Download Structure

CELLULAR TRANSPORT
The Gate-Keeper of the Cell
THE CELL MEMBRANE
•REMEMBER…The cell membrane controls the
movement of substances into and out of the cell
(selectively permeable)
THE CELL MEMBRANE
• Separates cell
from environment
& regulates what
enters and leaves
• It mainly consists
of:
– phospholipid
bi-layer
– embedded
proteins
– glycoprotiens
1. THE PHOSPHOLIPID BI-LAYER
• Structure:
– 2 layers of
phospholipid
molecules
• Function:
Mmm…
Water
Mmm…
Oil
– Keeps cell intact
– Hydrophilic heads
and Hydrophobic
tails regulate
what enters and
leaves the cells.
2. PROTEINS
• Structure:
– embedded
randomly in
membrane
• Function:
– Transport larger
items through the
membrane
– Allow hydrophilic
particles through.
3. GLYCOPROTEINS
• Structure:
– Proteins with attached sugar molecules.
• Function:
– Attachment sites for molecules needing to
enter, or for messenger molecules such as
hormones.
– These are very specific to each person and
play a role in recognizing our own cells
(organ transplants)
PASSIVE TRANSPORT - “COME ON AND TAKE A FREE RIDE”
No ATP (energy) needed
ATP = Energy Currency of the cell!!!
There are three types:
1. DIFFUSION
-Small molecules (CO2, H2O, O2, salts) can
move between the phospholipid molecules of
the bilayer.
-Molecules move from a HIGH concentration
([]) to a LOW [] along a CONCENTRATION
GRADIENT until a balance is achieved.
Diffusion
Passive Transport
2. OSMOSIS
-The movement of water (from High to Low [ ])
through a selectively permeable membrane.
Osmotic Conditions Surrounding Cells
Isotonic solution – Solute [ ] outside of cell is
equal to [ ] inside the cell.
Hypertonic solution – Fluid surrounding the cell
has a higher solute [ ] than inside.
Hypotonic solution – [ ] of solute is higher inside
the cell than outside.
What will happen to a cell if placed in
each of these conditions???
Come up with an answer!
Passive Transport
•Osmosis is a VITAL fluid control process (blood
and urine balance)
Passive Transport
3. FACILITATED DIFFUSION
-Some proteins in the cell membrane provide a
“tunnel” for larger molecules (glucose) to
diffuse through.
-They go with the concentration gradient!
ACTIVE TRANSPORT
• ATP is the energy used to “pump”
nutrients across cell membranes.
• Using ATP, carrier proteins “pump”
substances through a membrane from
an area of LOW [ ] to an area of HIGH [ ]
against the concentration gradient.
• Eg. Na+/K+ pump in nerve cells
ACTIVE TRANSPORT
A QUESTION!
HOW DO THE REALLY LARGE
MOLECULES (Hormones,
polysaccharides etc.) move in and
out of cells??
An Answer!!
By two processes called
ENDOCYTOSIS AND EXOCYTOSIS.
Both methods require the use of
vesicles and ATP!
ENDOCYTOSIS –Moving materials into the cell
Three Types…
1. Phagocytosis
(Cell Eating):
-Used by white
blood cells and
amoeba.
-The cell moves out
and surrounds the
solid particle.
ENDOCYTOSIS –Moving materials into the cell
2. Pinocytosis (Cell drinking)
-Same process as phagocytosis except the cell
is moving liquids.
ENDOCYTOSIS –Moving materials into the cell
3. RME –
Receptor
Mediated
Endocytosis
-E.g. Moving
cholesterol
into the cell
(or Hypercholesterolemia)
EXOCYTOSIS – Moving materials out of the cell
•The reverse of pinocytosis
•The vesicle (from the Golgi) fuses with the
membrane and releases it’s contents out of the
cell.
•E.g. Hormones
ANY QUESTIONS???
The End!!!