Plasma Membrane
Plasma Membrane
Plasma Membrane
to:
1) List the components on the surface of
membrane
2) Identify the general properties of plasma
membrane
3) Distinguish the differences between passive
and active transport
6.1 Fluid Mosaic Model
6.2 Transport of Small Molecules
6.3 Transport of Large Molecules
It’s like a fluid…
It’s like a mosaic…
It’s the
Fluid Mosaic Model!
• All movement of substances go through the
cell membrane, which is known as the plasma
membrane.
• The necessity for the movement of substances
across a plasma membrane are:
• a) Cells need nutrients and oxygen.
• b) Cells produce waste product which exit
through the plasma membrane.
• c) The plasma membrane control the types
and the amounts of substances needed by the
cell at any one time.
Cell membrane
▫ Lies immediately
against the cell wall
▫ Made of protein and
phospholipids
▫ Selectively permeable
▫ FUNCTION: Controls
the movement of
materials into and out
of the cell
Davson-Danielli, 1935
• Lipid/protein ‘sandwich’
• Thought that surface proteins might be flat beta
sheet.
Singer and Nicholson proposed the fluid
mosaic model, 1972 to explain the structure
of the plasma membrane.
• The fluid mosaic model is the currently
accepted model of the cell membrane.
• The basic unit of the plasma membrane is the
phospholipid molecule.
Sandwich and Fluid Mosaic Models
• The phospholipid molecule consists of:
a) A polar molecule carries an unequal
distribution of electric charge. This
unequal distribution of electric charge
produce a polar molecule which can
attract other polar molecule such as water
molecules.
b) Hydrophilic means ‘water-loving’ or
attracted to water molecule
c) Hydrophobic ‘water-hating’, or repelling
water molecules.
• Make up the cell
membrane
• Contains 2 fatty acid
chains that are
nonpolar
• Head is polar &
contains a –PO4
group
• Other molecule present in the plasma membrane
are:
a) Cholesterol molecules which fit in between the
phospholipid molecules, making the plasma
membrane more rigid and stable.
b) Carrier protein and channel protein which assist
and control the movement of water-soluble ions
and certain molecules across the membrane.
c) Glycolipids which are combination of lipids and
polysaccharides, help cells to recognise each
other.
d) Glycoprotein which are combination of protein and
polysaccharides, also help cells to recognise each
other.
1. Permeable means allowing something to pass
through.
2. The plasma membrane is selective permeable or
semi-permeable as it allows only certain substances
to pass through it but not others.
3. The phospholipid bilayer is permeable to:
a) Small non-polar (hydrophobic) molecules that are
lipid-soluble, such as fatty acids, glycerol, steroid,
vitamin A, D, E and K.
b) Small unchanged molecules, such as water, oxygen
and carbon dioxide. These molecules are small
enough to squeeze through between the
phospholipid gaps by simple diffusion or osmosis
down their respective concentration gradients.
The phospholipid bilayer is not permeable to:
a) Large polar molecule, that are not soluble in lipid,
such as glucose, amino acids, nucleic acids and
polysaccharides.
b) Ions (charged), regardless of size, such as: H+, Na+,
HCO3-, K+, Ca²+, and Mg²+
TYPES OF TRANSPORT ACROSS CELL
MEMBRANES
SMALL MOLECULES LARGE MOLECULES
Diffusion
movement from high low concentration
• Requires NO energy
• Molecules move from
area of HIGH to LOW
concentration
• Example: Oxygen or
water diffusing into a
cell and carbon
dioxide diffusing out.
In solids (like rock), diffusion is very slow
• ~ 10-5 mm/min
In liquids, it is much faster
• ~ 0.5 mm/min
In gases, it is fastest
• ~ 10 cm/min
Diffusion is faster with increased heat
• Takes place in gas rather than in liquid
AS Biology, Cell
membranes and
Transport
CONCENTRATED SOLUTION
DILUTE SOLUTION
Cell membrane
SEMI- permeable.
Sugar molecule
Hemolysis
Crenation
Red
Blood
Cells
• Firmness or tension (vacuole Water
full) that is found in plant cells Water
(cell wall) that are in a
hypotonic environment is
called TURGID. Central
Vacuole
• This process is called
Water Cell Water
TURGOR PRESSURE
Wall
• When the plasma membrane Water
Water
pulls away from the cell wall
(vacuole empty) in a
hypertonic environment (loss plasma membrane
of water) is called
PLASMOLYSIS. Cell
Wall Water
hypotonic hypertonic isotonic
extracellular intracellular
K+ K+
fluid
fluid
Na+ Na+
Sodium-Potassium Pump
non-specific
pinocytosis
process
Specific
receptor-mediated triggered by
endocytosis
molecular signal
• Endocytosis is the transport of materials into a cell.
• Materials are enclosed by a fold of the cell membrane,
which then pinches shut to form a closed vesicle.
• Materials digested form a small product molecules
Moving the “Big Stuff”
Exocytosis-
moving
things out.
Molecules are moved out of the cell by vesicles that fuse with
the plasma membrane.
This is how many hormones are secreted and how nerve cells
communicate with one another.
Endocytosis and Exocytosis:
Uses Uses
Specific Controllable
Method energy proteins
Lipid
Diffusion
N N N N
Osmosis N N Y N
Passive
N Y Y Y
Transport
Active
Y Y Y Y
Transport
Vesicles Y N Y Y
1. Enzymes: A protein built into the membrane may be an enzyme with an
active site exposed to the substances
2. Transport: Divided into channel (passsive transport) and carrier protein
(passive and active transport).
3. Cell identification markers: Glycolipids and glycoprotein function to
identify other cell. Important in in immune system – cell patrolling the body
tissues identify and destroying foreign invaders such as bacteria or viruses.
4. Cell adhesion-juction: serve to bind cell together, to prevent the movement
of material between the cell , or to allow cells to communicate with each
other.
5. Attachment to cytoskeleton: Function to maintain cell shapes and fixes
the location of certain membrane proteins.
6. Receptors: Hormones are molecules that cells use to communicate with
one another. Receptor enable cell to detect hormones and variety of other
chemicals. Eg: insulin to reduce glucose level in blood.
Any Questions??