A. Active transport
Active transport is the process of moving molecules across a cell membrane against their
concentration gradient, from regions of low concentration to high concentration. Unlike passive
transport, active transport requires energy input, typically derived from adenosine triphosphate
(ATP), to facilitate this movement. This process is essential for maintaining concentration
gradients of ions and molecules that are crucial for cellular functions.
Types of Active Transport
Active transport is broadly classified into two types:
1. Primary Active Transport
2. Secondary Active Transport
1. Primary Active Transport
Definition: Primary active transport directly uses the energy released from ATP hydrolysis
to transport molecules across the membrane. This process moves substances from areas of
lower concentration to higher concentration.
Mechanism:
The energy from ATP is used to change the conformation of transporter proteins,
which actively pump specific ions or molecules across the membrane.
One key example is the Sodium-Potassium (Na+/K+) Pump, which helps maintain
the electrochemical gradient in cells.
The pump binds to three sodium ions from inside the cell.
ATP is hydrolyzed, and the energy released causes the protein to change its shape,
releasing sodium ions outside the cell.
Two potassium ions then bind to the altered protein, which reverts to its original
shape, moving the potassium ions into the cell.
This process results in the movement of three sodium ions out of the cell for every
two potassium ions pumped in, which helps regulate the cell’s potential.
Examples:
Sodium-Potassium Pump: Maintains cellular electrochemical gradients.
Calcium Pumps: Move calcium ions (Ca²⁺) from the cytosol into the extracellular
fluid or organelles like the endoplasmic reticulum.
, 2. Secondary Active Transport
Definition: Secondary active transport, or co-transport, does not use ATP directly. Instead,
it uses the energy stored in the form of ionic gradients created by primary active transport.
Active transport is the process of moving molecules across a cell membrane against their
concentration gradient, from regions of low concentration to high concentration. Unlike passive
transport, active transport requires energy input, typically derived from adenosine triphosphate
(ATP), to facilitate this movement. This process is essential for maintaining concentration
gradients of ions and molecules that are crucial for cellular functions.
Types of Active Transport
Active transport is broadly classified into two types:
1. Primary Active Transport
2. Secondary Active Transport
1. Primary Active Transport
Definition: Primary active transport directly uses the energy released from ATP hydrolysis
to transport molecules across the membrane. This process moves substances from areas of
lower concentration to higher concentration.
Mechanism:
The energy from ATP is used to change the conformation of transporter proteins,
which actively pump specific ions or molecules across the membrane.
One key example is the Sodium-Potassium (Na+/K+) Pump, which helps maintain
the electrochemical gradient in cells.
The pump binds to three sodium ions from inside the cell.
ATP is hydrolyzed, and the energy released causes the protein to change its shape,
releasing sodium ions outside the cell.
Two potassium ions then bind to the altered protein, which reverts to its original
shape, moving the potassium ions into the cell.
This process results in the movement of three sodium ions out of the cell for every
two potassium ions pumped in, which helps regulate the cell’s potential.
Examples:
Sodium-Potassium Pump: Maintains cellular electrochemical gradients.
Calcium Pumps: Move calcium ions (Ca²⁺) from the cytosol into the extracellular
fluid or organelles like the endoplasmic reticulum.
, 2. Secondary Active Transport
Definition: Secondary active transport, or co-transport, does not use ATP directly. Instead,
it uses the energy stored in the form of ionic gradients created by primary active transport.
