Download - MCB 3020, Spring 2005
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MCB 3020, Spring 2005
Chapter 5: Nutrition and Metabolism I
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2The Generation of Energy:I. Metabolism (metabolic reactions)II. NutrientsIII. EnergyIV. Review of free energyV. EnzymesVI. Energy generation: oxidation and reduction reactions
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3I. Metabolism (metabolic reactions)
• all of the biochemical reactions in a cell
• includes catabolic (degradative) and anabolic (biosynthetic) reactions
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2. Anabolism• the biosynthesis of complex molecules from simpler compounds with the input of energy
1. Catabolism• the breakdown of complex molecules into simpler compounds with the release of energy
ENERG
Y
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Catabolismenergysource
wasteproducts
ATP,reductant
small molecules
Anabolism macromolecules(polymers)
B. Catabolic reactions generate ATP. ATP is used for biosynthesis and cell maintenance.
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6C. ATP is called the energy currency of the cell.
• anabolic (biosynthetic) reactions require energy in the form of ATP.
• catabolic reactions release energy and store it as ATP.
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7II. Nutrition
1. macronutrients2. micronutrients3. growth factors
chemicals taken up from environment and used for cellular reactions
A. Nutrients
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81. Macronutrients: chemicals taken up and required in relatively large amounts
CHONPS
K+
Mg2+
Na+
Ca2+
Fe2+/Fe3+
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CHONPSFe
nucleic acids, phospholipids
cysteine, methionine, vitamins like CoA
amino acids, nucleic acids, cell walls, etc.
many organic molecules
Where do macronutrients occur in cells?
Electron transport proteins
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102. Micronutrients: inorganic chemicals required in small amounts
• also called trace elements• usually metals in metabolic enzymes
Co (the metal center of vitamin B12)Cu (found in electron transport proteins)Se (found in selenocysteine)Ni, Zn, Mn, V, W
• examples
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113. Growth factors: organic chemicals required in small amounts by some (but not all) cells
a. Examples:vitamins, like B1, B6, B12, biotinsome amino acidspurines, pyrimidines
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12b. Many vitamins are precursors of coenzymes used in metabolism. Vitamin CoenzymeB2 (riboflavin) FAD, FMNniacin (nicotinic acid) NAD, NADPB12 cobalaminfolate tetrahydrofolate
Coenzymes are molecules that work together with enzymes to catalyze chemical reactions.
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13B. Cells can be grown in laboratory cultures.
Two classes of culture media1. Chemically defined medium
exact chemical composition is known;contains precise amounts of pure chemicals added to distilled water
2. Complex (undefined) mediumexact chemical composition is not known;contains digests of milk proteins, yeast, soybeans, etc. that have growth factors?
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14Different organisms can have vastly different nutritional requirements.
Escherichia coli can grow on a simple defined medium. It can synthesize most of the organic molecules required for biosynthesis.
Leuconostoc mesenteroides needs added amino acids, purines, pyrimidines, and vitamins for growth because it cannot synthesize these molecules by itself.
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15Laboratory growth medium for E. coliK2HPO4
KH2PO4
(NH4)2SO4
MgSO4
CaCl2Glucose
mineralsH2O
Glucose, H2O, K2HPO4, KH2PO4, NH4Cl, MgSO4, Na acetate, alanine arginine asparagine, aspartate, cysteine, glutamate, glutamine, glycine, histidine, isoleucine, leucine, lysine, methionine, phenylalanine, proline, serine, threonine, tryptophan, tyrosine, valine, adenine, guanine, uracil, xanthine biotin, folate, nicotinic acid, pyridoxal, pyridoxaminepyridoxine, riboflavin, thiamine, pantothenate, para-aminobenzoic acid, trace elements
Growth medium for L. mesenteroides
(don't memorize)
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ENERGY
Why do cells need energy?
Where do organisms get energy?
How do cells use energy sources?
the ability to do work
III. Energy
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17A. Why do cells need energy?
