In this article, you will learn about the three major macromolecules: carbohydrates, lipids, and proteins in detail.

Introduction

Macromolecules are defined as:

"The giant molecules that are essential for life and are created from smaller organic molecules are known as biological macromolecules"

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Classification of Macromolecules

Biological macromolecules are divided into four categories:

  • Carbohydrates
  • Lipids
  • Proteins
  • Nucleic acids

In this article, we will only focus on carbohydrates, lipids, and proteins.

Each of the above four macromolecules is a vital element of the cell and performs a wide range of functions. When combined, these molecules constitute the majority of the cell's mass. All biological macromolecules are organic which means that they contain carbon. Moreover, these molecules may also have oxygen, hydrogen, sulfur, phosphorus, and some other minor elements.

 

Carbohydrates

What are carbohydrates and why they are needed?

Most of us are already familiar with a popular macromolecule known as carbohydrates which are made up of carbon, oxygen, and hydrogen.  Carbohydrates are an important element of our daily diet. The carbohydrate-rich food items include bread, rice, pasta, grains, fruits, and vegetables. The main purpose of carbohydrates is to provide energy to the body through a simple sugar known as glucose. Carbohydrates also play other important roles in the bodies of animals and plants. We have often suggested a low-carb diet when we have to lose weight.

Sub-types of Carbohydrates

Carbohydrates are divided into three subtypes: monosaccharides, disaccharides, and polysaccharides.

Monosaccharides

  • They are simple sugars
  • Glucose is a monosaccharide
  • The number of carbon atoms in monosaccharides ranges from three to six

Disaccharides

  • When two glucose molecules join together, a disaccharide is created
  • Maltose, lactose, and sucrose are common disaccharides

Polysaccharides

  • Polysaccharides are created when many glucose molecules join together
  • Starch, glycogen, and cellulose are examples of polysaccharides

How does glucose form starch in plants?

Glucose is the crucial source of energy in the majority of living beings. During cellular respiration, glucose releases energy which is used to make ATP (adenosine triphosphate). The glucose is used by the plants for their energy needs. Plants use carbon dioxide and water to synthesize glucose during the process of photosynthesis. The excess synthesized glucose is stored as starch. Other organisms feeding on plants break down this starch.

How does glucose form glycogen in animals?

In humans and other vertebrates, glucose is stored in the form of glycogen. Glycogen is created from the monomers of glucose. In other words, just like plants store glucose in the form of starch, animals store glucose in the form of glycogen. Glycogen is basically a highly branched molecule that is often stored in muscle or liver cells of animals. When glucose levels in our bodies drop, the stored glycogen is broken down to release glucose.

 

Lipids

What are lipids?

Lipids are biological macromolecules that are made up of hydrogen, carbon, and oxygen atoms. Although carbohydrates offer an instant source of energy, however, lipids provide greater energy when compared to the same amount of carbohydrates. Our body tends to store fat and use it as an energy source only in the absence of carbohydrates.

What role do lipids play in our body?

Lipids constitute about 5% of the organic materials used to compose a living cell. They also play a vital role in the structure of the cell membranes. Lipids also act as a protective cover for the surfaces of animals and plants. Moreover, lipids act as a thermal insulator in humans and animals. It means that due to lipids, we are able to maintain temperatures in cold and harsh environments.

Composition of lipids

  • The majority of the fats (lipids) are made up of triglycerides
  • The fundamental unit of lipids is one glycerol molecule that is bonded chemically to three fatty acid chains
  • The fatty acids have varying size and structure
  • Lipids are classified as fats that are solids at room temperature and oils which are liquids at room temperature

 

Fats and oils made from fatty acids and glycerol

Fats and oils are often made up of fatty acids and glycerol. In other words, we can say that lipids are macromolecules that are made up of smaller units of glycerol and fatty acids. Glycerol refers to an organic compound that has three carbon atoms, five hydrogen atoms, and three hydroxyl groups. Fatty acids, on the other hand, are a long chain of hydrocarbons. An acidic carboxyl group is attached to fatty acids.

 

Proteins

What are proteins?

Proteins depict the structural composition of all living beings. All living organisms are made up of protein regardless of their size. This includes the biggest animal to the smallest microscopic organisms.

What role do proteins play?

Proteins play a vital role in the biochemical processes that preserve life. They are involved in the structure and functions of the living cells. They are also an essential element of the chromosomes. They are one of the fundamental components of the cell membranes. Proteins form organs, ligaments, nails, hair, muscles, tendons, and glands. They also make up the important fluids of the body such as lymph and blood that are critical for bone growth. Moreover, hormones and enzymes that stimulate and regulate all important processes of our body are proteins.

Composition of Proteins

  • Proteins play diverse functions because they are made up of 20 distinct amino acids.
  • Although the number of naturally occurring amino acids is 20, however, each molecule of protein is composed of hundreds or even thousands of these joined together in a unique sequence.
  • The unique sequence imparts distinct characteristics to each protein.
  • Amino acids are the monomers and each amino acid contains the same basic structure, i.e. a central carbon atom bonded to the hydrogen atom, amino group, and a carboxyl group.

Proteins as enzymes or hormones

Proteins can act as enzymes of hormones.

Enzymes

They are usually proteins that are produced by the living cells. They act as a catalyst in biochemical reactions such as digestion. Each enzyme acts upon its own substrate. They basically speed up the chemical reaction and do not change as a result of the reaction. Enzymes get folded into a complex shape that enables smaller molecules to fit into them. If there is a variation in the shape of the enzymes, then its active site may not work any longer. If it happens, then we say that the enzyme has been denatured. Denaturing of enzymes occurs in extremely high temperatures.

Hormones

Hormones refer to the chemical signalling molecules that are usually proteins or steroids. They are secreted by the group of endocrine cells or an endocrine gland. The main purpose of hormones is to control or regulate certain physiological processes such as metabolism, growth and development, and reproduction. For instance, insulin is a kind of protein hormone that is meant for maintaining blood glucose levels.

 

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Rafia Shabbir