This allows carbon-based (organic) molecules to form an immense variety of chemical arrangements.

Inflammation can break down this barrier allowing drugs and large molecules to penetrate into the eye.

This part of the Sun is cool enough to allow simple molecules such as carbon monoxide and water to form.

These holes are small enough to block large molecules and allow small molecules to pass.

Hence, they must remain very tiny to allow essential molecules to drift from one part of the cell to another.

They allow small molecules like those of traditional drugs to enter the brain.

Pre-cells would have had semi-permeable membranes, allowing only certain molecules to pass through.

The size of the channel is also regulated to allow molecules up to 10,000 Da in size.

Several new technologies are being investigated to allow larger molecules to be delivered transdermally.

These channels are tightly regulated and selectively allow molecules of specific sizes to pass between cells.