Download ACTIVE TRANSPORT

ACTIVE TRANSPORT
Energy Used to Move Cellular
Materials
Active transport always require ATP
energy molecules
• In order for ATP energy to be used by the
cell, a high energy bond in the ATP molecule
is broken, energy and a phosphate group is
released. ADP is formed
•
ATP
ADP + P (& energy)
EXAMPLES OF ACTIVE
TRANSPORT
• Cell Membrane Pumps (such as the
Sodium-Potassium pump)
• Endocytosis & Exocytosis (such as
pinocytosis and phagocytosis)
• Contractile vacuoles (such as the
organelles in some protozoans)
Cell Membrane Pumps:
• Carrier proteins not only assist in passive
transport, as in facilitated diffusion, but
they can be used for active transport as
cell membrane “pumps.”
During an active transport process, such
as a cell membrane pump…
The molecules transported by the carrier
proteins are moved against the
concentration gradient.
How does it work?
A carrier protein binds to a specific molecule on
one side of the membrane, changes shape
(shielding the molecule from the phospholipids),
transports the molecule to the other side, and
then releases it.)
1)
2)
Example: Sodium-Potassium pump.
Na+
K+
• To function normally, many animal cells must have a
higher concentration of Na+ ions outside the cell,
& a higher concentration of K+ ions inside the cell.
• The complete cycle of the sodium-potassium pump
transports 3 Na+ ions outside the cell, and 2 K+ ions
inside the cell. (At top speed, it can transport 450 Na+
ions and 300 K+ ions per second!)
Sodium-Potassium Pump
Sodium-Potassium Pump is important for
nerve cells.
• Carrying the 3 Na+ ions outside & 2 K+ inside
produced an electrical gradient across the
membrane. The outside of the membrane
becomes positively charged, while the inside of
the membrane becomes negative.
• The difference is important for the
conduction of electrical impulses along
nerve cells.
Endocytosis
• Endocytosis is a process by which cells
ingest external fluid, macromolecules, and
large particles including other cells.
During Endocytosis…
The cell membrane forms a small pouch
which pinches off in the cell to form a
vesicle.
Vesicles can fuse with lysosomes and
their contents are digested with enzymes.
Two major types of endocytosis:
• pinocytosis – transport of solutes or fluids
• phagocytosis – movement of large particles or
whole cells. unicellular organisms such as the
amoebae can ingest bacteria and other
protozoans, such as paramecia.
• Amoeba uses pseudopodia to engulf food.
phagocytes
• Some specialized white blood cells in animals,
called phagocytes, can engulf bacteria &
viruses.
• Lysosomes fuse with vesicles containing these
invaders so they can be destroyed.
Exocytosis (the reverse of endocytosis)
• Vesicles fuse with the cell membrane,
releasing their contents to the outside
environment.
Cell may use exocytosis to release large
molecules, such as proteins. (Vesicles from the
Golgi apparatus fuse with the cell membrane to
deliver their proteins to the outside of the
cell.)
• Unicellular organisms may get rid of
wastes through exocytosis.
Also nerve cells (release neurotransmitters) and
exocrine cells (release hormones to blood)
release molecules to control the activities of
other cells.
Contractile Vacuoles
Many freshwater unicellular organisms
must constantly rid themselves of excess
water. The can do this by special
structures called contractile vacuoles,
which collect and pump water out of the
cell.