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The cell membrane is a phospholipid bilayer that separates the cell from its external environment. It has two major functions: forming a boundary between the inside and outside of the cell, and controlling the passage of materials. The membrane also contains other molecules such as cholesterol, proteins, and carbohydrates that strengthen the membrane, aid in cell identification, movement of molecules, and cell signaling. The fluid mosaic model describes the flexible nature of the membrane, while its selectively permeable property allows some molecules to cross while others cannot. Chemical signals are transmitted across the cell membrane through receptors, which can be intracellular or membrane receptors.
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KEY CONCEPT The cell membrane is a barrier that separates a cell from the external environment.
Cell membranes are composed of two phospholipid layers. • Phospholipids form a double layer surrounding a cell • Made of a charged phosphate group, glycerol, and two fatty acid chains • Head is polar and forms hydrogen bonds with water (water-loving… “hydrophilic”) • Tail is non-polar (water-fearing… “hydrophobic”)
cell membrane • Cell membranes are composed of two phospholipid layers. • The cell membrane has two major functions.
cell membrane • Cell membranes are composed of two phospholipid layers. • The cell membrane has two major functions. • forms a boundary between inside and outside of the cell outside cell inside cell
cell membrane • Cell membranes are composed of two phospholipid layers. • The cell membrane has two major functions. • forms a boundary between inside and outside of the cell • controls passage of materials outside cell inside cell
carbohydrate chain protein cell membrane cholesterol protein protein channel • Cell membranes are composed of two phospholipid layers. • The cell membrane is made of a phospholipid bilayer. • There are other molecules embedded in the membrane.
Other molecules • Cholesterol strengthens membranes, • Proteins aid cell identification and movement of molecules across membranes and cell signaling • Carbohydrates aid cell identification
cell membrane • Cell membranes are composed of two phospholipid layers. • The cell membrane is made of a phospholipid bilayer.
carbohydrate chain protein cell membrane cholesterol protein protein channel • Cell membranes are composed of two phospholipid layers. • The cell membrane is made of a phospholipid bilayer. • There are other molecules embedded in the membrane. • The fluid mosaic model describes the membrane.
cell membrane • Cell membranes are composed of two phospholipid layers. • The fluid mosaic model describes the membrane. • The membrane is flexible like a fluid and has a variety of molecules like the variety of tiles in a mosaic (picture)
Cell membranes are composed of two phospholipid layers. • The cell membrane is selectively permeable. • Allows some molecules to cross • Can also use terms such as semipermeable and selectively permeable • Enables a cell to maintain homeostasis
Cell membranes are composed of two phospholipid layers. • The cell membrane is selectively permeable. Some molecules can cross the membrane while others cannot.
Cell membranes are composed of two phospholipid layers. • The cell membrane is selectively permeable. Some molecules can cross the membrane while others cannot.
Chemical signals are transmitted across the cell membrane. • Receptors bind with ligands and change shape. • Detect a signal molecule and perform an action in response • There are two types of receptors.
Chemical signals are transmitted across the cell membrane. • Receptors bind with ligands and change shape. • There are two types of receptors. • intracellular receptor: Located inside the cell; binds to molecules that cross the membrane
Chemical signals are transmitted across the cell membrane. • Receptors bind with ligands and change shape. • There are two types of receptors. • membrane receptor: Located in the membrane; Binds to molecules that Cannot cross the membrane
