Video Transcript
What type of reaction involves the
addition of water to break the bond between two monosaccharides?
This question is asking about the
bond between two monosaccharides. To answer the question correctly,
let’s review the key points about monosaccharides and disaccharides.
Carbohydrates are molecules
composed mainly of carbon and water. Carbo- means carbon, and “hydrate”
means water. The most basic building block of
carbohydrates is the monosaccharide, mono- meaning one and “saccharide” meaning
sugar.
The proportion of the carbons,
hydrogens, and oxygens in a monosaccharide usually follow the ratio (CH2O)𝑛, where
𝑛 is a number between three and seven. Examples of monosaccharides are
glucose, fructose, and galactose. Two monosaccharides can join
together to form a disaccharide, di- meaning two. Examples of disaccharides are
lactose made up of glucose and galactose, sucrose made up of glucose and fructose,
and maltose made up of two glucose molecules. But how do these monosaccharides
join together?
Bonds, called glycosidic bonds,
must form between the individual monomers in an enzyme-catalyzed reaction. To understand how this happens, we
need to look at the general structure of a monosaccharide, and we will use glucose
as an example.
Glucose is a hexose, hex- meaning
six. So its formula is C6H12O6, and its
structure looks like this. We can label the carbons one to six
as shown here. When maltose is formed, two glucose
molecules join together. The glycosidic bond forms between
carbon one of the first glucose and carbon four of the second glucose molecule. A molecule of water is lost, and so
this reaction is called a condensation reaction.
Now that we have seen how the
monosaccharides are joined together, let’s look at how they are broken apart. The reaction that formed this
maltose molecule can be reversed to form two glucose molecules by breaking the
glycosidic bond holding them together. Seeming as water was lost when the
bond was formed, it makes sense that water needs to be added to break the bond
apart. The name of this reaction is a
hydrolysis reaction, hydro- meaning water and “lysis” meaning to split. Again, it is an enzyme-catalyzed
reaction.
Having reviewed these key facts,
let’s return to the question. We now know that the type of
reaction that involves the addition of water to break the bond between two
monosaccharides is called a hydrolysis reaction.
