T-tubules, also known as transverse tubules, are narrow tubes that are continuous with the sarcolemma (i.e., the cell membrane of striated muscle cells). In skeletal/cardiac muscle cells, T-tubules form invaginations of the sarcolemma that contain many ion channels involved in excitation-contraction (e-c) coupling of muscle cells. Thus, transverse tubules function to conduct the action potential from the cell membrane (sarcolemma) to the interior of the muscle cell.
The answer is endoplasmic reticulum. There are two types of the organelle. The rough endoplasmic reticulum (RER) and smooth endoplasmic reticulum (SER). The RER has ribosomes attached to its outer membrane hence mainly folds, modifies and transports proteins. SER, on the other hand, is significant in the modification and transportation of lipids.
The structure of amino acids is of 20 types of amino acids which can get mixed in a lot of ways and in an uncountable quantity, they are almost like the numbers with an infinite ways to structure them.