lecture 31 Flashcards
what are the two main parts of a virus
the genetic material and the capsid
what is the sructure of the genetic material in a virus
that entirely depends, can be RNA or DNA. double stranded or single stranded
whats the capsid
. This is a protein coat which surrounds and protects the genetic material, this is also the part of the virus that normally interacts with the host cell. This Capsid is made of globular protein building blocks.
whats the other part of the viruses that not all virus have
Then there is the envelope. This is made of lipids and it surrounds the Capsid coating proteins. Not all viruses have this, those who do are called envelope viruses, those that don’t are naked viruses.
whats a naked virus
a virus without an envelope
whats an enveloped virus
a virus with an envelope
whats the capsid made of
Made of globular proteins.
what do the globular proteins of the capsid come together to form
These globular protein building blocks are put into subunits called capsomeres, or capsomers. Capsomers are arranged in different ways around the genome. There are three types of symetary for the arrangement of capsomers.
what are the three arrangements of capsid symmetry
There is helical: a kind of rod shape
Icosahedral: very much common
Complex: tend to be bacteriophage
describe the helical structure
Helical structures are lots of capsomers that have a slight rotation about their axis of joining to the overall structure. the slight angle resulting in the helical shape
describe the icosahedral capsid symmetry
Icosahedral: 20 faced polyhedron. 20 equatorial triangles attached at many veritcies. Many symetrical axis. This is an efficient way of packing in many globular proteins in the capsid.
describe the complex structure
Complex contains both. Maybe a icosahedral head and helical tail. These are the shapes we see commonly in bacteriophage, bacteriophage T4 for example.
what three shapes can the viral genome take
linear, circular or segmented
how long is the viral genome
They also vary largely in size, between 400-1million bases long, with anywhere between 3 genes to 100- 1000.
how do viruses like influenza change each year
How viruses like the influenza virus change every year is that they are segmented genomes, so the strains can share and recombine DNA to make a new strand and new strain.
Infulenza has 8 segements.
whats a positive sense RNA virus
positive sense acts like mRNA, so their genome can be directly translated into proteins.
whats negative sense RNA virus
Negative sense RNA viruses have to have their genome transcribed to then be translated then make the protein.
whats a bacteriophage
a virus that only affects bacterial cells
describe step one in Lytic (virulent) cycle of bacteriophage infection
attachment: the T4 phage uses its tail fibres to bind to specific surface proteins on an E coli cell that acts as receptors
describe step two in Lytic (virulent) cycle of bacteriophage infection
entry of phage DNA. The sheath of the tail contracts punching hole in cell membrane and, injecting the phage DNA into the cell leaving empty capsid outside.
describe step three in Lytic (virulent) cycle of bacteriophage infection
- degradation of host DNA. The cell’s DNA is then hydrolysed and released into the host cell.
describe step four in Lytic (virulent) cycle of bacteriophage infection
4: synthesis of viral genomes and proteins. The phage DNA directs production of phage proteins and copies the phage genome by host and viral enzymes, using components within the cell
describe step five in Lytic (virulent) cycle of bacteriophage infection
- three separate sets of proteins self-assemble to form phage heads, tails, and tail fibres. The phage genome is packed inside the capsid and head forms.
describe step six in Lytic (virulent) cycle of bacteriophage infection
- release. The phage directs the production of an enzyme that damages the bacterial cell wall, allowing fluid to enter. The cell swells and finally bursts releasing 100-200 phage particles which go onto affect cells of their own.
