Lipids for Kids - how lipids evolved to make the first cell walls
SIGN IN / SUBSCRIBE TO KIDIPEDE
LOG OUT


Lipids

Cell wall
Lipid membrane

Around four billion years ago, some of the amino acid molecules that were on the planet Earth began to join together into bigger molecules with hundreds of atoms in them, called lipids. This happened in the water in the oceans on Earth, because there wasn't any land on Earth yet four billion years ago.

Lipids are large hydrocarbon molecules - they're long chains of hydrogen and carbon atoms, mixed with a few oxygen, phosphorus, and nitrogen atoms. One end of this big molecule is chemically attracted to water, while the other end of the molecule tries to get away from water (one example is oil not mixing with water). Because of this, lipids tend to arrange themselves into a long line called a membrane, with the water-loving side of the membrane touching the water, and the water-hating side of the membrane out of the water.

Even better, the molecules can sometimes form a hollow sphere of molecules, with a space inside it (It looks like a circle in the picture because you are looking down at it from the top). That way the water-loving ends are all touching the water, but none of the water-hating ends are.

Lipid bilayer
Lipid molecules forming a membrane two molecules thick

A more complicated, but even better arrangement for the molecules, is to form a membrane two layers thick, so that all of the water-hating ends are safely enclosed, with the water-loving ends coating the outside *and* the inside of the sphere. That way, even if the sphere is full of water, the water-hating ends still don't touch any water. The whole sphere, or bubble, is still too small to see, and only two molecules thick.

These lipid membrane molecules, also, could move apart a little bit to let water or other molecules, like proteins, in or out of their bubble. Check out this experiment to see how that works.

In many ways, these lipid membrane bubbles were a lot like living cells, but they were not alive. In order to become alive, the membranes had to combine with RNA or DNA to make living cells.

More than a billion years later, some cells began to use lipid membranes to make specialized parts for the cell. Lipid membranes make the outside of cell parts like the nucleus, the endoplasmic reticulum, the golgi bodies, the lysosomes, vacuoles, mitochondria, chloroplasts, and eyespots.

An experiment with oil and water
The next step to living things: cells

To find out more about the origins of life, check out these books from Amazon.com or from your library:

Atoms
Electricity
Chemistry
Physics
Math
Biology
Science for Kids home page
Kidipede home page



Copyright 2012-2014 Karen Carr, Portland State University. This page last updated 2014. Powered by Dewahost.
About - Contact - Privacy Policy - What do the broom and the mop say when you open the closet door?
-->