Active Transport

Active Transport: A type of transport that requires energy to move molecules across a membrane, often against their concentration gradient.

Passive Transport: Movement of molecules along the concentration gradient without energy input.
Active Transport: Movement of molecules against the concentration gradient, requiring energy.
- Primary Active Transport: Direct use of ATP to transport molecules.
- Secondary Active Transport: Indirectly driven by the electrochemical gradient established by primary active transport.
- Bulk Transport: Involves endocytosis and exocytosis.

Carrier Proteins (Pumps): Proteins that transport molecules across the membrane using energy from ATP hydrolysis.
- ATP Hydrolysis: The breakdown of ATP into ADP and inorganic phosphate (Pi), releasing energy.
- Phosphorylation: The process of adding a phosphate group to the protein, altering its shape and function.

Binding: The pump is open to the inside of the cell, has a high affinity for sodium ions (Na+).
- Binds 3 Na+ ions from the cytosol.
ATP Binding: The pump binds ATP.
ATP Hydrolysis: ATP is hydrolyzed to ADP and Pi, leading to phosphorylation of the pump.
Shape Change: The pump changes shape, opening to the outside and lowering its affinity for Na+.
- Releases 3 Na+ ions into the extracellular fluid (ECF).
Potassium Binding: The new shape has a high affinity for potassium ions (K+), binding 2 K+ from the ECF.
Dephosphorylation: The Pi is released, causing another change in shape.
Release: The pump returns to its original conformation, releasing 2 K+ ions into the cytosol.

Maintains the necessary ionic gradients across the cell membrane vital for various cellular functions, including nerve impulse transmission.
Each cycle results in 3 Na+ exported and 2 K+ imported, contributing to an electrical gradient across the membrane.

Mechanism: Utilizes the established sodium gradient resulting from the sodium-potassium pump to transport other molecules.
Sodium-Glucose Cotransporter (SGLT): Example of secondary active transport.
- Drives the transport of glucose into cells against its gradient, coupled with sodium moving down its gradient.

Sodium Binding: Sodium ions (Na+) bind to the SGLT from the ECF.
Glucose Binding: Glucose also binds, utilizing the energy released from Na+ moving into the cell.
Shape Change: The cotransporter changes shape, releasing both Na+ and glucose into the cytosol.
Energy Source: The energy for glucose movement is indirectly provided by the Na+ concentration gradient, which was established by the primary active transport process (sodium-potassium pump).
SGLT Locations: Found in the intestines and kidneys, facilitating glucose absorption and reabsorption, respectively.

Invokana: A diabetes medication that inhibits the SGLT in the kidneys, preventing glucose reabsorption and promoting its excretion in urine.

Definition: The process by which cells take in substances by enveloping them in an organelle formed from the plasma membrane.

Phagocytosis (Cell Eating): Engulfment of large particles, such as bacteria by immune cells (e.g., macrophages).
- Involves lysosomes to degrade the ingested material.
Pinocytosis (Cell Drinking): Uptake of liquid and dissolved solutes.
- Forms vesicles that transport the fluid into the cell.
Receptor-Mediated Endocytosis: Selective uptake of specific molecules that bind to receptors on the cytoplasmic membrane, leading to facilitated vesicle formation.
- Examples include cholesterol entry into cells via low-density lipoproteins (LDL).

Definition: The process used to export materials out of the cell through the fusion of vesicles with the plasma membrane.
- Example: Release of neurotransmitters from neurons during synaptic transmission.
Mechanism: Vesicles containing substances to be expelled migrate to the cell membrane, fuse, and release their contents into the extracellular space (ECF).