• growth and biosynthesis• motility • nutrient uptake• reproduction• maintenance, etc.
polysaccharidesnutrients
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18B. Where do organisms get energy?
Chemotrophschemicals
Phototrophslight
Chemoorganotrophsorganic chemicals
(eg. sugars)
Chemolithotrophsinorganic chemicals (eg. H2, NH3, H2S)
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19C. How do chemotrophs derive energy from energy sources?
Remember: oxidation is the loss of electrons
Organisms capture energy that is released when an organic or inorganic chemical is oxidized.
glucose + 6 O2 6 CO2 + 6 H2O G°’ = - 686 kcal/mol
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kcal (kilocalorie)• a unit of energy
D. Units of energy
• amount of heat energy required to raise the temperature of 1 kg
of water 1°C• 1 kcal = 4.184 kilojoules (kJ)• 1 kcal = 1 “nutritional” calorie
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• energy that is available to do useful work
IV. Review of free energy (G)
change in free energychange in enthalpy (total energy)
change in entropy
Review from General Chemistry: G = H - T S
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22For biological reactions, the standard conditions for measuring the change in free energy (G°’ ) are
• 25°C• pH 7• reactants and products initially present at 1 M concentration
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23A. The G°’ can tell us about the direction a reaction tends to occur.
A + B C + D
FreeEnergy
Progress of reaction
A + B
C + D G°’ is negative
If G°’ is (-)products have lower free energy than substrates
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24 1. If G°’ is negative• free energy is released• the reaction is exergonic• the reaction tends to occur in the direction written
Examples: H2 + 1/2 O2 H2O - 57 kcal/mol glucose + 6 O2 6 CO2 + 6 H2O - 686 kcal/mol ATP + H2O ADP + PO4
- - 7.3 kcal/mol
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25 2. If G°’ is positive• energy input is usually required• the reaction is endergonic• the reaction does not tend to occur in the direction written
FreeEnergy
Progress of reaction
A + B
C + D If G°’ is (+)products have higher freeenergy thansubstrates
G°’ is positive
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26B. Coupled reactionsExergonic reactions (-G°’) can be used to "drive" endergonic reactions (+G°’) to make the overall "coupled" reaction favorable.
A B Go’ = +20 kJ/mole Reaction 1
Reactions 1 and 2 coupledA + C B + D Go’ = -10 kJ/mole
C D Go’ = -30 kJ/mole Reaction 2
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A + B C + D
C. Equilibrium
• equilibrium occurs when the rates of the forward and reverse reactions are equal
• usually at equilibrium, the concentrations of the products and reactants are not equal
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28C. Equilibrium (contd.)
• if the G°’ is large and negative, equilibrium lies towards product; very little of the reactants remain
A + B C + D
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H2 + 1/2 O2 H2O G°’ = - 57 kcal/mol
If H2 and O2 are mixed without a catalyst, no detectable amount ofwater is formed in our lifetime. Why?
D. “Activation energy” is required to break bonds.
Because before water is formed, chemical bonds have to be broken.
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30Activation energy: energy required to bring molecules to the reactive state
FreeEnergy
Progress of reaction
H2 + 1/2 O2
H2O
Activationenergy
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Activationenergy of catalyzed reaction
E. Catalystschemicals that increase the reaction rate by lowering the activation energy
FreeEnergy
Progress of reaction
H2 + 1/2 O2
H2OG
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• increase the rate of the reaction, • but DO NOT change the G, • DO NOT change the equilibrium • many reactions in living organisms are catalyzed by biological molecules called enzymes
Properties of catalysts
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33V. Enzymes• biological catalysts
• most enzymes are proteins, a few are nucleic acids (ribozymes or catalytic RNAs)
• most enzymes catalyze specific reactions or sets of reactions
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34A. Enzyme catalysis
Substrate(s) first combine with the enzyme to form an enzyme-substrate (E-S) complex.
