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Food Processing

Food Processing. Module 22.2: Nutrient pool substrates. Nutrient pool supplies molecules for catabolism, anabolism, and to fuel ATP production ATP used for metabolic makeover inside cell Organic compounds used for 2-carbon substrate molecules for mitochondrial activities. Figure 22.2 1.

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Food Processing

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  1. Food Processing

  2. Module 22.2: Nutrient pool substrates Nutrient pool supplies molecules for catabolism, anabolism, and to fuel ATP production ATP used for metabolic makeover inside cell Organic compounds used for 2-carbon substrate molecules for mitochondrial activities

  3. Figure 22.2 1 The centrality of the nutrient pool to both anabolism and catabolism Structural, functional, and storage components Triglycerides Proteins Glycogen Organic compounds that can be absorbed by cells are distributed to cells throughout the body by the bloodstream. Nutrient pool Fatty acids Glucose Amino acids Three-carbon chains Two-carbon chains MITOCHONDRIA ATP Citric acid cycle Electron transport system Coenzymes O2 KEY = Catabolic pathway H2O CO2 = Anabolic pathway

  4. Module 22.2: Nutrient pool substrates When nutrients absorbed from digestive tract are insufficient for cellular metabolism, energy reserves come from various cells Liver cells store triglycerides and glycogen Fatty acids and glucose can be released Adipocytes store triglycerides Fatty acids can be released Skeletal muscle cells store glycogen Amino acids can be released

  5. Figure 22.2 2 Adipocytes convert excess fatty acids to triglycerides for storage. If absorption by the digestive tract and reserves in the liver fail to maintain normal nurtient levels, the triglycerides are broken down and the fatty acids released. Liver cells store triglycerides and glycogen reserves. If absorption by the digestive tract fails to maintain normal nutrient levels, the triglycerides and glycogen are broken down and the fatty acids and glucose are released. The use of the body’s metabolic reserves to maintain normal nutrient levels in the blood Skeletal muscles at rest metabolize fatty acids and use glucose to build glycogen reserves. Amino acids are used to increase the number of myofibrils. If the digestive tract, adipocytes, and liver are unable to maintain normal nutrient levels, the contractile proteins can be broken down and amino acids released into the circulation for use by other tissues. Nutrients obtained through digestion and absorption Nutrients distributed in the blood Neural tissue requires a continuous supply of glucose. During starvation, other tissues shift to fatty acid or amino acid catabolism, conserving glucose for neural tissue. Cells in most tissues continuously absorb and catabolize glucose.

  6. Module 22.2: Nutrient pool substrates Cellular catabolic and anabolic pathways Cells must synthesize some organic molecules Insufficient nutrients from nutrient pool and diet Nutrients are often used to create 2-carbon chains for mitochondrial ATP production Oxygen required must be continuously provided by diffusion from ECF CO2 produced must diffuse out of cell to ECF

  7. Module 22.2: Nutrient pool substrates Cellular nutrient dynamics Fatty acids Can be stored as triglycerides Can be created from acetyl-CoA and triglycerides Glucose Can be stored as glycogen (glycogenesis) Can be created from: Glycogen catabolism (glycogenolysis) Smaller carbon chain anabolism (gluconeogenesis) Can be used to make two 3-carbon chains for ATP production (glycolysis)

  8. Module 22.2: Nutrient pool substrates Cellular nutrient dynamics (continued) Amino acids Can be stored as proteins Can be created from: 3-carbon chains Protein catabolism (only during starvation)

