7/23/2012
Introduction
Metabolism:
Transformations and
Interactions
Chapter 7
Whitney & Rolfes – Understanding Nutrition, 12th
Edition
Chemical Reactions in the
Body
 Energy Forms
 Heat (maintains a constant body temperature)
 Mechanical (moves muscles)
 Electrical (sends nerve impulses)
 Chemical (powers activities of the cells)
 Stored in food and body
 Metabolism
 Release of energy, water, and carbon dioxide
Whitney & Rolfes – Understanding Nutrition, 12th Edition
A Typical Cell
 Energy metabolism
 How body obtains & uses energy from food
 Cell type
 All cells- dependent on type
 Liver cells-most versatile and metabolically active
 Anabolism- building reactions
 Requires energy
 Catabolism-breakdown reactions
 Releases energy
Whitney & Rolfes – Understanding Nutrition, 12th Edition
Whitney & Rolfes – Understanding Nutrition, 12th Edition
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7/23/2012
Chemical Reactions in the
Body
Chemical Reactions in the
Body
 Transfer of energy in reactions – ATP
 Some energy released during breakdown of glucose, fatty acids, and
amino acids is captured in ATP
 ATP
 3 phosphate groups= negative charge, therefore vulnerable to
hydrolysis
 Hydrolyzed easily, releasing energy
 ATP provides energy for all cell activities
 Coupled reactions: Body uses ATP to transfer the energy released
during catabolic reactions to power anabolic reactions
 Efficiency 50%
 Heat loss
Whitney & Rolfes – Understanding Nutrition, 12th Edition
Capture and Release of
Energy by ATP
Whitney & Rolfes – Understanding Nutrition, 12th Edition
Chemical Reactions in the
Body
 Enzymes
 Facilitators of metabolic reactions
 Coenzymes
 Organic
 Associate with enzymes
 Without coenzyme, an enzyme cannot
function
Whitney & Rolfes – Understanding Nutrition, 12th Edition
Whitney & Rolfes – Understanding Nutrition, 12th Edition
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7/23/2012
Breaking Down Nutrients for
Energy
 Digestion
 Carbohydrates – glucose (& other
monosaccharides)
 Fats (triglycerides) – glycerol and fatty acids
 Proteins – amino acids
 Molecules of glucose, glycerol, amino acids,
and fatty acids
 Catabolism
 Carbon, nitrogen, oxygen, hydrogen
Whitney & Rolfes – Understanding Nutrition, 12th Edition
Breaking Down Nutrients for
Energy
Breaking Down Nutrients for
Energy
 Two new compounds
 Pyruvate
 3-carbon structure
 Can be used to make glucose
 Acetyl CoA
 2-carbon structure
 Cannot be used to make glucose
 Final energy pathway
 TCA cycle and electron transport chain
Whitney & Rolfes – Understanding Nutrition, 12th Edition
Breaking Down Nutrients for
Energy – Glucose
 Glucose-to-pyruvate
 Glycolysis
 2 pyruvate molecules
 Hydrogen atoms carried to electron transport
chain
 Pyruvate can be converted back to glucose
 Liver cells and kidneys (to some extent)
Whitney & Rolfes – Understanding Nutrition, 12th Edition
Whitney & Rolfes – Understanding Nutrition, 12th Edition
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7/23/2012
Glycolysis: Glucose to Pyruvate
Breaking Down Nutrients for
Energy – Glucose
 Pyruvate’s options
 Quick energy needs – anaerobic
 Pyruvate-to-lactate
 Sprinting & Weight Lifting
 Slower energy needs – aerobic
 Pyruvate-to-acetyl CoA
 Walking & Jogging
Whitney & Rolfes – Understanding Nutrition, 12th Edition
Breaking Down Nutrients for
Energy – Glucose
Whitney & Rolfes – Understanding Nutrition, 12th Edition
Pyruvate to Lactate
 Pyruvate-to-lactate
 Pyruvate accepts hydrogens
 Converts pyruvate to lactate
 Occurs to a limited extent at rest
 Produces ATP quickly
 Mitochondrial ability
 Accumulation of lactate in muscles
 Effects: drop in pH, burning and fatigue
 Cori cycle
 Path from muscle glycogen to glucose to pyruvate to lactate (to
liver) to glucose (back to muscles) to glycogen
Whitney & Rolfes – Understanding Nutrition, 12th Edition
Whitney & Rolfes – Understanding Nutrition, 12th Edition
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7/23/2012
Breaking Down Nutrients for
Energy – Glucose
Breaking Down Nutrients for
Energy – Glucose
 Pyruvate-to-Acetyl CoA
 Pyruvate enters mitochondria of cell
 Carbon removed – becomes carbon dioxide
 2-carbon compound joins with CoA becoming
acetyl CoA – irreversible
Whitney & Rolfes – Understanding Nutrition, 12th Edition
Breaking Down Nutrients for
Energy – Glucose
Whitney & Rolfes – Understanding Nutrition, 12th Edition
Paths of Pyruvate and Acetyl
CoA
 Acetyl CoA’s options – 2 functions
 Synthesize fats
 When ATP is abundant
 Any molecule that can make acetyl CoA (glucose,
glycerol, fatty acids and amino acids) can make fat.
