All life on Earth is built from four different types of molecules. These four types of molecules are often referred to as the molecules of life.
The four molecules of life are proteins, carbohydrates, lipids and nucleic acids. Each of the four groups is vital for every single organism on Earth. Without any of these four molecules, a cell and organism would not be able to live. All of the four molecules of life are important either structurally or functionally for cells and, in most cases, they are important in both ways.
Proteins are the first of the molecules of life and they are really the building blocks of life. Proteins are the most common molecules found in cells. If all the water is removed from a cell, proteins make up more than half of the remaining weight.
Protein molecules are involved in a range of aspects of a cell’s biology. They come in a huge variety of forms and perform a massive range of functions. They are involved in muscle movement, storage of energy, digestion, immune defence and much more.
The primary structure of a protein is a long chain made of many smaller molecules called amino acids. There are 20 different amino acids that are used to build proteins. The different amino acids can be arranged into trillions of different sequences that each creates a unique protein. The long chain of amino acids twists and folds on itself to produce the final shape of a protein.
Amino acids contain nitrogen. Nitrogen-based compounds are an essential part of the diet of all organism so they can produce new proteins for their cells. This is why farmers often add nitrogen-based fertilisers to help their crops grow and why it is important for humans to eat foods that contain proteins.
For more on proteins, click here.
The next of the four molecules of life are carbohydrates. Carbohydrates are an important source of energy. They also provide structural support for cells and help with communication between cells.
A carbohydrate molecule is made of atoms of carbon, hydrogen and oxygen. They are found in the form of either a sugar or many sugars linked together.
A single sugar molecule is known as a monosaccharide. Two sugar molecules bonded together is a disaccharide and many sugar molecules make a polysaccharide. The three different types of carbohydrates are all important for different reasons.
Carbohydrates are the most important sources of energy for many organisms. Plants use the sun’s energy to convert CO₂ into carbohydrates. The energy of these carbohydrates later allows plants to grow and reproduce.
Many organisms have what is known as a cell wall that surrounds their cell. The cell walls of plants and fungi are made from carbohydrates. Cell walls provide important protection for the cells of plants and fungi.
You can learn more about carbohydrates here.
Lipids are a highly variable group of molecules that include fats, oils, waxes and some steroids. These molecules are made mostly from chains of carbon and hydrogen called fatty acids. Fatty acids bond to a range of other types of atoms to form many different lipids.
Cells require lipids for a number of reasons. Probably the most important role of lipids is the main component of cell membranes. A type of lipid called a phospholipid is the primary molecule found in the membranes of cells.
Other important functions lipids have include insulation of heat, storing energy, protection and cellular communication. The importance of these various functions is why lipids are classed as one of the four molecules of life.
Almost all lipids are insoluble in water. The structure of lipid molecules means they are repelled by water. This is why oils and fats form globules in water and why the vinegar and oil of vinaigrette separate if the mixture is left for a while.
The final of the four molecules of life are the nucleic acids. There are two types of nucleic acids that are essential to all life. These are DNA (deoxyribonucleic acid) and RNA (ribonucleic acid).
DNA is a very well-known type of molecule that makes up the genetic material of a cell. DNA is responsible for carrying all the information an organism needs to survive, grow and reproduce.
RNA is a lesser-known molecule but it also plays an important role in cells. RNA molecules are used to translate the information stored in DNA molecules and use the information to help build proteins. Without RNA, the information in DNA would be useless.
Nucleic acids are long chains made from many smaller molecules called nucleotides. Each nucleotide is made of a sugar, a base and a phosphate group.
The two differences between DNA and RNA are their sugars and their bases. DNA has a deoxyribose sugar while RNA has a ribose sugar. DNA has four different bases – adenine (A), thymine (T), guanine (G), and cytosine (C). RNA has three of the same bases but the thymine base is replaced with a base called uracil (U).
Video produced by The Science Channel
Last edited: 3 November 2017
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