in RNA viruses with segmented genomes)
  • Recombination between RNA strands during replication
  • Recombination between DNA strands during replication

Slide 9

Importance of Viral Genetic Material

• Understanding the genetic material in viruses helps in:
  • Developing antiviral drugs
  • Designing vaccines against viral infections
  • Studying viral evolution and diversity
  • Unraveling the molecular mechanisms of viral replication

Slide 10

Summary

• Viruses possess either DNA or RNA as their genetic material
• DNA viruses can be single-stranded or double-stranded
• RNA viruses can be single-stranded or double-stranded
• Replication mechanisms differ for DNA and RNA viruses
• Recombination plays an important role in viral genetics
• Understanding viral genetic material is crucial in various aspects of virology

Slide 11

DNA Viruses

• DNA is the genetic material in DNA viruses

• Examples of DNA viruses:

  • Herpesviruses (e.g., herpes simplex virus, chickenpox virus)
  • Adenoviruses (e.g., common cold virus)
  • Poxviruses (e.g., smallpox virus)

• These viruses replicate their DNA using host cell machinery

• The replicated DNA is then packaged into new viral particles

Slide 12

RNA Viruses

• RNA is the genetic material in RNA viruses

• Examples of RNA viruses:

  • Influenza virus (causes flu)
  • Human immunodeficiency virus (HIV)
  • Measles virus

• RNA viruses can be either positive-sense or negative-sense

• Positive-sense RNA can be directly used as viral mRNA

• Negative-sense RNA needs to be converted to positive-sense RNA before translation

Slide 13

Positive-sense RNA Viruses

• In positive-sense RNA viruses, the genomic RNA acts as mRNA
• Examples: Poliovirus, Hepatitis C virus, Zika virus
• The viral genome can be directly translated into viral proteins by host ribosomes
• Also serves as a template for replication of viral RNA

Slide 14

Negative-sense RNA Viruses

• In negative-sense RNA viruses, the RNA strand is complementary to the mRNA
• Examples: Measles virus, Rabies virus, Ebola virus
• The viral RNA is first converted to a positive-sense RNA by viral enzymes
• The positive-sense RNA is then used as mRNA for viral protein synthesis

Slide 15

Retroviruses

• Retroviruses are a special type of RNA viruses
• Examples: Human immunodeficiency virus (HIV), Human T-lymphotropic virus (HTLV)
• These viruses use reverse transcriptase to convert RNA to DNA
• The viral DNA is then integrated into the host genome
• Host cell machinery transcribes and translates viral genes

Slide 16

Replication: DNA vs RNA Viruses

• DNA viruses:

  • Replicate their DNA using host cell enzymes
  • Take control over host cell machinery for viral replication
  • Replication can occur in either the nucleus or cytoplasm

• RNA viruses:

  • Directly use host ribosomes for protein synthesis
  • Can replicate in either the nucleus or cytoplasm, depending on the type of virus

Slide 17

Recombination in Viral Genetic Material

• Recombination is the exchange of genetic material between different viral strains
• Helps generate genetic diversity within a viral population
• Common in RNA viruses due to their high mutation rates
• Can occur through genetic reassortment or recombination during replication

Slide 18

Genetic Reassortment

• Occurs in RNA viruses with segmented genomes
• Segmented genome consists of multiple RNA chromosomes
• During co-infection, genetic material from different strains can be exchanged
• Results in the formation of new viral strains with a mixed genetic makeup

Slide 19

Recombination during Replication

• RNA viruses with a single genome can undergo recombination during replication

• Can occur through:

  • Template switching: The viral polymerase switches between different RNA templates
  • Strand breakage and rejoining: The RNA strands break and recombine

• Recombination can lead to the emergence of new viral strains with altered characteristics

Slide 20

Conclusion

• Genetic material in viruses can be DNA or RNA
• DNA viruses replicate their DNA using host cell enzymes
• RNA viruses can be positive-sense, negative-sense, or retroviruses
• Replication mechanisms vary between DNA and RNA viruses
• Recombination plays a crucial role in viral genetic diversity
• Understanding viral genetic material is essential for studying viruses and developing appropriate strategies for control and treatment.

