Carbohydrates, proteins and lipids

Structure and functions in living organisms · Biological molecules and enzymes · note 1 of 5

Spec 2.7, 2.8Download all Biological molecules and enzymes notes (PDF)Download all notes (PDF)7 pages

Carbohydrates, proteins and lipidsSpec 2.7, 2.8

Carbohydrates, proteins and lipids (fats and oils) are the three main groups of biological molecules. They are all made from a small number of chemical elements.

Elements in biological molecules
Biological molecule	Elements present
Carbohydrates	Carbon, hydrogen and oxygen (C, H, O)
Proteins	Carbon, hydrogen, oxygen and nitrogen (C, H, O, N), and sometimes sulfur (S)
Lipids (fats and oils)	Carbon, hydrogen and oxygen (C, H, O)

Carbohydrates, proteins and lipids are large molecules made up from smaller basic units. Many small units are joined together to make one large molecule.

Large molecules and their basic units
Large molecule	Made from
Starch	Many simple sugars (glucose) joined together
Glycogen	Many simple sugars (glucose) joined together
Protein	Amino acids
Lipid	Fatty acids and glycerol (one glycerol and three fatty acids)

Starch is the storage carbohydrate in plants. Glycogen is the storage carbohydrate in animals. Both are made from glucose, which is a simple sugar.

Three panels: a chain of glucose units making starch or glycogen (C, H, O); a chain of amino acids making a protein (C, H, O, N, sometimes S); one glycerol joined to three fatty acids making a lipid (C, H, O). — Large molecules are built from smaller units: glucose → starch or glycogen, amino acids → protein, glycerol + three fatty acids → lipid.

Exam tip:

A lipid is made from one glycerol and three fatty acids. Learn the numbers 1 and 3, and remember that, of the three groups, only proteins contain nitrogen.