Cytosine is a nucleotide found in DNA and RNA, and glucose is a sugar found in many polysaccharides. Both molecules are organic and have a hexagonal structure.
Cytosine is a pyrimidine that bonds with guanine in DNA and RNA. It consists of carbon, nitrogen, oxygen, and hydrogen, and is part of a nucleotide, which is the monomer of nucleic acids like DNA
Glucose is a carbohydrate (more specifically, a monosaccharide) that can either exist on its own or bond with other glucose molecules to form polymers like starch, glycogen, and cellulose. It consists of carbon, oxygen, and hydrogen, and is a monomer of polysaccharides.
These two molecules have very different functions within the body, but they do share some similarities. The two most notable similarities are the fact that they are both organic compounds, and the fact that they both consist of a hexagonal ring with a few atoms hanging off of the ring.