Collagen is made primarily of three amino acids: glycine, proline, and hydroxyproline. Together, these three building blocks account for 57% of all the amino acids in collagen, giving the protein its unique structure and remarkable strength. Collagen itself makes up about one-third of all the protein in your body, serving as the structural scaffolding for skin, bones, tendons, and organs.
The Three Key Amino Acids
Amino acids are the individual links in any protein chain, and collagen’s chain has a very distinctive recipe. Glycine, the smallest amino acid, appears at every third position along the chain. This precise spacing is what allows collagen to fold into its signature shape. Proline and hydroxyproline fill most of the remaining spots, creating a rigid, tightly wound structure that resists stretching.
Other amino acids round out the remaining 43%, but it’s the dominance of those three that sets collagen apart from every other protein in your body. No other human protein relies so heavily on glycine or contains hydroxyproline in such quantities.
How the Triple Helix Forms
What makes collagen physically tough is its architecture. Three individual protein chains wind around each other like a braided rope, forming what scientists call a triple helix. Each chain follows a strict repeating pattern: glycine, then a second amino acid (often proline), then a third (often hydroxyproline). This pattern, repeated hundreds of times, is what holds the braid together through hydrogen bonds between the three strands.
The structure is surprisingly fragile at the genetic level. If even a single glycine in the repeating pattern gets swapped for a different amino acid due to a gene mutation, the triple helix destabilizes at that point. This kind of disruption is the basis for conditions like osteogenesis imperfecta, sometimes called brittle bone disease.
From Raw Materials to Finished Fiber
Your cells don’t produce collagen in its final form. The process starts inside fibroblasts (the cells responsible for connective tissue) where individual protein chains are assembled and threaded into a cellular compartment called the endoplasmic reticulum. There, enzymes modify proline into hydroxyproline, the chains are folded, and three of them twist together to form a precursor molecule called procollagen.
Procollagen then travels through the cell and gets released outside it. Once in the space between cells, enzymes clip off the bulky end caps of the molecule. Removing these caps, especially at one end, dramatically lowers the threshold for the trimmed collagen molecules to start snapping together into fibrils, long cable-like structures visible under a microscope. These fibrils then bundle into the collagen fibers that give your tendons, skin, and bones their strength.
The tensile strength of collagen in tendons is estimated at about 100 megapascals. For context, a single collagen molecule is far stronger than the assembled fibril, which means the architecture of how molecules pack together matters as much as the molecules themselves.
The Four Main Types in Your Body
Not all collagen is identical. Your body produces at least 28 types, but four dominate:
- Type I makes up 90% of your body’s collagen. It forms densely packed fibers and provides structure to skin, bones, tendons, and ligaments.
- Type II is found in elastic cartilage, where it cushions joints.
- Type III shows up in muscles, arteries, and organs.
- Type IV exists in the deeper layers of your skin, forming sheet-like networks rather than fibers.
All four types share the same triple-helix backbone and the same glycine-heavy amino acid profile, but they differ in how they assemble and where they end up.
What Your Body Needs to Build It
Having the right amino acids available isn’t enough on its own. Collagen production depends heavily on vitamin C, which acts as a required helper molecule for the enzymes that convert proline into hydroxyproline. Without that conversion, the triple helix can’t fold properly, and collagen maturation stalls. This is exactly why severe vitamin C deficiency causes scurvy, a disease defined by collagen breakdown in gums, skin, and blood vessels.
Iron also plays a role: the enzymes that perform these chemical modifications have iron at their active sites and need it to function. So collagen production is, at its core, a collaboration between amino acids (especially glycine, proline, and their derivatives), vitamin C, and iron.
Why Production Drops With Age
Collagen synthesis slows significantly over a lifetime. Research comparing skin from people over 80 with skin from 18- to 29-year-olds found that collagen production in older skin was reduced by roughly 75%. About two-thirds of that decline comes from having fewer collagen-producing cells and those remaining cells being less active. The rest is tied to changes in the mechanical environment of skin, as aging tissue loses the tension that signals cells to keep producing collagen.
This decline is a major reason skin thins and wrinkles with age, joints stiffen, and bones lose density. It’s also what drives the enormous market for collagen supplements.
Where Supplemental Collagen Comes From
Collagen supplements aren’t synthetic. They’re extracted from animal tissues, then broken down into smaller peptides that dissolve in liquid. The most common sources are cow skin and bones (bovine collagen, typically types I and III), pig skin and bones (porcine collagen, also types I and III), and fish skin and scales (marine collagen, primarily type I). Chicken breast cartilage is the go-to source for type II collagen, which is marketed specifically for joint health.
Regardless of the animal source, the fundamental composition is the same: chains of amino acids dominated by glycine, proline, and hydroxyproline, broken into fragments small enough for your digestive system to absorb. Your body then uses those amino acid building blocks however it sees fit, which may or may not mean assembling new collagen in the places you’re hoping to target.