All four major macromolecules are important. Carbohydrates and lipids make up the majority of structures in cells. Proteins make up the majority of enzymes and drive energy production in the cell. But none would exist without the genetic code stored by nucleic acids in DNA.We could not live without any of those molecules. If you were to take out all of one of those types of molecules out of our bodies, we would die. If you were to stop production/intake of any one of these molecules in our bodies, we would die.
1.) Nucleic acids: Nucleic acid is the most important major macromolecule. Nucleic acids are the most important, as without these no one would be around, where as without the other ones we might be able to evolve to survive. Without nucleic acids, none of us would be alive, as none of us would have DNA! DNA is a nucleic acid and is essential for the life of eukaryotes (RNA in some prokaryotes). Nucleic acids code for the machinery an organism requires to survive (organelles, proteins, phenotypes essential to survival in various environments, etc.)
2.) Proteins: Proteins are chains of amino acids. Proteins have a wide variety of functions. They can be enzymes, to promote chemical reactions; they can have important structural functions like collagen does in your skin. They can also help structure your ligaments, tendons, bones, hair, and muscles. They are found in fibers that help your blood clot. Proteins called antibodies help your body defend against infection. Other proteins in muscles allow them to contract (making body movement possible). Yet another type of protein called hemoglobin carries oxygen to cells throughout the body. Without protein, some of our muscles wouldn't be able to contract, our blood wouldn't clot, certain ligaments and tendons wouldn't be secure, and our bodies wouldn't be able to fight against infection. This would make life shorter.
3.) Carbohydrates: Carbohydrates are organic compounds made of carbon, hydrogen, and oxygen atoms. Carbs are made of monosacharrides (single sugars) linked together. Their function is to provide a key source of energy for cells. An example is starch, made of many linked glucose molecules. Without carbohydrates, our cells wouldn't have a key source of energy. Without energy, cells can't do their job.
4.) Lipids: Lipids are nonpolar molecules that are not soluble in water. They include fats, phospholipids, steroids, and waxes. Lipids' functions are to provide energy and serve an important part in the structure and functioning of cell membranes. Some examples of lipids: butter (saturated fat), cholesterol (steroid), earwax (wax). I put this one last because if we didn't have lipids, we could use carbohydrates for energy and perhaps proteins could substitute for the functioning of cell membranes. We could get our fat from other sources. Of course, eating more fat than you need can lead to weight gain, but in proper amounts lipids are, respectively, a healthy part of your diet.