What Are Proteins? What Do They Do?
Protein sells. You can add a “protein boost” at your local smoothie joint, tuck into a DIY or Starbucks protein bistro box, or grab a protein bar at any convenience store.
As a biologist, it struck me that many of those flocking to eat more protein don’t actually know what proteins are, or what they do in our bodies. My goal for this article is to bring a face to the buzzword.
I believe that having a solid understanding of the nuts and bolts of your food will help you navigate conflicting nutritional advice — and make you a smarter consumer of health products.
This article is the first of a two-part Protein Primer. See Part 2: A Protein’s Journey from Bite to Bicep here.
What Is a Protein?
- A protein is a long chain of amino acids folded in a specific way. Picture a rainbow coloured bead necklace where each colour (or letter) represents one of the 20 different amino acids.
- An amino acid is a naturally occurring molecule made up of carbon, nitrogen, oxygen and hydrogen atoms (and sometimes sulfur). Amino acids share their core structure but vary in their “side chain” or “R group”.
- All living organisms use the same “alphabet” of 20 standard amino acids (letter beads) to build their proteins. These are called the “proteinogenic” amino acids — in contrast to other amino acids that are never found in proteins. Each amino acid has a 3-letter and a 1-letter abbreviation. See the “alphabet” of amino acids!
- Proteins are defined by their unique sequence of amino acids (beads). In humans, the average protein is about 350 amino acids (beads) long.
- Some proteins are made up of many small repeating units (e.g. F-I-T-F-I-T-F-I-T… aka Phenylalanine-Isoleucine-Threonine…), while others have no repeating units and use many different amino acids (like a very long word!).
- Inside your body, proteins are not simply limp chains lying around. They have a 3D structure that is critical to their function. If you say the word ‘protein’ to a biologist or chemist, they would have a clear picture in their mind — something like the haemoglobin molecule shown here in 3D.
- The human body uses about ~19,000 different proteins. Each cell and organ type uses a defined subset of them in a unique ‘cocktail’.
- Many plants use a larger set of proteins than humans! Corn has about 32,000 different proteins.
- There are two ‘bonus’ (rare) proteinogenic amino acids: selenocysteine, found in a few human and other proteins, and L-Pyrrolysine (non-humans only).
Understanding Amino Acids
Amino acids can be classified as essential / indispensable or non-essential / dispensable depending on whether or not our bodies can make them (from other molecules).
This label can change depending on stage of life and health status, and varies between organisms. In healthy adults, there are nine essential amino acids.
Amino acids can also be classified in other ways:
- Based on how they are broken down / catabolized when there is excess — either ketogenic, glucogenic, or both. Learn more …
- Using their chemical and physical properties (e.g. charged or neutral, aromatic / ring structure or not, etc). Learn more
Why Does My Body Need Protein?
Proteins are both the bricks and mortar of your body and the workhorses of your cells.
The jobs that proteins do in your body fall into five categories:
- Structural (e.g. keratin for hair / nails, myosin for muscles, collagen for skin)
- Transport / storage (e.g. hemoglobin for carrying oxygen)
- Immune system (e.g. antibodies)
- Messengers (e.g. hormones such as insulin)
- Enzymes (e.g. lactase for breaking down milk sugars)
Note: Proteins play largely the same roles in plants as in animals (using a different but related set of proteins).
You need to eat foods with protein in order to give your body building blocks to build new proteins and replace old ones. Unlike fats and sugars, your body does not have dedicated protein stores.
- About 15–20% of the dry weight of your body is made from proteins.
- About half of the weight of most cells is made up of proteins.
- Collagen is the most abundant protein in your body (by weight).
- Other abundant proteins include hemoglobin (blood), myosin (muscles) and actin (all cells).
- Busting the Myth of Incomplete Plant-Based Proteins (a science-based look at meeting your essential amino acid needs)
- Protein Primer 2: Is it True That You Are What You Eat? A Protein’s Journey From Bite to Bicep