UNIT 9 Metabolism and Energetics Part 1 of 2 (Chapter 24)

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UNIT 9 Metabolism and Energetics Part 1 of 2
(Chapter 24)

• Nutrition
• Overview of Metabolism
• Carbohydrate Metabolism

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Nutrition

• A balanced diet contains all the ingredients
  necessary to maintain homeostasis
• The absorption of nutrients from food is called
  nutrition
• Malnutrition can be avoided by eating from the
  six basic food groups
• Food Guide Pyramid (fig. 24.1b) the following
  table is presented in a different way than the
  textbook you do not need to memorize this table!
  It is presented here to perhaps help students to
  plan a healthier diet

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Nutrition

• Vitamins
• vitamins are essential components of the diet
• your body contains a significant reserve of
  fat-soluble vitamins, and thus you can overdo
  their intake
• water-soluble vitamins are components of
  coenzymes and are rapidly exchanged between the
  fluid compartments of the body because they are
  excreted from the body rapidly, it is difficult
  to take in too much of them

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Vitamins Table (this table is a modification of
Table 24.2 in your textbook)
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Nutrition

• Minerals
• essential components of the diet
• they are inorganic ions released through the
  dissociation of electrolytes
• minerals are important for 3 reasons
• ions such as Na and Cl- determine osmotic
  concentrations of body fluids
• ions in various combinations play major roles in
  important physiological processes (e.g.
  transmembrane potentials, skeletal construction,
  muscle contractions, action potential generation,
  transport of respiratory gases, etc.)
• ions are essential cofactors in a variety of
  enzymatic reactions some are needed in large
  amounts, whereas others are needed only in trace
  amounts the body has large mineral reserves
  (e.g. in the bones)

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Minerals Table (this table is a modification of
Table 24.3 in your textbook)
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Overview of Metabolism

• Metabolism is the sum total of chemical reactions
  taking place in the body
• chemical reactions provide the energy to maintain
  homeostasis and perform essential functions
• cellular metabolism provides the essential
  functions of
• periodic breakdown and replacement of organic
  components of the cell
• growth and cell division
• special processes such as secretion, contraction,
  and action potential propagation
• Catabolism - large organic molecules are broken
  down into smaller molecules
• energy is released which can be used to
  synthesize ATP or other high-energy compounds
• carbohydrates are broken down to short carbon
  chains
• triglycerides are broken down into fatty acids
  and glycerol

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Overview of Metabolism

• Anabolism - small molecules are bound together to
  create larger molecules
• anabolism is an uphill process that requires
  energy to form new chemical bonds the energy to
  drive anabolism comes from catabolism
• cells synthesize new organic components for four
  basic reasons
• to perform structural maintenance or repairs
  (metabolic turnover)
• to support growth
• to produce secretions (secretory cells must
  synthesize their products)
• to build nutrient reserves (cells store nutrients
  for when they are needed)
• Role of ATP (adenosine triphosphate)
• ATP is like currency cells earn it through
  exergonic (energy releasing) reactions and spend
  it in endergonic (energy consuming) reactions
  that drive cellular activities
• phosphorylation - transfer of a phosphate group
  (Pi), allowing a chemical reaction to be
  activated the 3 phosphates in a row (P-P-P)
  have repulsive negative charges that favor the
  removal of the last Pi (phosphate)

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Carbohydrate Metabolism

• Most cells generate ATP by breaking down
  carbohydrates, especially glucose
• Cellular Respiration (aerobic respiration)
• C6H12O6 (glucose) 6O2 ? 6 CO2 6H2O
• this catabolic reaction breaks down glucose to
  produce carbon dioxide and water, and of course
  energy (ATP)
• depending on how you do your calculations (and
  what textbook your are using), the catabolic
  breakdown of glucose by cellular respiration is
  thought to yield about 30-38 ATP thus, the yield
  is somewhat variable depending on the calculation
  method

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Carbohydrate Metabolism

• Overview of ATP Production from Carbohydrate
  Catabolism (fig. 24.3, 24.5)
• Glycolysis - occurs in the cytosol of the cell
  produces only a few ATP
• Citric Acid Cycle (CAC or Krebs Cycle) - occurs
  in the mitochondrial matrix produces only a few
  ATP
• Electron Transport Chain (ETC) - occurs in the
  mitochondrial matrix, inner mitochondrial
  membrane, and mitochondrial intermembrane space
  produces many ATP
• NAD and FAD are used as energy transfer
  molecules
• they carry electrons (e-) and hydrogen ions (H)
  to the Electron Transport Chain to optimize the
  production of ATP
• when they have the e- and H they are written as
  NADH and FADH2 when they are not carrying e- and
  H they are written as NAD and FAD

