Viruses Flashcards
What is a virus?
A biological entity that has no organelles or ribosomes so needs other living cells to reproduce
What is a vrius structure?
It’s a microbe with a capsid made of protein and nucleic acid
What is the role of a capsid with a virus?
To protect nucleic acids and allow for recognition of host cells.
Name 6 types of viruses?
Filamentous, isometric and enveloped
Bacteriophages, viroids and archeal viruses
What are filamentous viruses?
Look like rods/filaments due to cylindrical protein structure around the nucleic acids
What are Isometric viruses?
3D hexagons with nucleic acids in the centre
What are enveloped viruses?
These are isometric viruses covered in a lipid membrane contains envelope proteins
3 main origin theories of bacteria?
Regressive theory, escape theory and ancient theory
What is the regressive virus theory?
Theory that viruses descended from free living organisms becoming parasitic and losing functions
What is the virus escape theory?
Viruses originate from genetic material escaping from larger genomes- doesn’t explain structure
What is the virus ancient theory?
Viruses have their origin in self replicating molecules in precellular world- explains difference of viruses and cellular life
How are viruses classified?
Through structural traits such as capsid structure, nucleic acids and envelope structure
What are the 7 pillars of life?
Organisation, metabolism, response to stimuli homeostasis, growth, reproduction and evolution.
Viruses only have 3 pillars of life?
Organisation reproduction and evolution
What are 5 stages to viral replication?
1) attachment
2) penetration
3) synthesis or nucleic acids and protein
4) assembly and packing
5) release/ lysis
What is attachment of a virus?
The binding of a virus to receptor on the cell surface ( protein, sugars, lipids or complex)
How does HIV attach to cells?
Binds a low affinity receptor and moves over cell till it binds a high affinity receptor (CD4) then it binds to co-receptor (CCR5/CXCR4) to pull virus closer then envelope fuses with the membrane.
How do viruses penetrate cells?
They can move in by endocytosis if non-enveloped or by fusion if they are.
Bacteriophages use tail fibres and a needle to inject DNA into the cell
How does a bacteriophage cause penetration?
Tail fibres bind then flex, tail pin then binds, tail sheath contracts and core pin is pushed through - leading to nucleic acid injection
How does synthesis of viruses occur ?
Viruses use host cell to produce proteins all is regulated by virus nucleic acids
How does synthesis occur in RNA viruses?
They synthesise RNA polymerase and some have RNA that can work directly as mRNA
How does synthesis occur in ReTroviruses?
They contain ssRNA so need to use reverse transcriptase
What happens at virus assembly?
All parts of the virus are assembled seperately and then joined
What happens at virus release?
Viruses can either bud off or lyse the cell to be released budding off leads to lysis once all the membrane is used up
