Immunity
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What does HIV stand for
Human immunodeficiency virus
Why is HIV known as a retrovirus
it possess RNA and reverse transcriptase which can make DNA from RNA- a reaction that is the reverse of that carried out by transcriptase
What is the difference between HIV and AIDS
-HIV is a virus while AIDS describes the condition caused by infection with HIV
Describe how HIV is replicated
-attachment proteins attach to receptor on t-helper cell -RNA enters cell -reverse transcriptase converts RNA to DNA -HIV DNA inserts into host DNA -uses human enzymes (transcription and translation) to make copies of RNA and proteins -Viral protein assembled and released
Symptoms of HIV
-low number of T-helper cells -less antibodies which causes infection more
What does HIV cause
AIDS
How is HIV diagnosed
measure T helper cell count in blood
Pathogen
Microorganism that causes disease (bacteria, virus and fungi)
Immunity
When the bodies defence mechanisms overwhelm a pathogen and destroy it.
What are the 2 types of defence mechanisms
-General, immediate defences (skin, phagocytosis -Specific responses (T-cells, B-cells)
Antigens
part of an organism that is identified as non-self that triggers an immune response
What are 4 materials that the body can recognise as non-self
-Pathogens -Cells from other organisms -Toxins -Abnormal body cells (cancer)
Phagocytosis
-Pathogen secretes chemicals and phagocyte detects them -Pathogen binds to a receptor -membrane binds to the pathogen in a vesicle as a phagosome -Phagosome binds to the lysosome turning into a phagolysosome -Lysozymes hydrolyse pathogen -waste material leaves via exocytosis
Describe how phagocytosis of a virus leads to presentation of its antigens
-phagosome fuses with lysosome -Destroyed by lysozymes -antigen is displayed on the cell membrane
Describe how presentation of a virus antigen leads to the secretion of an antibody against the antigen
• Helper t-cells bind to the antigen -stimulates a specific B cell • B cell clones -Forms plasma cells that release antibodies
Describe how HIV is replicated once inside helper T cells
-RNA converted into DNA using reverse transcriptase -DNA inserted into nucleus -DNA transcribed to HIV mRNA -HIV mRNA translated into viral protein
Describe how a phagocyte destroys a pathogen present in the blood
-Engulfs -forming vesicle and fusing with lysosome -Enzymes hydrolyse
Give two cells other than a pathogen that can stimulate an immune response
-abnormal body cells (cancer) -Cells from other organisms
What is the role of the disulfide bridge in forming the quaternary structure of an antibody?
Joins two different polypeptides
Explain how HIV affects the production of antibodies when AIDS develops in a person
• less antibodies produced • because HIV destroys T helper cells -Fewer B cells activated
What response do T cells produce
Cell mediated
What response do B cells produce
Humoral
What is the cell mediated response
-pathogen invade body cells -phagocyte places antigen on cell surface -receptor on T helper fits antigen -activates rapid mitosis of T cells -Stimulates: memory cells to develop, phagocytes, B cells and cytotoxic cells
What is a cytotoxic T cell
Kill abnormal cells and body cells by producing perforin that makes hole in the cell surface membrane -Useful against viral infections