S
E
Substrates (S): reactants, starting materials
S
Enzyme (E): usually a protein E
Products (P): ending materials P
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35B. Typical enzymatic reaction sequence:
E + S E-S E-P E + P
Enzyme-substrate complex
At end of reaction, the enzyme returns to its original form
S
ES
EP
EP
E
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36C. Important notes on enzymes• Enzymes DO NOT alter the equilibrium of the reaction. • Enzymes can catalyze exergonic and endergonic
reactions.• Substrates bind at the enzyme active site.• Many enzymes contain nonprotein components:
coenzymes (loosely bound) or prosthetic groups (tightly bound).
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37Important notes on enzymes (contd.)
• Enzymes tend to be sensitive to pH and temperature.
• Enzymes are often named after the substrate or the reaction catalyzed, plus the ending “-ase” (eg. cellulase breaks down cellulose, ATP synthase makes ATP).
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38D. Sometimes enzymes change shape when substrates bind (“induced fit”)glucose + hexokinase (a protein used in glycolysis)
Active site
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39E. Metabolic reactions are catalyzed by enzymes.
glucose
ethanol + CO2
12 enzymes
O
OHHOOH
OH
CH2OH
glucose fermentation (anaerobic)
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40Respiration of glucose (aerobic)
glucose + 6 O2
6 CO2 + 6 H2O
~30 enzymes~36 [ADP + Pi]
~36 ATP
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For chemotrophs, utilization of a chemical energy source involves oxidation and reduction reactions (redox reactions).
VI. Energy generation: A. Oxidation and reduction reactions
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42Oxidation and reduction reactions
“LEO says GER”
Gain of Electrons = Reduction1/2 O2 + 2 H+ + 2 e- H2O
Loss of Electrons = Oxidation
Glucose (C6H12O6) 12 H+ + 12 e- + 6 CO2
H2 2 H+ + 2 e-
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43B. Complete redox reactions can be divided into oxidative and reductive half reactions.
Oxidative half-reaction: H2 2 H+ + 2 e-
e- donor e- acceptor
H2 and H+ are called a redox couple.
Reductive half-reaction: 1/2 O2 + 2 H+ + 2 e- H2O
Complete reaction: H2 + 1/2 O2 H2O
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44C. Because electrons do not typically exist alone in solution, complete redox reactions need
an electron acceptor (eg. O2) an electron donor (eg. H2) and
primary electron donor
terminal e- acceptor
glucose + 6 O2 6 CO2 + 6 H2O
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45D. Energy is released when an energy source is oxidized.
H2 + 1/2 O2 H2O - 57 kcal/mol
H2 2 H+ + 2 e-
Oxidative half-reaction
ENERG
Y
glucose + 6 O2 6 CO2 + 6 H2O - 686 kcal/mol
G°’
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46E. Cells oxidize energy sources and harness the energy released to make ATP.
Explosive release of energy as heat can't be harnessed to do work
H2 1/2 O2
H2O
Electrontransportsystem
H2
2 H+ 2 e-
Hydrogen atoms separated intoprotons & electrons
H2O
2 e-2 H+ 1/2 O2
Some released energy is harnessed to make ATP
H2 + 1/2 O2 H2O G°’ = - 57 kcal/mol
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47Study Objectives1. Understand metabolism, catabolism, anabolism, and the role of ATP in metabolism.2. Know the differences between macronutrients, micronutrients, and growth factors. Know where they occur in biological molecules and the examples presented in class.3. Contrast defined and complex media. Know one reason why nutritional requirements differ among organisms.4. Give examples of energy-requiring processes in the cell.5. Define chemotrophs, phototrophs, chemoorganotrophs, chemolithotrophs. (eg. chemotrophs are organisms that use chemicals as an energy source.) Given an energy source (eg. NH3), be able to identify the type of catabolism being used (eg. chemolithotrophy).6. Understand the terms kcal and free energy. What predictions can be made from the Go' value of a reaction. What is reaction coupling and how can it be used by the cell?
