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NTR 306 (22)
Chapter 7

NTR 306 Chapter 7 Metabolism Notes.docx

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Department
Nutrition
Course
NTR 306
Professor
Deanna Staskel
Semester
Spring

Description
Chapter 7: Metabolism Energy from Food:  During digestion, o Energy-yielding nutrients are broken down to [feasting]  Monosaccharides  Fatty acids  Glycerol  Amino acids o Fasting – the body breaks down stored macronutrients from stored glycogen (glucose); body fat (triglycerides); amino acids  During metabolism o They are converted into a usable form of energy for cells [ATP], water a2d CO o BODY ALWAYS NEEDS ENERGY SO METABOLISM NEVER STOPS Cellular Energy & ATP: Cells are unable to use macronutrients directly for energy! ATP (adenosine triphosphate):  Only source of energy that can be used directly by cells  High energy molecule o Composed of adenine, ribose and 3 phosphate molecules o  Must continually ‘recharge’ ATP to provide a constant supply of energy  When cells need energy, a phosphate group is broken off of ATP o Releases energy & inorganic phosphate (ADP) Anabolic and Catabolic Reactions: Anabolic reactions – use ATP to combine smaller molecules (like glucose) into larger compounds (like glycogen) and release small amounts of heat  During times of plenty, favored by metabolism  Excess carbohydrates are o stored as glycogen in the liver and muscle o stored as fat in the adipose tissue  Protein is used for building body proteins o Excess converted to fat and stored  Excess dietary fat is stored in adipose tissue  Glucose + glucose  glycogen  Glycerol + fatty acids  triglycerides  Amino acids + amino acids  protein Catabolic reactions – break down larger molecules into smaller compounds and release ATP and heat  Liver glycogen providing blood glucose  Muscle glycogen is used for fuel by the muscles  Adipose tissue released fatty acids to be transformed into ketone bodies in the liver and used by the brain as fuel  Body proteins are converted to glucose  Glycogen  glucose  Triglycerides  glycerol + fatty acids  Protein  amino acids Chapter 7: Metabolism METABOLISM TAKES PLACE WITHIN CELLS:  Cytosol/cytoplasm o Fluid portion of the cell o Site of anaerobic metabolism in the cell  Mitochondria o “the powerhouse of the cell” o The site of all aerobic metabolism o Contained in all cells  Except RBCs when they mature o Some have more than others, making some more metabolically active than others  Liver and heart cells have a lot Carbohydrates to Energy:  Glucose is the most important macronutrient for ATP production! o Important for brain and RBCs o Unique b/c it can produce ATP anaerobically & aerobically  Derived from ingestion, digestion and absorption of carb-rich foods o Or broken down from glycogen stores  Glycogenolysis o Or converted to glucose from amino acids, glycerol, lactate  Gluconeogenesis Glycolysis:  Breakdown of glucose  First step in forming ATP from glucose  Takes place in the cytosol of the cell  10-step catabolic process  1 six-molecule glucose process to two 3C molecules of pyruvate o Net of 2 molecules of ATP o 2 H are transposed to ETC Pyruvate:  An intermediate product formed during the metabolism of carbohydrates  Creation occurs in the cytoplasm of the cell  No oxygen is required to form it  Small amount of energy is formed o 2 ATPs + 2 NADH + H per glucose  Without adequate oxygen, pyruvate remains in the cytoplasm and is converted to lactate (lactic acid) o It is released into the blood and taken to the liver o Lactate is then converted to glucose  Can then undergo glycolysis to pyruvate again  Called the Cori Cycle Pyruvate to Lactate:  Pyruvate reduces to lactate to prevent H ions from building up in the cell +  During intense exercise+ lactate is not produced fast enough to keep up with H production o The buildup of H ions reduces pH in the muscle cell  Leads to the “burning” sensation in muscles after exercise Chapter 7: Metabolism Pyruvate to Acetyl-CoA:  After emerging from glycolysis, the 2 pyruvate are transported into the mitochondria o Pyruvate  acetyl-coenzyme A (acetyl-CoA)  The starting product in the TCA cycle  2 pyruvate + 2 coenzyme A + 2 NAD  2 acetyl-CoA + 2CO +22 NADH Anaerobic Metabolism:  Produces more ATP per minute  Limited in use o Provides only 1-1.5 minutes of maximal activity  Involved in high-intensity, short-duration activities o Ex: sprinting, heavy weight lifting Aerobic Metabolism:  Produces less ATP per minute  Is able to produce ATP indefinitely  Involved in low-intensity, long duration activties Enzymes, Cofactors & Coenzymes: Enzymes – protein catalysts that cause chemical reactions  Remains unchanged after the reaction Cofactors – inorganic components of an enzyme needed for the enzyme’s activity  Often a mineral  Must be attached to the enzyme’s active site Coenzymes – organic molecules that function as enzyme helpers  Accepts and donates H , electrons and other molecules during reactions +  NAD (nicotinamide adenine dinucleotide) o Derived from B vitamin [niacin (B3)] o Reduced to NADH +  It accepts 1 H atoms  FAD (flavin adenine dinucleotide) o Derived from B vitamin [riboflavin (B2)] o Reduced to FADH 2 +  It accepts 2 H atoms Triglycerides: Glycerol and fatty acids can be derived from diet OR lipolysis [enzymatic breakdown of triglycerides (from adipose tissue) into glycerol and fatty acids by hormone-sensitive lipase]!  Glycerol o Gluconeogenesis – converts glycerol to glucose in the liver  Fatty acids o Ketogenic – normally converted to acetyl CoA (fatty acid oxidation)  Acetyl-CoA can form ketones if glucose supply is inadequate o Fatty acid oxidation  Series of chemical reactions that break down fatty acids to molecules of acetyl-CoA  Fatty acid is taken apart 2C at a time  Hydrogen and electrons are released to ETC  Each 2C pairs are joined by other CoA and converted to acetyl-CoA  The acetyl-CoA then enters the TCA Cycle to produce energy Amino Acids:  Major role is as building blocks from proteins and other-containing compounds  If the AA is not used to build protein, the amine group must be removed through deamination o Ammonia, toxic to cells, is converted to urea o Deamination leaves an alpha-keto acid Chapter 7: Metabolism  Occurs mainly in the liver o Alpha-keto acids can be converted to acetyl CoA  To enter the TCA cycle or converted to body fat (lipogenesis) o OR converted by the liver to pyruvate to glucose (gluconegogenesis)  Excess can be used for energy production, converted to glucose or stored as fat  Used, in a limited extent, for energy in diets low in kilocalories and/or carbohydrate  Supply less than 10% of our daily ATP needs  Can be derived from dietary protein or breakdown of stored muscle  Proteolysis – breakdown of proteins (from body tissues) into amino acids
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