Chemistry II

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Ch. 24Metabolism and Energy

• Chemistry II
• MILBANK HIGH SCHOOL

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Introduction

• Photosynthesis
• 6CO2 6H2O 686kcal ? C6H12O6 6O2
• Metabolism
• Entire series of chemical reactions that keep
  cells alive
• Catabolism
• Breaking down of molecules to provide energy
• Anabolism
• Building up of molecules of living systems

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Introduction Cont

• Respiration
• All metabolic processes in which oxygen is used
  to oxidize organic matter to carbon dioxide,
  water, and energy
• Carbohydrate oxidation
• C6H12O6 6O2 ? 6CO2 6H2O 686 kcal
• Lipid oxidation
• C16H32O2 23O2 ? 16CO2 16 H2O 2340 kcal

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Sec. 24.1 ATP Universal Energy Currency

• ATP
• Adenosine triphosphate
• Figure 24.2
• Most important phosphate compound in metabolism
• Energy rich compound (energy currency of the
  cell)
• Lead to a release of energy upon hydrolysis

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ATP Cont

• ATP hydrolyis
• ATP ?ADP Pi 7.5 kcal/mol
• Reaction is reversible
• ATP is produced by processes that supply energy
• Radiant energy in plants, breakdown of food in
  animals)
• ATP is hydrolyzed by processes that require
  energy
• Synthesis of carbs, lipids, and proteins
  transmission of nerve impulses, muscle
  contractions, etc

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Sec. 24.2Digestion and Absorption of Major
Nutrients

• Catabolism
• Three stages (Fig. 24.5)
• Digestion (stage 1)
• Hydrolytic process that breaks down food
  molecules into simpler chemical units
• Absorption occurs mainly in small intestine
• Alimentary tract

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Digestion Cont

• Mechanical Aspects
• Chewed
• Saliva
• a-amylase
• Stomach
• Broken down by pepsin
• Chyme
• Moves into small intestine

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Digestion of Carbohydrates (Fig. 24.7)

• Mouth
• a-amylase attacks a-glycosidic linkages in starch
• Small Intestine
• a-amylase converts remaining starch to maltose,
  broken down by maltase to form two glucose units
• Sucrose and lactose broken down by sucrase and
  lactase form glucose, fructose, and galactose

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Digestion of Proteins (Fig. 24.9)

• Stomach
• Gastric juice
• Hydrochloric acid opens up folds in protein
  molecule
• Pepsin
• Endopeptidase that catalyzes the hydrolysis of
  peptide linkages
• Amino Acids
• Absorbed through lining of small intestine

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Digestion of Lipids (Fig. 24.13)

• Small intestine
• Bile salts from gallbladder act as emulsifiers
• Break down large molecules into small globules
  (more surface area)
• Lipases
• Mono and diglycerides absorbed
• Triglycerides transported by chylomicrons

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Absorption of Digested Nutrients

• Villi
• Small molecules
• Passive Transport
• Fatty acids, monoglycerides
• Active Transport
• Requires energy
• Monosaccharides and amino acids

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Sec. 24.3 Overview of Stage II of Catabolism

• Metabolic Pathway
• Series of biochemical reactions that enables us
  to explain how an organism converts a given
  reactant to a desired end product
• Stage II
• Conversion of subunits to a form that can be
  completely oxidized
• Acetyl-CoA
• Enzyme used in many biochemical pathways
• Starting material for biosynthesis of lipids

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Sec. 24.4The Krebs Cycle

• Krebs Cycle
• Stage III of catabolism
• AKA citric acid cycle, tricarboxylic acid cycle
• Produces ATP, NADH, FADH2, and metabolic
  intermediates for the synthesis of needed
  compounds during the cycle
• Occurs in mitochondria of the cell
• Essential for the breakdown of glucose and other
  simple sugars
• Very complex
• Utilizes condensation, dehydration, hydration,
  oxidation, decarboxylation, and hydrolysis
  reactions
• Each reaction is catalyzed by an enzyme

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Krebs Cycle Cont

• http//www.johnkyrk.com/krebs.html
• Starts when pyruvate produces Acetyl-CoA
• 1. Acetyl-CoA is the starting reactantsupplies
  the 2 carbons needed
• Acetic acid molecule linked to coenzyme A
• 2. Acetyl-CoA condenses with oxaloacetate to
  produce citrate (citric acid cycle)

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Krebs Cycle Cont

• 3. Isocitrate is reduced to NAD which leads to
  the NADH (nicotinamide adenine dinucleotide)
• (NADH used by Electron Transport Chain to create
  further ATP)
• 3 total NADH produces per 1 Acetyl-CoA
• 4. Alphaketogluterate producedmore NAD and
  acetyl-CoA added to produce two more NADH along
  with succinyl CoA
• 5. GTP is produced from GDP when another
  phosphate group is added. GTP (guanosine
  triphosphate) is easily converted to ATP11 ratio

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Krebs Cycle Cont

• 6. FAD (flavin adenine nucleotide) added to
  succinate which readily accepts and transfers
  electron pairs to Electron Transport Chain where
  FADH2 which is converted to ATPeach FAD yields 2
  ATP
• 7. Water added to fumerate to produce malate.
  NAD added, electrons are transferred to produce
  NADH and oxaloacetate
• 8. Two more pyruvate are added to start the
  Krebs Cycle all over again

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Sec. 24.5Cellular Respiration

• Occurs in mitochondria
• Mitochondria
• Power plants of the cell
• 100 to 5000 in a particular cell
• Outer and inner membranes that are folded into a
  series of ridges known as cristae
• Contains all of the enzymes and coenzymes needed
  for the Krebs cycle

