The cell membrane is a highly selective barrier that controls the movement of substances in and out of the cell. In fact, polar molecules are unable to go across unless
unless the molecules arent tight together and there IS'NT movement that are highly selective to the barrier.
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The cell membrane is a highly selective barrier that controls the movement of substances in and out of the cell. In fact, polar molecules are unable to go across unless
they react with other substances to become nonpolar.
they have specific transport mechanisms. One such mechanism is facilitated diffusion.
Facilitated diffusion is the passive movement of polar or charged molecules across the cell membrane, down their concentration gradient, with the help of specific transport proteins. These transport proteins are embedded within the cell membrane and act as channels or carriers for the molecules.
To understand how facilitated diffusion works, let's take the example of glucose, a common polar molecule. Glucose cannot freely diffuse across the cell membrane due to its polar nature and large size. Instead, it relies on glucose transport proteins (GLUTs) to facilitate its movement.
Here is how the process of facilitated diffusion occurs:
1. A glucose molecule in the extracellular fluid (outside the cell) encounters a glucose transport protein embedded in the cell membrane.
2. The glucose transport protein undergoes a conformational change, creating a binding site for the glucose molecule.
3. The glucose molecule binds to the transport protein through specific molecular interactions.
4. The transport protein changes its conformation, allowing the glucose molecule to move across the membrane.
5. Inside the cell, the glucose molecule is released from the transport protein.
6. The transport protein returns to its original conformation, ready to transport more glucose molecules.
It's important to note that facilitated diffusion is a passive process, meaning it does not require energy expenditure from the cell. The molecules move down their concentration gradient, from an area of higher concentration to an area of lower concentration.
Overall, facilitated diffusion enables polar or charged molecules to cross the cell membrane while maintaining the highly selective barrier characteristic of the membrane.