Movement of Molecules: Active Transport, Membrane Pumps, Exocytosis

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Active Transport

  • Active Transport is the movement or transportation of molecules through the cell membrane.

  • It needs energy molecules called ATP (Adenosine Triphosphate).

  • The molecular movement is that of the molecules like water and oxygen.

  • From a region of lower concentration to a region of higher concentration.

  • This movement is against the concentration channel with the help of enzymes.

  • Molecules such as amino acids, glucose including the ions inside the cell in higher concentrations require active transportation process.

  • Few examples of active transport are Sodium-potassium pump, uptake of mineral ions by the roots of the plants, etc.

Active Transport

Active Transport

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Membrane Pumps

  • Carrier proteins.

  • Moves substances from low concentration to high concentration.

Exocytosis

  • Is responsible for forcing molecules out of the cell.

  • A substance is released from a cell through a vesicle.

  • Transports it to the cell surface and fuses with the cell membrane.

Endocytosis

  • Cells ingest external fluid, macromolecules, or other large particles.

  • In Phagocytosis large molecules or whole cells get ingested.

  • In Pinocytosis solutes or fluids get ingested.

The Sodium Potassium Pump (Na+/K+ATPase)

Responsible for the movement of molecules from a region of high concentration to low concentration.

Importance of Active Transport

Essential for ensuring the entry of large, insoluble molecules into the cell.

Types of Active Transport

Primary Active Transport

  • Also known as direct active transport.

  • Chemical energy is used for pushing the molecules.

  • This transport directly uses ATP (an energy molecule)

    • During hydrolysis it breaks down releasing energy that gets stored in chemical bonds.

    • Regulates the resting potential of the cell.

  • Sodium ions shift from a lower concentration (11 mm) to a higher concentration (146 mm).

  • In case of potassium, the transfer of ions is from a higher (146 mm inside the cell) to a lower concentration (4 mm) of the extracellular fluid.

  • The substances that get transported across the cell membrane are Na+, K+, Mg2+, and Ca2+.

Primary Active Transport

Primary Active Transport

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Secondary Active Transport

  • Movement of multiple molecules across the membrane.

  • Uphill movement of the molecules with the downhill movement of the other.

  • Channel proteins can be recognized as co-transporters.

Co-transporters (types):

  • Symporters-SGL2 being a symporter co-transporter is responsible for transporting glucose into the cells along with the sodium ions.

  • Antiporters are responsible for shifting specific ion and the solute along the opposite directions.

The most common example for antiporters co-transporter is the Calcium/Sodium exchanger.

Secondary Active Transport

Secondary Active Transport

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