Metabolism—How do we obtain energy from foods? Susan Algert, Ph.D., R.D.

Metabolism Human body releases energy from chemical bonds in nutrients the body uses for fuel. As bonds break they release energy During metabolism, energy, water and carbon dioxide are released

Energy yielding nutrients From carbohydrates—glucose From lipids (trigylcerides)— glycerol and fatty acids From proteins—amino acids

The Cell Cells are work centers of metabolism Cells have similar structures Two basic parts—nucleus and cytoplasm Mitochondria are power generators that contain energy generating pathways

Breaking down glucose for energy--aerobic 6-C glucose split in half making two 3- Carbon compounds Glycolysis means glucose splitting -Carbon compounds become 2 pyruvates Pyruvates will break down further to form ATP and heat

Glucose retrieval via the Cori cycle--anaerobic When less oxygen is available, pyruvate is converted to lactic acid Liver can convert lactic acid to glucose in a recycling process Pathway is muscle glycogen to glucose to pyruvate to lactic acid ( in liver) to glucose to glycogen

Pyruvate to Acetyl Co-A Irreversible step Aerobic Acetyl Co A to Carbon Dioxide via the TCA cycle Electron Transport Chain Acetyl Co-A to fat

Pyruvate is pivotal ATP levels are low—metabolic pathways flow toward the production of ATP Depending on O-2; ATP routes pyruvate to acetyl Co-A or lactate ATP is abundant; pyruvate converted to oxaloacetate or amino acid alanine; oxaloacetate converted to glucose and then glycogen

Acetyl Co-A at the crossroads Breakdown pathways for glucose, fatty acids and some amino acids converge at acetyl-CoA. Acetyl Co-A cannot return to pyruvate, but enters energy making pathways Acetyl Co-A can also make ketone bodies and fatty acids

Glycerol and fatty acids Glycerol to pyruvate Fatty acids to Acetyl Co-A Beta oxidation Glucose not retrievable from fatty acids Breakdown of acetyl-Co-A Fat burns in flame of carbohydrate

When a person draws on stores Fat used to fuel brain Acetyl Co-A fragments from fatty acids combine to produce ketone bodies Ketone bodies can provide some fuel for brain cells When ketone bodies contain an acid group they are called keto acids (COOH)

Energy Compounds ATP used to power cellular functions NADH and FADH-2 carry energy for synthesis of ATP NADPH delivers energy for biosynthesis

Amino Acid Catabolism Amino acids are deaminated and enter TCA cycle Amino acids used to make pyruvate can make glucose Amino acids that make Acetyl Co-A provide energy or body fat but not glucose

Energy retrievable from amino acids- Glucogenic amino acids- a.a. broken down into pyruvate or intermediate of the TCA cycle; gluconeogenesis Ketogenic amino acids—an a.a.a broken down into acetyl CoA which can be converted into ketone bodies

Transamination Transfer of amino group from one amino acid to a keto acid, producing a new non essential amino acid and a keto acid

Electron Transport Chain Series of proteins that serve as electron carriers Mounted in sequence on membrane inside mitochondria Carriers receive electrons, it passes electrons and gives up energy until end when any usable energy has captured body’s ATP molecules

TCA and ETC Body’s most efficient means of capturing the energy from nutrients and transferring it into the bonds of ATP Last step of ETC low energy electrons with H atoms combine with O2 from the lungs to make H2O

Which fuels can make glucose Parts of protein and fat that can make pyruvate can provide glucose; parts that make acetyl Co A cannot, but provide fat Glucose is needed to fuel CNS and red blood cells If there is not enough glucose the body will break down protein

Making glucose on low Carb diets Fat delivers mostly acetyl, so that you need to break down protein tissue to make glucose High protein diets make your body convert protein to glucose and convert ammonia to urea in the liver Urea is excreted via the kidneys Water is needed to excrete urea

Energy yielding nutrients-fat provides most kcals per gram Nearly all bonds in a fatty acid are between carbons and hydrogens Oxygen can be added to all of them (making CO2 and H2O) Energy in bonds is released as they are oxidized Glucose has less potential for oxidation as oxygen is already bonded to each C

Feasting Surplus protein—Deaminate and convert to acetyl Co-A and fat Surplus carbohydrate--Glycogen Surplus fat--Lipogenesis