HNF 461 1st Edition Lecture 27 Outline of Last Lecture I Functions II Maintaining Blood Pressure III Blood pH IV Structure a Primary b Secondary c Tertiary d Quaternary V Amino Acids a Essential Amino Acids Outline of Current Lecture I Conditionally Indispensible Amino Acids II Digestion in the Stomach III Digestion in the Small Intestine IV Key Enzymes Involved in Protein Digestion V Protein Absorption VI Intestinal Amino Acid Use VII Functions of Amino Acids in Intestinal Cells VIII Sources of Protein Current Lecture Intro to Proteins Cont Digestion and Absorption 1 Conditionally Indispensible Amino Acids a Under disease conditions a certain amino acid may become indispensible if an organ fails to function properly or if an enzyme is missing These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute b The precursors to the amino acids will build up in the body so must take out from the diet then must obtain the amino acid from the diet 2 Digestion in the Stomach a Acidic environment denatures proteins breaks down proteins to linear structure b HCl is produced by parietal cells c Pepsinogen is produced by chief cells i Converted to pepsin by HCl 3 Digestion in the Small Intestine a Digestion of proteins into free amino acids or di tripeptides b Secertin and CCK released from mucosal endocrine cells c Pancreatic proenzymes released into small intestine d Enteropeptidase secreted from brush border of intestinal cells 4 Key Enzymes Involved in Protein Digestion a Pepsinogen Pepsin in the stomach b Pancreas secretes trypsinogen into the small intestine which is then converted to trypsin by enteropeptidase c Trypsin is then used to activate other enzymes i Chymotrypsinogen Chymotrypsin ii Procarboxypeptidases Carboxypeptidase or Aminopeptidases 1 Carboxypeptidase releases single amino acids at the carboxyl end of a peptide 2 Aminopeptidase releases single amino acids at the amine end of a peptide 5 Protein Absorption a Amino Acids i Free amino acids and di tripeptides are absorbed into intestinal cells ii Similar to glucose absorption iii Sodium amino acid cotransporter sodium and amino acids are transported into the cell and then sodium is pumped back out b Peptides i Transported via PEPT1 transporter along with a protons ii Proton is pumped back into intestinal lumen in exchange for sodium iii Peptides are absorbed more efficiently than free amino acids c Once amino acids and dipeptides are absorbed into enterocytes dipeptides are broken down into amino acids and then they are all transported into the blood to go to the liver 6 Intestinal Amino Acid Use a 30 40 of all absorbed dietary amino acids are used by the intestine b 90 of glutamate and glutamine absorbed are used by the intestine i More than half becomes CO2 which means it becomes oxidized and enters the TCA cycle for energy production 7 Functions of Amino Acids in Intestinal Cells a High turn over rate of cells needs proteins and nucleotides for cell reproduction b Energy i Glutamine and glutamate c Secretory Proteins i Mucins 1 Membrane attached 2 Soluble secreted into the mucous layer to form a mesh that hold the mucous layer together in one piece ii Enzymes iii B48 required to make chylomicrons 8 Sources of Protein a Diet 100 g for many adults b Endogenous proteins 70 g i Sloughed cells ii Enzymes secreted into the lumen
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