One of the main things a membrane has to be able to do is control what flows through it. Sometime, that's just opening a channel and letting the dissolved thing flow "down gradient." But, sometime the cell has to do active work to pump ions to one side or the other of a membrane.
Once that gradient is established, it can be used to do work…and in fact used in myriad ways you can hardly imagine. Since it is so important, we will spend some time on it.
By the way, the figure is a cartoon of a protein called "aquaporin." Guess what it transports. It's a fascinating protein. Think about how you can make a protein that allows water…and only water…to pass through.

While almost all the reactions in your body take place in, and even include interactions with, water, there are some that require a hydrophobic milieu. Moreover, you need something to keep the outside out, and the inside in…a membrane…which is made of something called lipids.

The image above was lifted from an article in "The Daily Mail," found here.
It is a really bad representative cell, since it is a famous cancer cell line known as HeLa cells and it behaves in ways very much unlike good, normal cells. But, you can see a nucleus (stained for DNA in blue) and some fibers that are part of the "cytoskeleton." To see those, the researchers have used a technique to make them glow either red (microtubules) or green (actin fibers…or microfilaments.

This blog covers some of the stuff I hope you learned in the DNA model lab.

Introduction to a new and fun form of isomer!