  9. Figure 22.2 3 KEY = Catabolic pathway A general overview of the catabolic and anabolic pathways of cells = Anabolic pathway Proteins Glycogen Triglycerides In glycogenesis, glycogen is synthesized from glucose. The release of glucose from glycogen is called glycogenolysis. Fatty acids can be stored as triglycerides. Stored triglycerides can be broken down into fatty acids. The primary use of amino acids is the synthesis of proteins. Amino acids are seldom broken down if other energy sources are available. However, in starvation the proteins of muscle tissues are mobilized, releasing amino acids that can be catabolized by other tissues. Nutrient pool Amino acids Fatty acids Glucose The breakdown of a fatty acid releases glycerol and acetyl-CoA suitable for use by mitochondria. Glycolysis: glucose break- down into two three-carbon molecules/chains Gluconeogen- esis: glucose synthesis from smaller carbon chains. Three-carbon chains Two-carbon chains Fatty acid synthesis begins with acetyl-CoA. Because this is the common intermediary for all aerobic catabolic pathways, fatty acids can be synthesized from excess carbohydrates or amino acids. MITOCHONDRIA ATP O2 must be continuously provided by diffusion from the ECF. This requires normal respiratory function and adequate tissue perfusion. Citric acid cycle Electron transport system Coenzymes O2 H2O CO2 CO2 must leave the cytosol by diffusion into the ECF, and the bloodstream must continuously absorb CO2 in peripheral tissues and eliminate it at the lungs to prevent potentially dangerous changes in body fluid pH.

  10. Module 22.2 Review a. Define nutrient pool. b. Why do cells engage in catabolism? c. Why do cells make new compounds?

  11. Section 2: Digestion and Metabolism of Organic Nutrients Overview of digestive process Oral cavity (mechanical processing and chemical digestion of carbohydrates and lipids) Stomach (acidic chemical digestion) Duodenum (various enzymes catalyze catabolism of all organic molecules needed by cells) Jejunum and Ileum (nutrient absorption) Nutrients stored and processed by liver Large intestine (water reabsorbed, nutrients and vitamins produced by bacteria, feces eliminated)

  12. Figure 22 Section 2 Steps in the Process of Digestion In the oral cavity, saliva dissolves some organic nutrients, and mechanical processing with the teeth and tongue disrupts the physical structure of the material and provides access for digestive enzymes. Those enzymes begin the digestion of complex carbohydrates (polysaccharides) and lipids. In the stomach, the material is further broken down physically and chemically by stomach acid and by enzymes that can operate at an extremely low pH. In the duodenum, buffers from the pancreas and liver moderate the pH of the arriving chyme, and various digestive enzymes are secreted by the pancreas that catalyze the catabolism of carbohydrates, lipids, proteins, and nucleic acids. Nutrient absorption then occurs in the small intestine, primarily in the jejunum, and the nutrients enter the bloodstream. Indigestible materials and wastes enter the large intestine, where water is reabsorbed and bacterial action generates both organic nutrients and vitamins. These organic products are absorbed before the residue is ejected at the anus. Most of the nutrients absorbed by the digestive tract end up in a tributary of the hepatic portal vein that ends at the liver. The liver absorbs nutrients as needed to maintain normal levels in the systemic circuit. Within peripheral tissues, cells absorb the nutrients needed to maintain their nutrient pool and ongoing operations.

  13. Module 22.3: Carbohydrates Carbohydrates are usually preferred substrates for catabolism and ATP production when resting Steps of carbohydrate digestion In mouth, salivary amylase digests complex carbohydrates into disaccharides and trisaccharides Enzyme active only down to pH 4.5 and denatured in stomach At duodenum, pancreatic alpha-amylase continues carbohydrate digestion

  14. Module 22.3: Carbohydrates Steps of carbohydrate digestion (continued) In jejunum, brush border enzymes finish carbohydrate digestion down to simple sugars (monosaccharides) Maltase (digests maltose: glucose + glucose) Sucrase(digests sucrose: glucose + fructose) Lactase(digests lactose: glucose + galactose) In large intestine, remaining indigestible carbohydrates (such as cellulose) are food source for colonic bacteria Produce intestinal gas (flatus) during metabolic activities

  15. Module 22.3: Carbohydrates Carbohydrate absorption and transport Transported into small intestine epithelial cells Leave cells by facilitated diffusion through basolateral surface Enter cardiovascular capillaries to transport to liver in hepatic portal vein Processed by liver to maintain glucose levels (~90 mg/dL) Released as glucose or Stored as glycogen

  16. Module 22.3: Carbohydrates Cellular use of digested carbohydrates Generally preferred for catabolism Proteins and lipids more important for structural components of cells and tissues In skeletal muscle, stored as glycogen In most tissues, transported into cell by carrier molecule (regulated by insulin) May be converted to ribose May be converted to 2 pyruvate molecules in glycolysis Produces 2 ATP Pyruvates used by mitochondria Uses 3 O2, generates 3 CO2, 6 H2O, 34 ATP

