What do we mean by a left- or right-handed object? Well, first consider an object with twists or spirals, such as the two cylinders shown above. It might not be apparent right away, but by twisting in one direction creates a structure which is unique from twisitng in the other direction. We'll talk more about this soon, but the following question arises - "How would you describe the direction of the twisting?" At first you might think to say they are being twisted in a clockwise or counter-clockwi

To describe the twisting in an unambiguous way, structures are refered to as having handedness. Consider the two screws shown above on the right - notice that that one is a mirror image of the other. To determine their "hand", identify the main axis (blue line) and the orientation of the outer threads (brown lines). For a left-handed structure, these threads "point upward" to the left, while for the right-handed they point to the right. Note that no matter what angle these screws are viewed at the thread

There are many examples of handed structures in biology - probably the most well known is DNA. This has two strands (shown here in yellow and green) which normally join to form a right-handed structure (DNA can form into a left-handed structure, "Z-DNA", if there is an abnormal amount of CG components, but this is rare).

Now that you know how to recognise the handedness of an object, you would be surprised at how many everyday objects whose "hand" you can now identify. Below are some common objects - see if you can identify their handedness. Hover the mouse pointer over the image the see if you were correct.