Question

In a Glucose ring structure, is a Carbonyl group present? Or is it just present in the chain-like structure?

Answer 1

http://www.scientificpsychic.com/fitness/carbohydrates.htm

Answer 2

The carbonyl group gets lost when glucose takes a cyclic form.
The ring arises from the open-chain form by a nucleophilic addition reaction between the aldehyde group -(C=O)H at C-1 and the hydroxyl group -OH at C-4 or C-5, yielding a hemiacetal group -C(OH)H-O-.
The chain form's only carbonyl group is that aldehyde group that gets converted to a hemiacetal group.