12.6 - The specific immune system

Question 1

What are antibodies?

Answer 1

• They are Y-shaped glycoproteins called immunoglobulins

- They bind to a specific antigen on the pathogen or toxin that triggered the immune response

Question 2

Structure

Answer 2

• 2 identical long polypeptide chains called the heavy chains and 2 identical short polypeptide chains called light chains
• ## the chains are held together by disulphide bridges

Question 3

Function

Answer 3

• antibodies bind to antigens with a protein based lock and key mechanism
• the binding site is an area of 110 amino acids on both the heavy and light chains - known as the variable region
• it is a different shape on each antibody and gives the antibody it’s specificity
• when an antibody binds to an antigen, it forms an antigen-antibody complex

Question 4

How do antibodies defend the body?

Answer 4

1) the antibody of the antigen-antibody complex acts as an opsonin so the complex is easily engulfed and digested by phagocytes
2) Most pathogens can no longer invade the host cell once they are part of an antigen-antibody complex
3) Antibodies act as agglutinins causing pathogens carrying antigen-antibody complexes to the clump together. This helps them prevent spreading through the body and makes it easier for phagocytes to engulf a number of pathogens at the same time
4) anti-bodies can act as anti-toxins, binding to the toxins produced by pathogens and making them harmless