Cell recognition and the immune system

• The phagocyte is attracted to the pathogen by the chemical products of the pathogen. It moves towards the pathogen along a concentration gradient. 
• The chemicals on the surface of the pathogen attaches to the receptors on the cell-surface membrane. 
• Lysosomes within the phagocyte move towards to the phagosome that formed around the engulfed bacterium. 
• The lysosome release their lysozymes into the phagosome where they hydrolyse the bacterium. 
• The hydrolysis products of the bacterium are absorbed by the phagocyte. 
• The antigens from the surface of the phagocyte are presented on the cell-surface membrane of the phagocyte. 

• Pathogens invade the body cells or are taken in by phagocytes.
• The phagocyte places teh antigens from the cell onto its cell-surface membrane. 
• Receptors on a specific T helper cell fit exactly onto the antigens.
  • This attachment activates the T helper cells and they begin to divide rapidly by mitosis to form clones.
• The cloned T cells can:
  • develop into memory cells that allow a rapid response to future infections by the same pathogen.
  • stimulate phagocytes to engulf pathogens.
  • stimulate B cells to divide and secrete their antibody.
  • activate cytotoxic T cells.

• Occurs in the body's humor (fluid).
• Plasma cells secrete antibodies into the blood, usually the plasma. 
  • These cells survive for a few days.
  • Leads to the destruction of the antigens so are responsible for the immediate defence of the body. 
  • The production of antibodies and memory cells is known as the primary immune response.
• Memory cells divide rapidly when they come into contact with a future infection. 
  • This forms plasma cells and more memory cells. 
  • The plasma cells destroy the pathogens and the memory cells stay in the blood until a future infection from the same pathogen occurs.
  • This provides long term immunity. 
  • This is called the secondary immune reponse.

• The B cell attaches to the antigens presented on the helper T cell and therefore is activated.
• The B cell divides by mitosis and gives either clone plasma cells or clone memory cells. 
• The plasma cells produce and secrete the exact antibodies for the antigen.
• The antibody attaches to the antigens on the pathogen and leads to its destruction. 
  • They cause the agglutination of bacterial cells. 
    • The clumps of cells formed make it easier for phagocytes to locate them.
  • They serve as markers that stimulate phagocytosis to engulf the bacterial cells. 

Structure of the HIV:

• Outermost layer is a lipid envelope with attachment proteins embedded into it. 
  
• Inside the envelope is a protein layer called the capsid that encloses two single strands of RNA and enzymes inculding reverse transcriptase. 
  • Reverse transcriptase catalyses the reaction of RNA to DNA. 
• Is a reterovirus because it has the ability to create DNA from RNA. 

Replication of HIV:

• Uses its genetic material to instruct the host cell's mechanisms to make the components of HIV. 
• Process is:
  • HIV binds to CD4 and the HIV attaches to the T helper cell. 
  • The protein capsid fuses with the cell-surface membrane and the RNA and enzymes enter the T helper cell. 
  • HIV's reverse transcriptase converts the RNA to DNA. 
  • The new DNA is inserted into the cell's DNA. 

Structure of the HIV:

• Outermost layer is a lipid envelope with attachment proteins embedded into it. 
  
• Inside the envelope is a protein layer called the capsid that encloses two single strands of RNA and enzymes inculding reverse transcriptase. 
  • Reverse transcriptase catalyses the reaction of RNA to DNA. 
• Is a reterovirus because it has the ability to create DNA from RNA. 

Replication of HIV:

• Uses its genetic material to instruct the host cell's mechanisms to make the components of HIV. 
• Process is:
  • HIV binds to CD4 and the HIV attaches to the T helper cell. 
  • The protein capsid fuses with the cell-surface membrane and the RNA and enzymes enter the T helper cell. 
  • HIV's reverse transcriptase converts the RNA to DNA. 
  • The new DNA is inserted into the cell's DNA. 

Structure of the HIV:

• Outermost layer is a lipid envelope with attachment proteins embedded into it. 
  
• Inside the envelope is a protein layer called the capsid that encloses two single strands of RNA and enzymes inculding reverse transcriptase. 
  • Reverse transcriptase catalyses the reaction of RNA to DNA. 
• Is a reterovirus because it has the ability to create DNA from RNA. 

Replication of HIV:

• Uses its genetic material to instruct the host cell's mechanisms to make the components of HIV. 
• Process is:
  • HIV binds to CD4 and the HIV attaches to the T helper cell. 
  • The protein capsid fuses with the cell-surface membrane and the RNA and enzymes enter the T helper cell. 
  • HIV's reverse transcriptase converts the RNA to DNA. 
  • The new DNA is inserted into the cell's DNA. 

How HIV causes the symptoms of AIDS:

• HIV causes AIDS by killing or interfering with the normal functions of the helper T cell.
• Without a sufficient number of T helper cells, the immune system cannot stimulate the B cells to produce plasma cells or the cytotoxic cells to kill pathogens.
• As a result, the body is unable to produce an adequate immune response and is susceptible to other infections and cancers.

The ELISA test:

• Enzyme linked immunosorbant assay
• Uses antibodies to detect the presence of proteins and the quantity present.
• Process for the test for a particular protein is:
  • Apply the sample to a surface to which all the antigens will attach to.
  • Wash the surface to remove any unattached antigens.
  • Add the specific antibody and leave the two to bond.
  • Wash the surface to remove excess antibody's.
  • Add the second antibody that binds with the first antibody. This antibody has an enzyme attached.
  • Add the colourless substrate of the enzyme. The enzyme acts on the substrate and forms a coloured product.
• Useful in drug and allergen tests.

• Antibiotics in many different ways, one being preventing the formation of normal cell walls.
  • In bacterial cells, water enters the cells via osmosis.
  • The reason the cell does not burst is because they have a cell wall made of murein, which is an inelastic material.
  • Antibiotics inhibit certain enzymes that are required for the synthesis and assembly of the cross-links in bacterial cell walls.
    • This weakens the walls and makes them unable to withstand the pressure of water entering the cell.
    • Water enter naturally by osmosis and the cell bursts, killing the bacterium.
• Virus rely on the host cell to carry out metabolic processes. They are lacking in the processes that antibiotics interupt so the antibiotics are ineffective.