Transport Across Cell Membrane 2

Question 1

PRIMARY ACTIVE TRANSPORT

Answer 1

• Mechanism which transport substances against their concentration gradient through carrier proteins by utilizing energy directly from ATP.
  ✓Transport substances against gradient (uphill)
  ✓Carrier mediated
  ✓Carrier proteins has ATPase activity
  ✓Energy utilized from ATP hydrolysis
  ✓Carrier protein act as a ‘pump’
• Na+-K+ ATPases: Almost all cells
• H+-K+ ATPases: Gastric mucosal cells and the renal tubular cells
• Ca2+ ATPase: Sarcoplasmic reticulum
• H+ ATPases (Proton pump): Golgi complex and lysosomes

Question 2

Mechanism of Na+-K+ ATPase pump

Answer 2

Electrogenic pump
* Pumps 3 Na+ outside
* Pumps 2 K+ inside
* Creates more negativity inside

1.Binding of cytoplasmic Na+ to the pump protein triggers ATP.
2.Energy from breakdown of ATP causes the protein to change its shape.
3.The shape change expels Na+ to the outside, and extracellular K+ binds.
4.K+ binding triggers release of the phosphate group.
5.Loss of phosphate restores the original conformation of the pump protein.
6.K+ is released and Na sites are ready to bind Na+ again; the cycle
repeats.

Question 3

Functions of Na+-K+ ATPase pump

Answer 3

• Maintain cell volume.
• Maintains Na+ and K+ gradient across the membrane which for genesis for RMP
• large part of basal metabolism.
• Stores energy for secondary active transport.
• Participates in the secondary active transport of amino acids and glucose
  through co-transport system by creating Na+ gradient.
• facilitates a passive movement of Cl-, HCO3-, H20.

Thyroid hormones, insulin, aldosterone increase and dopamine inhibits the activity of
Na+-K+ pump.

Question 4

treatment of heart failure.

Answer 4

-Blockage of Na+-K+ ATPase in myocardial cells by cardiac glycosides (digoxin & oubain) leads to disappearance of Na+ gradient across the cell membrane.
- This inactivates the Na-Ca+ pump as it is dependent on Na+ gradient across the membrane. -This causes accumulation of calcium ions inside and facilitates myocardial contractility.

Question 5

SECONDARY ACTIVE TRANSPORT

Answer 5

indirectly uses energy obtained from the hydrolysis of ATP.

Symport : Both substances are transported in the same direction.
Example:
* Na+- glucose symport in intestine & renal tubules
* Na+- amino acid symport

Antiport : Transport of second substance is in the opposite direction of the first one.
Example:
* Na+- Ca+ antiporters
* Na+- H+ antiporters

Question 6

VESICULAR TRANSPORT

Answer 6

transport process that occurs by either fusion of vesicle or formation of vesicle
1) Exocytosis - Fusion of vesicle with the cell membrane
2) Endocytosis - Formation of vesicle from the cell membrane

Question 7

ENDOCYTOSIS

Answer 7

Process by which substances move into a cell.
a) Pinocytosis
b) Phagocytosis
c) Receptor-mediated endocytosis

Question 8

Pinocytosis

Answer 8

-cell drinking.
* The process of engulfing liquid
substances dissolved in water.
* Eg: Protein reabsorption in the renal tubule, ECF along with ions,
look at pic

Question 9

Phagocytosis

Answer 9

The process of ingestion of large particles or microorganisms by phagocytes.
Eg: Neutrophils, monocytes, macrophages
3 stages:
-attachment stage
-engulfing stage
-killing stage
look at pic

Question 10

Receptor-mediated endocytosis

Answer 10

look at pic
* Eg:Cholesterol

Question 11

Exocytosis

Answer 11

Process by which certain hormones, neurotransmitters, digestive enzymes and undigested foreign particles are released from cells.
* The molecules are synthesized in endoplasmic reticulum and packaged in Golgi apparatus to form the transport vesicles.
* The vesicles then move to the cell surface and fuse with the cell membrane.
* The contents are released into the ECF.

Question 12

LO

Answer 12

2.7 Explain the mechanism of active transport with suitable examples.
2.8 Mention the differences between primary and secondary active transport.
2.9 Explain the mechanism of exocytosis and endocytosis with suitable examples.