Slide 21

• Structure of DNA in DNA viruses

  • Double helix shape
  • Complementary base pairing (A-T, G-C)
  • Presence of genes coding for viral proteins

• Structure of RNA in RNA viruses

  • Single-stranded or double-stranded
  • Different types of RNA: mRNA, tRNA, rRNA

• Difference in viral genetic material affects replication and transmission of the virus

Slide 22

• Viral evolution and genetic variability

  • Viruses have high mutation rates due to lack of proofreading mechanisms
  • Mutations can lead to changes in viral proteins, affecting viral replication and pathogenicity
  • Recombination and reassortment can generate new viral strains with different characteristics

• Understanding viral evolution is important for:

  • Predicting and preventing outbreaks
  • Developing effective antiviral drugs and vaccines

Slide 23

• Examples of viruses with DNA as genetic material:

  • Herpesviruses: Herpes simplex virus (HSV), Varicella-zoster virus (VZV)
  • Adenoviruses: Human adenovirus (HAdV)
  • Poxviruses: Smallpox virus, Vaccinia virus

• Examples of viruses with RNA as genetic material:

  • Influenza virus: causes flu
  • Human immunodeficiency virus (HIV): causes AIDS
  • Measles virus: causes measles

Slide 24

• Importance of viral genetic material in antiviral drug development:

  • DNA viruses can be targeted by antiviral drugs that inhibit viral DNA replication (e.g., acyclovir)
  • RNA viruses can be targeted by drugs that prevent viral protein synthesis or inhibit viral enzymes (e.g., protease inhibitors for HIV)

• Designing vaccines against viral infections:

  • Understanding viral genetic material helps in selecting appropriate vaccine strategies, such as using attenuated viruses or viral protein subunits

Slide 25

• Molecular techniques used to study viral genetic material:

  • Polymerase Chain Reaction (PCR): Amplification of viral DNA/RNA for detection and analysis
  • DNA sequencing: Determining the nucleotide sequence of viral genes
  • Reverse transcription: Conversion of RNA to complementary DNA for further analysis

• These techniques aid in diagnosing viral infections, tracking viral outbreaks, and studying viral evolution

Slide 26

• Significance of viral genetic material in understanding host-virus interactions:

  • Identification of host factors that interact with viral genetic material
  • Understanding mechanisms of viral pathogenesis
  • Studying host immune responses to viral infections

• Viral genetic material provides insights into the complex interactions between viruses and their hosts

Slide 27

• Importance of viral genetic material in studying viral diseases:

  • Genetic material helps in identifying specific viral strains causing diseases
  • Understanding genetic variations can explain differences in disease severity and clinical outcomes
  • Genetic material aids in epidemiological studies and developing targeted control measures

• Genomic data is crucial in monitoring and managing viral diseases

Slide 28

• Genetic material in viral vectors for gene therapy:

  • Viruses can be used as delivery vehicles for introducing therapeutic genes into host cells
  • Viral genetic material carries the therapeutic gene of interest
  • Understanding viral genetic material is essential for designing safe and efficient viral vectors

• Viral vectors have potential applications in treating genetic disorders and various diseases

Slide 29

• Future directions in viral genetics research:

  • Advancements in sequencing technologies for large-scale genome analysis
  • Elucidating the role of non-coding regions in viral genomes
  • Studying the interaction between viral genetic material and host factors
  • Developing novel antiviral strategies based on targeting viral genetic material

• Viral genetics research continues to evolve, offering new insights and possibilities

Slide 30

• Summary:

  • Viruses possess either DNA or RNA as their genetic material
  • Replication mechanisms differ between DNA and RNA viruses
  • Recombination plays a crucial role in viral genetic variation
  • Understanding viral genetic material is vital for antiviral drug development, vaccine design, and studying viral evolution and host interactions
  • Molecular techniques enable the characterization and analysis of viral genetic material

• Genetic material in viruses opens up avenues for further research and application in various fields.