Physiology · MU Pleven

Active Transport

Covers active transport across the cell membrane, distinguishing primary active transport, illustrated by the sodium-potassium pump, from secondary active transport through cotransport. It then explains endocytosis, with phagocytosis and pinocytosis, receptor-assisted uptake and exocytosis, and closes with cell junctions, the four tissue types and sugar transport across epithelial membranes.

Inside: 4 sections · 10 labelled pictures · 33 flashcards · 4 min

Topic 3 of 17 in the MU Pleven syllabus for Physiology (Medicine, Year 2). The free AceMed note covers it in 4 sections, about 514 words (4 min of reading), with 33 flashcards.

In this note

  1. TOPIC 3. ACTIVE TRANSPORT THROUGH THE CELL MEMBRANE – PRIMARY AND SECONDARY ACTIVE TRANSPORT. INGESTION BY THE CELL – ENDOCYTOSIS. TRANSPORT THROUGH CELLULAR SHEETS.
  2. ACTIVE TRANSPORT THROUGH THE CELL MEMBRANE – PRIMARY AND SECONDARY ACTIVE TRANSPORT.
  3. INGESTION BY THE CELL – ENDOCYTOSIS.
  4. TRANSPORT THROUGH CELLULAR SHEETS.

ACTIVE TRANSPORT THROUGH THE CELL MEMBRANE – PRIMARY AND SECONDARY ACTIVE TRANSPORT.

ACTIVE TRANSPORT – transport proteins within the membrane must use energy (ATP) to move substances either to the inside or outside of the membrane. A cell membrane moves molecules or ions “uphill” against a concentration gradient (or “uphill” against an electrical or pressure gradient).

Divided in two types according to the source of the energy used to facilitate the transport:

  • PRIMARY ACTIVE TRANSPORT à the energy is derived directly from breakdown of ATP or some other high-energy phosphate compound
  • SECONDARY ACTIVE TRANSPORT. the energy is derived secondarily from energy that has been stored in the form of ionic concentration differences of secondary molecular or ionic substances between the two sides of a cell membrane, created originally by primary active transport.

Primary active transport – Sodium/Potassium pump.

The sodium-potassium pump must break ATP down into ADP in order to pump three sodium ions outside the cell (continued below), while it pumps two potassium ions into the cell. The ATP phosphorylates (adds a phosphate to) the membrane protein as it binds to the sodium and breaks down, and it dephosphorylates the protein as it binds with the potassium. Cellular respiration must occur to add the phosphate back to ADP, thus restoring the ATP.

Secondary active transport – Cotransport.

In cotransport, one process (the Na/K pump), is coupled with the movement of a molecule of sugar (glucose) out of the cell, while allowing sodium to enter through the protein.

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