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487. Understand equilibrium, activation energy, catalysts and their properties. Understand the effect of catalysts on equilibrium. Can catalysts make a nonspontaneous reaction spontaneous?8. Understand enzymes and all the properties presented in class. What is the function of enzymes in the cell?9. Define oxidation, reduction, half reactions, redox couples, electron donor, electron acceptor.10. Describe how cells derive energy from an energy source. What are the roles of the primary electron donor and the terminal electron acceptor?
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49Energy generation and glycolysis
I. Oxidation of the energy sourceII. Reduction of NAD+III. Making ATP through substrate level phosphorylationIV. GlycolysisV. Reoxidation of NADH
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glucosewasteproducts
ATP
I. Oxidation of the energy source: A. Energy released when an energy source is oxidized can be conserved in the form of high energy chemical bonds.
oxidation
ADP + Pi
chemicals with high energy bonds
ENER
GY
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energy sourceprimary electron donorglucose
one or more intermediate electron carriers, e.g. NAD+
electrons[carbon]
terminal electron acceptor (the last molecule to accept electrons), e.g. O2
B. Electrons are transferred during catabolism.
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52C. Redox terminology1. Oxidation is the loss of electrons
Compounds become oxidized afterlosing electrons.
An oxidant is a compound thataccepts electrons. It canoxidize other compounds. TB
Glucose (C6H12O6) 12 H+ + 12 e- + 6 CO2
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2. Reduction is the gain of electrons
Compounds become reduced aftergaining electrons.
A reductant is a compound thatdonates electrons. It can reduceother compounds.
TB
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A(red) A(ox)B(ox) B(red)+ +
electron donor
electron acceptor
D. Redox reactions
TBglucose + 6 O2 6 CO2 + 6 H2Oe.g.
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551. Redox couples are substances interconverted by redox reactions
Note: the oxidized substance is written to the left. Two redox couples are needed for a redox reaction.TB
A(red) A(ox)B(ox) B(red)+ +
A(ox)/A(red) is a redox couple (CO2/ glucose)
B(ox)/B(red) is a redox couple (O2/ H2O)
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pyruvate can be reduced to lactate lactate can be oxidized to pyruvate
Example: pyruvate and lactate are a redox couple.
pyruvate/lactate
Eo' (reduction potential) = -0.19 volts
pyruvate + 2H+ + 2e- lactate
half-reaction (hypothetical)
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(Eo') is a measure of the tendency of a redoxcouple to donate electrons in a redox reaction.
2. Redox couples have associated standard reduction potentials (Eo').
TB
Eo' values can be summarized in a "table of reduction potentials."
In this table, the REDUCED substance of theredox couple is written on the right.
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583. Partial table of reduction potentials
Oxidized form / Reduced form Reduction potentialEo' (Volts)
CO2 / glucose (C6H12O2) (- 0.43)2 H+ / H2 (- 0.42)NAD+ / NADH (- 0.32)
NO3- / NO2- (+ 0.42)
pyruvate / lactate (- 0.19)
O2 / H2O (+ 0.82)
fumarate / succinate (+ 0.03)
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59a. In a table of reduction potentials, the reduced compound of redox couple with a more negative Eo'
can give electrons to
the oxidized compound of a redox couple lower in the table
electr
ons
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Eo’ = -0.19 Vpyruvate/lactate
b. Example
In a redox reaction, NADH can donate electrons to pyruvate.
NADH + pyruvate NAD+ + lactate
Two redox couples
NAD+/NADH Eo’ = –0.32 V
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Reduction potentialEo' (Volts)
CO2 / glucose (C6H12O2) (- 0.43)
O2 / H2O (+ 0.82)
electr
ons
Eo'
4Eo' is the change in standard reduction potential.
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625. A large Eo' corresponds to a large Go'. Go' = -nF Eo' (don't memorize equation)
Reduction potentialEo' (Volts)
CO2 / glucose (- 0.43)
pyruvate / lactate (- 0.19)
O2 / H2O (+ 0.82)
small Eo'= -0.24 V
not much energy
large Eo'= -1.25 V
(lots of energy)
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636. Electrons can be transferred to intermediate electron carriers in a series of redox reactions.
