Expert: Florence M Rollwagen - 11/6/2008

Question
Why do galactose and sorbose not breakdown in yeast when glucose, fructose and mannose do? These are all hexose sugars but do not have the same outcome when combined with yeast but I dont understand why.
Is it something to do with enzyme specificity?


Answer
Hi Ashley:  Thanks for your question.

You are correct, it has everything to do with enzyme specificity.  Remember that all biological reactions take place in three dimensional space (we draw them on paper in two dimensions).  So the tertiary structure (remember your proteins?) has significance when encountering substrates.

Look up the structures of the sugars in question and you will see that the -OH groups are in different places, and that they extend above or below the ring.  This gives the molecules a specific tertiary structure that will bind only with the correct enzyme.

For a good explanation and excellent illustrations go to JMOL at http://www.umass.edu/microbio/chime/#atlas

Click on the "Atlas of Macromolecules" and select "enzymes".  Then you will come to a window where you can select different enymes to look at.  You can rotate them and examine their tertiary structure to get an idea of the three dimensional space that they occupy.

There is also the option to use the program "Chime", but it requires a download.  It's up to you what you decide to look at.

Hope this helps.

FM Rollwagen, PhD