Download A. Metabolism

Chapter 25
Metabolism and Energetics
I. An Overview of Metabolism
A. Metabolism
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Metabolism is all the chemical reactions that occur in an organism
Cellular metabolism
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Cells break down excess carbohydrates first, then lipids
Cells conserve amino acids
40% of the energy released in catabolism is captured in ATP
• Rest is released as heat
B. Anabolism
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Performance of structural maintenance and repairs
Support of growth
Production of secretions
Building of nutrient reserves
C. Cells and Mitochondria
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Cells provide small organic molecules for their mitochondria
Mitochondria produce ATP used to perform cellular functions
II. Carbohydrate Metabolism
A. Most cells generate ATP through the breakdown of carbohydrates
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Glycolysis
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Aerobic metabolism (cellular respiration; pyruvate oxidation, TCA cycle, ETC)
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One molecule of glucose = two pyruvate ions, two ATP, two NADH
Two pyruvates = 34 ATP
The chemical formula for this process is
C6H12O6 + 6 O2  6 CO2 + 6 H2O
B. Glycolysis
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The breakdown of glucose to pyruvic acid
This process requires:
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Glucose molecules
Cytoplasmic enzymes
ATP and ADP
Inorganic phosphate
NAD (nicotinamide adenine dinucleotide)
The overall reaction is:
Glucose + 2 NAD + 2 ADP + 2Pi 
2 Pyruvic acid + 2 NADH + 2 ATP
C. Mitochondrial ATP Production
(cellular respiration)
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Pyruvic acid molecules enter mitochondria
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Broken down completely in TCA cycle
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Hydrogen atoms passed to coenzymes
• Decarboxylation
• Oxidative phosphorylation
D. Oxidative phosphorylation and the ETS
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Requires coenzymes and consumes oxygen
Key reactions take place in the electron transport system (ETS)
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Cytochromes of the ETS pass electrons to oxygen, forming water
The basic chemical reaction is:
2 H2 + O2  2 H2O
E. Energy yield of glycolysis and cellular respiration
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Per molecule of glucose entering these pathways
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Glycolysis – has a net yield of 2 ATP
Electron transport system – yields approximately 28 molecules of ATP
TCA cycle – yields 2 molecules of ATP
F. Synthesis of glucose and glycogen
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Gluconeogenesis
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Glycogenesis
• Synthesis of glucose from noncarbohydrate precursors
• Lactic acid, glycerol, amino acids
• Liver cells synthesis glucose when carbohydrates are depleted
• Formation of glycogen
• Glucose stored in liver and skeletal muscle as glycogen
• Important energy reserve
III. Lipid Metabolism
A. Lipid catabolism
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Lipolysis
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Triglycerides are split into glycerol and fatty acids
• Glycerol enters glycolytic pathways
• Fatty acids enter the mitochondrion
Beta-oxidation
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Lipids broken down into pieces that can be converted into pyruvate
Breakdown of fatty acid molecules into
2-carbon fragments
Enter the TCA
Lipids and energy production
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Cannot provide large amounts in ATP in a short amount of time
Used when glucose reserves are limited
B. Lipid synthesis (lipogenesis)
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Almost any organic molecule can be used to form glycerol
Essential fatty acids cannot be synthesized and must be included in diet
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Linoleic and linolenic acid
IV. Protein Metabolism
A. Amino acid catabolism
• If other sources inadequate, mitochondria can break down amino acids
• TCA cycle
• removal of the amino group (-NH2)
• Transamination – attaches removed amino group to a keto acid
• Deamination – removes amino group generating NH4+
• Proteins are an impractical source of ATP production
B. Protein synthesis
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Essential amino acids
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Cannot be synthesized by the body in adequate supply
Nonessential amino acids
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Can be synthesized by the body via amination
• Addition of the amino group to a carbon framework
V. Diet and Nutrition
A. Diet and Nutrition
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Nutrition
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Absorption of nutrients from food
Balanced diet
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Contains all the ingredients necessary to maintain homeostasis
• Prevents malnutrition
B. Food
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Food groups and food pyramids
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Used as guides to avoid malnutrition
C. Food Groups
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Six basic food groups of a balance diet arranged in a food pyramid
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Milk, yogurt and cheese
Meat, poultry, fish, dry beans, eggs, and nuts
Vegetables
Fruits
Bread, cereal, rice and pasta
• Base of pyramid
Fats, oils and sweets
• Top of pyramid
D. Nitrogen balance
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N compounds contain nitrogen
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Amino acids, purines, pyrimidines, creatine, porphyrins
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Body does not maintain large nitrogen reserves
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Nitrogen balance is an equalization of absorbed and excreted nitrogen
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Dietary nitrogen is essential
E. Minerals
• Act as co-factors in enzymatic reactions
• Contribute to osmotic concentrations of body fluids
• Play a role in transmembrane potentials, action potentials
• Aid in release of neurotransmitters and muscle contraction
• Assist in skeletal construction and maintenance
• Important in gas transport and buffer systems
• Aid in fluid absorption and waste removal
F. Vitamins
• Are needed in very small amounts for a variety of vital body activities
• Fat soluble
• Vitamins A, D, E, K
• Taken in excess can lead to hypervitaminosis
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Water soluble
• Not stored in the body
• Lack of adequate dietary intake = avitaminosis
VI. Bioenergetics
A. Introduction - Bioenergetics
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The study of acquisition and use of energy by organisms
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Energy content of food expressed in Calories per gram (C/g)
B. Food and energy
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Catabolism of lipids yields 9.46 C/g
Catabolism of proteins and carbohydrates yields ~4.7 C/g
C. Metabolic rate
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Total of all anabolic and catabolic processes underway
Basal metabolic rate (BMR) is the rate of energy used by a person at rest