Because of its pale color, the prominent Greek physician and philosopher Galen wrote that bone was made of sperm. One thousand years later, Avicenna, a Persian astronomer, physician, and prolific writer, thought that bone was made of earth because it was cold and dry. Now another millennium later, different notions prevail about the nature of bone. We have to start with a little organic chemistry. Don’t glaze over. This is more interesting that it might seem at first.
Five carbon atoms can combine with one each of oxygen and nitrogen along with several of hydrogen to make proline, an amino acid. It is one of the essential building blocks of life, and we can either make proline from scratch or break it down from proteins we eat. Certain cells then assemble a proline-rich mix of amino acids into a chain.
This amino acid chain faintly resembles an ultramicroscopic, limp strand of spaghetti. Now an enzyme comes along and attaches an extra hydrogen and oxygen atom to many of the proline molecules. This causes the chain to curl sharply at regular intervals, and it now looks more like teensy corkscrew pasta.
Three of these corkscrews nest together to form a collagen molecule, which even at this supra-submicroscopic level is strong and stable because the nooks in one strand nest into the crannies of the adjacent ones. Legos work the same way.
Several different types of cells make collagen. For me, the most interesting ones are the osteoblasts (from Greek: bone + germinator). Osteoblasts produce collagen molecules and then push these chemical-mechanical wonders out through their cell membranes into the minuscule spaces between the cells.
Here the collagen molecules snuggle side to side and overlap to make a multi-stranded fiber. Stack a million of these strands together and the cable is finally large enough to be visible under a microscope. The collagen fibers are locked together both by mechanical nesting (nook-cranny) and by chemical (sticky pasta-like) bonds.
If you consider how strong three tiers of Legos would be if you smeared them with super glue before snapping them together, then you begin to understand the strength of collagen fibers. When stretched, these tough amino acid chains are stronger than equally thick strands of steel wire.
Let’s take a brief time out to understand the connection between Limies, shoe leather, furniture glue, and jiggly gelatin desserts. Remember the hydrogen-oxygen appendages on proline molecules? Vitamin C catalyzes those attachments. Without them, there is no tight corkscrew configuration. A vitamin C deficiency leads to faulty collagen production, which is the cause of scurvy. Symptoms include bleeding gums and easy bruising. Early mariners were at sea for months and endured diets almost entirely devoid of fresh fruits and vegetables. Between bouts of sea sickness, British sailors in particular learned to squeeze fresh limes into their fetid drinking water to mask its taste. By doing so, collagen production returned to normal, and the sailors discovered serendipitously that a lime a day kept the scurvy away.
Here is another collagen connection. Shoe leather is tanned cow hide. It is tough because the tanner adds chrome to the vats. This increases the number of chemical weld points among the collagen fibers in the hide.
Just the opposite is true for paint ball covers, medicine capsules, hide-based furniture glue, gelatin desserts, and gummy bears. They are all made from partially unlinked collagen, which comes from boiled byproducts of meat and leather production. This is where the expression, sending a horse to the glue factory, came from. Warning: do not read about gelatin manufacture if you want to enjoy your next marshmallow.
Collagen–the word comes from Greek glue + producing–holds us together, better than would steel. Collagen is the quintessential connective tissue and resists stretching. It is the main constituent of tendons, which turn muscle contractions into joint motions, and ligaments, which keep joints properly aligned. Consider standing on your toes. If your Achilles tendons were rubbery, they would stretch like bungee cords when you contracted your calf muscles, and your heels would remain on the floor. This would not be good. Or consider putting your fingertips on your cheek and stretching your fingers away from your palm. If your ligaments were not tough, you could push your fingers until your fingernails touched the back of your hand. This would not be pretty. Some people just naturally have ligaments that are extremely stretchable. We call them double jointed. These contortionists enjoy demonstrating their great flexibility while watching the rest of us wince.
In the next post, I will discuss calcium, which is the other major component of bone. Two videoclips will show what happens when bone is missing calcium or collagen. Then I will answer the question in the blog title: Does plaster on lath replicate nature?