Metabolism of Nutrients Eko Widodo

Metabolism Metabolism Energy Metabolism The sum total of all the chemical reactions that go on in living cells Energy Metabolism Includes all the reactions by which the body obtains & spends energy from food All energy sustaining life initially comes from the sun

The Site of Metabolic Reactions Metabolic reactions take place inside cells, especially liver cells Anabolism is the building up of body compounds and requires energy. Catabolism is the breakdown of body compounds and releases energy. Type & extent of metabolic activity vary depending on type of cell.

The Site of Metabolic Reactions Cytosol (jelly like fluid of cytoplasm) – enzymes involved in glycolisis Ribosomes – assemble proteins Mitochondria – powerhouses of cells Pyruvate to acetyl coA Fatty acid oxidation TCA cycle and electron transport chain

Energy Yielding Nutrients From CHO → glucose From fats → glycerol & FA From proteins → AA 4 basic units used in metabolic pathway Alcohol can disrupt normal metabolic pathways (Highlight 7)

The Transfer of Energy in Reactions - ATP ATP – adenosine triphosphate High-energy storage compound Captures some energy released during breakdown of glucose, glycerol, fatty acids, and amino acids Think of ATP as our energy currency

Adenosine Triphosphate (ATP) Red squigly lines denote high energy bonds between the 3 phosphates

The Transfer of Energy in Reactions - ATP Hydrolysis of ATP occurs simultaneously with reactions that will use that energy Coupled reactions Energy released from breakdown of one compound used to create bond in formation of another Think of ATP as our energy currency

Enzymes & Co-enzymes – Helpers in Metabolism Co-enzymes are organic molecules that work with enzymes to facilitate their activity. Enzymes & co-enzymes are helpers in metabolic reactions. Some B vit serve as coenzymes to enzymes that release energy from glucose, glycerol, FA & AA.

Breaking Down Nutrients for Energy Basic units enter metabolic pathways. During catabolism, the body separates atoms of basic units. Glucose: 6 C Glycerol: 3 C FA: even number of C (commonly 16 or 18) AA: 2, 3 or more C, with N attached While each starts down a different path – 2 by- products are common pyruvate & acetyl-coA Eventually all enter the TCA cycle & electron transport chain Pyruvate – 3 carbon structure Acetyl-coA – 2 carbon structure with coA attached

Glycolysis Glucose Glucose splitting 6-C Glucose → two 3-C compounds → Pyruvate Glucose anaerobic Pyruvate

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Pyruvate to Acetyl CoA Pyruvate Pyruvate Lactate Acetyl CoA If cell needs energy (& O2 is available), it removes COOH group from pyruvate to produce 2 C compounds that bonds with CoA to form Acetyl CoA Pyruvate Acetyl CoA Absence of sufficient O2 (or mitochondria) pyruvate is converted to lactic acid Pyruvate anaerobic Lactate Lactate recycled to glucose in liver by Cori cycle aerobic

Paths of Pyruvate & Acetyl CoA Point out that once turned into acetyl coA cannot go back to pyruvate (can go back to fatty acids)

Glycerol to Pyruvate Glucose Glycerol Pyruvate 3-C glycerol is easily converted to pyruvate Also easily converted to glucose Glucose Glycerol Pyruvate

Fatty Acids to Acetyl CoA FA are taken apart in 2-C units through fatty acid oxidation. 2-C units split off & combine with CoA to form Acetyl CoA. If cell doesn’t need energy, acetyl CoA molecules combine to create TG.

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Amino Acids Breakdown Deaminated first (lose N) Catabolized in a variety of ways: Pyruvate  glucose Acetyl CoA  more energy or body fat Directly into TCA Cycle  generate energy

Amino Acids Breakdown Amino Acids Deamination results in two products: Keto acid Ammonia Transamination is the transfer of the amino group from an amino acid to a keto acid. Ammonia is converted to urea—a much less toxic compound—in the liver. Urea is excreted through the kidneys to rid the body of unused nitrogen.

Breaking Down Nutrients for Energy In Summary Glucose and fatty acids are primarily used for energy, amino acids to a lesser extent. Glucose is made from all carbohydrates, most amino acids and the glycerol portion of fat. Protein is made from amino acids. Glucose can be made into nonessential amino acids if nitrogen is present. All energy-yielding nutrients consumed in excess can contribute to fat storage.

Breaking Down Nutrients for Energy – the final steps TCA Cycle – tricarboxylic acid cycle (aka Kreb’s cycle) Oxaloacetate picks up acetyl CoA & drops off 2-C & returns to pick up another acetyl CoA. As acetyl CoA breaks to CO2, H atoms with their electrons are removed. Coenzymes made from B vitamins take H & electrons & transfers them to ETC. Show animation

Breaking Down Nutrients for Energy – the final steps Electron Transport Chain (ETC) Consist of a series of proteins that serve as electron carriers. These carriers are inside inner membrane of mitochondria. In ETC, energy is captured in bonds of ATP molecules. ATP leaves mitochondria & enters cytoplasm, where it can be used for energy. Show animation

Kcal/gram Each ATP holds energy & Kcal measures energy, so the more ATP generated the more Kcal collected. One glucose molecule yield 36-38 ATP when oxidized completely. One 16 carbon FA yield 129 ATP when oxidized completely.

Energy Balance - Surplus When energy intake exceeds energy output, there is a gain in weight. Fat cells enlarge & multiply regardless of whether the excess comes from protein, CHO or fat. Most direct & efficient pathway to body fat is dietary fat.

Energy Balance Body needs energy all the time Relies on energy stores between meals glycogen fatty acids lean mass tissue .. least preferred

Energy Balance – Fasting/Starvation Fasting—Inadequate Energy Glucose needed for the brain Protein meets glucose needs The shift to ketosis Ketones are produces when glucose is not available. Ketosis causes a suppression of the appetite. Slowing of metabolism

Energy Balance – Fasting/Starvation Fasting—Inadequate Energy Symptoms of starvation Muscle wasting Decreased heart rate, respiratory rate, metabolic rate, and body temperature Impaired vision Organ failure Decreased immunity Depression, anxiety, and food-related dreams

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