The vesicles involved in secretion are called secretion vesicles . These form around the molecules to be secreted as they pinch off of the Golgi apparatus. They function to digest materials that enter by endocytosis . Their inner membrane is arranged in a series of folds called cristae to provide an enormous surface area for chemical reactions. The respiratory enzymes for the electron transport system are located within this inner membrane .
Mitochondria replicate within the cell and have their own DNA and ribosomes.
We will see later in Unit 3 that peroxisomes digest protein antigens into peptides called epitopes as part of immune recognition during the immune responses. Like mitochondria, they replicate within the cell and have their own DNA and ribosomes. The cytoskeleton is a network of microfilaments, intermediate filaments, and microtubules. Microtubules Microtubules are hollow tubes made of subunits of tubulin protein . They provide structural support for the cell and play a role in cell division, cell movement, and movement of organelles within the cell .