The three quarks that make up a proton—two up quarks and one down quark—contribute to its mass through their individual masses and the strong interaction binding energy between them. The up quark has a mass of approximately 2.2 to 2.6 megaelectron volts (MeV), while the down quark has a mass of about 4.7 to 5.3 MeV.
However, the combined mass of the three quarks is not sufficient to explain the total mass of a proton. Most of the mass of a proton actually arises from the strong interaction binding energy, which is a result of the strong nuclear force that holds the quarks together. This binding energy is due to the exchange of gluons, which are the force-carrying particles of the strong nuclear force.
The strong interaction binding energy is a manifestation of Einstein's mass-energy equivalence principle (E=mc²). According to this principle, the energy associated with the strong interaction binding between the quarks contributes to the total mass of the proton. In other words, the binding energy and the mass of the quarks together account for the mass of the proton.
It is worth noting that the masses of quarks are not directly additive when combined to form a hadron like a proton. The strong interaction between quarks results in a complex interplay of their masses and binding energies, making it challenging to precisely assign individual contributions to the proton's mass. Nevertheless, it is generally understood that the bulk of the proton's mass is due to the strong interaction binding energy.