virus Flashcards
characteristics of viruses (june paper)
- living/non-living
- small, 10nm to 300nm
- acellular (no membrane bound organelles)
- organelles, cytoplasm
- capsid capsomeres
- geometric shape, crystalline
- metabolic processes, respiration
- genetic material, RNA/DNA
- reproduce and replicate
- host cells’ enzymes, RNA polymerase for transcription, ribosome for translation
- obligate parasite
- show metabolic activity
- can grow and develop
what is genome’s structure
- single/several, circular/linear
- DNA/RNA
- ss/ds
capsid structure
- determined by the viral genome
- composed of p subunits called capsomeres
- capsid and viral NA= nucleocapsid
envelope structure
- composed of phospholipids and glycoproteins arranged to form the lipid bilayer
- derived from the host cell membrane by budding
- embedded with viral glycoprotein spikes - involved in host cell recognition
what are the five stages for viral replication
- attachment
- penetration (digest cell wall)
- replication (genome)
- maturation (assembly)
- release
how does the viral nucleic acid enters a bacterial cell
- when tail fibres of t4 bacteriophage attaches to receptors on the bacterial host cell wall,
- it will release lysozyme, an enzyme that digests the bacterial cell wall resulting in release of molecules that changes the base plate conformation
- in turn causes the tail sheath to contract and thurst the hollow tube through the bacterial cell
- viral DNA genome will then be injected into the bacterial host cell via the hollow tube
where is the lysogenic cycle found
lambda phage: undergoes both lytic and lysogenic cycles (aka temperate phage)
function of temperate phage
incorporate its DNA into the bacterium’s DNA to form a (non-infectious) prophage OR
replicate by means of the lytic life cycle and cause lysis of the host bacterium
what possible defense mechanisms of bacteria against phages?
- mutant bacteria with receptor sites that are no longer complementary to the phage attachment sites
- develop restriction enzymes that recognize foreign phage DNA and cleave them. Modify bacteria’s own DNA to prevent attack by restriction enzymes
what organ does the influenza virus target
epithelial cells of the respiratory tract; virus binds to the sialic acid receptor
what is a retrovirus
- RNA virus
- contains reverse transcriptase
- produces DNA from its RNA genome
- dsDNA incorporated into host genome (provirus)
what is an obligate parasite
- cannot live independently of its host
- depends on its host to complete its life cycle
why can viruses be regarded as non-living organisms?
- acellular and lack cellular organelles
- do not carry out metabolism
- lack ability to REPRODUCE on their own independently and only undergo REPLICATION in living cells
- do not GROW and undergo developmental changes and require a host cell–> new products such as coat protein and nucleic acids
- do not respond to stimuli when outside the host cell
- ONLY EVOLVE by natural selection WITHIN A HOST CELL
describe the replication process
- inside the cell, the bacteriophage DNA is IMMEDIATELY TRANSCRIBED –> mRNA using host RNA polymerase
- high virulent phages–> early proteins that completely TAKE CONTROL –> degrade host cell DNA into nucleotides
- e coded take over BACTERIUM’S MACROMOLECULAR synthesising machinery for own use
- use host cell NucLEOtiDES to synthesise many copies of phage DNA
define antigenic drift
a mechanism of variation by viruses that involves the accumulation of mutations in the genes encoding the surface glycoproteins of the virus.
resulting viruses have surface antigens/glycoproteins that have a different conformation from prev virus strain
define antigenic drift
a mechanism of variation by viruses that involves the accumulation of mutations in the genes encoding the surface glycoproteins of the virus.
resulting viruses have surface antigens/glycoproteins that have a different conformation from prev virus strain
define antigenic shift
sudden and major change in surface antigens of a virus and occurs;
when 2/more different strains of a virus/strains of 2/more diff viruses combine to form new subtype
specific type of genetic reassortment that confers a phenotypic change; enabling a flu strain jump from animal specieis to another
characteristics of viruses
- obligate parasites: totally dependent on a host cell for replication
- genome is made up of only 1 type of nucleic acid: DNA/RNA
- viral components MUST ASSEMBLE into complete viruses to be able to infect another cell
describe the maturation process of lysogenic process
phage genome no longer repressed–> phage components produced using host metabolic machinery
more copies of viral genome produced by DNA replication using host cell machinery
bacteriophage components then assemble into complete virions
describe the genome in an influenza (enveloped) virus
influenza genome organised into 8 segments of ssRNA
RNA genome is a -ve strand; packaged with protein–> helical nucleoprotein form: 3 RNA segments coding for 3 different polymerases–> enzyme complex: RNA-dependent-RNA-polymerase/ RNA replicase: replication and transcription
other 5 RNA segments code for haemaglutinin, neuraminidase, nucleoprotein etc
how does new strains of influenza virus arise (drift)
new strains of viruses are formed as a result of the accumulation of mutations in the gene leading to changes in ribonucleotide sequences known as antigenic drift due to lack of proof reading ability of RNA-dependent-RNA polymerase in influenza, HIGH RATE of replication and the viral RNA is ss and do not have backup copy to carry out REPAIR MECHANISM–> changes in the conformation of the glycoproteins
