Understanding Nutrition and Metabolism in Human Biology

1. Biology 212Anatomy & Physiology I Nutrition and Metabolism

2. Body requires, among many other things: a) Water = solvent for all body fluids b) Electrolytes (ions, minerals) for osmotic balance electrical signals • Vitamins = cofactors for enzyme-catalyzed reactions, growth, antioxidants, vision, blood clotting • Proteins • Carbohydrates • Lipids Structural molecules to build/repair cells and tissues and Fuel molecules to produce energy

3. We have already discussed water balance Let’s focus on the nutritional needs and metabolic uses of other nutrients which are absorbed into the blood from the intestines and distributed to all other cells in the body.

4. Two types of metabolism: Catabolism = breaking larger molecules into smaller ones e.g. proteins amino acids starch glucose glucose CO2 + H20 + energy fatty acid CO2 + H20 + energy Occurs: digestive system, inside cells Anabolism = building smaller molecules into larger ones e.g. glucose glycogen fatty acids + glycerol triglycerides amino acids proteins Occurs: inside cells

5. Body requires, among many other things: Water = solvent for all body fluids Electrolytes (ions, minerals) for osmotic balance electrical signals Vitamins = cofactors for enzyme-catalyzed reactions, growth, antioxidants, vision, blood clotting Structural molecules to replace damaged ones Fuel molecules to produce energy

6. Human body consumes 2,000 – 5,000 kilocalories per day and must replace this through fuel molecules in the diet 1 kilocalorie (Kcal) = 1,000 calories 1 calorie = measurement of energy Specifically = amount of heat necessary to increase the temperature of one gram of water by one degree centigrade Just to put things in perspective: 5,000 kcal = amount of energy needed to heat 50 kg (~110 pounds) of water from freezing to boiling

7. kcal/hour Activityper kg body wt Running – 9 minute mile 5.3 Cross-country skiing 4.4 Jogging 4.2 Racquetball 3.9 Basketball 3.8 Swimming 3.5 Tennis 3.0 Cycling @ 9 mph 2.7 Hiking 2.5 Walking 2.2 Housecleaning 1.6

8. Primary sources of fuel molecules in diet: Monosaccharides from breakdown of polysaccharides (mostly glucose) (mostly starch) Fatty acids from breakdown of diglycerides & triglycerides Also possible: amino acids from breakdown of proteins One gram of fatty acids: 9 kcal of energy One gram of monosaccharides: 4 kcal of energy One gram of amino acids: 4 kcal of energy

9. Primary sources of fuel molecules in diet: Monosaccharides from breakdown of polysaccharides (mostly glucose) (mostly starch) Fatty acids from breakdown of diglycerides & triglycerides Also possible: amino acids from breakdown of proteins If diet contains more fuel molecules than body needs for immediate needs, the excess can be stored in a variety of cells, e.g. diglycerides & triglycerides in adipocytes & other cells glycogen in hepatocytes myocytes

10. Regardless of type of Complete catabolism results in fuel molecule used: release of energy which is stored as adenosine triphosphate (ATP)

11. This ATP can later be broken down to release this energy for cellular functions which need it: e.g. Active transport of molecules across membranes Pumping ions for polarization Moving molecules or organelles within cell Synthesizing proteins Contraction of myocytes Movement of cilia or flagella etc.

12. Most commonly used fuel molecule = glucose First stage of glucose catabolism inside cells = glycolysis One molecule of glucose (C6H1206) produces 2 molecules pyruvic acid (C3H6O2) 2 molecules ATP Oxygen not required Occurs in cytoplasm, outside mitochondria

13. Most commonly used fuel molecule = glucose First stage of glucose catabolism inside cells = glycolysis One molecule of 2 molecules pyruvic acid glucose (C6H1206) 2 molecules ATP If oxygen IS NOT available, pyruvic acid molecules are converted to lactic acid, which diffuses out of cell as waste product produces

14. Most commonly used fuel molecule = glucose First stage of glucose catabolism inside cells = glycolysis One molecule of 2 molecules pyruvic acid glucose (C6H1206) 2 molecules ATP If oxygen IS available, pyruvic acid molecules further catabolized in tricarboxylic (“Krebs”) cycle (Your book may refer to this as the “matrix reactions”) produces

