FIGURE 1-18 Endosomes and other cellular structures deliver materials to lysosomes. Schematic overview of three pathways by which materials are moved to lysosomes. Soluble macromolecules and molecules bound to proteins on the cell surface are taken into the cell by invagination of segments of the plasma membrane and delivered to lysosomes through the endocytic pathway 1. Whole cells and other large, insoluble particles move from the cell surface to lysosomes through the phagocytic pathway 2. Worn-out organelles and bulk cytoplasm are delivered to lysosomes through the autophagic pathway 3. Within the acidic lumen of a lysosome, hydrolytic enzymes degrade proteins, nucleic acids, lipids, and other large molecules.