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Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: constant thinker on October 05, 2005, 08:11:29 PM

Title: Sugar Molecules & Rings
Post by: constant thinker on October 05, 2005, 08:11:29 PM
I'm doing a little bit of organic chemistry in chemistry class and I understand that sugar molecules form rings. In nature do sugar molecules always make rings or is it found in "linear" form? I'm talking about just a simple monosacharride.

P.S. Linear is probably a really bad word to use I know, but I was just wondering.
Title: Re:Sugar Molecules & Rings
Post by: mike on October 05, 2005, 08:14:01 PM
Yes, sugars are rings.
Title: Re:Sugar Molecules & Rings
Post by: mike on October 05, 2005, 08:17:25 PM
and straight chains...
Title: Re:Sugar Molecules & Rings
Post by: Yggdrasil on October 06, 2005, 03:29:23 AM
Most aqueous hexoses and pentoses exist in an equilibrium between their hemi-acetal/hemi-ketal ring forms and their straight chain aldehyde/ketone forms.  The equilibrium will generally favor the formation of the hemi-acetal/-ketal ring.
Title: Re:Sugar Molecules & Rings
Post by: movies on October 06, 2005, 03:52:33 PM
Maybe a little off topic, but I am curious...

Can sugars be metabolized in their cyclic form, or are the "unwrapped" into the linear form and then metabolized?
Title: Re:Sugar Molecules & Rings
Post by: Yggdrasil on October 07, 2005, 03:56:45 AM
That's a good question.  I didn't know so I had to look up the answer.  Hexokinase, the enzyme catalyzing the first step of glycolysis, aparently binds the cyclic form of glucose (which makes sense since that is the predominant form in aqueous solution).  You can clearly see in the structure of hexokinase that the glucose (colored purple in the image) is in its cyclic form.
Title: Re:Sugar Molecules & Rings
Post by: Mitch on October 07, 2005, 04:28:32 AM
Maybe a little off topic, but I am curious...

Can sugars be metabolized in their cyclic form, or are the "unwrapped" into the linear form and then metabolized?

Its probably not known since both forms are found in cells.