Biology Active Transport

• Movement of substances from low concentration to high concentration or against the concentration gradient/ electrochemical gradient.  

• ATP supplies the energy needed for active transport

• Usually done by a carrier protein or protein pump.

  • Antiport: moves molecules in opposite directions

  • Symport: moves molecules in one direction across the membrane

Types of Active Transport

Primary Active Transport

• directly uses a source of chemical energy to move molecules against their gradient 

Ex) Na/K pump

Secondary Active Transport

• uses an electrochemical gradient – generated by passive transport – as an energy source to move molecules against their gradient.

• Does not directly require ATP

• Also referred to as cotransport

Na/K pump

• One of the most important pumps in animal cells by maintaining correct concentrations of Na+ and K+ in living cells. 

• Plays a major role in generating voltage across the cell membrane

  • Electrogenic pump 

• Moves 3 Na+ out of the cell and 2 K+ into the cell

Secondary Active Transport-cotransporters

• Studies of this pump have led to beneficial research for treating diarrhea that is common in developing countries. 

  • Na is naturally absorbed but with diarrhea- waste is being expelled so quickly it cannot be absorbed

  • Patients are treated by giving them a drink with high levels of glucose and salt. 

Bulk Transport- requires energy 

Exocytosis

• Cell secretes biological molecules by fusing vesicles with the plasma membrane 

  • Vesicle typically comes from the Golgi apparatus 

Endocytosis

• Cell takes in molecules and particulate matter by forming new vesicles from the plasma membrane. 

• 3 types of endocytosis 

  • Phagocytosis 

  • Pinocytosis 

  • Receptor-mediated endocytosis