Cellular Transport
Cell Membrane Structure
and Function
1A. What is the function of the cell
membrane?
•The cell membrane
regulates what
enters and leaves
the cell
1B. Why is the cell membrane called
selectively permeable?
• Permeable means: to have holes or
pores through which substances can
pas through
• To be selective:
–Some substances pass across, some
cross with assistance, and others do
not cross at all
1C. How does the cell membrane being
selectively permeable allow it to fulfill
it’s function?
• If the membrane was not permeable,
there would be no way for
substances to pass into or out of the
cell
• If the membrane was not selectively
permeable, there would be no
control over what entered or left the
cell
2. How many layers is the cell
membrane made up of?
•The cell membrane
consists mostly of a
phospholipid bilayer
3. What are the structural components
of the cell membrane?
• Phospholipids with the following
located within and between the
phospholipids
–Cholesterol
–Proteins (channel, transport)
–Carbohydrates
*Functions of structural components of
cell membrane:
• Proteins:
–Assist substances into and out of the
cell
• Cholesterol:
–Rigid molecules which gives the cell
membrane strength
• Carbohydrates:
–Involved in cell communication and cell
recognition
Question…
• How does a phospholipid having two
“sides” - a hydrophobic and a
hydrophilic side – lead to their self
assembling into bilayer?
• *Thinking hint: both the inside and
outside of your cell is a watery
environment
• http://telstar.ote.cmu.edu/biology
/downloads/membranes/index.ht
ml
6. Why is the model for the cell membrane called
the fluid mosaic? What’s the “fluid” part & what’s
the “mosaic” part?
• The fluid part is the
phospholipids
• The mosaic part are the
proteins and other structures
within the phospholipids
*Why is it called fluid?
• The phospholipids that
make up the cell
membrane are always in
motion
• http://www.stolaf.edu/people/giannini/flashanimat/lipids/membrane%20f
luidity.swf
• http://telstar.ote.cmu.edu/biology/downloads/membranes/index.html
Why is regulation of what enters and
leaves a cell important?
• Protect the cell
• Cells must always maintain a
constant internal environment
HOMEOSTASIS!!
• Homeostasis is maintained by the
regulating the movement of
molecules into and out of a cell