 Acetyl CoA can be used as a building block for fatty
acids, but not to make glucose or amino acids
 Generate ATP through TCA cycle
 Hydrogens – electron transport chain
Whitney & Rolfes – Understanding Nutrition, 12th Edition
Whitney & Rolfes – Understanding Nutrition, 12th Edition
5
7/23/2012
Glucose Enters the Energy
Pathway
Breaking Down Nutrients for
Energy – Glycerol and Fatty Acids
 Glycerol-to-pyruvate
 Glycerol can be converted to form either
 Glucose
 Pyruvate
 Fatty acids-to-Acetyl CoA
 Fatty acid oxidation
 2-carbon units at a time then join with CoA
 Hydrogens and electrons carried to electron
transport chain
Whitney & Rolfes – Understanding Nutrition, 12th Edition
Fatty Acid to Acetyl CoA
Whitney & Rolfes – Understanding Nutrition, 12th Edition
Whitney & Rolfes – Understanding Nutrition, 12th Edition
Fats Enter the Energy Pathway
Whitney & Rolfes – Understanding Nutrition, 12th Edition
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7/23/2012
Breaking Down Nutrients for
Energy – Amino Acids
Amino Acids Enter the
Energy Pathway
 Deamination of amino acids
 Amino acids-to-energy
 Several entry points in energy pathway
 Converted to pyruvate (glucogenic)
 Converted to acetyl CoA (ketogenic)
 Enter TCA cycle directly (glucogenic)
 Amino acids-to-glucose
 Amino acid to pyruvate can produce glucose
 Amino acid to acetyl CoA can provide energy or make
body fat, but not produce glucose
Whitney & Rolfes – Understanding Nutrition, 12th Edition
Whitney & Rolfes – Understanding Nutrition, 12th Edition
Final Steps of Catabolism
Summary
Nutrient
Yields energy?
Yields glucose?
Yields amino
acids and body
protein
Yields fat stores?
Carbohydrate
(glucose)
Yes
Yes
Yes- when nitrogen
is available, can
yield nonessential
amino acids
yes
Lipids (fatty acids)
Yes
No
No
Yes
Lipids (glycerol)
Yes
Yes-when
carbohydrate is
unavailable
Yes-when nitrogen
is available, can
yield nonessential
amino acids
Yes
Proteins (amino
acids)
Yes
Yes- when
carbohydrate is
unavailable
Yes
Yes
Whitney & Rolfes – Understanding Nutrition, 12th Edition
 TCA or Kreb’s Cycle
 Inner compartment of mitochondria
 Circular path
 Acetyl CoA- one way only
 Oxaloacetate – made primarily from pyruvate
 First step
 Synthesized as last step
 Can not be made from fat
 Carbon dioxide release
 Hydrogen atoms and their electrons
 Niacin and riboflavin
Whitney & Rolfes – Understanding Nutrition, 12th Edition
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Kreb’s Cycle
Final Steps of Catabolism
 Electron transport chain
 Energy captures in ATP
 Series of proteins
 Electron “carriers”
 Inner membrane of mitochondria
 Electrons passed to next carrier
 Join oxygen at end of chain – water released
 ATP synthesis
Whitney & Rolfes – Understanding Nutrition, 12th Edition
Whitney & Rolfes – Understanding Nutrition, 12th Edition
Electron Transport Chain and
ATP Synthesis
Whitney & Rolfes – Understanding Nutrition, 12th Edition
Whitney & Rolfes – Understanding Nutrition, 12th Edition
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7/23/2012
Energy Balance – Feasting
 Metabolism favors fat formation
 Regardless of excess from protein, fat, or
carbohydrates
 Dietary fat to body fat is most direct and
efficient conversion
 Carbohydrate and protein have other roles to
fulfill before conversion to body fat
 Fuel mix
Whitney & Rolfes – Understanding Nutrition, 12th Edition
Feasting and Fasting
Energy Balance – Transition
from Feasting to Fasting
 Glucose, glycerol, and fatty acids are used
then stored
 Fasting state draws on these stores
 Glycogen and fat are released
 Basal metabolism
 Fasting vs. starving
 Choice vs. no choice
Whitney & Rolfes – Understanding Nutrition, 12th Edition
Energy Balance – Fasting
 Carbohydrate, fat, and protein are all
eventually used for energy
 Begin with release of glucose and fatty
