Week 4 – Proteins
Proteins are composed of chains of amino acids.
There are 20 different amino acids.
All amino acids have the same basic structure:
- Acid (carboxyl) group
- Amino group
- Side chain (R)
The side chain determines whether it is more hydrophilic or hydrophobic.
Essential amino acids: Amino acids that are needed in the diet because the body cannot make
these (there are 9).
The remaining 11 can be made from the 9 essential amino acids.
Linkages between carboxyl and amino group of different amino acids is called a peptide bond
leading to a dipeptide.
Raising young children on a vegan diet should be discouraged, but it is possible.
Digestion of dietary protein:
- No protein digestion in mouth
- Major protein digestion in stomach
- Major protein digestion in small intestine
- No digestion of protein in the colon
- A small amount of protein is lost in the feces
Amino acids, unlike proteins, can pass the intestine and enter into the bloodstream.
Stomach:
The acid environment causes proteins to unfold, allowing the enzyme pepsin easier to access.
Pepsin is produced by Chief cells lining the stomach. It is secreted as an inactive pro-enzyme
called pepsinogen.
Pepsinogen is activated by the acid environment resulting in self-cleavage to form pepsin.
Pepsin cleaves peptide bonds between specific amino acids:
Proteins pepsin polypeptides
Small intestine:
Two proteolytic enzymes called: trypsin and chymotrypsin produced by the pancreas. Also,
these enzymes are produced as inactive pro-enzymes which are activated once they reach the
small intestine.
They cleave the polypeptides at positions to release smaller peptides.
Polypeptides trypsin and chymotrypsin smaller peptides
Also the intestinal cells produce enzymes: aminopeptidases and carboxypeptidases. These
remove single amino acids from both ends, yielding single amino acids.
Smaller peptides amino/carboxypeptidase amino acids
The amino acids are absorbed into the portal circulation and are taken to the liver. Amino
acids will be used as building blocks for the synthesis of body proteins.
Proteins are composed of chains of amino acids.
There are 20 different amino acids.
All amino acids have the same basic structure:
- Acid (carboxyl) group
- Amino group
- Side chain (R)
The side chain determines whether it is more hydrophilic or hydrophobic.
Essential amino acids: Amino acids that are needed in the diet because the body cannot make
these (there are 9).
The remaining 11 can be made from the 9 essential amino acids.
Linkages between carboxyl and amino group of different amino acids is called a peptide bond
leading to a dipeptide.
Raising young children on a vegan diet should be discouraged, but it is possible.
Digestion of dietary protein:
- No protein digestion in mouth
- Major protein digestion in stomach
- Major protein digestion in small intestine
- No digestion of protein in the colon
- A small amount of protein is lost in the feces
Amino acids, unlike proteins, can pass the intestine and enter into the bloodstream.
Stomach:
The acid environment causes proteins to unfold, allowing the enzyme pepsin easier to access.
Pepsin is produced by Chief cells lining the stomach. It is secreted as an inactive pro-enzyme
called pepsinogen.
Pepsinogen is activated by the acid environment resulting in self-cleavage to form pepsin.
Pepsin cleaves peptide bonds between specific amino acids:
Proteins pepsin polypeptides
Small intestine:
Two proteolytic enzymes called: trypsin and chymotrypsin produced by the pancreas. Also,
these enzymes are produced as inactive pro-enzymes which are activated once they reach the
small intestine.
They cleave the polypeptides at positions to release smaller peptides.
Polypeptides trypsin and chymotrypsin smaller peptides
Also the intestinal cells produce enzymes: aminopeptidases and carboxypeptidases. These
remove single amino acids from both ends, yielding single amino acids.
Smaller peptides amino/carboxypeptidase amino acids
The amino acids are absorbed into the portal circulation and are taken to the liver. Amino
acids will be used as building blocks for the synthesis of body proteins.