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Carbohydrate Metabolism

• Glycolysis (fig. 24.6) - breaking or lysis of
  glucose molecule occurs in the cytosol
• STEPS
• 1 ATP is used to phosphorylate glucose
• glucose is converted to fructose
• 1 ATP is used to phosphorylate fructose
• fructose is cleaved into two molecules
• the following steps (5-7) occur twice -- once
  for each of the 2 cleaved fructose molecules
• 1 NAD combines with an e- and H to get 1 NADH
  this is the step that drives glycolysis
• 1 ATP is produced
• the molecule is rearranged to produce 1 ATP and 1
  pyruvate (note because steps 5-7 are done twice,
  there are actually 2 ATP, 2 pyruvates, and 2 NADH
  produced)
• Products of Glycolysis
• 1 glucose molecule enters the pathway and
  results in the production of 2 net ATP (4
  produced minus the 2 used in steps 1 3), 2
  pyruvate, and 2 NADH

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Carbohydrate Metabolism

• Pyruvate (pyruvic acid) Metabolism - after
  glycolysis Is there enough O2 present?
• No, there is not enough oxygen - pyruvate is
  converted into lactate (anaerobic) e.g. what
  happens during strenuous exercise -- this occurs
  in the cytosol of the cell
• lactate production occurs so that the cell can
  continue glycolysis and continue to produce 2 net
  ATP e.g. this allows the skeletal muscles to
  continue for a longer period of time in the
  absence of oxygen
• NADH must be reconverted to NAD to replenish
  stores (remember that NAD drives glycolysis)
• note lactate or lactic acid has traditionally
  been thought of as a toxin that must be removed
  by the liver because its pathway contributes to
  the burn you feel when exercising however,
  recent research suggests lactate could be used as
  a fuel source and may not be so bad after all
• also when yeast replenish their NAD stores
  (from NADH) in order for glycolysis to continue,
  they produce CO2 and ethanol as by-products
  thus, beer is a result of anaerobic metabolism
  (fermentation)!

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Carbohydrate Metabolism

• Pyruvate (pyruvic acid) Metabolism - after
  glycolysis Is there enough O2 present?
• Yes, there is enough oxygen - pyruvate goes to
  the Citric Acid Cycle and Electron Transport
  Chain (aerobic) -- this occurs in the
  mitochondrion
• 1 pyruvate is transported into the mitochondrion
  where it is converted to acetyl CoA (acetyl
  coenzyme A)
• 1 NAD combines with an e- and H to get 1 NADH
• CoA is a coenzyme that helps to transport the
  acetyl unit to the Citric Acid Cycle it is just
  the postman delivering the package
• remember that 2 pyruvates were formed in
  glycolysis so for each glucose molecule that we
  started with, 2 pyruvates are converted to 2
  acetyl-CoA molecules and 2 NADH molecules are
  formed

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Carbohydrate Metabolism

• Citric Acid Cycle (CAC) (fig. 24.7) -- occurs in
  the matrix of the mitochondrion
• STEPS
• the acetyl compound is dropped off by CoA
  (coenzyme A) into the CAC
• the acetyl compound combines with oxaloacetate
  and the resulting carbon compound is rearranged
  as it goes around the CAC
• the CAC continues as long as pyruvate is
  available

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Carbohydrate Metabolism

• Citric Acid Cycle (CAC) (fig. 24.7) -- occurs in
  the matrix of the mitochondrion
• products of the CAC
• 3 NADH per turn however, the CAC turns twice
  because 2 Acetyl units were produced from
  pyruvate metabolism thus 6 NADH are formed from
  one initial glucose molecule
• 1 ATP per turn however, the CAC turns twice
  because 2 Acetyl units were produced from
  pyruvate metabolism thus 2 ATP are formed from
  one initial glucose molecule
• 1 FADH2 however, the CAC turns twice because 2
  Acetyl units were produced from pyruvate
  metabolism thus 2 FADH2 are formed from one
  initial glucose molecule
• 2 CO2 however, the CAC turns twice because 2
  Acetyl units were produced from pyruvate
  metabolism thus 4 CO2 are formed from one
  initial glucose molecule (this CO2 is waste that
  must be removed from the body!)
• notice that few ATP are produced, but many
  energy transfer molecules (NADH and FADH2) are
  made