  17. Figure 22.3 The events in carbohydrate catabolism and ATP production from glucose Carbohydrates (such as glucose) are generally preferred for catabolism because proteins and lipids are more important as structural components of cells and tissues. In most tissues, the transport of glucose into the cell is dependent on the presence of a carrier protein stimulated by insulin. GLUCOSE (6-carbon) Inside the cell, the glucose may be converted to another simple sugar, such as ribose, used to build glycoproteins, other structural materials, or nucleic acids. They may also be converted to glycerol for the synthesis of glycerides. Insulin Other simple sugars ATP If needed to provide energy, the 6-carbon glucose molecule is broken down into two 3-carbon molecules of pyruvate. This anaerobic process, called glycolysis, yields a net gain of 2 ATP for every glucose molecule broken down. Pyruvate (3-carbon) Pyruvate (3-carbon) CO2 Coenzyme A Each pyruvate molecule can then be used by mitochondria, after conversion to acetyl-CoA. For each molecule of pyruvate processed by mitochondria, the cell gains 17 ATP, consumes 3 molecules of O2, and generates 3 molecules of CO2 and 6 molecules of water. Thus for each pair of pyruvate molecules catabolized, the cell gains 34 ATP. Acetyl-CoA (2-carbon) ATP Citric acid cycle Electron transport system Coenzymes O2 H2O CO2

  18. Module 22.3 Review a. Describe the source of intestinal gas. b. Explain the role of glycogen in cellular metabolism. c. Explain why carbohydrates are preferred over proteins and fats as an energy source.

  19. Module 22.4: Catabolism of glucose Glycolysis Anaerobic process making two 3-carbon pyruvate from one 6-carbon glucose Occurs in cytosol Produces a net gain of 2 ATP Also produces hydrogen atoms that are transferred by NAD to mitochondria for ETS

  20. Module 22.4: Catabolism of glucose Steps of glycolysis Phosphate group attached to glucose in cytosol 2nd phosphate attached (cost of 2 ATP) 6-carbon molecule split into two 3-carbon molecules Another phosphate attached to each molecule and processed further 2 NADH generated 2 ATP generated 2 H2O released Further processing creates an additional 2 ATP

  21. Figure 22.4 1 The steps in glycolysis, the breakdown of a six-carbon glucose molecule into two three-carbon pyruvate molecules INTERSTITIAL FLUID Glucose ATP CYTOSOL ADP Steps in Glycolysis Glucose-6-phosphate ATP As soon as a glucose molecule enters the cytosol, a phosphate group is attached to the molecule. ADP Fructose-1,6-biphosphate A second phosphate group is attached. Together, steps 1 and 2 cost the cell 2 ATP. Dihydroxyacetone phosphate Glyceraldehyde 3-phosphate The six-carbon chain is split into two three-carbon molecules, each of which then follows the rest of this pathway. 2 NAD From mitochondria 2 To mitochondria 2 NAD•H Another phosphate group is attached to each molecule, and NAD•H is generated from NAD. Energy Summary 1,3-Bisphosphoglycerate Steps 1 & 2: –2 ATP ADP 2 ATP Step 5: +2 2 ATP One ATP molecule is formed for each molecule processed. 3-Phosphoglycerate ATP Step 7: +2 H2O 2 The atoms in each molecule are rearranged, releasing a molecule of water. +2 ATP NET GAIN: Phosphoenolpyruvate A second ATP molecule is formed for each molecule processed. Step 7 produces 2 ATP molecules. ADP 2 2 ATP Pyruvate To mitochondria

  22. Module 22.4: Catabolism of glucose Summary of aerobic ATP production 4 ATP from NADH produced in glycolysis 24 ATP from NADH generated in citric acid cycle 4 ATP from FADH2 generated in citric acid cycle 2 ATP via GTP produced during enzymatic reactions 34 ATP total

  23. Figure 22.4 2

  24. Module 22.4 Review a. List the molecular products from a glucose molecule after glycolysis. b. Identify when most of the CO2 is released during the complete catabolism of glucose. c. Explain when glycolysis may be important in cellular metabolism.

