Page 511 - Veterinary Immunology, 10th Edition

position of its electrons. This force, although very weak, may
VetBooks.ir become collectively important when two large molecules come into

contact. It can therefore contribute to antigen-receptor binding.
The binding of a receptor to its antigen is therefore mediated by

multiple noncovalent bonds. Each bond is relatively weak in itself,
but collectively they may have a significant binding strength. All
these bonds act only across short distances and weaken rapidly as
that distance increases. Electrostatic bond and hydrogen bond

strengths are inversely proportional to the square of the distance
between the interacting molecules; the van der Waals forces and
hydrophobic bonds are inversely proportional to the seventh power
of that distance. Thus the strongest binding between an antigen and

its receptors occurs when their shapes match perfectly and multiple
noncovalent bonds form. Antigens can bind to receptors when they
fit less than perfectly, although the binding affinity will be much
reduced.

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