Antibodies
Laura Armstrong & Joe Wolfensohn
Teachers
Contents
Recall Questions
This topic requires prior knowledge of the humoral immune response and protein structure. You can test your knowledge on these below.
What type of bond is responsible for maintaining the quaternary structure of a protein?
Hydrogen bonds, disulfide bonds, ionic bonds, and hydrophobic interactions maintain the quaternary structure.
Antibodies have a quaternary structure, what does this mean?
Antibodies consist of multiple polypeptide chains (4 in total).
Outline the key stages of the humoral immune response.
- Antigen recognition: B-cells bind to antigens via specific receptors.
- Clonal selection: Helper T-cells activate the selected B-cells.
- Clonal expansion: B-cells rapidly divide via mitosis.
- Plasma cell production: Some differentiate into plasma cells, which secrete antibodies.
- Memory cell formation: Some differentiate into memory B-cells, providing long-term immunity.
Topic Explainer Videos
Check out this @JoeDoesBiology video that explains antibodies or read the full notes below. Once you've gone through the whole note, try out the practice questions!
If you want another explainer of antibodies, check out this video from @LauraDoesBiology and once you've gone through the whole note, try out the practice questions!
Structure of Antibodies
- Antibodies are globular proteins made up of four polypeptide chains: two heavy chains and two light chains.
- They have variable regions forming two specific antigen-binding sites.
- They have constant regions which consist of very similar amino acid sequences in all antibodies.
- Disulfide bonds maintain the antibody’s stable quaternary structure by holding the 4 polypeptide chains together.
- Antibodies belong to a group of proteins called immunoglobulins (Ig).
How Antibodies Work
Antibodies contribute to pathogen destruction in several ways:
- Agglutination: Antibodies have two antigen binding sites (allowing them to bind to antigens on two different pathogens), clumping pathogens together to make them easier for phagocytes to engulf.
- Neutralisation: Blocking toxins or preventing viruses from binding to host cells and replicating within them.
- Opsonisation: Coating pathogens to mark them and enhance phagocytosis.
Humoral Immune Response & Role of B-Cells (Re-Cap)
The humoral immune response involves B-lymphocytes and occurs in response to pathogens.
Primary Response:
- On first exposure, B-cells bind to a foreign antigen on a pathogen.
- They are then stimulated/ activated by helper T-cells.
- They will then divide by mitosis forming many clones.
- They then differentiate into plasma cells and memory cells.
- Plasma cells secrete large quantities of specific antibodies.
- This response is relatively slow (several days).
Secondary Response:
- Memory B-cells (that remain in circulation) allow a faster, stronger response upon re-exposure to the same foreign antigen.
- They can quickly differentiate into many plasma cells.
- More antibodies are produced in a shorter time. The concentration of antibodies rises higher and more quickly.
- This is the principle behind vaccination.
Monoclonal Antibodies
- Monoclonal antibodies are lab-produced antibodies with the same tertiary structure that bind to one specific antigen.
- They are produced by a clone of B-cells.
- Uses include targeted drug delivery for cancer treatment, pregnancy tests, and medical diagnosis.
Key Terms
- Antibody: A Y-shaped protein that binds to a specific antigen. Produced by B-cells (plasma cells).
- Antigen: A molecule (usually a protein) on a pathogen’s surface that triggers an immune response.
- Opsonisation: The process by which antibodies enhance phagocytosis.
- Memory B cells: Long-lived cells that enable a faster immune response upon re-exposure to an antigen.
- Monoclonal antibodies: Identical antibodies with the same tertiary structure produced from a single clone of B-cells.
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Exam Tips
Antigens are proteins found on a pathogen surface and trigger an immune response.
Antibodies are proteins produced by plasma cells and bind to a specific antigen.
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Describe the role of antibodies in agglutination and explain how this process helps the body fight infection. (3 marks)
- Antibodies have two binding sites, allowing them to bind to antigens on two different pathogens.
- This causes pathogens to clump together in a process called agglutination.
- Agglutination makes it easier for phagocytes to engulf and destroy the pathogens by phagocytosis.
Practice Question
Try to answer the practice question from the TikTok on your own, then watch the video to see how well you did!