It is hard to imagine binding forces as a scientist develops an immune-assay and often times the commonly used antibodies are often thought to be the tightest binders. But these forces are very interesting to measure and compare among different types of interactions. But first what is the measurement unit of the force?
The force unit is called Newton and it is the amount of force that is applied on 100gm of weight by earth’s gravity. So, the weight of an apple that weights about 100 gms would be defined as 1N. The forces that are used to measure forces between molecules are many times less – about 10-12 N or pico-Newtons (pN). So let us compare the forces to break these interactions.
3000 pN : Breakage of a 12-mer DNA hybridization bond
1600 pN: Breakage of a C-C covalent bond.
200-300 pN : Biotin-Streptavidin link
50-100 pN : Antigen-antibody bond
30 pN: Force generated by rotaxane molecule on AFM tip.
5-30 pN: Force developed by a myosin-actin interaction, Similar forces for DNA polymerases.
0.01 pN: Force felt by small particle like bacteria due to Brownian effects.
This makes one realize that a covalent bond requires significant energy and an antigen-antibody bond is not as powerful as imagined by biologists. However, a Biotin-Strepavidin bond is sometimes so strong that if correct forces are applied, it will lead to breakage of weaker bonds in a molecule. One thing to note in these numbers is that the force involved is dependent also on the distance and weight. Therefore, small molecular forces are strong forces at very small distances as compared to the larger forces at larger distances.