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The Electron Transport Chain

• Sequence of enzymes used to oxidize coenzymes and
  transfer the resulting electrons to oxygen
• Coenzymes involved NADH and FADH2
• Closely linked to the Krebs cycle
• Very little ATP actually produced in Krebs
• Aids in oxygen participation
• Assists significantly in ATP production
• ETC consists of four complexes (I, II, III, IV)
• Each complex contains several enzymes, other
  proteins, and metal ions that each have different
  tasks

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Electron Transport Chain Cont

• CoQ (coenzyme quinone, or ubiquinone)
• Mobile electron carrier that acts as an electron
  shuttle between Complexes I and II and Complex
  III
• Reactions of the ETC are a series of
  oxidation/reduction reactions involving
  cytochromes
• Cytochromes iron-sulfur proteins and other
  molecules that ultimately reduce oxygen to water
  in Complexes III and IV
• Passes electrons through a series of protein
  complexes, moving towards increasing electron
  potential
• Electrons flow from molecules that easily
  transfer electrons to those that easily accept
  them
• Reduction Potential

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Oxidative Phosphorylation

• Metabolic pathway that uses energy released by
  the oxidation of nutrients to produce ATP
• Tightly coupled with ETC
• Used by almost all forms of life
• Highly efficient way of storing energy
• NADH and FADH2 only work if ADP is phosphorylated
  to ATP

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Oxidative Phosphorylation Cont

• Electrons are transferred from electron donors to
  electron acceptors such as oxygen, in a redox
  reaction
• Reactions release energy, which is used to form
  ATP
• http//www.wiley.com/legacy/college/boyer/0470003
  790/animations/electron_transport/electron_transpo
  rt.htm

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Theoretical Yields
Step Coenzyme Yield ATP Yield Source of ATP
Glycolysis preparatory phase -2 Phosphorylation of glucose and fructose uses 2 ATP
Glycolysis pay-off phase 4 Substrate level phosphorylation
Glycolysis pay-off phase 2 NADH 4 (6) Oxidative Phosphorylation
Oxidative decarboxylation of pyruvate 2 NADH 6 Oxidative Phosphorylation
Krebs Cycle 2 Substrate level phosphorylation
Krebs Cycle 6 NADH 18 Oxidative Phosphorylation
Krebs Cycle 2 FADH2 4 Oxidative Phosphorylation
Total Yield 36 (38) ATP Complete oxidation of one glucose molecule to CO2 and oxidation of all the reduced coenzymes
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ATP and Fibromyalgia

• Fibromyalgia
• Chronic pain in muscular system
• Afflicts 7-10 million Americans
• Mainly women ages 20-50 (3.4 of all women in US)
• Possible Cause
• Unable to process ATP and abnormally low levels
  of ATP

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Sec. 24.6Muscle Power

• Exercise
• Prolongs life
• Lowers chance of disease
• Makes muscles stronger, more flexible, more
  efficient in use of oxygen
• Muscles
• 600 in human body
• Strong muscles can do more work than weak
• Heart is a muscleexercise pulse and blood
  pressure usually decline
• Training Effect
• Person who exercises regularly is able to do more
  physical work with less strain

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Muscle Power Cont

• Muscle stimulation and contraction requires
  energy (ATP)
• Two proteins that play important roles in muscle
  movement
• Actin
• Myosin
• Acts as an enzyme for removal of phosphate group
  from ATP
• Directly liberates the energy required for
  contraction
• Actomyosin
• Contractile protein of which muscles are made

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Muscle Power Cont

• Aerobic
• In presence of oxygen
• Respiration is aerobic under usual conditions and
  during moderate exercise
• Anaerobic
• Absence of oxygen
• Oxygen debt
• Not enough oxygen available during strenuous
  exercise
• Energy obtained from carbohydrates through the
  breakdown of glycogen and anaerobic glycolysis

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Muscle Power Cont

• Muscle Tissues
• Slow twitch (Type I)
• Light and moderate activity
• Respiratory capacity is high
• Can provide much energy via aerobic pathways
• Geared to oxidative phosphorylation
• High myoglobin
• Heme-containing protein in muscle that stores
  oxygen obtained from hemoglobin
• Needs high levels of oxygen
• Many mitochondria in Type I muscle cells
• Long, sustained activities (marathon runners)

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Muscle Power Cont

• Muscle Tissues Cont
• Fast-twitch (Type IIB)
• Opposite characteristics of slow twitch
• Low respiratory capacity
• Low myoglobin levels
• Fewer mitochondria
• Generates ATP rapidly
• Short bursts of activity, muscles fatigue rapidly
• Sprinters, weightlifters

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Muscle Power Cont

• Training
• Endurance
• Increases size and number of mitochondria
• Increases level of enzymes required for transport
  and oxidation of fatty acids, the Krebs cycle,
  and oxidative phosphorylation
• Doesnt increase muscle size significantly
• Strength
• No increase in mitochondria
• Causes neovascularization which increases
  efficiency of lactic acid removal
• Lactic acid inhibits ATP production and use

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Creatine Phosphate

• Storage form of energy in muscles of vertebrates
• As ATP is utilized, creatine phosphate reacts
  with ADP to produce more ATP and creatine
• Concentration limitedused up after about 10-15
  seconds of strenuous exercise
• Found in high amounts in meat and fish
• Naturally produced in body in synthesis of
  arginine
• Creatine supplements may increase muscle
  performance and body mass