19. A group of cells are ruptured and mixed in a tube to produce a uniform mixture. This is then centrifuged to produce four distinct layers
of cell contents. The material in one of the layers contained a large
amount of protein. What is this layer composed of? *

What is the significance of the protein-lined pits? a. protein attracts other proteins needed for atp synthesis within the cell. b. protein-lined pits are able to transport one molecule at a time down the concentration gradient within the cell. c. the polarity of proteins allows other polar molecules to attach and be transported in the cell by transport channels. d. receptors within the pits allow ligands to fuse and be transported into the cell by endocytosis.