Nutrients and their metabolic pathways

Hi everybody. I am Rong Hong Hsieh, professor of school of nutrition and health sciences, Taipei Medical University. Today, I will show you the important and interesting organelle mitochondria and the role in energy homeostasis. The makeup of a cell when it reproduces and large and small cellular molecules are synthesized within a cell or move these molecules in or out of a cell All of these activities require energy The cell obtains this energy from small molecules oxidized to provide heat and chemical energy The small molecules that are constantly required are supplied by the nutrients in food Energy used by the body is ultimately derived from the energy contained in the macronurtients like carbohydrate fat and protein

Macronutrients may be digested to small units Carbohydrate may be released in glucose Fat be digested to fatty acids and glycerol Protein be digested to amino acids

If the energy contained in the glucose fatty acids or amino acids are released it may simply be expressed as heat or be preserved in the form of other chemical energy Energy cannot be created or destroyed it can only be transformed

In the metabolic oxidation a significant portion of the released energy is salvaged as chemical energy in the form of new high-energy bonds The stored energy is generally contained in phosphate anhydride bonds This anhydride bond is formed in the adenosine triphosphate ATP Cells use energy stored in the form of a molecule called ATP ATP is like cash for the cell Glucose occupies a central position in the metabolism of many plants animals and microorganisms It is relatively rich in potential energy and thus a good fuel By storing glucose as a high molecular weight polymer such as starch or glycogen a cell can stockpile large quantities of hexose units while maintaining a relatively low cytosolic osmolarity Glucose is not only an excellent fuel it is also a remarkably versatile precursor capable of supplying a huge array of metabolic intermediates for biosynthetic reactions A microorganism can obtain from glucose the carbon skeletons for every amino acid nucleotide coenzyme fatty acid or other metabolic intermediate it needs for growth

In animals glucose has three major fates it may be stored as a polysaccharide like glycogen starch or sucrose Glucose also may be oxidized to a three-carbon compound pyruvate via glycolysis to provide ATP and metabolic intermediates or oxidized via the pentose phosphate pathway to yield ribose 5 phosphate for nucleic acid synthesis and NADPH for reductive biosynthetic processes When energy demands increase glucose can be released from these intracellular storage polymers and used to produce ATP either aerobically or anaerobically Glycolysis is the pathway by which glucose is degraded into two 3 carbon units pyruvate Glycolysis can function under either aerobic or anaerobic conditions Under anaerobic conditions pyruvate is converted to lactate For example in times of strenuous exercise when the demand for oxygen by the working muscles exceeds that which is available Lactate produced under anaerobic conditions can also diffuse from the muscle to the blood stream and be carried to the liver for conversion to glucose Under these anaerobic condition glycolysis releases a small amount of usable energy that can help sustain the muscles even in a state of oxygen debt