Brief Summary
This video explains the process of protein digestion and absorption in the human body. It covers the mechanical and chemical digestion of proteins, starting from the mouth and stomach, and continuing into the small intestine where enzymes from the pancreas and intestinal cells break down proteins into amino acids, dipeptides, and tripeptides. The video also details how these smaller peptides and amino acids are absorbed into the bloodstream and transported to the liver.
- Mechanical and chemical digestion of proteins.
- Role of enzymes like pepsin, trypsin, chymotrypsin, and carboxypeptidase.
- Absorption of amino acids, dipeptides, and tripeptides in the small intestine.
- Transport of amino acids to the liver for protein synthesis or storage.
The video introduces protein digestion and absorption, explaining that proteins from food sources like meat are composed of amino acids linked together. Proteins have an amino terminal with an amine group and a carboxy terminal with a carboxy group, which allows amino acids to link. The presenter notes that the explanation is simplified and not a full biochemistry lesson.
The process begins with mechanical digestion in the mouth, followed by chemical digestion in the stomach. The stomach secretes pepsinogen, which converts to pepsin in the presence of hydrochloric acid. Pepsin hydrolyzes peptide bonds, breaking proteins into large polypeptides. Hydrochloric acid triggers the conversion of pepsinogen to pepsin, which then breaks down proteins into large polypeptides.
The polypeptides move into the duodenum, the first part of the small intestine, where the pancreas secretes enzymes like trypsinogen, chymotrypsinogen, and procarboxypeptidase. These enzymes are zymogens, or precursors, that need to be activated. These enzymes are activated by enteropeptidases found on the surface of intestinal cells. Enteropeptidases convert trypsinogen to trypsin.
The pancreas secretes inactive enzyme precursors: chymotrypsinogen, trypsinogen, and procarboxypeptidase. Enterokinase, found on intestinal cells, converts trypsinogen to trypsin. Trypsin then activates more trypsinogen, chymotrypsinogen (to chymotrypsin), and procarboxypeptidase (to carboxypeptidase). Chymotrypsin and trypsin hydrolyze peptide bonds, while carboxypeptidase hydrolyzes bonds from the carboxy end of the protein.
After encountering enzymes like trypsin, chymotrypsin, and carboxypeptidase, large polypeptides are further digested into smaller polypeptides, dipeptides, and tripeptides. Brush border enzymes, such as dipeptidases and aminopeptidases, on the surface of intestinal cells further break down these peptides into tripeptides, dipeptides, and amino acids. Dipeptidases hydrolyze dipeptides, and aminopeptidases hydrolyze peptide bonds from the amino terminal.
Amino acids are absorbed with sodium via a specific channel. Tripeptides and dipeptides are absorbed through co-transport with hydrogen ions. Inside the cell, peptidases hydrolyze tripeptides and dipeptides into amino acids, which then diffuse into the bloodstream. Hydrogen ions are pumped back out in exchange for sodium.
The absorption of amino acids, dipeptides, and tripeptides leads to a net absorption of sodium, which causes water to be absorbed as well. Sodium is reabsorbed into the extracellular matrix in exchange for potassium via the sodium-potassium pump. The absorbed amino acids are transported to the liver, where they are used to synthesize new proteins or stored.
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Transcript
Full transcript of “Protein Digestion and Absorption”. Click a timestamp to open the video at that moment. Need another video? Use the YouTube transcript generator.
