Biology

3.9 - Biological Molecules

3 min

note 1 of 3

Carbohydrates are made of simple sugars

Carbohydrates are one of the main groups of large biological molecules.
A large carbohydrate is built from many small basic units called simple sugars - the most important simple sugar is glucose.
These simple sugars are joined together in long chains to make large, complex carbohydrates.

Starch and glycogen are large carbohydrates made this way - each is a long chain of glucose molecules joined together. Because they're built from a repeating small unit, large carbohydrates can also be broken back down into their simple sugars when the bonds between the units are broken.

A wavy chain of green hexagons labelled starch and a branching chain labelled glycogen, each with an arrow marked broken down leading to a row of five separate hexagons labelled simple sugars (glucose).

note 2 of 3

Proteins are made of amino acids

Proteins are one of the main groups of large biological molecules.
A protein is built from small basic units called amino acids, joined together in a long chain.
There are many different amino acids, and a protein can contain a great many of them linked in a particular order.

What makes each protein different

Each protein is defined by the number of amino acids it contains and the order they are joined in.
This order gives each protein its own shape.
The shape is what lets a protein do its job - for example as an enzyme, a hormone, or a structural material in the body.

A box of scattered coloured circles labelled amino acids, with an arrow to a second box where the same circles are joined in a single winding chain labelled protein.

note 3 of 3

Lipids are made of fatty acids and glycerol

Lipids are the fats and oils - one of the main groups of large biological molecules.
A lipid is built from two kinds of smaller unit: fatty acids and glycerol.
One lipid molecule is made from one glycerol molecule joined to three fatty acid molecules.
Different lipids have different fatty acids, which is part of why fats and oils vary.
Unlike carbohydrates and proteins, a lipid is not a long chain of repeating units - it's this fixed arrangement of one glycerol and three fatty acids.

A tall blue bar labelled glycerol on the left, joined by three short lines to three pink bars stacked one above another, each labelled fatty acid.

key terms

TermDefinition

CarbohydrateA biological molecule that is either a simple sugar, such as glucose, or made from simple sugars joined together, such as starch.

Simple sugarA small carbohydrate molecule, such as glucose, that joins with others in long chains to form large carbohydrates.

ProteinA large biological molecule built from a long chain of amino acids.

Amino acidA small basic unit that joins in a long chain to form a protein.

LipidA large biological molecule built from one glycerol molecule joined to three fatty acid molecules.

end of notes

Key points to remember

Carbohydrates are made of simple sugars

Carbohydrates are one of the main groups of large biological molecules.

A large carbohydrate is built from many small basic units called simple sugars - the most important simple sugar is glucose.

These simple sugars are joined together in long chains to make large, complex carbohydrates.

Proteins are made of amino acids

Proteins are one of the main groups of large biological molecules.

A protein is built from small basic units called amino acids, joined together in a long chain.

There are many different amino acids, and a protein can contain a great many of them linked in a particular order.

What makes each protein different

Each protein is defined by the number of amino acids it contains and the order they are joined in.

This order gives each protein its own shape.

The shape is what lets a protein do its job - for example as an enzyme, a hormone, or a structural material in the body.

Lipids are made of fatty acids and glycerol

Lipids are the fats and oils - one of the main groups of large biological molecules.

A lipid is built from two kinds of smaller unit: fatty acids and glycerol.

One lipid molecule is made from one glycerol molecule joined to three fatty acid molecules.

Different lipids have different fatty acids, which is part of why fats and oils vary.

Unlike carbohydrates and proteins, a lipid is not a long chain of repeating units - it's this fixed arrangement of one glycerol and three fatty acids.