viruses origin and evolution

WELCOME

VIRUSES ORIGIN AND EVOLUTIONELHALABI HASANCHEBAT DIMASUPERVISION: DR. F. MONEM,

VIROLOGY

PhD

TABLE OF CONTENTS SECTION 1

•0.1 What are viruses?•1. Origin of viruses• 1.1 introduction• 1.2 Theories• RNA molecules that existed before cells• cell components• micro-organisms.

• 1.3 Conclusion: How did viruses originate?

TABLE OF CONTENTS• 2. Evolution of viruses:• 2.1 Introduction• 2.2 Evolution drivers:

• 2.2.1 Progeny• 2.2.2 Mutation• 2.2.3 Quasispecies effects• 2.2.4 Selection

• 2.7 Evolution in 2012• 2.8 Conclusion

WHERE DID VIRUSES COME FORM?

!THE MAIN QUESTION NEEDS TO BE ANWERED IS:

WHAT ARE VIRUSES?

• Parasites, selective infection.• Living or not?• Genetics:• RNA viruses• DNA viruses

• Structure:• Capsid• Genome

1.1 INTRODUTION

• Where did viruses come from?• Fossils-origin relationship.• Speculation on how viruses may have

orginated.• How old are Viruses? Related to Bacteria?• The age of Eukaryotic viruses vs. the age

of prokaryotic?

TIME LINE OF EARTH HISTORY

THEORIES ON THE ORIGIN OF VIRUSES

• 1. Molecular precursors of cellular organisms• 2. Components of cells• 3. Intracellular micro-organisms.

1. MOLECULAR PRECURSORS OF CELLULAR ORGANISMS

• RNAs were originated before cells and had many features.• What happened as cells

evolved?

2. COMPONENTS OF CELLS

• 1. Independent from host cell control, components could replicate?• 2. Structural similarities between

mRNA and some viruses.Covalently:

• 3. Could some DNA viruses be descendant of plasmids?• 4. Or Transposons maybe?

2. COMPONENTS OF CELLS

• 5. Are we made of viruses?:• Chicken-and-egg situation

betweenretrotransposons and retroviruses!!• HGSP: 8% of genom is LTR-

flanked

3. INTRACELLULAR M.O.

• degeneracy of intracellular M.O. until the it becomes a virus?

CONCLUSION: THE MAIN QUESTION’S STILL UNANSWERED

• Multiple sugessted ancestors, unknown origin• Many processes may have participated • Viruses selectivity to host may refer to the origin.

Evolution of viruses

Evolution is the constant change of a viral population in the face of selection pressures

Why?

Proliferate faster than

•New viral diseases•Regular bouts every day•Drug resistent

Evolution has 4 main drivers:

Large number of progenyLarge number of mutantsQuasi-species effectsSelection



Large number of progeny



Large number of mutantsDiversity Successful

Viruses

DNA

DS

SS

RNA

SS

DS

A quasispecies is a well-defined distribution of mutants that is generated by a mutation-selection process.



Quasi-species effects



SelectionSurvival of the fittestSurvival of the survivors

Error Threshold

Upper limit of mutation rate

Genetic bottle neck

examples

How to avoid?

Recombination

Selection: genetic Shift & Drift

Selection: In virulence a positive or negative trait?

Evolution in 2012

Nice idea

Assumption:New viruses can only arise from viruses that are already existed, not de novo

Constrains on virus evolution:Viral genome is constrainPhysical nature of capsidExtreme alteration in viral consensus genome do not survive selection

REFERENCES

• 1. Virology principles and application, JHON CARTER AND VENETIA SAUNDERS.• 2. The origin and Evolution of Viruses, ESTEBAN DOMINGO

AND JOHN J. HOLLAND.• 3.

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viruses origin and evolution

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