  25. Module 22.5: Lipids Steps of lipid digestion In mouth, mechanical processing and chemical digestion by lingual lipase In stomach, lingual lipase continues to function but can only access surface of lipid drops that have formed In duodenum Bile saltsbreak up lipid drops into smaller droplets (= emulsification) Pancreatic lipasedigests triglycerides into fatty acids, monoglycerides, and glycerol Forms micelles (lipid–bile salt complexes)

  26. Module 22.5: Lipids Absorption and transport of digested lipids Lipids diffuse from micelle into intestinal epithelial cell Intracellular anabolic reactions synthesize new triglycerides from digested lipids New triglycerides packaged in chylomicrons(chylos, milky lymph, mikros, small) and released via exocytosis Chylomicrons diffuse into intestinal lacteals due to their size Transported through lymphatic vessels (including thoracic duct) to bloodstream Enzyme in capillaries (lipoprotein lipase) breaks down chylomicron and releases digested lipids to tissues

  27. Module 22.5: Lipids Digested lipid distribution and processing Tissues that use or process digested lipids Skeletal muscles Use fatty acids to generate ATP for contraction and to convert glucose to glycogen Adipose tissue Uses fatty acids and monoglycerides to synthesize triglycerides for storage Liver Absorbs intact chylomicrons and extracts triglycerides and cholesterol from chylomicron

  28. Module 22.5: Lipids Cholesterol distribution Released from liver attached to low-density lipoproteins (LDL) for distribution to peripheral tissues LDLs absorbed and broken down by lysosomes in cells Cholesterol extracted and used Unused cholesterol released into bloodstream High-density lipoproteins (HDL) (plasma proteins from liver) absorb peripheral cholesterol and return to liver Cholesterol released again with LDLs or excreted in bile Ratio of LDL/HDL and total cholesterol used diagnostically for cardiovascular problems

  29. Figure 22.5 Resting skeletal muscles absorb fatty acids and break them down, using the ATP provided both to power the contractions that maintain muscle tone and to convert glucose to glycogen. The chylomicrons enter the bloodstream at the left subclavian vein, then pass through the pulmonary circuit before entering the systemic circuit. Capillary walls contain the enzyme lipoprotein lipase, which breaks down the chylomicrons and releases fatty acids and monoglycer- ides that can diffuse into the interstitial fluid. Thoracic duct Adipocytes absorb the monoglycerides and fatty acids, and use them to synthesize triglycer- ides for storage. Lipoproteins and Lipid Transport and Distribution The liver absorbs chylomicrons, removes the triglycerides, combines the cholesterol from the chylomicron with synthesized or recycled cholesterol, and alters the surface proteins. It then releases low-density lipoproteins (LDLs) into the circulation, which deliver cholesterol to peripheral tissues. Some of the cholesterol is used by the liver to synthesize bile salts; excess cholesterol is excreted in the bile. Triglycerides removed Chylomicrons The LDLs released by the liver leave the bloodstream through capillary pores or cross the endothelium by vesicular transport. LDL Cholesterol extracted The HDLs return the cholesterol to the liver, where it is extracted and packaged in new LDLs or excreted with bile salts in bile. Once in peripheral tissues, the LDLs are absorbed. Excess cholesterol is excreted with the bile salts LDL HDL HDL Low cholesterol High cholesterol From the lacteals, the chylomicrons proceed along the lymphatic vessels and into the thoracic duct. Lysosomal breakdown Used in synthesis of membranes, hormones, other material HDL Cholesterol release

  30. Module 22.5 Review a. What is the difference between a micelle and a chylomicron? b. What does the liver do with the chylomicrons it receives? c. Describe the roles of LDL and HDL.

