virus key information- 3a

Question 1

virus key facts:

Answer 1

• small organic particles, not cells
• sized 20nm - 1um (1000nm)
• outer protein coat (capsid)
• encased genetic material of either rna or dna
• the dna can be either single or double stranded

Question 2

the viral envelope contains

Answer 2

host proteins (glycoproteins), lipids (from cell membranes), viral proteins (glycoproteins) act as antigens (molecules recognised as foreign by the hosts immune system) or VAPs (virus attachment particles)

Question 3

the envelope helps the virus attatch to the

Answer 3

host cell and penetrate the surface membrane- viruses will only infect specific types of cells/ tissues

Question 4

viral genetic material is adapted to take over the host

Answer 4

• viral dna acts directly as a template for both new viral dna and for mRNAs needed to induce synthesis of viral proteins
• viral rna directs the synthesis of reverse transcriptase which proceeds to make dna corresponding to the viral genome which is then used as a template for new viral proteins and ultimately a new viral rna genome

Question 5

viruses require host cells to replicate because

Answer 5

they lack internal structures for growth and reproduction such as ribosomes, therefore viruses hijack the hosts cells metabolic machinery and disrupt the normal working of the cell, following replication the new virus particles may bud out of the infected cells or may lyse the cell completely splitting it open, this causes viruses and cell contents to be released into surrounding tissues, this can cause symptoms of the disease

Question 6

viral replication- lyric pathway

Answer 6

• viral genetic material is replicated independently of the host dna straight after entering the host cell
• mature viruses are made by the host cell
• cell bursts and releases large numbers of new virus particles
• these go on to invade other host cells
• the virus is said to be virulent

Question 7

viral replication- lysogenic pathway

Answer 7

• viruses are non- virulent when they first get into the host cell
• they insert their dna into the host dna so it’s replicated every time the host cell divides
• no mRNA is produced from the viral dna because one of the viral genes causes the production of a repressor protein
• this makes it impossible to translate the rest of the viral genetic material
• the virus remains dormant and becomes lytic and therefore virulent under the right conditions

Question 8

arguments for viruses being alive

Answer 8

they reproduce, contain genetic material, undergo evolution, obligate intracellular parasites

Question 9

arguments against viruses being alive

Answer 9

they don’t feed, respire, excrete, move, show any sensitivity

Question 10

diseases caused by bacteria

Answer 10

food poisoning, cholera, tuberculosis

Question 11

diseases caused by viruses

Answer 11

influenza, measles, HIV/AIDS