4 Viruses(1) Flashcards
What is the most numerous microorganisms on earth?
Viruses
What are viruses made up of and where is their genetic material found?
- Made up of genetic material and protein (bare minimum)
- Genetic material can be RNA
What do viruses need to replicate?
A host cell (can’t replicate alone)
What are the types of viruses (general) (2)
DNA (Non-enveloped/Enveloped)
RNA (Non-enveloped/Enveloped)
What is a consequence of viruses being so small?
Restricts the size of genome
What is the extracellular form of a virus know as?
Virion
What is the intracellular form of the virus known as?
Replicative state
Are viruses single or double stranded?
Can be both
Are viruses linear or circular?
Can be both
How are capsids made in viruses?
Protein subunits wrap around genome
-Single protein so single gene needed for coat
-Assembly process is self-assembly, no additional machinery required for process
can be reproduced in vitro, no chaperone proteins required
What is the structure of spherical viruses?
- Spherical animal viruses have protein shells built up of many copies of one or a few identical subunits
- Icosahedral shells have the highest possible symmetry for any fully enclosed shell
Describe the process of viral replication? (5)
1) Attachment of virus
2) Penetration of viral DNA
3) Synthesis of nucleic acid and protein
3) Assembly and packaging
5) Release (lysis)
Describe the process of viral replication? (5)
1) Attachment of vision
2) penetration of viral DNA
3) Synthesis of nucleic acid and protein
3) Assembly and packaging
5) Release (lysis)
How are viral proteins expressed? (2)
The timing of protein expression is very important
• Early proteins- for replication of viral nucleic acid etc., such as enzymes
• Late proteins- include coat proteins
What are bacterial viruses mostly made up of?
dsDNA
How is viral transcription in T4 phage infection assured? (4)
1) Injection phase- energy harvested, needed to get through cell envelope
2) Uses ribosomes to make early MRNA - this forms early proteins- these are enzymes (nucleases and polymerases) involved in making phage DNA (middle proteins)
3) Late proteins- Structural proteins made from viral DNA, making head of virus
4) Self assembly occurs - final enzyme formed - this is lysozyme breaks through viral cell wal
What do sigma factors do?
Why is this relevant to viruses?
Sigma factors tell RNA polymerase where to bind in the DNA, directs it to particular part of genome and recognise particular promotors
Virus can mess with sigma factors, makes host recognise viral factors instead
How is viral transcription assured? (4)
- T4 does not encode its own RNA polymerase - it uses that of the host
- this is modified to specifically recognise promoters on the phage DNA
- for early proteins host sigma factors are used
- the phage also encodes an anti-sigma factor that binds to one of the host sigma factors, σ70, so preventing subsequent host transcription
How is the switch to middle proteins achieved? (4)
- Some early phage proteins modify the host RNA polymerase α subunits
- Other early proteins bind to the host RNA polymerase
- These modifications alter the polymerase specificity so as to recognise middle promoters
- One of the early proteins, MotA, recognises a sequence in the middle promoters and guides RNA polymerase to the correct sites
Describe transcription from late promoters? (2)
- This requires a new T4-encoded sigma factor
* Most of the late genes encode structural proteins