  31. Module 22.6: Lipid catabolism and synthesis Lipolysis(lipid catabolism) Triglycerides absorbed into cells through endocytosis Lysosomal enzymes break down to glycerol and fatty acids Glycerol Converted to pyruvate in glycolysis (+ 2 ATP) Fatty acids Enzymes convert two carbons to acetyl-CoA directly (= beta-oxidation) used in mitochondria More efficient than glucose catabolism (6-carbon glucose = 36 ATP; 6 carbons from FAs = 51 ATP)

  32. Module 22.6: Lipid catabolism and synthesis Lipid synthesis (lipogenesis) Begins with acetyl-CoA Almost any organic substrate (lipids, amino acids, carbohydrates) can be converted to acetyl-CoA Fatty acids synthesized from acetyl-CoA Series of enzymatic steps (different from beta-oxidation) Essential fatty acids Cannot be synthesized and must be obtained from diet Examples: linolenic acid (omega-3 fatty acid) and linoleic acid (omega-6 fatty acid) Structural and functional lipids created from fatty acids Fatty acids + glycerol (from glycolysis) = triglycerides

  33. Figure 22.6 2 CYTOSOL The glycerol required for triglyceride production is synthesized from one of the intermediate products of glycolysis. Triglycerides Steroids Glucose All of the other structural and functional lipids can be synthesized from fatty acids. Glycerol Cholesterol Fatty acid synthesis involves a reaction sequence quite distinct from that of beta-oxidation. As a result, body cells cannot build every fatty acid they can break down. For example, our cells lack the enzymes to insert double bonds in the proper locations to synthesize two 18-carbon fatty acids synthesized by plants: linolenic acid (an omega-3 fatty acid) or linoleic acid (an omega-6 fatty acid). However, these fatty acids are needed to synthesize prostaglandins and some of the phospholipids found in plasma membranes throughout the body. They are therefore called essential fatty acids, because they must be included in your diet. Prostaglandins Fatty acids Pyruvate Phospholipids Glycolipids CO2 Coenzyme A ADP ATP Acetyl-CoA Citric acid cycle Start The synthesis of most types of lipids, including nonessential fatty acids and steroids, begins with acetyl-CoA. Lipogenesis can use almost any organic substrate, because lipids, amino acids, and carbohydrates can be converted to acetyl-CoA. MITOCHONDRIA The major pathways for lipogenesis, the synthesis of lipids

  34. Module 22.6: Lipid catabolism and synthesis Lipids as energy reserves Beta-oxidation is very efficient Can be easily stored as triglycerides Although water-soluble enzymes cannot access, so not used for quick energy but for long-term storage

  35. Module 22.6 Review a. Define beta-oxidation. b. What molecule plays a key reactant role in both ATP production from fatty acids and lipogenesis? c. Identify the fates of fatty acids.

  36. Module 22.7: Protein digestion and amino acid metabolism Steps of protein digestion In mouth, mechanical processing occurs In stomach: Mechanical processing due to churning Stomach acid denatures protein secondary and tertiary structures Pepsin (from parietal cells) attacks certain peptide bonds Digests proteins to polypeptide and peptide chains

  37. Module 22.7: Protein digestion and amino acid metabolism Steps of protein digestion (continued) In duodenum: Enteropeptidase(from duodenal epithelium) converts trypsinogen (pancreatic proenzyme) to trypsin Trypsin activates other pancreatic proenzymes Chymotrypsin, carboxypeptidase, and elastase Activated pancreatic enzymes digest specific peptide bonds producing short peptides and amino acids

  38. Module 22.7: Protein digestion and amino acid metabolism Digested protein absorption and transport Epithelial brush border enzymes (peptidases) finish protein digestion Amino acids absorbed through: Facilitated diffusion Cotransport Released from epithelial cell basal surface through same cell transport mechanisms Amino acids transported to liver through intestinal capillaries to hepatic portal vein

  39. Module 22.7: Protein digestion and amino acid metabolism Amino acid processing in liver Control of plasma amino acid levels is less precise than glucose Normal range: 35–65 mg/dL Can increase after protein-rich meal Liver amino acid use Synthesize plasma proteins Create 3-carbon molecules for gluconeogenesis

  40. Module 22.7: Protein digestion and amino acid metabolism Amino acid processing in liver (continued) Amino acid catabolism Deamination(removal of amino group) Ammonium ions released are toxic Liver enzymes convert to urea excreted into urine = Urea cycle

