Transcript The Plasma Membrane

The Plasma Membrane
AP Biology
Selective Permeability
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Brings in certain substances
Releases or keeps out certain substances
Maintains water balance
Essential for life
Structure of the membrane
• Composed largely of
phospholipids
• Arranged in a bilayer
• The hydrophilic heads
face the outside of the
membrane
• The hydrophobic tails are
inside the membrane away
from water
Phospholipid Bilayer
Water bathes the outside of the cell and makes up most of
the cytoplasm
Fluid Mosaic Model
• The membrane has a
fluid quality: will ooze
if punctured
• Parts move and
interact
• Mosaic means many
parts or components
Components of the Mosaic
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Phospholipids
Glycolipids
Sterols
Proteins
Glycoproteins
Types of Proteins
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Transport proteins
Receptor proteins
Recognition proteins
Adhesion proteins
Cell to cell
communication
proteins
Transport Proteins
• Allows water soluble
molecules to move
through membrane
• Binds substance on one
side, and releases it on the
other
• Glucose, ions, large polar
molecules
• May be active or passive
Receptor Proteins
• Bind substances
outside the cell which
triggers some cellular
activity
• Hormones
• Perfect fit: lock and
key
Recognition Proteins
• Identify each person’s
cells as their own
• Must be matched in
transplants, blood
transfusions, etc.
Adhesion Proteins
• Help cells of the same
type stick together in
tissues
• These are
glycoproteins with
oligosaccharides
attached.
Cell to Cell Communication Proteins
• Cell to cell
communication
proteins: match up
with another cell to
pass on a signal
Permeability
• Some substances
move across easily
• These include
substances which are
soluble in lipids (nonpolar) CO2, O2, and
some H2O.
• Glucose, amino acids,
and other large
molecules that do not
dissolve in lipids
cannot pass through
• Most water molecules,
and ions such as H+,
NA+, K+, and Ca+
cannot pass through
• Need transporter
proteins
Permeability