A 2.3 Viruses

common strucrures to all viruses

no cytoplasm

Genetic material

Protein capsid

Type of viruses

Bacteriophage lambda (DNA, capsid, neck, tail fibres, tail sheet), coronavirus (RNA, viral envelope, capsid, spikes), HIV (two RNA strands, reverse transcriptase, viral envelope, capsid, pikes)

lytic vs lysogenic cycle

lytic:

virus attaches

inserts genetic material

genetic material directs the synthesis of viral elements

Virons are assembled

cell lyses

lysogenic:

virus attaches

inserts genetic material

inserts itself into the DNA of host cell, becoming a prophage

cell duplicates

stimulus activates the genetic material, the genetic material exits the host DNA

genetic material directs the synthesis of viral elements

Virons are assembled

cell lyses

Origin of viruses hypothesis + convergant evolution

Virus first: due to the simplicity of viruses, it is suggested that viruses existed before living organisms

regression: cells became parasites, attacking other cells, over millennia, they shed some of the structural elements, becoming viruses

escape: Genetic material from a large cell escaped and got surrounded by a membrane

Viruses are all quite similar

obliagte parasites

no cytoplasm

universal genetic material

Antigenic drift and shift

Drift is a gradual change in the genome of viruses, caused by mutations and an example of this is HIV. HIV is unique tho as it undergoes genetic drift very quickly, making it hard to control

Shift is a abrut change in the genome due to two viruses exchanging genetic material, this causes a drastic change in the surface of viruses, making them invisible to the immune system. An example of this is the influenza virus which due to this evolution provcess causes a number of epidemic a every now and then