Ehlers Danos syndrome is an inherited condition characterized by a lack of functional collagen. Collagen is a protein expressed in the extracellular matrix that provides strength and toughness and is involved with tissue repair. Collagen deposition is therefore involved in maintaining the integrity of the skin, bones, and joints, preventing excessive mobility. Individuals with Ehlers Danos syndrome express an abnormal form of collagen protein, which can be caused by a mutation to an enzyme that functions to modify a collagen precursor protein once it is synthesized. This enzyme is in the endomembrane system and is in the same organelle that synthesizes protein. This condition can also be caused by a mutation to collagen itself. In the instance in which collagen is not properly processed, dysfunctional collagen is still expressed in the extracellular matrix. In the instance in which DNA encoding collagen itself is mutated, synthesis of collagen protein is significantly reduced. A mutation to collagen-encoding DNA prevents the synthesis and processing of collagen at the step involving which organelle?