Unit 2- Viruses Flashcards
What 3 components make up a virus?
- nucleic acid
- a protein coat
- a lipid envelope
Do Viruses have RNA or DNA?
Viruses can have double and single strands of RNA or DNA
Describe the structure of a protein coat:
- it is also called a capsid
- made of subunit capsomeres
- simple geometrical shapes such as helix or icosahedrons
How does the lipid protein stay attached to the capsid? And where does the lipid envelope come from?
- the lipid envelope is derived from a host cell membrane, so the virus doesn’t make it
- the lipid envelope contains matrix proteins that link to glycoproteins in the capsid
What is a virus particle outside of a cell called?
A vision
Name the kind of nucleic acid the following bacteria have: Lambda phage, TMV, Ebola, HIV
Lambda phage- ds DNA
TMV- ss RNA (+ve sense strand)
Ebola- ss RNA (-ve sense strand)
HIV- ss RNA (retrovirus)
Structure of a lambda phage:
- icosahedral head containing ds DNA
- helical sheath
- base plate
- tails
- considered complex
Structure of the TMV:
- coil of single stranded RNA
- surrounded by a helical capsid
- very small
Structure of Ebola virus:
- very large
- negative sense single strand RNA
- surrounded by a large flexible helical capsid
- enclosed in a lipid envelope
Structure of HIV:
- Single stranded RNA
- surrounded by icosahedral capsid
- surrounded by a sphere of proteins attached to a lipid envelope
- contains the enzyme reverse transcriptase
How do we classify viruses?
By type of nucleic acid
Summary of how a virus infects a host cell:
- virus nucleic acid in injected into host cell
- capsid remains outside the cell
- the host cells ribosomes, enzymes, nucleotides, amino acids etc are used to synthesise new viral nucleic acid and proteins
What is meant by a positive sense strand?
It can be directly translated into the proteins
How does TMV replicate?
- TMV infects plant cells through damaged cell walls and contains positive sense RNA into the host
- the viral RNA is uncoated
- the RNA sequence can be translated directly by ribosomes to synthesise viral proteins
- the virus particles can also spread through the plant via plasmodesmata
How does phage lambda replicate?
- Lambda phage attaches to host cell and injects its DNA into host cell cytoplasm
- the viral DNA is integrated into hosts bacterium DNA becoming a PROPHAGE
- prophage means bacterial DNA with viral DNA (like a vector)
- prophage remains latent and is replicated every time the host cell divides
- that was the lysogenic phase
- due to an environmental signal the viral DNA starts being expressed into phage proteins which assemble into phage capsid
- the cell bursts by lysis
- this is the lytic phase