  41. Figure 22.7 Amino Acid Synthesis The liver does not control circulating levels of amino acids as precisely as it does glucose concentrations. Plasma amino acid levels normally range between 35 and 65 mg/dL, but they may become elevated after a protein-rich meal. The liver itself uses many amino acids for synthesizing plasma proteins, and it has all of the enzymes needed to synthesize, convert, or catabolize amino acids. In addition, amino acids that can be broken down to 3-carbon molecules can be used for gluconeogenesis when other sources of glucose are unavailable. Liver cells and other body cells can readily synthesize the carbon frameworks of roughly half of the amino acids needed to synthesize proteins. There are 10 essential amino acids that the body either cannot synthesize or that cannot be produced in amounts sufficient for growing children. In an amination reaction, an ammonium ion (NH4+) is used to form an amino group that is attached to a molecule, yielding an amino acid. NH4+ H2O H+ Glutamic acid α–Ketoglutarate In a transamination, the amino group of one amino acid gets transferred to another molecule, yielding a different amino acid. The remaining carbon chain can then be broken down or used in other ways. Transaminase Organic acid 1 Glutamic acid Organic acid 2 Tyrosine

  42. Module 22.7 Review a. Name the enzyme secreted by parietal cells that is necessary for protein digestion. b. Identify the processes by which the amino group is removed. c. What happens to the ammonium ions that are removed from amino acids during deamination?

  43. Module 22.8: Absorptive and postabsorptive states Absorptive state Period following a meal, when nutrient absorption is occurring Commonly continues for ~4 hours Insulin is primary regulating hormone by stimulating: Glucose uptake and glycogenesis Amino acid uptake and protein synthesis Others can be involved (GH, androgens, estrogens) Triglyceride synthesis ATP can be produced from nutrient pool

  44. Figure 22.8 1 The activities during the absorptive state following a meal KEY Glucose levels elevated = Catabolic pathway = Anabolic pathway = Stimulation Insulin CARBOHYDRATES LIPIDS PROTEINS Glycogen Proteins Triglycerides Insulin Glucose Insulin G l y c o l y s I s Insulin Androgens Estrogens ATP Growth hormone Amino acids elevated Lipid levels elevated Fatty acids Glycerol Amino acids Insulin, Growth hormone Pyruvate In the absorptive state: CO2 • Insulin stimulates (1) glucose uptake and glycogenesis, (2) amino acid uptake and protein synthesis, and (3) triglyceride synthesis. Insulin Acetyl-CoA ATP Citric acid cycle • Androgens, estrogens, and growth hormone also stimulate protein synthesis. Electron transport system Coenzymes O2 O2 • Glycolysis and aerobic metabolism provide the ATP needed to power cellular activities as well as the synthesis of lipids and proteins. MITOCHONDRIA H2O CO2

  45. Module 22.8: Absorptive and postabsorptive states Postabsorptive state Period when nutrient absorption in not occurring and body relies on energy reserves (~12 hours/day) Metabolic activity focused on mobilizing energy reserves and maintaining blood glucose Lipid levels decrease = fatty acids released by adipocytes Amino acid levels decrease = amino acids released by liver Glucose levels decrease = glucose released by liver Coordinated by several hormones Glucagon, epinephrine, glucocorticoids, growth hormone

  46. Module 22.8: Absorptive and postabsorptive states Postabsorptive state (continued) Catabolism of lipids and amino acids in liver produce acetyl-CoA Leads to formation of ketone bodies Diffuse into blood and are used by other cells as energy source

  47. Module 22.8: Absorptive and postabsorptive states Postabsorptive state (continued) Hormone effects Glucocorticoids Stimulate mobilization of lipid and protein reserves Enhanced by growth hormone Glucagon Stimulates glycogenolysis and gluconeogenesis Mainly in liver Epinephrine Glycogenolysis in skeletal and cardiac muscle Lipolysis in adipocytes

  48. Module 22.8 Review a.Define absorptive state and postabsorptive state. b. When and how do ketone bodies form? c. How do the absorptive and postabsorptive states maintain normal blood glucose levels?

  49. Module 22.9: Vitamins Nutrition Absorption of nutrients from food Vitamins Organic compounds required in very small quantities for essential metabolic activities Two classes Fat-soluble vitamins (A, D3, E, and K) Water-soluble vitamins (B vitamins and C)

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