Membrane Transport: Active vs. Passive Transport

Active Transport

Moving particles against their gradient requires input of external energy.

Passive Transport

Moving particles down/with gradient from high to low concentration; no additional energy input needed.

Thermodynamic Coupling

Coupling a thermodynamically favorable process with a thermodynamically unfavorable process to drive transport.

Channel Proteins

Proteins that don't appreciably bind solute; a single shape change allows many ions to pass; always passive transport.

Carrier Proteins

Proteins that bind solute and undergo allosteric change to deliver a small number of molecules across the membrane; can be passive or active transport.

Primary Active Transport

Active transport that directly uses energy from ATP hydrolysis to move substances against their gradient.

ATP Hydrolysis Reaction

ATP + H2O → ADP + phosphate; the reaction releases energy used for active transport.

Energy for Active Transport

Comes from coupling the movement of a substance against its gradient to the hydrolysis of ATP.

Gradient

The difference in concentration of a substance across a membrane, which can be used as a source of energy in passive transport.

Transporters

Proteins that facilitate the movement of substances across a membrane, can be classified as pumps or channels.

Shape Change in Proteins

The conformational change in proteins that occurs during transport, allowing the movement of substances across membranes.

Energy Input for Active Transport

Requires external energy, typically from ATP, to move substances from low to high concentration.

Concentration Gradient

The process of particles moving through a solution or gas from an area with a higher number of particles to an area with a lower number of particles.

Allosteric Change

A change in the shape of a protein that occurs when it binds to a substrate, allowing it to perform its function.

Pumps

Primary active transporters that couple energy from ATP hydrolysis to move substances against their gradient.

Energy in Passive Transport

Is derived from the gradient itself, allowing substances to move from high to low concentration without additional energy.

Sodium-Potassium Pump

An example of a primary active transport mechanism that moves sodium out of and potassium into cells against their concentration gradients.

External Energy Source

Energy required for active transport, which can come from ATP or other energy sources.

Hydrolysis of ATP

The process of breaking down ATP to release energy, which is used in active transport.

Transport Mechanisms

Different methods by which substances are moved across cell membranes, including passive and active transport.

Energy Transfer

The process of transferring energy from ATP to transport proteins to facilitate active transport.

Secondary active transport

Energy to move S against gradient comes indirectly, from harnessing energy of another gradient (here of X).

Primary Active Transport

The Na+ / K+ Pump establishes and maintains gradients that contribute to osmotic balance and the resting electrical potential.

Na+ / K+ Pump

Moves 3 Na+ out and 2 K+ in, both against their gradients.

Na+ gradient

Established by primary active transport (Na+/K+ pump) and provides energy for secondary active transport.

Na+ / glucose co-transporter

Exploits the Na+ gradient; both Na+ and glucose must bind for the transporter to change conformation and transport.

Passive transport

Facilitates movement down solute's gradient; not pumps.

Affinity

Strength of binding of Na+ and K+ changes through the cycle of transport.

Allosteric change

Shape changes that occur during the cycle of transport.

Conformational changes

Allow 'process proteins' (enzymes, transporters, signaling molecules etc.) to perform their jobs.

ATP

Role is to provide energy for active transport mechanisms.

ATP hydrolysis

Process that releases energy for cellular activities.

Membrane transport proteins

Include carrier proteins, channel proteins, and pumps (ATPase transport proteins).

Carrier protein

Facilitates the transport of specific substances across a membrane.

Channel protein

Forms pores in the membrane to allow specific ions or molecules to pass through.

Pump (ATPase transport protein)

Uses ATP to transport substances against their concentration gradient.

Uniporter

Transports a single type of molecule across the membrane.

Symporter

Transports two different molecules in the same direction across the membrane.

Antiporter

Transports two different molecules in opposite directions across the membrane.

Adenosine triphosphate (ATP)

Energy currency of the cell, used in various biochemical processes.

Adenosine diphosphate (ADP)

Product of ATP hydrolysis, can be converted back to ATP.

Phosphate group

Part of ATP that is released during hydrolysis to provide energy.