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Carbohydrate Metabolism

• Electron Transport Chain or ETC (fig. 24.8) --
  occurs in the mitochondrial matrix, inner
  membrane, and intermembrane space
• Overview
• NADH and FADH2 are carriers of e- and H
• cytochromes (shown in figures as large, purple
  proteins within the inner mitochondrial
  membrane) are e-grabbing, H pumping
  proteins
• ATP Synthases are ATP-producing proteins that
  are located in the inner mitochondrial membrane
• STEPS
• a cytochrome of the ETC grabs e- from NADH or
  FADH2
• e- jumps from cytochrome to cytochrome (thus
  named the Electron Transport Chain)
• the e- jumping produces energy (notice this
  energy is NOT from ATP!) which pumps H out of
  the mitochondrial matrix and into the
  mitochondrial intermembrane space

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Carbohydrate Metabolism

• Electron Transport Chain or ETC (fig. 24.8) --
  occurs in the mitochondrial matrix, inner
  membrane, and intermembrane space
• STEPS
• the pumped H build a H gradient in the
  intermembrane space
• (this is the COOL part!) the ATP Synthase enzyme
  is a H channel so when it opens, H will simply
  diffuse across the mitochondrial inner membrane
  membrane and into the mitochondrial matrix (from
  high H concentration ? low H concentration)
• the natural flow of H through the ATP Synthase
  protein causes the enzyme to phosphorylate ADP
  producing ATP the process of H diffusing
  through the ATP synthase and creating ATP is
  called chemiosmosis
• When the e- gets to the end of the ETC, it must
  be taken out of the system so O2 (it only comes
  into play at the VERY end!) grabs e- and H to
  produce H2O (a clean product)
• note if the cell lacks O2 (it is anaerobic)
  the e- is stuck in the ETC and the entire system
  gets backed-up so the cell is forced to go
  through anaerobic metabolism involving only
  glycolysis

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Carbohydrate Metabolism

• Electron Transport Chain or ETC (fig. 24.8) --
  occurs in the mitochondrial matrix, inner
  membrane, and intermembrane space
• Products of the ETC
• H2O
• for every NADH get we get a maximum of about 3
  ATP, and for every FADH2 we get a maximum of
  about 2 ATP

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Carbohydrate Metabolism

• Calculation of Aerobic ATP production (assuming
  maximum possible outcome)
• energy conversions
• 1 NADH 3 ATP
• 1 FADH2 2 ATP
• 1 ATP 1 ATP
• ATP from glycolysis
• 2 ATP 2 ATP
• 2 NADH (2 X 3 ATP) 6 ATP (after being
  shuttled into the ETC)
• 8 ATP
• ATP from pyruvate metabolism
• 2 NADH (2 X 3 ATP) 6 ATP
• From CAC and ETC
• 2 ATP 2 ATP
• 6 NADH (6 X 3 ATP) 18 ATP
• 2 FADH2 (2 X 2 ATP) 4 ATP

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Carbohydrate Metabolism

• Gluconeogenesis - is the synthesis of glucose
  from non-carbohydrate precursors such as lactic
  acid, glycerol, or amino acids
• some of the steps in glycolysis are irreversible
• you cannot make glucose out of acetyl-CoA
• fatty acids and many of the amino acids cannot be
  used to create glucose because their catabolic
  pathways produce acetyl-CoA
• glucose molecules created by gluconeogenesis can
  be used for cellular respiration or to
  manufacture other simple sugars, complex
  carbohydrates, proteoglycans, or nucleic acids
• Glycogenesis (fig. 24.13) - anabolic pathway
  whereby glycogen is formed from many glucose
  molecules glycogen is an important energy
  reserve found in the liver and in skeletal
  muscles
• Glycogenolysis (fig. 24.13) - catabolic pathway
  from glycogen to glucose

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This concludes the current lecture topic

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  Metabolism and Energetics Part 2 of 2
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