Same ingredients. Why two names?
If a and a are made of the same thing, why bother making the distinction between the two?
Both use amino acids joined by bonds. The everyday distinction is mostly length: usually means a shorter chain, while usually describes a larger molecule made from one or more chains.
A fuzzy line, not a magic number
You may see about 50 amino acids used as a rough dividing line. It is a useful starting point, not a rule every scientist follows. Do not worry about an exact bead count.
is a good example of the overlap. Its mature form has 51 amino acids in two linked chains, and it is described as both a and a .
Why the distinction can be useful
Length matters when scientists discuss how molecules are made. Shorter chains can lend themselves to chemical synthesis. That does not mean every is easy to manufacture.
Shape matters too. Proteins often fold into forms that help them do their work, but peptides can also have structure. Small is not the same as simple.
And what about swallowing them?
and medicines can face two obstacles when swallowed: breakdown in the digestive system and difficulty crossing into the bloodstream. Many are delivered by injection, but that is not the definition of a .
Some medicines have approved oral formulations. The molecule and the formulation matter; the word alone cannot tell you how a medicine should be taken.