A(red) A(ox)
B(red)B(ox)
C(red) C(ox)
A(red) = primary electron donor (energy source)
C (ox) = terminal electron acceptorB = intermediate electron carrier
(glucose) (CO2)
(O2)(H2O)
TB
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64II. NAD+ is an intermediate electron carrier.
A(red) A(ox)
NADHNAD+
C(red) C(ox)
"A" and "C" can be many numerous compoundsmany of which are catabolic intermediates.
TB
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65A. NAD+ and NADP+
1. NAD+nicotinamide adenine dinucleotidecarries 2 electrons and a proton;usually involved in catabolic rxns
2. NADP+similar to NAD+ with an extra PO4
-;usually involved in biosynthesis
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66
O
OH HO
adenine
P-P O
OHHO
N
H
NAD+
O
NH2
+
B. The NAD+/NADH couple (Eo' = –0.32V)
H
N
R
H
NADH + H+
O
NH22e– + 2H+
+ H+
TB(look at but don't memorize structures)
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67
NAD+ is made by cells in limitedamounts.
The reduction of NAD+ to NADH depletes NAD+.
NAD+ must be regenerated by theoxidation of NADH to NAD+.
C. NAD+ must be recycled
TB
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68III. Making ATP by substrate level phosphorylation (SLP)
TB
A. Substrate Level Phosphorylation:
Example
PEP + ADP pyruvate + ATP
*ATP synthesis driven by a high-energy compound, NOT the proton motive force (PMF).
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69
COO-
CO~ P
CH2
OP ~ P OCH2 R
OP ~ P ~ P OCH2 R
PEP + ADP
COO-
C=O
CH3
pyruvate + ATP
Ex. of Substrate level phosphorylation
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70B. High energy compounds
Compounds that can release large amounts of energy when they react.
Catabolism conserves energy in theform of high energy compounds which can be used to perform cellular work.
TB
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71High energy compounds
phosphoenolpyruvate1,3-bisphosphoglycerateacetyl phosphatesuccinyl CoA, acetyl CoA ATPADP
Go' of hydrolysis(kJ / mol)
-52-52-45
-32-32
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72
ATP + H2O ADP + Pi
Go' = - 32 kJ / mol
1. ATP is the most important high energy compound in cells.
TB
2. ADP
ADP + H2O AMP + PiGo' = – 32 kJ/mol
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73
PEP + H2O pyruvate + Pi
Go' = - 52 kJ / mol
3. Phosphoenolpyruvate (PEP)
COO-CO~PO3
-
CH2
COO-C=O +CH3
PO43-
TB
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744. 1,3-bisphosphoglycerate (BPG)
BPG + H2O 3-phosphoglycerate + Pi
Go' = – 52 kJ/mol
The hydrolysis of the above high energycompounds is coupled to energy-consuming cellular reactions to drive them forward.
TB
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75SLP and glycolysis
During glycolysis, the hydrolysis of the high-energy compounds PEP or 1,3-bisphosphoglycerate (BPG)is "coupled" to ATP synthesis. This is an example of SLP.
PEP + ADP pyruvate + ATPTB
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76 AMP and glucose-6-phosphate are examples of compounds with low energy bonds.
