Metabolism: Transformations

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Metabolism Transformations Interactions

• Chapter 7

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Metabolism

• 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

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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.

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The Site of Metabolic Reactions
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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
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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

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Adenosine Triphosphate (ATP)
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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

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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.

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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

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Glycolysis

• Glucose splitting
• 6-C Glucose ? two 3-C compounds ? Pyruvate
• Glucose
• anaerobic
• Pyruvate

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Pyruvate to 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
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Paths of Pyruvate Acetyl CoA
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Glycerol to Pyruvate

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

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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 doesnt 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

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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 ureaa much less toxic
  compoundin the liver.
• Urea is excreted through the kidneys to rid the
  body of unused nitrogen.

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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.

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Breaking Down Nutrients for Energy the final
steps

• TCA Cycle tricarboxylic acid cycle (aka
• Krebs 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.

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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.

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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.

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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.

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Energy Balance

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

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Energy Balance Fasting/Starvation

• FastingInadequate 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

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Energy Balance Fasting/Starvation

• FastingInadequate 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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Alcohol Nutrition
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Alcohol

• For most adults, moderate consumption of alcohol
  is no more than 1 drink a day no more than 7
  drinks a week.
• Pregnant women are advised to avoid alcohol.

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Alcohol in body

• Doesnt need digestion quickly absorbed.
• About 20 is absorbed directly across walls of an
  empty stomach can reach brain within minutes.
• Stomach breaks down alcohol with its alcohol
  dehydrogenase enzyme.
• Can reduce amount of alcohol entering blood by
  about 20.

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Alcohol in small intestine

• Rapidly absorbed
• From then on, its absorbed metabolized before
  most nutrients which ensures a speedy disposal.

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Alcohol in liver

• Liver cells make alcohol dehydrogenase enzyme to
  oxidize alcohol.
• It can process about ½ ounce of ethanol per hour
• Rate is set by amount of alcohol dehydrogenase
  available.
• Extra alcohol circulates until liver enzymes are
  available to process it.

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Liver deterioration

• 1st stage fatty liver
• 2nd stage fibrosis
• 3rd stage cirrhosis (damage least reversible)

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Alcohol Metabolism
Fat (triglycerides)
Fatty acids
NAD
NADH H
NAD
NADH H
Alcohol (ethanol)
Acetyl CoA
Acetaldehyde
Acetate
Alcohol dehydrogenase
Acetaldehyde dehydrogenase
CoA
TCA Cycle
Acetyl CoA molecules are blocked from getting
into the TCA cycle by the high level of NADH.
Instead of being used for energy, the acetyl CoA
molecules become building blocks for fatty acids.
Fig. H7-3, p. 241
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Alcohol Metabolism

• Alcohol alters amino acid protein metabolism
• Synthesis of protein important to immune system
  slows down, weakening bodys defense against
  infection.
• Protein deficiency can develop.

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Alcohol Effects
Fig. H7-4, p. 242
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Alcohol Effects

• Alcohol reduces production of Anti-diuretic
  hormone which retains H2O.
• Drinking alcoholic beverages ? water loss -
  leads to dehydration.

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Alcohol Effects

• Alcohol can contribute to body fat
• promote obesity.
• High in calories
• Most often associated with central obesity
• More Kcal from alcohol - fewer Kcal from
  nutritious food

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Alcohol Effects

• Deficiency in folate thiamin
• Acetaldehyde (intermediate in alcohol metabolism)
  interferes with nutrient use.

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Alcohol Effects

• Alcohol causes stomach cells to over secrete
  gastric acid histamine.
• Beer stimulates gastric secretion, irritating
  stomach esophagus linings making them
  vulnerable to ulcer formation.

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Next

• Nutrients involved in fluid electrolyte balance
  - Chapter 12