Membranes
Membranes serve multiple functions. They form a unique membrane at the cell surface (plasma membrane), surround the nucleus, and form membranous intracellular organelles, such as rough endoplasmic reticulum (RER), mitochondria and vesicles. All membranes consist of a phospholipid bilayer composed of cholesterol and protein; integral membrane proteins span the bilayer; peripheral proteins associate with the inner surface of the membrane.
Plasma membrane >
The plasma membrane is the membrane at the cell surface, enclosing the cytoplasm of the cell.
Nuclear envelope >
Two membranes surround each nucleus, forming the nuclear envelope. Arrows indicate the outer nuclear membrane. Intracellular membranes have a similar structure and appearance as the plasma membrane.
RER >
Rough endoplasmic reticulum (RER) is also composed of membranes with a similar structure and appearance as the plasma membrane. RER is studded with ribosomes.
Mitochondria >
Intracellular membranes, e.g., those associated with mitochondria, have a similar structure and appearance as the plasma membrane. Mitochondria possess two membranes.
Vesicles >
Vesicles contained within the cell, such as secretory vesicles, lysosomes and transport vesicles, are surrounded by membranes.