15. Tricarboxylic acid / Krebs cycle: Oxygen required Each pyruvic acid molecule (3 carbons) gives off one carbon atom, then combines with 3 molecules of oxygen (O2) to produce 3 molecules CO2 3 molecules H2O 18 molecules ATP Occurs inside mitochondria

16. Electron Transport Chain and ATP Synthesis:

17. Thus: If no oxygen available: 1 glucose yields 2 ATP If oxygen available: 1 glucose yields 38 ATP

18. Carbohydrates such as starch are readily available in diet & Can easily be broken down to form glucose, which is easily absorbed from intestine into blood You don’t need all of that glucose immediately for production of energy so Excess glucose must be removed from blood and stored

19. (Excess glucose must be removed from blood and stored) 1. Joined into glycogen Primarily in hepatocytes and skeletal myocytes

20. (Excess glucose must be removed from blood and stored) 2. Converted to fatty acids through process of lipogenesis Bonded to glycerol to form diglycerides & triglycerides

21. Similarly: If enough glucose not available in diet, Other molecules, primarily products of fat catabolism & amino acid catabolism can be converted to glucose molecules through gluconeogenesis and also stored as glycogen; primarily in liver While all of the reactions are not the same, gluconeogenesis is essentially a reversal of glycolysis:

22. Glucose not only fuel molecule many cells can use Recall: fatty acids contain long chains of carbon atoms

23. Glucose not only fuel molecule many cells can use Recall: fatty acids contain long chains of carbon atoms These can be catabolized by breaking off two-carbon pieces “acetyl groups” and feeding these into the tricarboxylic acid cycle

24. Body requires, among many other things: Water = solvent for all body fluids Electrolytes (ions, minerals) for osmotic balance electrical signals Vitamins = cofactors for enzyme-catalyzed reactions, growth, antioxidants, vision, blood clotting Structural molecules to replace damaged ones Fuel molecules to produce energy

25. Recall: Two types of metabolism: Catabolism = breaking larger molecules into smaller ones e.g. proteins amino acids starch glucose glucose CO2 + H20 + energy fatty acid CO2 + H20 + energy Occurs: digestive system, inside cells Anabolism = building smaller molecules into larger ones e.g. glucose glycogen fatty acids + glycerol triglycerides amino acids proteins Occurs: inside cells

26. Many macromolecules constantly need replacement through anabolism from smaller molecules, for example: Amino acids Enzymes, Antibodies, Contractile proteins, Membrane proteins, Lipoproteins Monosaccharides Glycoproteins, Nucleic acids, ATP Fatty acids Glycolipids + glycerol Phospholipids Nucleotides Nucleic acids

27. These anabolic reactions occur by dehydration synthesis

28. Many of these smaller molecules (monomers) are recycled from catabolism of larger molecules (polymers) Others must be obtained through diet

29. Amino acids which can’t be formed from other amino acids = Essential amino acids Fatty acids which can’t be formed from other fatty acids = Essential fatty acids

30. All monosaccharides can be formed from so no essential monosaccharides other monosaccharides Nucleotides can be formed from other so no essential nucleotides nucleotides & other molecules

31. Body requires, among many other things: Water = solvent for all body fluids Electrolytes (ions, minerals) for osmotic balance electrical signals Vitamins = cofactors for enzyme-catalyzed reactions, growth, antioxidants, vision, blood clotting Structural molecules to replace damaged ones Fuel molecules to produce energy

32. We have already discussed many important minerals (Na+, K+, Ca++, Fe++, Cl-), but there are about a dozen more which the body needs in smaller amounts. These are needed in the diet to replace those lost in urine, feces, menstruation, sweat, cell death, etc. Different amounts of each are needed for homeostasis

33. 13 molecules are vitamins. Many of these are cofactors needed for many enzymes to function. Others are antioxidants. Some form parts of molecules needed by cells. With the exception of Vitamin D (which can be made by the skin), all of these must be ingested to replace those lost through metabolism and through the urine, feces,

34. To maintain homeostasis 1. Fuel molecules, structural molecules, vitamins, minerals, and water must be obtained through diet 2. Water balance must be maintained 3. Fuel molecules catabolized to produce ATP 4. Large structural molecules formed as Old molecules broken down and lost 5. Ions used for many purposes 6. Vitamins used for many purposes 7. Waste products must be removed