We get energy from the biological molecules present in our diet. The biological molecules in our food contain chemicals that are critical for our growth. They are made up of long chains that are broken down into simpler units during digestion. These molecules help our bodies to repair themselves and are essential for the proper functioning of the cells. In this article, we will discuss three types of biological molecules: carbohydrates, lipid/fats, and proteins.
Carbohydrates are composed of carbon, hydrogen, and oxygen atoms. Carbohydrates are the most basic source of energy. Foods like potatoes, bread and cereals contain a high proportion of carbohydrates.
Types of Carbohydrates
They are of two types: simple and complex.
They include sugars such as lactose and glucose. When we consume simple carbohydrates, we get instant energy. Examples of foods that contain simple carbohydrates are energy bars or biscuits.
Complex carbohydrates also give us energy, but they do so slowly. It means that the foods containing these carbohydrates release energy slowly rather than instantly. Examples of foods that contain complex carbohydrates are pasta and rice.
Carbohydrates are comprised of sugar molecules that are joined with each other in long chains. A single sugar is referred to as a monosaccharide and two sugar molecules joined together is known as a disaccharide. For instance, sucrose is a disaccharide because it has two monosaccharides (fructose and glucose) bonded with each other. If many sugars are joined with each other in a single long chain, then the chain is referred to as a polysaccharide. Examples of polysaccharides are cellulose, starch, and glycogen. Cellulose, starch, and glycogen fall under the category of complex carbohydrates because they are made up of a long chain of sugars that are joined with each other.
- Cellulose: Cellulose is present in the cell wall of the plant cells and we cannot digest it. However, we can consume it as fibre as it helps the muscles of our intestinal wall to push food through our digestive system.
- Starch: Digestive enzymes break down the starch into glucose. Our body then uses glucose to make energy.
- Glycogen: In our bodies, glycogen is a carbohydrate store that can be transformed into glucose when the levels are low.
Lipids include fats and oils. Fats are solids at room temperature whereas oils are liquids at room temperature. Fats are composed of fatty acids and glycerol that are made up of carbon, hydrogen, and oxygen atoms. A healthy and balanced diet should contain lipids because the body employs them as an energy reserve, insulation, and to create cell membranes.
Fats provide us two times as much energy as carbohydrates and proteins do. Most fats (lipids) in our body are composed of triglycerides. Their primary unit is a single glycerol molecule that is bonded chemically to three fatty acid chains. The fatty acids have different sizes and structures. Examples of foods that are high in fats include cheese, oils, and butter.
How much lipid is needed by our body?
For a balanced diet, it is vital to consume foods that contain lipids. When we take in the food that has lipids, our body breaks down the lipid molecules into smaller molecules of glycerol and fatty acids. Some fatty acids are referred to as essential fatty acids and they are critical for our health. We can take them by consuming foods such as seeds, nuts, or fish. Remember that even a small amount of foods rich in lipid can store large amounts of energy. So, we need to consume lipid-rich foods in moderation. Eating food items rich in fats can cause obesity.
Proteins are composed of a long chain of amino acids and are essential for the growth and repair of our cells. Amino acids are comprised of carbon, oxygen, hydrogen, and nitrogen atoms. Proteins are also utilized as a source of energy by our bodies if we fall short of fat and carbohydrates reserves. When foods that are high in proteins are digested, the amino acids in them get absorbed into our bloodstream and brought to the cells so that they can reassemble them into proteins such as enzymes that are required by our body.
Proteins are long chains of amino acids that are joined together by peptide bonds. When two amino acids are joined with each other, then the chain is referred to as dipeptide. When more than two long chains of amino acids are joined together, then it is referred to as a polypeptide. Examples of foods that are high in proteins include fish, meat, beans, and eggs.
Protein is one of the most widely found molecules in our body. There are more than 20 different amino acids that are arranged in different ways to make up various proteins such as enzymes and antibodies.
- Enzymes: Enzymes refer to proteins that have a specific shape. They usually bind to a certain substrate molecule to speed up the metabolic reactions in our body.
- Antibodies: Antibodies also have a unique shape that is formed by a specific sequence of amino acids. Their unique sequence helps them to bind to antigens on external pathogens and kill them.
A summary of the three primary biological molecules, i.e. carbohydrates, lipids and protein is given in the table below:
|Molecules||Chemical Elements||Composition||Food sources|
|Carbohydrates||Carbon, Hydrogen and Oxygen||Made up of sugar molecules||Bread, rice, pasta, energy bars|
|Fats/Lipids||Carbon, Hydrogen and Oxygen||Made up of glycerol and fatty acids||Cheese, butter, oil|
|Proteins||Carbon, Hydrogen, Oxygen and Nitrogen||Made up of amino acids||Meat, fish, beans, eggs|
Tests for Carbohydrates, Fats and Proteins
In this section of the article, we will discuss different types of tests that are used to detect carbohydrates, proteins, and fats in foods items. These tests involve adding a reagent to the sample food that alters colour depending on the biological molecules that are present in it. Sometimes the test requires crushing the food or adding water to it before adding a reagent. All the tests are explained below in detail:
- Benedict reagent: It is employed to test the presence of glucose. If the colour changes from blue to orange or red, then it signifies the presence of glucose.
- Iodine solution: It is used to test the presence of starch in the food item. If the colour changes from brown/yellow to blue or black, then it means that the starch is present in the food item.
- Biuret reagent: It is employed to test for the presence of protein in the food sample. It will turn purple if there is a protein.
- Emulsion test: It is employed to identify the presence of lipids. In this test, ethanol is added to the sample food, along with an equal amount of water. In the presence of the lipid, a milky-white emulsion will appear.
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