Integration of Metabolism in Energy, Protein and Lipids

1. Integration of Metabolism in Energy, Protein and Lipids

2. Metabolism • A term referring to all chemical reactions necessary to maintain life. Substances are constantly being broken down and built up. • Catabolism: complex structures broken down into simpler ones (digestion) • Anabolism: larger molecules are built from small ones (like AA’sproteins)

3. The Nutrient Pool • Contains all organic building blocks cell needs: • to provide energy • to create new cellular components 6 categories of nutrients • Carbohydrates • Lipids • Proteins • Vitamins • Minerals • Water Lipids release 9.46 C/g Carbohydrates release 4.18 C/g Proteins release 4.32 C/g

4. Carbohydrates • Dietary sources • Predominately plants • Sugars – fruits, honey, milk, candy, soda • Starch – grains, legumes, root veggies • Cellulose – veggies

5. Carbohydrates, cont. • Uses in the body • Glucose is a major fuel to make ATP • Carbohydrate digestion yields fructose and galactose, liver converts them to glucose before circulation • *when glucose is in excess, it is converted to glycogen or fat and stored for later use*

6. Lipids • Dietary sources • Saturated fats • Animal products (meat & dairy) & coconut, palm,etc. • Unsaturated fats • Seeds, nuts, most veggie oils • Storage as triacylglycerol (TAG) inadipose tissues • Glycogen (branched polymerα-D-glucose)found in Liver, MM. • More TAG(give 9 kcal/g ) > glycogen in body strorage

7. Brown fat had a small molecule, more blood vessels, low ATP produced and make more EN than White fat (Birth animal) • Wild animal had lean meat (low marbling) and more PUFA ( >30% total FA vs. 12% in domestic animal ) • FUFA in wild ani. made unfavour meat from FUFA-phospholipids form.

8. Lipids, cont. • Dietary fats help the body absorb fat-soluble vitamins • triglycerides are the major EN source for liver cells & skeletal muscle • Cholesterol is not used as an EN source. It is a precursor to bile salts, steroid Hormones, and other essential functional molecules • Non ruminant fat intake and fat in body found in the same proportion (Unsat --> Unsat, Sat Sat) • Ruminant always had biohydrogenation in rumen.

9. Glycogen & Lactic cycle ( Cori cycle) Insulin moving glucose to glycogen (storage in liver, mm) Glucagon activate glycogenolysis for glucose in Liver, and Lactic in MM.

10. Proteins • Dietary sources • Primarily animal products (eggs, milk, meat) • Legumes, nuts, & cereals are nutritionally incomplete because they are low in one or more essential AA’s

11. Proteins, cont. • Uses in the body • Structural materials (collagen, elastin, keratin) • Functional proteins (enzymes, hemoglobin, H’s) • Hormonal controls • Anabolic hormones accelerate protein synthesis • i.e. growth hormone, sex hormones, adrenal glucocorticoids, etc.

12. Proteins, cont. • Adequacy of caloric intake • For protein synthesis you must have adequate intake of carb’s & fats for ATP production • If not…dietary & tissue proteins are used for En

13. Energy Yield of Aerobic Metabolism • For 1 glucose molecule processed, cell gains 36 molecules of ATP: • 2 from glycolysis • 4 from NADH generated in glycolysis • 2 from TCA cycle (through GTP) • 28 from ETS

14. Carbohydrate Synthesis and Breakdown • Gluconeogenesis - the synthesis of glucose from noncarbohydrate precursors: • lactic acid, glycerol, & AA’s • Stores glucose as glycogen in liver and skeletal muscle • Glycogenesis - the formation of glycogen from glucose • Glycogenolysis - Is the breakdown • of glycogen to glucose Figure 25–7

15. Lipolysis • Breaks lipids down into pieces that can be converted to pyruvic acid & channeled directly into TCA cycle • Hydrolysis splits triglyceride into component parts: • 1 molecule of glycerol & 3 fatty acid molecules • Different enzymes convert fatty acids to acetyl- CoA (beta-oxidation)

16. Fat & Glucose in Non Ruminant

17. Fat & Glucose in Ruminant

18. 3 Energy Benefits of Beta-Oxidation • For each 2-carbon fragment removed from fatty acid, cell gains: • 12 ATP from acetyl-CoA in TCA cycle • 5 ATP from NADH • Cell can gain 144 ATP molecules from breakdown of one 18-carbon fatty acid molecule 3. Fatty acid breakdown yields about 1.5 times the energy of glucose breakdown

