Chapter 3.3 Notes

3.3 Cell Membrane
KEY CONCEPT The cell membrane is a barrier that
separates a cell from the external environment.

3.3 Cell Membrane
3.3 Objectives
Describe the structure of the cell membrane.
Summarize how chemical signals are transmitted across
the cell membrane.

3.3 Cell Membrane
Cell membranes are composed of two phospholipid
layers.

3.3 Cell Membrane
Cell membranes are composed of two phospholipid
layers.
• The cell membrane has two major functions.
cell membrane

3.3 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
cell membrane
outside cell
inside cell

3.3 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
cell membrane
outside cell
inside cell

3.3 Cell Membrane
Cell membranes are composed of two phospholipid
layers.

3.3 Cell Membrane
Cell membranes are composed of two phospholipid
layers.
• The cell membrane is made of a phospholipid bilayer.
cell membrane

3.3 Cell Membrane
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.
cell membrane
carbohydrate
chain
protein
cholesterol
protein
protein channel

3.3 Cell Membrane
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
carbohydrate
chain
protein
cholesterol
protein
protein channel

3.3 Cell Membrane
Cell membranes are composed of two phospholipid
layers.

3.3 Cell Membrane
Cell membranes are composed of two phospholipid
layers.
• The cell membrane is selectively permeable.
Some molecules can cross the membrane
while others cannot.

3.3 Cell Membrane
Cell membranes are composed of two phospholipid
layers.
• The cell membrane is selectively permeable.
Some molecules can cross the membrane
while others cannot.

3.3 Cell Membrane
Chemical signals are transmitted across the cell
membrane.
• Receptors bind with ligands and change shape.
• There are two types of receptors.

3.3 Cell Membrane
Chemical signals are transmitted across the cell
membrane.
• Receptors bind with ligands and change shape.
• There are two types of receptors.
– intracellular receptor

3.3 Cell Membrane
Chemical signals are transmitted across the cell
membrane.
• Receptors bind with ligands and change shape.
• There are two types of receptors.
– intracellular receptor
– membrane receptor

3.3 Cell Membrane
3.3 Assessment: Hwy do phospholipids form a
double layer?
Phospholipids form a double layer in response to the
presence of polar water molecules surrounding them.
The polar heads of phospholipids interact with the water
inside and outside the cell, forming transient hydrogen
bonds. The nonpolar tails are repelled by water and
interact with each other inside the membrane.

3.3 Cell Membrane
3.3 Assessment: Explain how membrane
receptors transmit messages across the cell
membrane.
Membrane receptors bind to a signal molecule on the
outside of a cell. Upon binding, the membrane receptor
changes shape, which sends a message inside the cell.

3.3 Cell Membrane
3.3 Assessment: Describe the similarities
between enzymes and receptors.
Both enzymes and receptors are proteins that bind to a
specific ligand or substrate, change shape in response
to binding, and cause some sort of action or response.

3.3 Cell Membrane
3.3 Assessment: If proteins were rigid, why
would they make poor receptors?
If proteins were rigid, they would be unable to change
shape. Therefore, they could not effectively transmit a
message to the cell interior.