[constant thinker]

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.

[mike]

Yes, sugars are rings.

[mike]

and straight chains...

[Yggdrasil]

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.

[movies]

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?

[Yggdrasil]

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.

[Mitch]

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.