The Standard Model of particle Physics states that electrons do not have an internal structure. Each of the three quarks that make up proton and neutron are composed of three quarks. A proton is made up of two up and one down quarks, while a neutron is made up of one up and two down quarks. Quarks do not have an internal structure as per The Standard Model.
This may not answer 95% of your questions. These are natural questions: Are there alternatives to Standard Model? Why is the Standard Model so…standard? What is it that gives us the confidence in the Standard Model? How confident is that level of confidence?
Here are some answers
The Standard Model is a model we have high confidence in. The Standard Model was developed largely in the mid-to-late 20th century and is based upon a lot of experimental evidence. With the development of particle detectors and accelerators in the 1950s, there was a huge explosion of new particles. There were literally hundreds of them. Each particle was considered to be fundamental at the time.
The theory of quarks was created by some clever theoretical methods that used “exotic” mathematics. The mathematics was not only unfamiliar to the physicists at the time but was well-known to mathematicians for many generations. It is now a part of almost all undergraduate physics courses. It had everything you could want in a scientific theory. It explained current phenomena and predicted unknown phenomena that would later be observed. The “phenomena”, in each case, were mainly the existence of certain particles, decay products, and masses.
What is the Standard Model’s scope? Although it is quite good, no one would say that it is complete. It doesn’t incorporate gravity at all. It does not include dark matter and dark energy. There are also subtler problems. The Standard Model, for example, suggests that matter and nonmatter should be found equally in the universe. However, this is not consistent with experiment. People want to see a theory with a “broken” relationship between matter and antimatter.
People are interested in extensions to the Standard Model. Supersymmetry, for example, is a concept that… it kind of sounds like. It suggests that the current Standard Model can only describe half of all particles in the universe. Every Standard Model particle has a supersymmetric partner. Quarks and electrons are paired with each other, selectrons with selectrons, and so on. A “particle” is usually paired with a’sparticle”.
Supersymmetry seems to have a dim future, as far as I am aware. To date, no “sparticles have been discovered.” It was expected that they would be found in the LHC. However, supersymmetry is still a topic of discussion, at least according to my knowledge.
Other possible extensions to the Standard Model include string theory in different flavors.
What does this leave us with?
The Standard Model can be used for tons of things. It is not clear that anyone who knows it can claim it represents the entire universe. What does it mean for electrons and quarks to have no internal structure in Standard Model? These particles do not necessarily have an internal structure. We don’t know enough about the universe to understand how these particles, if any, might be structured.