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The Cell Membrane
A structure that functions to maintain
homeostasis at the cellular level
Big Idea #2
Cellular Engineering
• Design a “screen” according to the guidelines
– Steroids can dissolve and pass though.
– Large proteins can interact with the surface but
cannot penetrate.
– Allows small, nonpolar molecules to pass through.
– Glucose goes through slower than a smaller
molecule like oxygen gas
– Ions cannot pass directly through
How did you do?
• Did you come up with
the cell membrane?
• Complete Campbell’s
Activity 8A, sketch
and label the
Campbells Picture
Let’s Discuss the following:
• Structure of a phosopholipid bilayer
• Evidence for the fluid mosaic model of the cell
• Properties of proteins embedded in cell membrane
and freeze fracture
• How does winter wheat avoid cell membrane
• Role of emergence in the functionality of the
membrane (sidedness)
• How cells attach together through an extracellular
• Functions of proteins in membrane
Phospholipid Bilayer
• Hydrophilic
• Hydrophobic
Term: Amphipathic
How are phospholipids different
than triglycerides?
• What is the difference
between the two?
• Where might the
phosphate group come
• Where do the fatty
acids come from?
Site of Lipid Biosynthesis
• The organ where
everything happens!
Fluid Mosaic Model
• Proteins are embedded in cell membrane rather
than sandwiched.
• Evidence: freeze fracture technique
Freeze Fracture
Structure of Integral proteins
• Amphipathic
• Aquaporin is an
example of an
amphipathic protein
that spans the cell
membrane and has a
hollow core to allow
water to pass through
• Where might the
hydrophobic parts be?
• Hydrophilic?
• How might influx of
water be controlled?
Role of substances within the
lipid bilayer
• What keeps
membranes flexible?
• Unsaturated vs.
Saturated fats
• Role of cholesterol
– Depends on
• High Temperatures
• Low Temperatures
Winter Wheat…eh?
• Why is this such an
important crop in
• How might he
composition of the cell
membranes be
different than wheat in
more temperate
Sidedness of Membranes
• Proteins are part of a fluid mosaic and they can
disperse in cell membrane.
• How is the above experiment evidence of this
Cell with sidedness?
• How would a nerve
cell display sidedness?
• Would a cell in the
intestine need to
display sidedness?
• What cell might not
have a sidedness?
How does this tissue show
• Where are
Extracellular Matrix 6.7
Cellular Junctions
• Plants
– Plasmodesmata
• Allow ions to pass
from cell to cell.
• Animals
– Junctions are
specialized for
certain functions
Animal Junctions
• Tight Junction:
Prevents movement of
fluid between cells.
• Desmosome: Adheres
two cells, very common
in epidermis
• Gap Junction: Allows
ions to pass directly
from cell to cell
Interaction Between Membrane
and Outside of Cell 6.6
Adhesion to ECM
can alter tension
on cytoskeleton.
Plastic on petri
dishes mimics an
ECM. Why do
cells usually grow
in a single layer?
??Cancer cells??
Comparing Cytoskeletal
Motor Proteins
• Myosin can bind
and walk along
– Muscle conractions
– Ameoboid
– Movement of
organelles around
cytoplasm (plant
and animal cells)
Functions of Membrane Proteins
Getting Across!
• Campbell’s Activities B, C, D
We will begin an investigation of cell
tissues. It will be important to recognize
how these tissues are organized and
connected through the ECM.