Lesson Explainer: Biological Macromolecules Biology • First Year of Secondary School

In this explainer, we will learn how to describe key components found in the cells of organisms, including inorganic and organic compounds and large biological molecules.

From single-celled bacteria to the trillions of cells in your body right now, all living organisms are made of at least one cell. Cells contain organelles. Organelles are structures within a cell that carry out a specific function. Those organelles are made of molecules that are made of atoms. Cells need to obtain organic and inorganic nutrients to sustain life. Biological macromolecules are large, organic molecules that are especially important to the maintenance of life in every living thing, from bacteria to human. Figure 1 shows the biological levels of organization of multicellular organisms arranged from the simplest to the most complex.

A complex organism like a human is multicellular, which means that its body is made of many cells. However, the body of such an organism is not just a big clump of cells as every cell has needs to be viable, and if they were just a clump of a million unspecialized cells, those needs could not be satisfied. To ensure that the organism and its cells are viable, different cells have very specific functions, and those cells work together with other highly specialized cells to create a functioning organism. For example, a neuron is a highly specialized cell that can detect a change in the organism’s external or internal environment and transmit this information in the form of signals to other cells in the body. Many neurons together with other supporting cells form a nervous tissue. And different tissues together can form an organ, like the brain. The brain can process the information and initiate the appropriate responses. When organs work together, this is called an organ system, and different organ systems together build the organism’s body, which is viable and can adapt and respond to its environment.

Example 1: Arranging Biological Structures by Size

Put the following structures in the order in which they are organized in the human body, from largest to smallest: cells, molecules, atoms, organelles.

Answer

The levels of biological organization describe how, within the bodies of living organisms, larger structures are made up of smaller structures. The traits and characteristics of smaller units determine the function of the larger structures they are a part of. A complex multicellular organism, or an organism that is made of many cells organized into tissues, will contain several organ systems. Organ systems contain several organs. Organs are made of tissues. Tissues are made of cells. Cells contain several organelles that are made of molecules, and molecules are made of atoms. Even atoms are made of smaller, subatomic particles. An example of this arrangement can be observed in the human body.

Therefore, the order of these structures from largest to smallest is as follows: cells organelles molecules atoms.

There are four types of biological macromolecules. These are proteins, lipids, carbohydrates, and nucleic acids. Each of these molecules is relatively large when compared to a smaller molecule, such as oxygen or glucose. The “macro-” in “macromolecule” means “large.”

Biological macromolecules are organic molecules. This means that they possess atoms of carbon that are bonded to atoms of hydrogen. Molecules that do not possess carbon–hydrogen bonds are considered inorganic with regards to biology. There are a few exceptions to this rule. One example of these exceptions is hydrogen cyanide, which is classified as inorganic despite its possession of a carbon–hydrogen bond. This is due to some of the other specific properties of these molecules. Figure 2 shows the difference in composition between water molecules, as an example of an inorganic molecule, and a glucose molecule, as an example of an organic molecule.

Most biological macromolecules are also considered to be polymers. “Poly-” means “many,” and “-mer” means “unit.” Polymers are macromolecules that are built of repeating subunits called monomers. “Mono-” means “one.” When monomers join together to form a polymer, we call this “polymerization.”, as shown in Figure 3. The structure and function of the monomers within a polymer determine its function and properties.

Example 3: Describing the Formation of Macromolecules from Monomer Subunits

Biological macromolecules can be formed from subunits (monomers) joining together in a chain. What is the name of this general process?

Answer

Biological macromolecules are large, organic molecules made up of multiple subunits bonded together. They can be polymers that are made of many smaller units called monomers. An example of a polymer is a polysaccharide, which is a complex carbohydrate made of monomers called “monosaccharides.” Different types of polymers are made of different monomers that give them different properties. When monomers join together to form polymers, the process is called polymerization.

This means that the name of the process of monomers joining together is polymerization.

As mentioned earlier, carbohydrates are one of the 4 major classes of macromolecules that are found in living cells. Carbohydrates are molecules that contain carbon, hydrogen, and oxygen in a particular ratio. Some of the functions of carbohydrates are storing energy in a form that can be easily used by living cells and providing structure to certain kinds of cells.

Carbohydrate polymers are also referred to as polysaccharides. “Saccharide” means sugar. So, you can probably guess that the monomers of carbohydrates are monosaccharides, also called simple sugars. Some examples of complex carbohydrates are starch, cellulose, and glycogen.

The term “carbohydrate” actually refers to both simple sugars and polysaccharides. But, when we are talking about macromolecules, we are referring to complex carbohydrates, not simple sugars. Figure 4 shows a large polysaccharide molecule that is made of many small, repeating monosaccharide molecules.

Like carbohydrates, lipids are also made of combinations of carbon, hydrogen, and oxygen, but they have a different ratio of these elements. Specifically, they have less oxygen and more carbon and hydrogen than carbohydrates. Some of the functions of lipids are storing energy for longer periods of time and making up the membranes of our cells and organelles. Lipids are characterized by chains of carbon and hydrogen atoms bonded together, called “hydrocarbon chains.” All lipids are insoluble in water. This is because lipids are typically nonpolar molecules, meaning that the molecule does not possess separate positive and negative poles of charge. A common example of a lipid is any typical cooking oil, which we know does not mix with water. The following photograph shows how lipids, such as cooking oil, are not soluble in water.

While lipids are macromolecules, they are not considered by most scientists to be polymers. Polymers are molecules that are made of many similar subunits, called “monomers,” which are bonded together in large complexes. Lipids generally consist of few, different subunits that are not generally considered to be monomers. Some examples of lipids are triglycerides, fatty acids, phospholipids, and cholesterol; the general structures of these compounds are shown in Figure 6.

Proteins are polymers made of many amino acid monomers, as demonstrated in Figure 7. There are 20 different types of amino acids with varying traits of their own. Amino acids share a similar structure but vary in their side chains or R group, as shown in Figure 8. Chains of amino acids are referred to as polypeptides because of the peptide bonds that form between them. These chains of amino acids must be folded and shaped into functional proteins. The final sequence and arrangement of amino acids is what gives each different protein its traits.

Proteins have widely varying structures that allow them to carry out their different functions. Some of the functions of proteins are structural support, movement, protection, signaling, and speeding up chemical reactions. Some examples of proteins are the protein hormone insulin, enzymes, and antibodies that help to fight infections.

The final group of biological macromolecules we will look at are nucleic acids. Nucleic acids are DNA and RNA. DNA stands for “deoxyribonucleic acid” and RNA stands for “ribonucleic acid,” which makes their category especially easy to remember. Nucleic acids are macromolecules that store and transfer genetic information. As shown in Figure 9, nucleic acids are polymers made of monomers called nucleotides. DNA is an extremely stable molecule; it can hold a lot of information in the arrangement of its nucleotides. The arrangement of nucleotides in the DNA and RNA molecules is also called a nucleotide sequence.

Compared to proteins, nucleic acids have a structure that is easy to replicate. This is why nucleic acids are perfect for storing genetic information, which contains the instructions for making proteins. This also makes them ideal for being passed from parent to offspring.

Biological macromolecules, lipids, proteins, carbohydrates, and nucleic acids are important cellular components that play a wide range of functions in the life processes of living things.

Let’s review what we have learned so far.