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Ch. 4 Cell Membrane
Part 3
Active Transport
• Definition:
• The energy consuming transport of molecules or ions across a
membrane AGAINST the concentration gradient
• requires cell energy (by hydrolysis of ATP)
• Require CARRIER integral proteins
• Each carrier protein is specific for just one type of ion or molecule
• Examples
1. Sodium–Potassium pump
• Exchanges 3 sodium (Na+) ions for 2 potassium (K+) ions
2. Hydrogen ion pump (proton pump)
• Pump hydrogen ions against the concentration gradient
3. Endocytosis
4. Exocytosis
Importance of Active transport
 Important is sending signals down axons of nerve cells via
Sodium-Potassium pump
 Important in re-absorption in the kidneys
 When useful molecules need to be re-absorbed into the blood after filtration
into the kidney tubules
 Important in absorption of some products of digestion
 Important in plants
 Used to load sugar from photosynthesizing cells of leaves into the
phloem tissue for transport around the plant
 Used to load inorganic ions from the soil into root hair dermal cells to be
transported via the xylem around the plant for metabolism
Active Transport
 Requires ATP (that’s made by cell
respiration)
 ATP adenosine triphosphate
 ATP attaches to carrier protein in cell
membrane
 PHOSPHORYLATES the carrier protein
 PHOSPHORYLATION The addition of a
phosphate (PO4) group (From ATP) to a protein or a
small molecule
 carrier protein changes shape
(conformational change)
 molecules or ions are transferred across
the membrane (against the gradient)
Hydrolysis of ATP
 Protein pumps
 act as ATPase enzyme
 Have a receptor site for
ATP on the inner
membrane
 Speed up the hydrolysis
reaction
 ATP is hydrolyzed into
ADP
 Energy from hydrolysis is
used to change the
protein shape
Sodium-Potassium Pump
 Found in membrane of animal cells
 ROLE: Pumps out 3 Na+ ions and pumps in 2 K+ ions for
each ATP molecule
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Na and K are both cations (positive)
Pumping out more Positives than it takes in…
Inside of the cell become more negative than the outside
Creates a potential difference across the membrane (p.d.)
Important in relaying signals in nerve cells
 Pump runs all the time
 Uses up 30% of the ATP produced by the cell
 Nerve cells use up 70% of its ATP running this pump
 There are separate Na+ and K+ channel proteins that allow
ions to diffuse out of cell
 There are more K+ channel proteins so K+ ions diffuse out
of cell more readily/faster than Na+
Types of Transport through Carrier
Proteins
Active Transport (Uniport)
Active Transport Na-K Pump
Na-K Pump Antiport
Glucose-Sodium Symport
Bulk Membrane Transport
• Diffusion and active transport refer to then transport of
individual molecules and/or ions across membrane
• Sometimes large quantities of materials must be transported
across the membrane
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•
•
•
Large molecules (proteins, polysaccharides)
Parts of cells
Require lots of energy
Bulk transport is a type of ACTIVE transport
Bulk Transport: Endocytosis
• Endocytosis
• Vesicle is created from the infolding of the plasma membrane,
which pinches off, bringing large molecules into the cell (forms
ENDOCYTIC vacuole)
• Pinocytosis – Cell drinking
•
•
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Bulk uptake of liquids
Extremely small vacuoles (vesicles) are formed
Sometimes referred to as micropinocytosis
Ex. Human egg cell takes up nutrients from cells that surround it (the
follicle cells)..called PINOCYTES
• Phagocytosis – Cell eating
• Cells specializing in this type of transport are called
PHAGOCYTES
• Forms phagocytic vacuoles
• Ex. White blood cells
• Receptor Mediated Endocytosis – Substrate binds to receptor
found on the plasma membrane to be brought into the cell
Ligand – molecule that binds specifically to a receptor site of another molecule
LDL uses receptors to enter cells (hypercholesterolemia is due to receptor defect)
Bulk Transport: Exocytosis
 Exocytosis – Vesicle binds to the
plasma membrane releasing the
contents outside of the cell
 Reverse of endocytosis
 Materials removed from cell
 Secretory vesicles from Golgi
apparatus carry proteins to cell
surface and release the proteins
 Ex. Secretion of digestive enzymes from
pancreatic cells
 Ex. Plant cells get their cell wall building
materials (cellulose) from secretory vesicle
Cells are always trying to Maintain Equilibrium by…
3 ways…
 PASSIVE Transport
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2 types
Requires NO energy
Goes with Conc. Gradient
types:
 SIMPLE DIFFUSION No protein required
 Small, uncharged particles
 FACILITATED DIFFUSION CHANNEL or CARRIER proteins
 Trans-membrane protein channel
 Protein with a specific shape; open-close
mechanism
 Ex. Osmosis and ligand-gated channels
 ACTIVE Transport
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REQUIRES Energy
Goes Against Conc. Gradient
 ACTIVE TRANSPORT
 Involves “transporter”
membrane protein and
ENERGY (ATP)
 Bulk Transport
 Endocytosis
 Pinocytosis
 phagocytosis
 Exocytosis