4.6 Viruses Flashcards
Viruses do not have…
A cell-like structure and are about 50 times smaller than bacteria
Viruses can only reproduce when…
They are inside other living cells
They have a core containing…
Genetic material, which can either be DNA or RNA
Surrounding the core is…
A protective cost of protein called a capsid
The capsid is made up of…
Protein sub-units called capsomeres
Some viruses have a membrane around the capsid made of…
Lipids and proteins
HIV stands for…
Human immunodeficiency virus
HIV is…
Spherical shaped with an envelope made of lipids and glycoproteins
Protein knobs on the surface of the envelope
Capsid is cone-shaped, contains RNA, an enzyme called REVERSE TRANSCRIPTASE (allows the virus to make a DNA copy of its RNA when it infects a host cell)
The DNA then inserts itself into the host cell’s chromosomes- the DNA may remain inactive for a long time, sometimes many years. When it becomes active it instructs the cell to make new virus particles -this kind of virus is known as RETROVIRUS
HIV causes disease by?
HIV enters the bloodstream, here it infects a particular kind of white blood cell called a helper T-cell
A DNA copy is made of the virus RNA. The DNA copy is inserted into the chromosome of the helper T-cell. Every time the helper T-cell divides it copies the virus DNA . However the cell itself remains normal. During this time the infected person has no symptoms - a blood test will show that the person has antibodies against HIV (HIV+ at this stage)
Some years later the virus DNA becomes active. It takes over the and causes more HIV to be made, as a result the cell dies and releases thousands of HIV particles - these enter new helper T-cells (important in defending the body from disease). Gradually these are destroyed
Now that the immune system isn’t working properly the infected person suffers from diseases that might not have caused problems in a healthy person (known as opportunistic diseases) this stage called full-blown AIDs
As a result of these diseases the person dies
HIV can pass from an infected person to another person when body fluids mix- virus can’t survive outside the human body so the our fluids must come into direct contact - main ways in which HIV is passed on are:
During sexual intercourse
When an intravenous drug abuser shares a needle already used by a person with HIV
When a transfusion of blood from a person infected with HIV is given to another
From a mother to her unborn baby across the placenta
Viruses do not show any activity until…
They are inside a living cells which means antiviral drugs have to get inside a host cell - where they may cause harm to the host cells
Most antiviral drugs interfere with the process by which the host cell makes new viruses
Antibiotics are very effective against bacteria as…
They kill bacteria by interfering with their metabolism. However viruses do not have any metabolism of their own- this means antibiotics can’t be used to destroy viruses
