Antibodies

Question 1

Antibodies

Answer 1

Antibodies: proteins (immunoglobins) produced by plasma cells, that have a specific shape that is complementary to that of 1 particular antigen, they attach to antigens rendering them harmless. They are released in response to infection.
Each B cell has slightly different DNA, so produce different antibodies. Plasma cells made by clonal expansion are genetically identical and so produce the same antibody (large numbers).

Structure:
Y shaped, 4 polypeptide chains, 2 distinct regions.
Variable region – specific shape, binds to specific complementary antigen – antigen-binding site.
Constant region – same in all antibodies, binds to phagocytic cells. Hinge region – allows flexibility so molecule can bind to multiple antigens.
Disulfide bridges – hold polypeptides together.
2 heavy 2 light chains.

Question 2

Opsonins - opsonisation:

Answer 2

Opsonins bind to antigens on a pathogen, and then act as binding sites (constant region) for phagocytes, so they can more easily bind to and engulf the pathogen – aid phagocytosis.
Opsonins may bind to cell surface receptors used by pathogen to bind to and infect host cells, preventing pathogens from entering host cells, rendering the pathogen harmless– neutralisation.

Question 3

Agglutinins – agglutination:

Answer 3

As each antibody has 2 identical binding sites it is able to ‘crosslink’ pathogens by binding to 2 pathogens at the same time. This causes pathogens to clump together – they are agglutinated.
- Agglutinated pathogens are more easily engulfed by phagocytes (many engulfed at once). - Agglutinated pathogens are physically prevented from entering host cells.

Question 4

Anti-toxins:

Answer 4

Some antibodies bind to toxins released by pathogens. This binding prevents toxins from binding to host cells, rendering the toxin harmless – neutralisation (inactivation).

Question 5

Investigation: Looking at blood smears – Eye protection.

Answer 5

Investigation: Looking at blood smears – Eye protection.
Blood cells viewed from blood smears, thin layer of blood is separated out on a slide and stained to make white blood cells more visible.
- Erythrocytes have no nucleus.
- Monocytes are the largest white blood cell, have kidney-bean shaped nucleus, non-grainy cytoplasm.
- Neutrophils have a multi-lobed nucleus and grainy cytoplasm.
- Lymphocytes are smaller than neutrophils, large nucleus almost fills the cell (very little cytoplasm).