Cell membrane components are synthesized in the endoplasmic reticulum, transported as vesicles to the Golgi apparatus where they are modified, and then are transported to the cell surface where they deliver their contents to the cells exterior and become a part of the cell membrane in a process called ____________. The reverse of this process, bringing nutrient containing particles from out side to the inside of the cell is called _________.

A.	exocytosis; endocytosis
B.	active transport; passive transport
C.	simple diffusion; facilitated diffusion
D.	osmosis; diffusion

Tutorial

Graphic of important concepts about cell membranes

The membranes of the cell are dynamic, constantly being formed, recycled, and degraded. Membranes flow between cellular compartments and the cell surface, and also are endocytosed or taken up from the cell surface. This process results in both cell membranes and extra-cellular materials being taken up by cells.

The materials ingested by endocytosis are frequently added to lysosomes for degradation. The membrane lipids, proteins, and carbohydrates are also degraded in the lysosome. If one or more of the lysosomal enzymes are defective, then cell membrane material may build up causing a lysosomal storage disease.

In Tay Sach's disease, the enzyme hexosaminidase A is defective, and carbohydrate containing glycolipids can't be degraded. The build up of lysosomal glycolipids leads to serious neurological abnormalities and death. These processes are very important in many diseases. Most gene mutations causing cystic fibrosis end up with the receptor stuck in the endoplasmic reticulum and unable to reach the cell surface. Problems with receptors on the cell surface is a major factor in the development of heart disease.