0:00 AR biology and Medicine videos please make sure to subscribe join the for main group for the latest videos please visit Facebook Aran in this video we will talk about protein digestion and absorption so here we have a person and his digestive tract you have the esophagus stomach small and large intestine a good source of protein can be found in foods such as meat if we zoom into this Meat part of the meat is made up of proteins proteins are made up of amino acids proteins are basically chains of amino acids proteins have uh Amino terminal
0:47 where the amine group is and then they have a carboxy terminal where the carboxy group is if we were to look at the biochemical structure of a protein here for example we have four amino acids linked together each amino acid has an amine and carboxy group on them and it's with these um amine and carboxy groups that allow amino acids to link together therefore there will always be um a carboxy group on one end of a protein and an amine group on the other end of the protein anyways I hope this makes sense it's not a biochemistry lesson so if this human were to digest the meat
1:35 which contains high amounts of protein the mouth will first help to um uh digest it through mastication breaking it down the protein will then make its way from the mouth through the esophagus into the stomach here so here are all the proteins that have not been digested by any enzymes yet it has only been a physic digested with the mouth anyways the chemical digestion of protein actually begins in the stomach because the stomach secretes pepsinogen which once secreted will convert to pepsin pepsin hydrolyzes peptide bonds so it breaks the protein
2:22 bonds the amino acid bonds let's look at how pepsin becomes activated a little a little further well if here's your stomach cells we have mucus on top of these cells and here is the protein in the Lumen the stomach cells will begin secreting pepsinogen in the presence of food at the same time hydrochloric acid will be secreted to assist in breaking down uh the food it's actually the hydrochloric acid that triggers the conversion of pepsinogen to pepsin and so now pepsin is able to hydroly the peptide bonds breaking down the protein to large poly peptides from the stomach the large
3:08 polypeptides or polypeptides will enter the small intestine now the first part of the small intestine which is called the duodenum is the main site where protein digestion and absorption takes place so what happens with these uh proteins these polypeptides once they're in the inum well the pancreas will actually begin to secrete uh some enzymes that will help digest the proteins these are TR cinogen kyoten and procarboxypeptidase so let's take a Clos closer look at these enzymes so zooming into the duodenum here the first part of the small intestine we are in the Lumin of the small intestine and here are the
3:55 intestinal cells called interos sites and here is and here are the large polypeptides that came from the stomach just before below the interos sites the intestinal cells we have blood vessels that supplies the inyes with blood and that will carry the nutrients to the liver once they are absorbed so now let's go back and focus on the enzymes secreted by the pancreas again the pancreas will secrete kimot cinogen trypsinogen and procarboxypeptidase all these are actually zymogens which are precursors to the active enzyme form here I am just drawing the shapes
4:42 uh to represent each of these enzyme precursors these enzyme precursors need to be activated these enzyme precursors are activated by um special enzymes found on the surface of the intestinal cells these these enzymes are called ocase so ocase will actually convert trypsinogen to trsin tripin is the active form and is an enzyme that will hydroly peptide bonds so it will break down amino acid acids that are linked together so here Tron is attacking these peptide bonds now Tron is a big deal and there
5:27 are three reasons why uh the first is the presence of tripin will automatically stimulate the conversion of more trip cinogen to make more trsin during protein digestion second reason why trsin is a big deal is that Tron will actually help convert kimot trinen to the active form kyoten kyot triin just like Tron hydes peptide bonds so here they are breaking down these bonds the third reason the third reason tripsin is a big deal is that it also stimulates the conversion of procarboxypeptidase to carboxy peptidase which is the active form so tripin
6:15 really uh Buffs up or stimulates protein digestion um in the small intestine now carboxypeptidase is an enzyme that hydes peptide bonds from the carboxy end of the prot protein so from this end of the protein you can remember this because the name of the enzyme carboxy peptidase is like Caro car boxal group carboxy N so anyway after the large polypeptide encounters all these enzymes the trsin the kyot triin the carboxy peptidase these these large polypeptides will be further digested to small polypeptides as well as Dy or Tri peptides
7:00 the body needs to break down these small polypeptides further in order for the body to absorb them the last part of protein digestion occurs uh on top of the intestinal cells because on top of the intestinal cells there are these special enzymes called brush B enzymes and there are many types of brush B enzymes but we will focus on the brush B enzymes that specific specifically hydroly peptide bonds these enzymes are the dipeptidases which hydroly dipeptides which are and dipeptides are just two amino acids linked together so
7:45 these and the other main brush B enzyme for protein digestion are aminopeptidases which hydrolize peptide bonds from the amino terminal of the protein so here where the amino group is and so these small polypeptides will be digested further into tripeptides dipeptides and amino acids now the body can then begin to absorb these amino acids the small peptides such as the tripeptides can be absorbed through co-transporter with hydrogen once inside the cell the tripeptide can be hydrolized by cell's own peptid phases which will break it
8:31 down to amino acids once in the amino acid form the amino acid can diffuse into the bloodstream where it will be carried to the liver the D peptides can also follow the same absorption method it enters the cell through uh the hydrogen co-transporter channel the hydrogen can actually be pumped back out into the Lumin in exchange for sodium so when hydrogen goes back out into the Lumen sodium gets pumped inside the D the dipeptide which is inside the cell now is can also be broken down into amino acids by intracellular peptidases the amino acid can then be
9:18 reabsorbed into the blood finally the amino acid the amino acids which are just in the Lumin are absorbed through a different method through a different mechanism the amino acids are absorbed with sodium in a in a channel so as one sodium as one sorry as one amino acid is absorbed so is one sodium ion the amino acid can then be reabsorbed into the blood now you can see from this diagram that when amino acids and also Dy and tripeptides are absorbed into the cell there will also be a net absorption of sodium and because of this water is also
10:05 absorbed sodium is reabsorbed into the extracellular Matrix this should be in exchange with potassium via the sodium pottassium pump those amino acids as I mentioned earlier will travel to the liver where they will be used to synthesize new proteins or stored somewhere else hope you enjoyed this video on protein digestion and absorption and hopefully makes sense thank you for watching bye
