Viruses, structure, growth and taxonomy Flashcards
Why are viruses filterable
Because they’re small
Structure of viruses
- Simple
- nucleic acid
- proteins
- Some have lipids
Properties of viruses
- Metabolically inert
- Rely on host cell
- Obligate intracellular parasites
Where does replication occur in a eukaryotic cell of a virus
Nucleic acid and protein synthesis may be in different parts of host cells
What do mature virus particles have
Nucleic acid (genome) Protein coat (capsid) Some have lipid coat (envelope)
Different type of nucleic acids that viruses can have
DNA or RNA
What can the nucleic acid in a virus have
Negative polarity or positive polarity
How are positively polar nucleic acids different from negatively polar nucleic acids
Positive ones can go straight to ribosome and build proteins
Negative ones have to be copied to complementary sequence so it can be positive and go to the ribosome
Functions of protein within a viral cell
- Formation of capsid
- Attachment (specific interaction between viral ligand and cellular receptors)
(viral ligands are proteins on surface)
Whats tropism
Ability to only inject certain types of cell
what do many viral proteins do to cell function and how is this useful
Interfere with it (e.g. have protein to stop apoptosis as cells would normally start apoptosis if they are infected)
What is the lipid envelope derived from
Host cell membranes
What does the lipid envelope contain
external attachment proteins
How are viruses classified
Families—> genea—> strains
Is RNA in viruses double or single stranded
Can be both. The single stranded RNA can be -ve or +ve
What can the capsid be like in a virus
Isocahedral/helical
First 3 steps of viral replication
1) attachment
2) Entry (via endocytosis for some or via fusion by those with lipids on surface
3) Uncoating (where the nucleic acid leaves the lipid envelope and capsid)
How does uncoating happen
When endocytosed int the cell, becomes vesicle. Vesicle goes to the lysosome and lysosome releases nucleic acid
Steps of how copies of the genome are produced in a viral cell
Macromolecular synthesis
- MUltiple copies of viral genome and proteins
- Needs to produce +ve single stranded RNA (i.e. mRNA)
For viruses with -ve single stranded RNA, what must they contain and why
Contain genome which codes for RNA polymerase so you can make complementary +ve strand of -ve RNA
What do viruses that have double stranded DNA need to do
Eukaryote will produce +ve RNA
What do viruses with single stranded DNA need to do
Synthesis of complementary strand to make double stranded DNA and so cell can then transcribe it
What does a retrovirus do
Single stranded +ve RNA—-> Reverse transcriptase turns it into single stranded DNA and then there is synthesis of the other strand of DNA
Why are retroviruses beneficial
Turns RNA to DNA which incorporates in host cell chromosome so whenever the cell divides, virus is part of it
