Food macromolecules

Transcript

Making glucose

Green plants manufacture glucose through a process that requires light, known as photosynthesis.

This process takes place in the leaf chloroplasts.

Carbon dioxide and water molecules enter a sequence of chemical reactions within the chloroplasts.

The end products of these reactions are glucose and oxygen gas, which is released into the air. Glucose is used by the plant, with much of it being converted into other carbohydrates like starch and cellulose.

Glucose is a simple sugar with the molecular formula C6H12O6. It belongs to the carbohydrate class of macronutrients.

Glucose structures

The molecular formula of glucose is C6H12O6.

The structure of the glucose molecule can be either a linear or a ring arrangement.

In this animation, this symbol will represent a glucose molecule.

Linking glucose molecules

Glucose molecules can link together.

When 2 glucose molecules link up, this sugar is known as maltose. It is a disaccharide (2 sugars).

When many glucose molecules link together in a long chain, molecules called polysaccharides (many sugars) are formed.

The link formed between each molecule is known as a glycosidic bond.

Amylose has several hundred glucose monomers linked together in this way.

Types of starch

The common food starch amylose is found in potatoes, corn and cereal grain. It has low water solubility and takes longer to digest.

Amylopectin is a branched polysaccharide and makes up about 80% of the starch found in potatoes, corn and cereal grain. It is water soluble and easy to digest.

Carbohydrates not immediately used for energy supply are stored as glycogen in the liver and muscles.

This polysaccharide is highly branched and contains up to 100,000 glucose units.

Cellulose

When the cyclic form of glucose forms, 2 different versions of it are produced. One is alpha, the other beta.

Starches like amylose and amylopectin link only alpha-type glucose molecules together. With cellulose, it is the beta molecules that link together.

The glycosidic bonds in cellulose have a different orientation from those in starch.

As a result of this, human digestive enzymes can break down starch but not cellulose.

Cellulose consists of linear molecules each made up of at least 3,000 glucose units linked together.