Macromolecules: Carbs, Lipids, Proteins

Though our food is composed of a variety of ingredients, from flour and sugar, to spices, vegetables and meat, our body compartmentalizes much of the food that we eat into three main groups! Composed of mostly carbon, hydrogen and oxygen, these big molecules, called macromolecules are the building blocks of growth, energy and strength in our bodies.


The Main Macromolecules: Carbs, Lipids and Proteins

The three macromolecules that we will be discussing today are carbs, lipids, and proteins. Our bodies need many other vitamins and minerals to thrive as well, but when it comes to energy production and storage, along with muscle building and repair, these are the stars that do most of the heavy lifting!




As we discussed in the cellular respiration article, most of our energy comes from glucose or sugar. Glucose in its purest form, is a simple carbohydrate, and is the compound that makes half of table sugar, the other molecule being fructose. Though glucose is the most common example of a simple carbohydrate that provides energy, there are other sugars that share a similar structure to glucose, but due to minor differences, have different names. Nonetheless, these sugars are able to be broken down and incorporated into the cellular respiration pathway at different steps to provide energy to the body.

We rarely consume pure glucose, and often eat sugar when it is part of a larger molecule. Table sugar is what is called a disaccharide which is a molecule composed of two six carbon sugars, usually a pair of either glucose, fructose, or galactose. More complex carbohydrates are long chains of connected sugar molecules, or polysaccharides, and these large molecules are abundant in foods high in starch, like potatoes, rice, pasta, and bread! We often think of sugar as something that is only high in foods that taste sweet, but we can still get plenty of sugar from these other foods.



Lipids, also known as fats, serve several important purposes in our bodies! At a molecular level, they are composed largely of hydrogen and carbon, and the unique qualities of these bonds allow for lipids to occupy several important roles. A few of the more significant roles of lipids include energy storage, hormone creation, vitamin storage, as well as a significant component the barrier that encloses our cells. More specifically, there are three main types of lipid molecules that have differing functions.

Triacylglycerols or triglycerides are the main molecule that is used to store energy. These molecules can be broken down into Acetyl-CoA through a series of steps, and this molecule enters the citric acid cycle of cellular respiration and generates large volumes of ATP.

Phospholipids are molecules composed of the element phosphorous, oxygen, and lipid regions that compose our cell membranes. For cells to control what comes in and out of the cell, and communicate with others, it requires a membrane that allows only some components in and out. The phospholipid structure, due to specific chemical qualities, allows for a cell membrane that is both protective and permeable.

Sterols are molecules that both contribute to the cell membrane in addition to phospholipids, but also are key in our body’s creation of hormones. Specifically, sterols are a precursor to cholesterol which is a main ingredient in the compound bile which helps us digest fats. These molecules are shaped slightly differently than the triacylglycerols and phospholipids and are the only lipid group of these three that is not able to be used for energy.




Last but certainly not least, we have proteins, which are the building blocks of the vast majority of structure in our bodies. Proteins are macromolecules that are created through DNA expression via the central dogma of gene expression and are the material that is used to build the machinery to carry out the thousands of functions necessary to support life. Protein is a component of every cell in the body, and broadly is necessary for cell repair and regeneration, maintaining homeostasis through enzymes, transporting nutrients and our immune function!

Proteins are macromolecules composed of molecules called amino acids. In the human body, there are 20 distinct amino acids that can create all the proteins we need. Like polysaccharides, proteins are created in long strands of unique combinations of amino acids. When individual amino acids linked together in a chain, which is encoded by our DNA, these strands can then fold and connect to other chains and units to build much larger structures such as hair, and muscle fibers, and enzymes. These macromolecules, due to their infinite variety and hefty list of functions, tend to be complex and sometimes mysterious, but they are very cool to study!



Author: Sydni Britton