Download CELL MEMBRANE

CELL MEMBRANE
Structure & Function
This lesson meets the following DoE Specific Curriculum Outcomes for Biology 11: 314-1, 314-2, 314-3, 314-8
CELL MEMBRANE
• Each cell is a separate unit of life, therefore, it has
a boundary – the plasma membrane (a.k.a., cell
membrane).
• The cell membrane separates the inner contents
of a cell from its external environment - it
maintains a constant internal environment despite
changes to its outside world.
• It forms spontaneously - no energy is required of
the cell to maintain the integrity of the plasma
membrane.
CELL MEMBRANE
• Cells live in a fluid environment (i.e. blood,
water, extra-cellular fluid) and exchange
materials with this fluid.
• The plasma membrane is the cell’s “gate
keeper” - it allows the passage of some
materials in and out of the cell but not
others.
• The plasma membrane brings in the ‘good’
things and keeps them in, and it exports the
‘bad’ things and keeps them out.
CELL MEMBRANE
• Small particles (e.g., O2, CO2) generally
pass through the plasma membrane easily.
• Lipids (and particles that are soluble in
lipids) pass through with least difficulty.
• The plasma membrane tends not to be
permeable to polar molecules unless they
are small.
CELL MEMBRANE
• Membrane consists of
two layers of
phospholipids
(phospholipid bilayer).
• Phospholipids consist of
a polar phosphate
containing head and two
non-polar lipid tails.
A phospholipid bilayer
One phospholipid molecule
CELL MEMBRANE
• Phospholipid heads
are hydrophylic
(water loving) they orient toward
water both inside
and outside the cell.
• Phospholipid tails
are hydrophobic
(water hating) they orient toward
each other
CELL MEMBRANE
• Fluid Mosiac Model:
components of membrane
are constantly moving
(like a fluid).
• The phospholipids can
move and slide past each
other.
• In some cells, cholesterol
molecules bind to the
phospholipids to help
restrict their movement.
CELL MEMBRANE
• The plasma membrane is embedded with
proteins.
• They have polar and non-polar ends to
determine their position in the bilayer.
• They can move sideways throughout the
plasma membrane.
CELL MEMBRANE
• The roles of these proteins include:
– regulation of the movement of particles
across membrane
– involvement in chemical reactions
– act as ‘marker’ on the cell.