• Where can you find
membranes in a cell?

Membranes are found around the cell
and each organelle

• The cell boundary; separates
cellular materials from
external environment
• Regulates which materials
can enter and exit the cell
• Maintains homeostasis in cell

SEMIPERMEABLE
MEMBRANE

FLUID MOSAIC
MODEL

AMPHIPATHIC
MOLECULE

PHOSPHOLIPID
BILAYER

Semipermeable
membranes
• Membranes that allow certain
materials to pass through based on
certain properties
–size
–hydrophobicity
–charge

The Fluid Mosaic
Model: The membrane
is made up of many
smaller parts and the
structure moves like a
fluid

Phospholipids and proteins make up most of the
membrane. Cholesterol helps with flexibility, and
carbohydrate chains help communicate with other
cells

A phospholipid is a type of lipid that has 2 fatty acid
tails and a phosphate head.
• http://telstar.ote.cmu.edu/Hughes/tuto
rial/cellmembranes/
The phosphate head is
hydrophilic
because it is attracted to
water
The fatty acid tails are
hydrophobic
Because they are repelled
by water
Use E-Life animation 6.3
https://www.youtube.com/watch?v=pzpZdijj
qX8

The phospholipid bilayer forms because the
inside and outside of the cell are mostly
water:

Assignment
1. What are the features of the fluid mosaic model of cell
membranes?
2. How do you describe the cell membrane’s selective
permeability property?
3. What are the various types of proteins and their functions
in the cell membrane?
4. Describe the role of the cholesterol in the cell membrane.

• Membrane receptor proteins relay signals between the
cell’s internal and external environments.
• Transport proteins move molecules and ions across the
membrane. They can be categorized according to the
Transporter Classification database.
• Membrane enzymes may have many activities, such as
oxidoreductase, transferase or hydrolase.

• Cell adhesion molecules allow cells to identify each
other and interact.
• Cell surface markers are proteins that identify the cell
type and the tissue of origin.

• Integral membrane proteins are permanently embedded
within the plasma membrane. They have a range of
important functions, such as acting as channels, carriers,
receptors, enzymes, or structural components2.
• Peripheral membrane proteins are temporarily attached
to the membrane or to integral proteins by weak
interactions. They are often involved in cell signaling, cell
recognition, or enzymatic activity2

• Lipid-anchored proteins are covalently attached to a
lipid molecule that is inserted into the membrane. They
can be either on the inner or outer surface of the
membrane. They are involved in various cellular
processes, such as cell signaling, cell adhesion, or
membrane trafficking3