This is part two of the miniseries about macronutrient uptake. This time, I will discuss the break-down and uptake of proteins. Like last time, this information can be found in the book ‘Medical Physiology’ by Boron & Boulpaep, 2nd edition. My goal in this post was to let the figures speak for themselves and add as little extra text as possible. I hope you will let me know if I succeeded :). The text in the blog will not always be needed to understand the figures, but is mainly some extra information for those interested in it.
Take note: It will be useful for your understanding to have read the previous post on carbohydrate digestion and uptake, since I will be using the same method of depicting things like salt ions and enzymes.
I forgot to mention in my previous post that the purple-tinted text blocks contain the most important information for understanding the process of protein digestion, while the green-tinted text block are extra, containing some facts that are not essential. For those people who would like some more depth.
Proteins can be found in almost any type of food, unless it has been highly processed. Both plants and animals make proteins. Actually, all living organisms make proteins (with the exception of viruses, but you could argue viruses aren’t actually ‘alive’).
Pro-enzymes can often be activated by their already-active forms. For example: propepsine can be turned on by pepsin. This will cause an amplifying reaction: more active enzymes will activate more enzymes, which will activate more enzymes etc. This is called a positive feedback loop: the result of the reaction will stimulate the reaction.
A fact about trypsin: this enzyme is often used in laboratories when culturing cells (I know this from personal experience). Cells are cultured in dishes or flask. Some cells float in the medium (culturing liquid), while others stick to the bottom. Cells that stick to a surface can easily be released by adding trypsin. Trypsin cuts the anchors on the outside of the cells, which causes the cells to release from the dish or flask. Cells don’t really like this, so it is best not to do it too often or for too long.
Salt ions drive the transport of oligopeptides and amino acids. This transport mechanism is used a lot by the body, so it is very important to understand it well. Please let me know if this is still unclear, so I can provide a better explanation of the mechanism if needed.
Unlike carbohydrates, proteins don’t need to be digested entirely to be absorbed by gut epithelial cells. This is due to oligopeptide transporters. According to Boron & Boulpaep, it is more efficient and faster for cells to take up 2-4 amino acids at a time as oligopeptides than to take up the same amount of amino acids individually.
The next and last post in this miniseries will cover the break-down and uptake of fats (my energy source of choice 😉 ). Of course I safe the best (and most complex) for last!