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A. Active Transport
• a. Active transport is the transport of a
substance across the cell membrane
against its concentration gradient (from
low to high concentration).
• b. Active transport requires energy in
the form of ATP.
1. Carrier Proteins act as “pumps”
• a. Bind to a specific substance on one
side of cell membrane
• b. Moves the substance against the
concentration gradient
• c. From low to high concentration
2. Sodium Potassium Pump
• a. A form of active transport
• b. Carrier protein transports 3 Na+ out
of the cell and 2 K+ into the cell
• c. Both are being moved against the
concentration gradient
• i. Na+ is usually more concentrated
outside the cell
• ii. K+ is usually more concentrated
inside the cell
• d. Sodium Potassium pump uses ATP as
energy source, can use up most of a
cell’s ATP
Phosphorylate:
attachment of
phosphate
removal of
phosophate
3. Purpose of the SodiumPotassium Pump
• a. The pump prevents sodium from
accumulating in the cell thereby preventing
excess osmosis into the cell, which could
potentially cause the cell to burst.
• b. The pump maintains the concentration
gradients of Na+ and K+ across the cell
membrane, which many cells use to help in the
transport of other substances, such as
glucose across the cell membrane
B. Bulk Transport
• a. Movement of large molecules into and
out of the cell.
• b. Molecules that are too large for
carrier proteins (e.g. proteins,
polysaccharides)
• c. Transported by vesicles
1. Endocytosis
• -movement of substance into the cell by
vesicle (Endo = in)
• a. fuse with a lysosome or other organelles
• b. Two main types of endocytosis: pinocytosis
and phagocytosis.
i. Pinocytosis
• a. Movement of liquid and solutes into the
cell
• b. “cell drinking”
• c. Example: maturing human egg cells use
pinocytosis to take in dissolved nutrients
ii. Phagocytosis
• a. Movement of food particles into the cell
• b. “cell eating”
• c. Example: Amoeba eating or white blood
cells engulfing bacteria
2. Exocytosis
• -movement of substance out of the cell
by vesicle (Exo = out)
• a. vesicle fuses with the cell membrane,
releasing contents outside the cell
• b. cells use exocytosis to export
modified contents from Golgi (e.g.
proteins)
C. Receptor Proteins
• a. Binds to a specific signal molecule,
allowing the cell to respond
• Example- Signal molecules tell muscles
when to contract and relax
• b. Binding of a signal molecule to its
matching receptor protein causes a
change in the activity of the receiving
cell.
c. 3 common changes that may occur:
• 1. changes in permeability
• a. When paired with an ion channel,
signal causes channel to open, allowing
ions to cross
• 2. triggers a
second messenger
• a. Second
messenger sends
another message
to somewhere else
in the cell
• 3. enzyme action
• a. Binding of signal may speed up
chemical reactions in the cell