Active Transport

1
Active Transport
2
Active Transport

• Cellular energy is used to to transport
  substances across the membrane against a
  concentration gradient
• Energy is derived from splitting ATP

3
Pumps

• A transporter protein that uses energy from
  splitting ATP to change shape and carry a
  substance across a cellular membrane against its
  concentration gradient

4
Substances Transported

• Na
• K
• H
• Ca
• I-
• Cl-

5
Sodium-Potassium Pump

• Expels Na from the cell, brings K into the cell
• Acts as an enzyme to split ATP
• Used to maintain a low Na concentration in the
  cytosol by pumping Na into the extracellular
  fluid

6
Continuous Operation

• Na and K slowly leak back across the membrane
  down their gradients, so the pumps must
  continuously move these ions back across the
  membrane to maintain the concentration gradient.

7
Concentration Gradient

• The differing concentrations are crucial for
  osmotic balance of the 2 fluids and also for the
  ability of some cells to generate electrical
  signals

8
(No Transcript)
9
(No Transcript)
10
Operation of the Sodium Potassium Pump

• 1. Three Na in the cytosol bind to the pump
  protein
• 2. Na binding triggers the splitting of ATP into
  ADP plus a phosphate group which attaches to the
  pump protein. This causes a change in the shape
  of the pump protein
• 3. Three Na are expelled into the extracellular
  fluid

11
Operation of the Sodium Potassium Pump

• 4. The changed shape allows 2 K in the
  extracellular fluid to bind to the protein
• 5. The binding of the K causes the phosphate
  group to be released which causes the pump
  protein to return to its original shape
• 6. As the pump protein returns to its original
  shape, it releases the 2 K into the cytosol.
• The pump protein is then ready to bind Na and
  the cycle can repeat

12
Malfunctions of Transporters

• Drugs some turn off ATP production which would
  stop active transport of substances throughout
  the body
• Cystic Fibrosis a defective gene causes an
  abnormal Cl- transporter. There is a failure to
  secrete adequate amounts of Cl- resulting in
  extremely thick mucus secretions that result in
  obstruction and infection.

13
Transport in Vesicles

• Vesicle a small sac formed by the budding off
  from an existing membrane

• Movement of vesicles requires energy supplied by
  ATP.

14
ENDOCYTOSIS

• Materials move into a cell is a vesicle formed
  from the plasma membrane
• Phagocytosis
• Bulk Phase Endocytosis

15
Phagocytosis

• Large solid particles (like whole cells) are
  taken in by the cell.
• The particle binds to the plasma membrane
  receptor, the cell extends projections called
  pseudopods that surround the particle, then the
  membranes fuse to create a vesicle in the
  cytoplasm.

16
(No Transcript)
17

• Any undigested material remain indefinitely in a
  vesicle called a residual body
• Phagocytosis occurs only in special cells called
  phagocytes
• They are specialized cells used to engulf and
  destroy bacterial and other foreign substances
• These cells include certain white blood cells and
  macrophages.
• Phagocytosis is one of the bodys defense
  mechanisms against disease

18
Bulk Phase Endocytosis

• Cells take up vesicles containing tiny droplets
  of extracellular fluid and any solutes dissolved
  in that fluid
• The vesicle detaches from the membrane and enters
  the cytosol
• The vesicle fuses with a lysosome where enzymes
  digest the solutes into smaller molecules

19
(No Transcript)
20
Exocytosis

• Results in secretion materials exiting the cell
• Secretory cells give off digestive enzymes,
  hormones, mucus or other secretions
• Nerve cells give off neurotransmitters

21
Secretory Vesicle

• Vesicle containing substance to be secreted forms
  in the cytosol, fuses with the plasma membrane
  then releases the contents into the extracellular
  fluid

22

23
CHECKPOINT

• What is the key difference between active and
  passive transport?
• Briefly compare/contrast facilitated diffusion
  and active transport through a membrane pump
• Describe the process of phagocytosis.
• Name one way phagocytosis helps to maintain
  homeostasis.