Digestion: Polymers --> Monomers

Digestion is the process of breaking down larger molecules into smaller molecules. This process happens in the digestive system (learn more about the digestive system below). 

Polymers are large molecules such as carbohydrates, lipids, and proteins. These large molecules can be broken down into smaller molecules called monomers. 

Monomers are small enough to enter the blood stream where they can be moved into individual cells.

The chemical reaction that breaks polymers into monomers is called hydrolysis. The word "hydrolysis" comes from Greek: hydro- meaning "water" and -lysis meaning "to split" or "to break apart."

• To break the bond between two monomer, a water molecule (H2​O) is added.
• The water molecule splits, with a hydrogen atom (H) attaching to one side of the bond and a hydroxyl group (OH) attaching to the other.
• This addition of the water's components breaks the chemical bond between the monomers, splitting the large molecule into two smaller molecules.

POLYMER --> MONOMERS
​Large organic molecule --> small organic molecule      

    Proteins --> amino acids   
Carbohydrates --> sugars                     
                      Lipids --> glycerol + fatty acids   

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Biosynthesis: Monomers --> Polymers

Biosynthesis is the process that builds larger molecules from smaller ones. In simple terms, monomers enter the cell and are then combined to make polymers. Monomers of sugar combine to make carbohydrates. Monomers of amino acids combine to make proteins. Monomers of glycerol and fatty acids are combined to make lipids. 

Monomers can be thought of as legos, they are building blocks that can be combined in different ways to make different structures. Different combinations of amino acids make different proteins. Different combinations of sugars make different carbohydrates. The cell will combine the monomer building blocks together into the polymers that it needs in order to grow. 

The chemical reaction that builds polymers is called dehydration synthesis. In order to bind two monomers together you have to remove atoms from the original monomers and build a new bond. 

• One monomer gives up a hydrogen atom (H).
  
• The other monomer gives up a hydroxyl group (OH).
  
• When these two parts (H and OH) combine, they form a water molecule (H2​O), which is released as a byproduct.
  

MONOMERS --> POLYMERS
    Small organic molecules --> Large organic molecules

Amino acid + amino acid ...  --> proteins                              
Sugar + sugar + sugar ... --> carbohydrates            
Glycerol + fatty acid ... --> lipids                          
​                                       

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Chemical digestion could not take place without the help of digestive enzymes. Enzymes are substances that speed up chemical reactions. Digestive enzymes speed up the breakdown of polymers into monomers. Digestive enzymes are secreted by glands in the mucous membranes of the mouth, stomach, small intestine, and pancreas. Enzymes are specific to the type of molecule they can work with, so there are different digestive enzymes help break down different types of food molecules. 

• Carbohydrates are broken down into sugars by carbohydrases.
• Proteins are broken down into amino acids by proteases.
• Lipids are broken down into glycerol and fatty acids by lipases.

The name of a digestive enzyme typically ends with the suffix -ase' (which means “enzyme”). The rest of the name refers to the type of food molecules the enzyme helps digest.