4.1 - Biological Molecules

Carbohydrates are made of simple sugars

• Carbohydrates are one of the main groups of large biological molecules.
• They contain three chemical elements: carbon, hydrogen, and oxygen.
• A large carbohydrate is built from many small basic units called simple sugars.
• The most important simple sugar is glucose.
• Simple sugars are joined together in long chains to make large, complex carbohydrates.

Large carbohydrates are chains of glucose

• Starch, glycogen, and cellulose are all large carbohydrates - 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.

Carbohydrates for energy

• Carbohydrates are sources of energy. Sugars such as glucose and lactose (the sugar in milk) are broken down in respiration to release energy.
• Large carbohydrates are stores of energy. Starch stores glucose in plants and glycogen stores it in animals, until it is needed.

Proteins are made of amino acids

• Proteins are one of the main groups of large biological molecules.
• They contain the chemical elements carbon, hydrogen, oxygen, and nitrogen; some proteins also contain sulfur.
• The nitrogen is what sets proteins apart from carbohydrates and lipids, which do not contain it.
• A protein is built from small basic units called amino acids, joined together in a long chain.

What makes each protein different

• There are many different amino acids, and a protein can contain a great many of them linked in a particular order.
• It's the number of amino acids and the order they're joined in that makes each protein different.
• This order gives each protein its own shape, and 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.
• They contain three chemical elements: carbon, hydrogen, and oxygen.
• A lipid is built from two kinds of smaller unit: fatty acids and glycerol.
• One lipid molecule is made from a single molecule of glycerol joined to three fatty acid molecules.

How lipids differ from carbohydrates and proteins

• 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.
• Instead, it is this fixed arrangement of one glycerol and three fatty acids.

Lipids for energy

• Lipids are sources of energy and stores of energy.
• They release a lot of energy when they are broken down in respiration, and animals and plants store spare energy as fats and oils.