Sheet: Digestion of Lipids, Proteins,& Carbohydrates Done by: Obadah Abubaker & Yousef Qandeel

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1 Sheet: Digestion of Lipids, Proteins,& Carbohydrates Done by: Obadah Abubaker & Yousef Qandeel

2 In this lecture, we are going to talk about the biochemical aspects of digestion of carbohydrates, lipids and proteins. هاي المحاضرة والل بعدها سهالت وان شاء هللا ما بوخذوا منكم وقت كب ر فتفاءلوا و يال طالعة... So we will understand the process of digestion of the major dietry intake conserning the lipids, proteins and carbohydrates. Once you understand these processes and recognize the organs in which they are taking place as well as the enzymes and end products of these processes you will be able to practice any defect in the digestive process,you will be able to understand any disorder and what are the consequences of the rest order in that process.

3 Lipid digestion What is the major lipid component in our diet? Triacylglycerol (TAG) Mostly we are taking TAG and it represents 90% of our dietary lipids intake, and the 10% are composed of some fatty acids, cholesterol, cholesterol esters and phospholipids. *example of phospholipids: -Phosphatidylcholine: it is a phosphatidic acid attached to it a base choline, serine, ethanolamine, inositol all these are bases that are attached to phosphatidyl acid that will produce different types of phospholipids such as phosphatidylserine, phosphatidylinositol, etc. what is the phosphatidic acid? الدكتور طلب نقرأ عنه... ونص حة للش ت بشكل عام انه تركزوا على زبدة المحاضرة واالش اء الل بتكون موجودة بالسال دات والشرح مع بعض.

4 -Cholesterol ester: it is a cholesterol attached to it a fatty acid. The main end products of the digestion of these lipids are: - 2-monoacylglycerol - free fatty acids - cholesterol - glycerylphosphoryl base 2-monoacylglycerol: it is a glycerol backbone and one fatty acid is esterified on carbon number 2. (glycerol has 3 carbon atoms ) glycerylphosphoryl base: we get this after we break the ester bond that binds the phosphate in glycerophospholipid this table summarizes the process: *You are supposed to memorize the enzymes in each organ. In mouth, lipid digestion will not take place, it will take place in stomach and small intestine. -Only 30% of the lipids are digested in stomach. Why? Because lipases are not active at low ph.

5 **In the intestine The enzymes which are involved in small intestine are pancreatic enzymes. Co-lipase is not an enzyme, it is a protein that will be attached to lipase during Emulsification and digestion, and without this co-lipase, lipase will be inactive. -The substrate of cholesterol esterase is cholesterol ester that (cholesterol esterase) will hydrolyze the ester bond and release the fatty acid and cholesterol. -The substrate of phospholipase A2 is phospholipid and usually it hydrolysis the fatty acid which is esterified at carbon number 2. -The substrate of lysophospholipase is *lysophospholipid that is going to hydrolyze the ester bond that links the fatty acid at carbon number 1 and produces phosphatidic acid. *lyzophospholipid is a type of phospholipid that is hydrolyzed at carbon number 2 and has a fatty acid that is esterified at carbon number 1 مالحظة : هذه الصور ليست ضمن ساليدات الدكتور هي فقط للتوضيح ال أكثر, اذا عجقتك اتركها.

Concerning the lingual and gastric lipases, only they are important to hydrolyze fatty acids of short or medium carbon atoms, which are found usually in milk,so they are important in neonates and

6 Concerning the lingual and gastric lipases, only they are important to hydrolyze fatty acids of short or medium carbon atoms, which are found usually in milk,so they are important in neonates and infants because of the milk lipid digestion, but they are not working in the adult stage. so many lipids consist of short or medium carbon atom fatty acids, while the adult Triglyceride intake is composed of long chain carbon atom fatty acids (such as stearic acid, linoleic acid, palmitic acid, etc.) In order for lipases to work there must be emulsification process Emulsification process: bile salts will increase the surface area of interaction between the lipase, co-lipase and the lipids (lipids are amphipathic) And by that letting the lipase, co-lipase hydrolyzing the lipids (like TAG) Note: Lingual & Gastric Lipases act only on short and medium chain fatty acids therefore, their effect on TAG has little significance in adults. But important for digestion of milk fat in neonates and infants because Milk fat has short and medium chain fatty acids.

7 After emulsification we ll have what is called mixed micelle which has increase surface area. هاي شبه كاسة ف ها ز ت و ماء اذا حركناها رح ختلط الز ت بالم على شكل قطرات صغ رة و هاي القطرات الصغ رة ه ال mixed micelle و مساحة السطح الها بتز د بانه بدل ما تكون قطعة وحدة كب رة بتص ر قطع صغ رة. *Bile salt = bile acid + glycine or taurine *Cholesterol is the source of bile acid substrates products so we have to sites :- 1- stomach (lingual and gastric lipases important for infants because it s specific to hydrolyze short and medium chain fatty acids) 2- small intestine (four enzymes from pancreas that digest different types of lipids)

for long chain fatty acids to enter systemic circulation it must be absorbed to the cells in small intestine, re-synthesis of TAG, assembly & secretion of chylomicrons so first thing is the

8 for long chain fatty acids to enter systemic circulation it must be absorbed to the cells in small intestine, re-synthesis of TAG, assembly & secretion of chylomicrons so first thing is the absorption of fatty acids by the epithelial cells after the TAG is hydrolyzed into 2-monoacylglycerol and fatty acid (as you see in the previous table) then in the intestinal cells what happens is re-synthesizing of TAG by first forming of fatty acyl CoA (activation of FA) then they will be linked to 2-monoacylglycerol. Now TAG, cholesterol, and phospholipids will be assembled into chylomicrons that will enter the lymphatic system and then to bloodstream. for better understanding watch this video:

9 Proteins are hydrolyzed into single amino acids by protease (not denatured) *renin found in infants and it s for the digestion of casein in milk. and in adults we have pepsin to hydrolyze proteins into oligopeptides *pancreas synthesis proteases as zymogens (inactive protease) that needs activation and these zymogens are chymptrypsinogen, proelastase, and procaboxypeptidase A&B. Protease are either endoprotease or exoprotease Endoprotease(enteropeptidase) :- hydrolyze internal peptide bonds in oligopeptides Exoprotease(exopeptidase) :- hydrolyze peptide bonds from the ends (N-terminal & C-terminal)

In order for these pancreatic enzymes to function they need to be activated first by covalent modification (cleavage) and they are 1-trypsinogen trypsin 2- chymotrypsinogen chymotrypsin 3-

10 In order for these pancreatic enzymes to function they need to be activated first by covalent modification (cleavage) and they are 1-trypsinogen trypsin 2- chymotrypsinogen chymotrypsin 3- proelastase elastase 4- procaboxypeptidase A&B caboxypeptidase A&B Each one of these enzymes hydrolyze proteins at specific site for example trypsin breaks the bond after basic AA and chymotrypsin after aromatic AA. and they all have an active site where substrates bind and the catalysis happen. After digestion of proteins the products are amino acids and Di & Tri-peptides and there are some mechanisms to transport those amino acids using gamma-glutamyl cycle.

L1, 2 : Biochemical Aspects of Digestion of Lipids, Proteins, and Carbohydrates

L1, 2 : Biochemical Aspects of Digestion of Lipids, Proteins, and Carbohydrates OBJECTIVES: Understand the process of digestion of dietary lipids, protein and carbohydrates including, the organs involved,