Biological Macromolecules
Carbohydrates, lipids, proteins, and nucleic acids are four major groups of biological molecules found in living things. Understanding their basic structures, functions, and building blocks is essential to understanding how cells work.
What Are Biological Macromolecules?
Living organisms are made of many different types of molecules. Some are small and simple, while others are large and complex. Biological macromolecules are large molecules that play essential roles in the structure and function of living organisms.
The word macromolecule simply means a very large molecule. In Biology, four major groups are especially important: carbohydrates, lipids, proteins, and nucleic acids.
These four groups do not all have the same structure or perform the same jobs. Carbohydrates can provide readily available energy and structural support. Lipids are important for long-term energy storage, membranes, and signaling. Proteins perform an enormous variety of jobs in cells. Nucleic acids store and transmit genetic information.
The four major biological macromolecules have different structures and functions, but all are essential to the organization and survival of living organisms.
Monomers and Larger Molecules
Many biological molecules are built from smaller molecular units. A smaller building block is often called a monomer, while a larger molecule made from repeating or connected subunits can be called a polymer.
The relationship between monomers and polymers is especially important for carbohydrates, proteins, and nucleic acids. However, it is important not to assume that every macromolecule is a polymer. Lipids are considered biological macromolecules, but they are not true polymers made from repeating monomers in the same way that proteins and nucleic acids are.
The Four Major Macromolecules
A useful first step is to learn the basic identity of each group. You should be able to recognize each macromolecule, identify its basic building blocks, and describe several important functions.
Carbohydrates
Built from simple sugar units and important for energy and structure.
Examples include glucose, starch, glycogen, and cellulose.
Lipids
A diverse group of mostly water-insoluble molecules important for energy storage, membranes, and signaling.
Examples include fats, oils, phospholipids, and steroids.
Proteins
Built from amino acids and responsible for a wide range of cellular structures and functions.
Examples include enzymes, antibodies, and structural proteins.
Nucleic Acids
Built from nucleotides and involved in storing and transmitting genetic information.
The major examples are DNA and RNA.
Carbohydrates
Carbohydrates are biological molecules made primarily of carbon, hydrogen, and oxygen. They are especially important for energy and structural support.
Basic Structure
The basic building blocks of carbohydrates are monosaccharides, or simple sugars.
Glucose, fructose, starch, glycogen, and cellulose.
Immediate or short-term energy, energy storage, and structural support.
Small sugar units can be joined together to form larger carbohydrates.
A carbohydrate made from one sugar unit is a monosaccharide. Two sugar units joined together form a disaccharide. Larger carbohydrates made from many sugar units are polysaccharides.
Not all carbohydrates serve the same purpose. For example, glucose is an important cellular fuel, while cellulose provides structural support in plant cell walls.
Lipids
Lipids are a diverse group of biological molecules that are generally nonpolar and do not dissolve well in water. They have several important roles in living organisms.
Basic Structure & Functions
Many lipids contain glycerol and fatty acids, although lipid structures vary considerably.
Fats, oils, phospholipids, and steroids.
Long-term energy storage, insulation, cell membranes, and chemical signaling.
Lipids are a broad group and should not be treated as one single type of molecule.
One important lipid is the phospholipid. Phospholipids are major components of cell membranes. Their structure allows them to interact differently with water in different parts of the molecule.
Another important group is the steroids, which have a characteristic ring-based structure. Some steroids function as hormones involved in communication within the body.
Proteins
Proteins are large biological molecules built from amino acids. They perform more different jobs in cells than almost any other major class of biomolecule.
Amino Acids: The Building Blocks of Proteins
Proteins are built from amino acids.
Enzymes, antibodies, hemoglobin, and structural proteins.
Catalysis, transport, defense, movement, structure, communication, and many other cellular functions.
The order and interactions of amino acids help determine the structure and function of a protein.
Amino acids can be linked together to form a polypeptide. A protein may consist of one or more polypeptide chains that fold into specific three-dimensional structures.
Protein structure matters because a protein's shape is closely connected to its function. Enzymes, for example, have specific shapes that allow them to interact with particular molecules.
Nucleic Acids
Nucleic acids are biological molecules that store, transmit, and help express genetic information. The two major nucleic acids are DNA and RNA.
Nucleotides: The Building Blocks
Nucleic acids are built from nucleotides.
DNA and RNA.
Storing and transmitting genetic information and helping direct the production of proteins.
Nucleotides contain a sugar, phosphate group, and nitrogen-containing base.
DNA contains the genetic instructions used by cells. RNA plays several roles in using that information, including participating in the process by which cells make proteins.
The structure of nucleic acids allows information to be stored in the sequence of their nucleotide bases.
Building and Breaking Down Macromolecules
Cells constantly build and break down biological molecules. Two important reactions you should recognize are dehydration synthesis and hydrolysis.
Dehydration Synthesis
Dehydration synthesis joins smaller molecules together. During the reaction, a molecule of water is removed as a new bond forms.
Hydrolysis
Hydrolysis breaks a larger molecule into smaller molecules. Water is added during the reaction.
Dehydration removes water while building a larger molecule. Hydrolysis adds water while breaking a larger molecule apart.
These reactions are important because cells need to continuously assemble molecules when they are needed and break molecules down when their components are needed elsewhere.
Comparing the Four Macromolecules
One of the most common Biology questions asks you to distinguish between the four major macromolecules. Rather than memorizing one isolated fact about each, look at their building blocks, structures, and major functions together.
| Macromolecule | Basic Building Block | Major Functions | Examples |
|---|---|---|---|
| Carbohydrates | Monosaccharides | Energy; structure | Glucose, starch, glycogen, cellulose |
| Lipids | Often glycerol and fatty acids | Energy storage; membranes; signaling | Fats, oils, phospholipids, steroids |
| Proteins | Amino acids | Enzymes, structure, transport, defense, movement, communication | Enzymes, antibodies, hemoglobin |
| Nucleic Acids | Nucleotides | Genetic information | DNA, RNA |
The word monomer does not mean exactly the same thing as "small molecule found in every macromolecule." Carbohydrates, proteins, and nucleic acids have recognizable building blocks that can form larger chains. Lipids are macromolecules, but they are not true polymers.
Common Misconceptions
Watch Out for These
If You See This on a Test, Think This
You don't always need to memorize an entire paragraph to identify a macromolecule. Look for clues in the question.
Practice Your Understanding
Try answering these questions before opening the explanations.
Quick Check
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Protein. Amino acids are the building blocks of proteins.
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Nucleotides. DNA and RNA are nucleic acids made from nucleotide subunits.
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Carbohydrates. Starch and cellulose are polysaccharides made from sugar units.
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Smaller molecules are joined to form a larger molecule, and water is removed during the reaction.
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Water is added as a larger molecule is broken into smaller molecules.
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Lipids. Phospholipids are major components of biological membranes.
Key Takeaways
- The four major biological macromolecules are carbohydrates, lipids, proteins, and nucleic acids.
- Carbohydrates are important for energy and structure.
- Lipids are important for energy storage, membranes, insulation, and signaling .
- Proteins are built from amino acids and perform many different cellular functions.
- Nucleic acids are built from nucleotides and are involved in genetic information.
- Dehydration synthesis joins molecules while removing water.
- Hydrolysis uses water to help break larger molecules apart.
- Not every macromolecule is a true polymer. In particular, lipids are not true polymers.
Teachers.
Need a worksheet to go with this lesson?
Give your students purposeful practice with carbohydrates, lipids, proteins, nucleic acids, dehydration synthesis, and hydrolysis.
Browse Macromolecule Resources →Macromolecules
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