Viruses Flashcards
What are viruses?
Tiny non-cellular structures that cannot be seen by a light microscope
Virus structure
Outer protein coat called a capsid and inside the capsid nucleic acid [either DNA or RNA] never both
Metabolic reactions
They do not carry any metabolic reactions on their own and require the organelles of a host to carry out limited number of reactions
Living factors of viruses
Possess genetic material [DNA or RNA]
Posses a protein coat
Can replicate [inside a living cell]
Non living features of viruses
Non-cellular
Cannot reproduce by themselves
Do not possess ribosomes, mitochondria etc
Only have one type of nucleic acid [living things have both DNA and RNA]
What is a bacteriophage?
It is a virus that infects bacteria
Stages in virus replication?
Attachment - proteins on virus match up with receptor sites on host wall/membrane
Entry - hole pushes nucleic acid
Synthesis - host nucleic acid is made inactive and uses organelles to produce new viral nucleic acid and proteins
Assembly - new viruses made
Release - cell bursts and releases
Another way that viruses replicate
Won’t destroy host cell but join with host DNA and remain inactive so when host DNA is copied, the virus DNA is also copied
Disadvantages of viruses
Human diseases - chickenpox, measles, polio
Plant diseases - potato mosaic disease
Animal diseases - cowpox, myxomatosis, rabies
Benefits of viruses
Genetic engineering - used to transfer genes from one organism to the other
Control of infections - bacteriophages used to control bacterial infected and reduce infections by antibiotic resistant bacteria
Distinguish between HIV and AIDS
HIV is the virus that enters the body and disables helper t-cells results in not being able to produce antibodies
How can AIDS be prevented
Avoid sexual intercourse
Use protection during intercourse
Do not use shared needles
Why can a person be HIV positive but not suffer from AIDS
Because AIDS is the advanced stage that occurs after HIV enters body
Why do viruses not cause decay?
They are obligate parasites
Control and immunity of viruses
- General defence system and specific defence system
- injections and vaccinations
- antibiotics do not affect viruses
What is a retrovirus and give an example
They contain RNA and an enzyme that converts RNA to DNA
example is ; HIV
What is the bursting of the host cell in virus multiplication known as?
Lysis
What are obligate parasites?
Can only replicate using a cell
Name one virus that causes disease in plants
Mosaic
How do scientists distinguish between different viruses
Shape of protein coat
Type of nucleic acid
Antibody - antigen reaction
Why are viruses difficult to classify into a kingdom?
Non-cellular
Give one example of a beneficial virus
Bacteriophages - kill bacteria
How does the genetic make up of the new yeast cell relate to that of the parent cell and why
Identical - asexual
Mitosis
A virus has been described as a piece of genetic material that has escaped from a cell. Give one piece of evidence that supports this description
Composed of nucleic acid
During 2009, swine flu spread through the population of many countries. Younger people were more at risk of becoming ill than older people. Using your knowledge of the immune system, suggest a reason for this
Older people have had previous exposure and therefore developed memory cells. They are able to produce the specific antibodies in large amounts if virus was to enter body again.
What is the economic importance of viruses?
Damage crops - bad economically - viruses such as mosaic plant disease
What is the medical importance of viruses?
Human diseases such as chicken pox
-just over fifty years ago the myxoma virus was brought to Ireland. The disease for which it is responsible in rabbits, myxomatosis, quickly decimated the wild population. Now however, the disease is much less common and is responsible for far fewer deaths-
Why do you think the rabbit population was decimated when the virus was first brought to Ireland?
No immunity against virus - first time
-just over fifty years ago the myxoma virus was brought to Ireland. The disease for which it is responsible in rabbits, myxomatosis, quickly decimated the wild population. Now however, the disease is much less common and is responsible for far fewer deaths-
Suggest a reason why myxomatosis is no longer a major threat to the Irish rabbit population?
Natural immunity - memory cells
Suggest one advantage and one disadvantage of biological control
Advantage - environmentally friendly
May be inexpensive
Disadvantage - upsets balance of nature
Introduced species may become pest