acids
 Acetyl CoA
 Low blood glucose levels signal
 Fat breakdown
 Release of amino acids from muscles
Whitney & Rolfes – Understanding Nutrition, 12th Edition
Whitney & Rolfes – Understanding Nutrition, 12th Edition
9
7/23/2012
Energy Balance – Fasting
Ketone Body Formation
 Glucose needs
 Nervous system and red blood cells
 Amino acids yielding pyruvate
 Breakdown of body proteins
 Shift to ketosis
 Use fat to fuel brain
 Ketone bodies
 Slows the rate of body protein breakdown
Whitney & Rolfes – Understanding Nutrition, 12th Edition
Energy Balance – Fasting
 Ketosis causes a loss of appetite
 Slowing of metabolism
 Hormones
 Reduces energy output
 Supports weight loss but not fat loss
 Symptoms of starvation
 Physical symptoms
 Psychological symptoms
Whitney & Rolfes – Understanding Nutrition, 12th Edition
Whitney & Rolfes – Understanding Nutrition, 12th Edition
Low-Carbohydrate Diets
 Metabolism similar to fasting
 Uses glycogen stores first
 Gluconeogenesis when glycogen is depleted
 Body tissues used somewhat even when
protein provided in diet
 Urine monitoring
 Ketosis
Whitney & Rolfes – Understanding Nutrition, 12th Edition
10
7/23/2012
Alcohol in Beverages
Highlight 7
 Potential health
benefits
 Alcohols
 Glycerol
 Ethanol
Alcohol and Nutrition
 Lipid solvents
 Moderation
 Definition of “drink”
Whitney & Rolfes – Understanding Nutrition, 12th
Edition
Whitney & Rolfes – Understanding Nutrition, 12th Edition
Alcohol in the Body
Alcohol Arrives in the Liver
 Alcohol’s special privileges
 No digestion
 Quick absorption
 Slowing absorption by eating
 Stomach
 Alcohol dehydrogenase
 Women vs. Men
 Small intestine
 Alcohol takes priority over nutrients
 Liver cells
Whitney & Rolfes – Understanding Nutrition, 12th Edition
Whitney & Rolfes – Understanding Nutrition, 12th Edition
 First to receive alcohol-laden blood




Alcohol dehydrogenase
Disrupts liver activity
Can permanently change liver cell structure
Rate of alcohol metabolism
 Acetaldehyde
 Acetate
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Alcohol Metabolism
Alcohol Disrupts the Liver
 Nicotinamide adenine dinucleotide (NAD)
 Glycolysis
 TCA cycle
 Electron transport chain




Whitney & Rolfes – Understanding Nutrition, 12th Edition
Alternative Route for Acetyl
CoA to Fat
Development of fatty liver
Damage to central nervous system
Inflammation of joints
Amino acid and protein metabolism
Whitney & Rolfes – Understanding Nutrition, 12th Edition
Alcohol Arrives in the Liver
 Immune system functioning
 Alcohol interferes with drug metabolism
 Microsomal ethanol-oxidizing system
(MEOS)
Whitney & Rolfes – Understanding Nutrition, 12th Edition
Whitney & Rolfes – Understanding Nutrition, 12th Edition
12
7/23/2012
Alcohol Arrives in the Brain
Alcohol Effects on the Brain
 Sedates inhibitory nerves
 Acts as central nervous system depressant
 Blood alcohol levels and brain responses
 Death of liver and brain cells
 Depression of antidiuretic hormone (ADH)
 Loss of body water
 Loss of important minerals
Whitney & Rolfes – Understanding Nutrition, 12th Edition
Alcohol Arrives in the Brain
Whitney & Rolfes – Understanding Nutrition, 12th Edition
Alcohol and Malnutrition
 Can contribute to body fat and weight gain
 1 ounce of alcohol represents 0.5 ounce of
fat
 Central obesity- beer belly
 Substituted energy
 7 kcalories per gram
 Nutrient displacement
 B vitamins
Whitney & Rolfes – Understanding Nutrition, 12th Edition
Whitney & Rolfes – Understanding Nutrition, 12th Edition
13
7/23/2012
Alcohol’s Effects
Alcohol’s Effects
 Short-term effects
 Excessive drinking
 Heavy drinking
 Binge drinking
 Long-term effects
 Third leading preventable cause of death in
U.S.
 Sobering up
Whitney & Rolfes – Understanding Nutrition, 12th Edition
Whitney & Rolfes – Understanding Nutrition, 12th Edition
14