viruses

Question 1

the structure of a virus

Answer 1

-tiny non cellular structures
-have an outer protein coat called a capsid
-in some viruses the capsid is enclosed in a complex out membrane
-inside is a nucleic acid either DNA or RNA
-viral genes carry instructions to form new viruses
-have no ribosomes, mitochondria or other cytoplasmic organelles
-they don’t carry out metabolic reactions, they need a host to do it for them instead

Question 2

living features of viruses

Answer 2

-contain genetic material (DNA or RNA)
-have a protein coat
-can replicate inside a living host cell

Question 3

non living features of viruses

Answer 3

-non cellular and don’t carry out metabolic reactions
-cannot reproduce independently
-have no ribosomes, mitochondria or any other cell organelles
-only have one type of nucleic acid, either DNA or RNA

Question 4

shapes of viruses

Answer 4

-round shaped
-rod shaped
-complex in shape

Question 5

virus replication

Answer 5

-they are not cells so they cannot reproduce
-we say replicate instead of reproduce
-they can only multiply by using the energy and structures of a living host cell
-they are obligate parasites

Question 6

what is bacteriophage

Answer 6

-a virus that infects bacteria
-the most complex and studied of all viruses
-replication takes about thirty minutes
-the way most viruses infect human cells

Question 7

the first stage of replication in bacteriophage

Answer 7

attachment
-virus attaches to host cell
-proteins from virus match receptors sites on a host cell
this is why only certain viruses can infect certain host cells

Question 8

second stage of replication in bacteriophage

Answer 8

entry
-virus forms a hole in the host cell and viral nucleic acid is pushed through
-the protein coat of a bacteriophage stays outside while protein of other viruses enter animal cells and are broken down

Question 9

third stage of replication in bacteriophage

Answer 9

synthesis
-the host nucleic acid is made inactive
-the viral nucleic acid uses the host organelles to produce new viral nucleic acids and proteins (capsid)

Question 10

fourth stage of replication in bacteriophage

Answer 10

assembly
-new viruses are made inside host cell using viral molecules that have been produced

Question 11

final stage of replication in bacteriophage

Answer 11

release
-the host cell bursts to release between 100 and 100,000 new viruses

Question 12

what is the bursting of a host cell called

Answer 12

lysis

Question 13

retroviruses

Answer 13

-contain RNA and an enzyme that converts the virus RNA to DNA
-this DNA makes new copies of the virus RNA and new viruses inside the host cell
-some viruses do not destroy the host DNA

Question 14

give an example of a retro virus

Answer 14

HIV

Question 15

what happens when a virus that does not destroy the host DNA

Answer 15

-the viral DNA intergrates with the host DNA and remains inactive
-when the host DNA is copied the viral DNA is copied and passed onto daughter cells

Question 16

disadvantages of viruses

Answer 16

1. human disease: cold, flu, polio, rabies, mumps, measles, chickenpox, warts etc
2. plant diseases: tobacco mosaic disease, potato and tomato mosaic disease
3. animal diseases: rabies-transferred by saliva and can cause choking, paralysis or death
   foot and mouth- causes blisters in feet and mouth

Question 17

benefits of viruses

Answer 17

-can be used to transfer genes from one organism to another in genetic engineering, these viruses are called vectors
-control of infection, bacteriophage can be used to control bacterial infections, they help to reduce infection due to antibiotic resistant bacteria

Question 18

what is AIDS

Answer 18

acquired immune deficiency syndrome
-a person cannot make antibodies due to infection with human immunodeficiency virus (HIV)
-HIV enters body in fluids such as blood or semen

Question 19

effects of AIDS

Answer 19

-enters a white blood cell and either remains dormant or disables the cell
-when the virus lays dormant other white blood cells produce antibodies against it.
-if present in a blood sample a person is HIV positive, these antibodies do not disable the virus as it mutates too quickly
-it affects the lymphocytes called helper T-cells which prevents a person from producing antibodies
-an AIDS sufferer usually dies from a common infection they would normally fight off eg pneumonia

Question 20

control and immunity of viruses

Answer 20

-antibodies produced by white blood cells will kill viruses
-we become immune to viruses after we have had a viral infection (natural immunity)
-if we are vaccinated against them (artificial immunity) eg flu vaccine
-antibiotics do not kill viruses