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I searched a lot in the net but don't found a clear answer. I just want to know if plasma membrane is permeable to sucrose.

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No, but yes.

Sucrose is a large polar solute. Because it is polar, it cannot easily pass the hydrophobic core of the membrane. So, if the lipids of the plasma membrane are mostly impermeable to sucrose, how do cells take in sucrose?

Plants

In biology, membrane-bound proteins are used for efficient transport across the membrane (Brian, 2011 from a review of Suc transport in plant cells). The specific group of membrane proteins used for sucrose transport are unimaginatively called Suc transporters (SUT).

So in a plant cell, sucrose can be moved across the membrane.

Humans

In mammals, there are no SUTs. Instead, sucrose is broken down into fructose and glucose by the enzyme sucrase.

A diagram showing the chemical structure of sucrose, glucose and fructose.

From there, glucose transporters GLUT proteins carry glucose and fructose across the plasma membrane.enter image description here

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  • $\begingroup$ What I don't understand is that in the osmosis experiment, potatoes shrink for a long time in the solution of sucrose. if plant cells were permeable to sucrose the potatoes will gain their initial size $\endgroup$
    – med morad
    Sep 12, 2019 at 18:04
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    $\begingroup$ @medmorad it depends on sucrose concentration and whether sucrose transporters are expressed in that particular tissue. $\endgroup$
    – WYSIWYG
    Sep 13, 2019 at 15:20

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