-Is polar as a result of the electrons spending more times near the electronegative oxygen atom
-Can form Hydrogen bonds with water molecules, helping dissolve organic compounds such as sugars

-A ketone and an aldehyde may be structural isomers with different properties, as is the case for acetone and propanal
-Ketone and aldehyde groups are also found in sugars, giving rise to two major groups of sugars: ketoses and aldoses

-Acts as an acid; can donate H+ because the covenant bond between oxygen and hydrogen is so polar
-Found in cells in the ionized form with a charge of 1- and called a carboxylate ion

-Acts as a base; can pick up H+ from the surrounding solution (water, in living organisms)
-Found in cells in the ionized form with a charge of 1+

-two of these groups can react, forming a covalent bond. this "Cross- linking" helps stabilize protein structure
-the Cross link can cause curly hair

-Contributes negative charge to the molecule of which it is a part (2- if at the end of a molecule, 1- when located internally in a chain
-Molecules containing this groups have the potential to react with water, releasing energy

-addition of this group to DNA, or to molecules found to DNA, affects the expression of the genes
-arrangement of these groups in male and female sex hormones affect their shape and function