Everything on this Earth – living and non-living, is made up of atoms. An atom is the smallest unit of matter that has the characteristic properties of a chemical element. Two or more different or similar atoms will combine to form “Molecules” with the help of chemical bonds. Many molecules, joined together in an organized manner by means of different chemical bonds are termed as “Macromolecules”. These macromolecules have evolved over a period of millions of years to perform a range of biological functions inside a cell.
The four major classes of biological macromolecules are carbohydrates, lipids, proteins, and nucleic acids. Along with water, these four macromolecules are indispensable for maintaining life inside a cell. Many recognize the first three as macronutrients and fourth one contains two molecules. The first nucleic acid is essential for storing the genetic information of the cell (DNA) and the second one is responsible for extracting the stored information for proper functioning on the cell (RNA).
One common aspect of these macromolecules is that they all have very high amounts of carbon in them. However they also contains significant amounts of Nitrogen, Phosphorus, oxygen, hydrogen, and to a lesser extant some other elements (in minute quantities). The unique properties exhibited by carbon makes it a central player of biological molecules. Carbon can bind to oxygen, hydrogen, and nitrogen covalently to form the many molecules important for cellular function.
Carbohydrates are also termed as Sugars or polysaccharides. Sugars, starches and fiber are carbohydrates.
The moment one hears the word carbohydrate, we think of food. The major food source around the world such as Rice, wheat, vegetables and fruits, contains significant amount of carbohydrates and are natural sources for carbohydrates. They are vital for our survival as they happen to be major energy source for our body. However they are more than just the source for energy for our body ( see functions of carbohydrates below).
Carbohydrates are the most abundant of all the major macromolecules found in the human body. We get most of the nutrients for our survival from the food we eat. Many of these nutrients are the biological macromolecules, necessary for life.
The general formula for many carbohydrates is (CH2O)n, where n is the number of carbon atoms present. This means that the Carbon :Hydrogen :Oxygen ratio is 1:2:1. eg: C6H12O6 is the formula for glucose. We can classify carbohydrates into three subtypes: monosaccharides – Simple sugars like glucose, disaccharides – two monosaccharides undergo a dehydration reaction like sucrose, and polysaccharides – monosaccharides linked by glycosidic bonds like glycogen.
Functions of carbohydrates:
- They are excellent source of energy for all activities of our body by converting carbohydrates into usable biochemical energy, ATP
- Essential for very existence of life as it forms a vital component of DNA and RNA backbone structure in the form of Ribose sugars.
- A polymer of glucose called as cellulose, forms a important component of plant cell walls to provides stability to and strength to the cell and hence plays structural function.
- Some sugar polymers helps in storing carbohydrates for emergency use eg: glycogen found in all animals is synthesized and stored in the liver and the muscles.
- Carbohydrates in plasma membrane of cells helps in communication, cell adhesion and identification between “self” and “non-self”.
Proteins are large molecules made up of series of monomers called as “amino acids”. All amino acids share similar fundamental structure, which consists of a central carbon atom, or the alpha (α) carbon, bonded to an amino group (NH2), a carboxyl group (COOH), and to a hydrogen atom. Every amino acid also has another atom bonded to the central atom known as the R group.
Proteins are made up of 20 amino acids, out of which 11 are synthesized by our body and remaining 9 are termed as essential amino acids. These essential amino acids should be supplemented through our diet. The chemical nature of the side chain determines the amino acid’s nature – acidic , basic , polar or non-polar ). The sequence and the number of amino acids eventually dictates the protein’s shape, size, and function. Once the protein is translated completely, majority of proteins undergo what is called as post-translational modification, which is vital for proper function of protein formed.
Structure of protein:
The protein structure or the way the polypeptide (after translation) is folded, eventually affects the function of that protein. The way a protein folds depends on sequence of amino acids in the polypeptide, side chains of those amino acids and the environment . The structure of protein can be divided into four hierarchical levels of organization:
Primary Structure : The sequence of amino acids constitutes the primary structure of that protein.
Secondary Structure : The proteins usually contains some regions or motifs which fold in a particular manner. This gives rise to the secondary structure of the protein. The most common are the α-helix and β-pleated sheet structures found in many proteins.
Tertiary structure: The unique three dimensional structure of protein, mainly due to R-groups of involved amino acids, creates tertiary structure.
Quaternary Structure: Some proteins are made up of more than one polypeptide and the way these polypeptides interacts forms the quaternary structure of protein eg: Insulin hormone.
chaperones (or chaperonins) are proteins that assist the target protein during the folding process. They protect them from other proteins which might affect the folding process and thus ensures correct folding of the protein, essential for its normal function. Chaperones are attached to target proteins till they are folded in required manner and they disassociate once the target protein is folded.
Functions of proteins:
Proteins exhibit most diverse set of functions among all 4 major biomolecules. They are involved in range of functions in our body such as structural, transport, storage, important component in cell membranes. Hormones and enzymes are also proteins regulating many important functions in our body.
Lipids are also called as “fats” are primarily made up of carbon and hydrogen but also contains sufficient amounts of oxygen, nitrogen, sulfur, and phosphorous. Lipids are a broad class of compounds such as fatty acids, triacyl glycerides, phospholipids etc.
Fatty acids – triacyl glycerides and phospholipids :
A simple lipid molecule usually consists of two main components—glycerol (organic compound – alcohol) and fatty acids. The fatty acids are lipids with long-chain hydrocarbons with a carboxylic acid functional group. It is due to the long hydrocarbon chain, fatty acids are hydrophobic (“water fearing”) or nonpolar. when compared to simple lipids, complex lipids have an additional phosphate group (phospholipids) or a carbohydrate moiety (glycolipids). eg: Phospholipids are important component of plasma membrane . Steroids also categorized under lipids as they are hydrophobic and insoluble in water. Cholesterol is most common and well studied steroid. our liver has the ability to make cholesterol and is the precursor to steroid hormones such as testosterone. Cholesterol is also a starting material for synthesis of Vitamin D.
Functions of Lipids:
Lipids have a diverse set f functions and the most important is to store energy for long-term use in the form of fats.
They also also provide insulation from the environment for plants and animals.
Lipids are main components of many hormones and are crucial for proper functioning of cellular membranes.
Nucleic acids are important macromolecules which carry the genetic blueprint of a cell and help in functioning of the cell.
The two main types of nucleic acids are deoxyribonucleic acid (DNA) and ribonucleic acid (RNA).
(for extensive reading about macromolecules please refer)
Image Credit :
Images were assembled from smartserivier.com and openstax.org
Functions of proteins table credit: openstax.org