Biological Molecules

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Biological Molecules


  • The structure of living organisms is made up of gradual levels. These levels begin with the systems, then the organs, tissues, cells and organelles. If we follow up this structural sequence of living organisms, we will find that the cells of any living organism are made up of organic and inorganic molecules, and each of these molecules is made up of atoms.
  • Inorganic molecules in living organisms, such as water and salts, often do not contain carbon atoms, while organic molecules such as carbohydrates, lipids, proteins, and nucleic acids are large molecules containing carbon and hydrogen and are known as biological macromolecules.
  • Biological macromolecules are large-sized organic compounds made up of smaller molecules. All these compounds contain the carbon element and they are vital for the life of living organisms. Most biological macromolecules are called polymers. Polymers are made up of a combination of smaller molecules called monomers as a result of a process called polymerization.
  • Biological macromolecules are divided into four groups according to their molecular structures and the functions they perform:

1. Carbohydrates

  • Carbohydrates are biological macromolecules made up of smaller molecules called monomers. Carbohydrates include sugars, starches, and fibers. They are symbolized by the formula (CH2O)n. According to this formula, carbohydrates are made up of carbon (C), hydrogen (H) and oxygen (O) atoms in the ratio 1:2:1.
  • Carbohydrates are considered the fastest and most basic way for obtaining energy. Carbohydrates are used for storing energy in living organisms’ bodies until they require it. Plants store carbohydrates in the form of starches but they are stored in human and animal bodies in the form of glycogen in the liver and muscles.
  • Carbohydrates are a basic component for some parts of a cell, such as cellulose in the root of plant cells. Carbohydrates are also found in cell membranes and in the protoplasm of a cell.

2. Lipids

  • Lipids are biological macromolecules made up of carbon, hydrogen and oxygen atoms. Lipids are also made up of a large group of heterogeneous compounds such as fats, oils, waxes, phospholipids and derived lipids such as steroids. All these compounds are insoluble in water, but they dissolve in non-polar solvents such as benzene and carbon tetrachloride.
  • Although carbohydrates are a rapid resource of energy, the energy obtained from lipids is greater than the energy obtained from the same amount of carbohydrates. The body does not automatically get energy from the fats stored in it, only when there is an absence of carbohydrates.
  • Lipids represent about 5% of the organic materials involved in the composition of a living cell. Lipids also have an important role in the structure of cell membranes.
  • Furthermore, lipids work as a thermal insulator in animals and human, meaning organisms can maintain their temperatures in cold regions and harsh environments. Lipids also work as a protective cover for the surfaces of several plants and animals, and some of them can work as hormones.

3. Proteins

  • Proteins represent the structural composition of all living organisms. All living organisms – from the biggest animal to the smallest microscopic organisms – are mainly made up of proteins. Proteins contribute to the biochemical processes that preserve life.
  • Proteins are involved in the structure and functions of living cells. They are one of the basic components of cellular membranes. In addition, proteins form the muscles, ligaments, tendons, organs, glands, nails, hair and a lot of the vital fluids of the body, such as blood and lymph that are necessary for bone growth. Furthermore, enzymes and hormones which stimulate and regulate all the vital processes in the body are proteins. Proteins are a basic component of chromosomes.

4. Nucleic acids

  • Nucleic acids are biological macromolecules containing oxygen, hydrogen, carbon, nitrogen and phosphorus. There are two types of nucleic acids: ribonucleic acid (RNA) and deoxyribonucleic acid (DNA). Nucleic acids are made up of basic units called nucleotides which bind together by covalent bonds to form a polynucleotide or the nucleic acid.
  • Nucleic acids are carried on the chromosomes inside the cell nucleus. They are responsible for passing on the genetic traits from one generation to another when cells divide. DNA carries the genetic information responsible for the distinctive characteristics of a living organism and it organizes all the vital activities of the cell.
  • On the other hand, RNA is transcribed from the nucleic acid DNA. It transfers into the cytoplasm to be used by the cell to synthesize the proteins responsible for genetic traits, and those responsible for organizing the vital activities.