Question

Which of the following can "slide" right through a cell membrane? (no protein channel needed) a) fatty acid b)steroid hormone c) monosaccharide d) a,b,c e) a and b The answer my teacher provided was e but my notes say that monosaccharides can pass through a cell and that the other two cannot.

Answer 1

Structure of a cell membrane: Lipid bilayer.

According to this structure, Cell membrane is made of the lipid layers with integral as well as peripheral proteins in between them.

These cell membranes are semi permeable, means that they allow only specific molecules to pass through them by simple diffusion.

Let's check what are those specific molecules:

• The molecules should be small and less/non polar.

Here we are asked to find those molecules which doesn't require a protein channel (hence through passive/active diffusion) .

Among the given molecules, steroid hormones can easily pass through the cell membrane without any requirement of protein channels, because steroid hormones are lipid soluble.

Fatty acids are comparatively larger molecules with larger molecular mass. Hence fatty acids cannot pass through the cell membrane without a protein channel.

Monosaccharides (such as glucose) have relatively larger mass and is polar molecules. Hence, it requires a specific medium (protein channels) to pass through cell membrane.

So the correct option is (b) Steroid hormones