19. Free Fatty Acids (FFAs) • Are lipids that can diffuse easily across cell membranes • In blood, are generally bound to albumin (most abundant plasma protein) • Are an important energy source: • during periods of starvation when glucose supplies are limited • Liver cells, cardiac muscle cells, skeletal muscle fibers, etc. metabolize free fatty acids

20. Proteins • The body synthesizes 100,000 to 140,000 proteins: • each with different form, function, and structure • All proteins are built from the 20 amino acids

21. Protein Metabolism • Cellular proteins are recycled in cytosol: • peptide bonds are broken • free amino acids are used in new proteins • If other energy sources are inadequate: • mitochondria generate ATP by breaking down amino acids in TCA cycle • Not all amino acids enter cycle at same point, so ATP benefits vary

23. 3 Factors Against Protein Catabolism • Proteins are more difficult to break apart than complex carbohydrates or lipids • A by-product, ammonium ion, is toxic to cells • Proteins form the most important structural and functional components of cells

24. Protein Synthesis • The body synthesizes half of the amino acids needed to build proteins (Nonessential AA’s) • amino acids made by the body on demand • 10 essential AA’s: • 8 not synthesized: isoleucine, leucine, lysine, threonine, tryptophan, phenylalanine, valine, and methionine • 2 insufficiently synthesized: arginine and histidine

25. Summary: Pathways of Catabolism and Anabolism Figure 25–12

26. Metabolic Interactions Body has 2 patterns of daily metabolic activity: • absorptive state • postabsorptive state

27. The Absorptive State • Is the period following a meal when nutrient absorption • most excess metabolites will be converted to fat for storage if not used in anabolism • carbs-->liver to covert to glu-->released to blood or makes & stores glycogen & makes fat to release to blood for storage by adipocytes • triglycerides-->FA’s + glycerol-->sk mm, liver cells, & adipocytes use FA’s as primary E source-->most FA’s & glycerol re-enter adipose tissue & reconvert to triglycerides for storage • AA’s-->some to liver for deamination to keto acids-->Kreb’s for ATP formation or conversion to liver fat stores; liver uses some AAs for plasma protein synthesis but most go into general circulation for uptake by other body cells to use for anabolism

28. The Postabsorptive State • When nutrient absorption is not under way (fasting state) • Primarily catabolic to maintain blood glucose levels w/in normal range b/t meals • glycogenolysis in liver can maintain blood glu levels for ~ 4 hrs • glycogenolysis in skeletal mm - glucose cannot be released to blood as w/liver (lacks all necessary enzymes) but…partial oxidation to pyruvic acid (or lactic acid) occurs-->goes to liver for conversion back to glucose & is released to blood • lipolysis in adipose tissue & liver -->leads to glycerol-->liver converts to glucose & releases to the blood • catabolism of cellular protein - primary source of blood glucose w/fasting (glycogen stores are depleted)-->AAs are deaminated & coverted to glucose in liver & are released to blood

29. Glucose for Energy • enzymes break apart glucose – yielding energy • inadequate supply of carbohydrates • ketone bodies (fat fragments) are an alternate energy source during starvation • excess ketones can lead to ketosis: imbalance of acids in body

30. Protein Metabolism • protein turnover • constant making and breaking of proteins • frees amino acids to “amino acid pool” • can be used to make body proteins • nonessential amino acids can be made from other amino acids

31. amino acid pool • Excreat of nitrogens and made available for energy • deamination • make fat • amino acids are deaminated, nitrogen is excreted, carbon is converted to fat and stored • protein-rich foods can cause weight gain

32. Feasting and Fasting

33. Feasting and Fasting

34. Fasting • several hours after a meal, glucose is used up • protein is used for energy • shift to ketosis • suppresses appetite • hormones slow metabolism • eventually starvation

35. Regulatory Hormones on Metabolism Table 25–1

36. Basal Metabolic Rate (BMR) • Is the minimum resting energy expenditure: • Involves monitoring respiratory activity • Energy utilization is proportional to oxygen consumption

37. Hormonal Effects • Thyroxine: • controls overall metabolism • Cholecystokinin (CCK): • suppresses appetite • Adrenocorticotropic hormone (ACTH): • suppresses appetite • Leptin: • released by adipose tissues • binds to CNS neurons that suppress appetite

38. Heat Production • BMR estimates rate of energy use • Energy not captured is released as heat: • serves important homeostatic purpose

39. Thermoregulation • The body produces heat as by-product of metabolism • Increased physical or metabolic activity generates more heat • Body controls heat gains and losses to maintain homeostasis