The Cell Membrane
Cell membranes are composed of two
phospholipid layers. (bilayer)
The cell membrane has two major
functions.
1. Forms a boundary between inside and
outside of the cell
2. controls passage of materials
outside cell
cell membrane
inside cell
The fluid mosaic model describes the
membrane.
With a partner, define the two words and discuss how
this might relate to the cell membrane:
FLUID – bendable, movable, not solid
MOSAIC – made up of many pieces
The fluid mosaic model describes the
membrane.
There are other molecules embedded in the
membrane.
cell membrane
carbohydrate
chain
protein
cholesterol
protein
protein channel
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.
– A ligand is a specific molecule that binds
with a receptor to make something
happen.
There are two types of receptors.
• intracellular receptor
• Ligand moves through the cell membrane to
reach receptor on inside of cell.
• Example: hormones
There are two types of receptors.
• membrane receptor
• Ligand on outside of cell binds with a receptor
within the cell membrane.
• Ex: Neurotransmitters, growth factors