Go' of hydrolysis -14 kJ / mol
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77IV. Glycolysis
• one pathway of making energy from glucose• glucose is partially oxidized to pyruvate• NAD+ is the intermediate electron carrier that accepts the electrons• ATP is made by substrate level phosphorylation (SLP) • glycolysis occurs in the cytoplasm
Glucose 2 pyruvate + 2 NADH + 2 ATP
A. Overall reaction of glycolysis:
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78
glucose
2 pyruvate (C3)
ATPATP
2 ATP2 ATP
2 NADHredox step
ATP synthesis by SLP
energy input
hexose splitting
(C6)B. Important steps in glycolysis
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79
glucose
glucose-6-phosphate
ATP*
ADP
(1)
(1)
hexokinase
energy input*TB
C. Individual steps of glycolysis
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80glucose-6-phosphate(1)
fructose-6- phosphate(1)
TB
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81fructose-6- phosphate
fructose-1,6- bisphosphate
ATP*
ADP
(1)
(1)
energy input*TB
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82fructose-1,6- bisphosphate
glyceraldehyde3- phosphate
dihydroxyacetone phosphate
(1)
splitting reaction
TB
(C3 molecule) (C3 molecule)
(C6 molecule)
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83 glyceraldehyde-3- phosphate
1,3-bisphosphoglycerate
(2) NAD+
(2) NADH + (2) H+
Pi
Redox reaction
(2)
(2)
TB
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841,3 bisphosphoglycerate (BPG)
3-phosphoglycerate2 ATP
2 ADP
substrate level phosphorylation
(2)
(2)
TB
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852-phosphoglycerate
phosphoenolpyruvate
(2)
(2)
TB
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86phosphoenolpyruvate
2 ATP
2 ADP
pyruvate
substrate level phosphorylation
(2)
(2)
TB
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87V. Reoxidation of NADH to NAD+
Important: in the cellNAD+ is limited, so NADH must be reoxidized
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88 A. The reoxidation of electron carriers
1. Fermentation2. Aerobic respiration3. Anaerobic respiration
All organisms on earth that have beenstudied use one or more of 3 generalmethods to reoxidize electron carriers
Organisms that use all three methodsusually prefer aerobic respiration. TB
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89
glucose 2 pyruvate
2 NADH + H+2 NAD+
Glycolysis
re-oxidation1. Fermentation reactions2. Aerobic respiration3. Anaerobic respiration TB
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90 1. Fermentation
TB
catabolic process in which NADH is re-oxidized using a compound derived from the growth substrate
•
ATP synthesis is by substrate level phosphorylation (SLP) only.
•
Generally used when O2 is not available
•
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91a. Fermentation producing ethanol
2NADH + H+2NAD+
2 CO2
2 Acetaldehyde
2 NADH + H+2 NAD+glucose 2 pyruvate
TB
2 Ethanol
2 CH3CH2OH
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92b. Fermentation producing lactate
2NADH + H+
2NAD+
2 lactate
2 NADH + H+2 NAD+glucose 2 pyruvate
TB
COO-C=O CH3
COO-HC-OH
CH3
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93Fermentation does not use electron transport chains for the reoxidation of electron carriers. Cytoplasmic enzymescatalyze the reoxidation of NADH.
Some of the products of fermentationare valuable.
Many different fermentations are known.
TB
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94Study objectives1. Describe how cells derive energy from an energy source. What are the roles of the primary electron donor and the terminal electron acceptor? 2. Understand redox reactions and the terminology used to talk about them.3. Understand redox couples.4. Be able to use the table of standard reduction potentials to predict the direction of a redox reaction.5. Understand the relationship between Eo' and Go'. (Basically, a large Eo' corresponds to a large Go' ) You will NOT be asked to do a calculation.6. Understand how NAD functions in cells.7. Compare and contrast NAD and NADP.8. Understand high energy compounds. Know the examples of high energy and presented in class. Know that GTP is a high energy compound.9. Describe substrate level phosphorylation. Understand the difference between substrate level phosphorylation and oxidative phosphorylation.10. Understand the process of glycolysis. Know the overall reaction. Memorize all the steps. Know which steps involve energy input, hexose splitting, redox reactions, substrate level phosphorylation, ATP synthesis.
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9511. What are the 3 general methods microbes use to reoxidize reduced electron carriers formed during catabolic processes? 12. Why must reduced electron carriers be reoxidixed?13. Understand fermentation and its purpose. Memorize the examples and reactions presented in class.
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96Respiration and the TCA cycle:I. Aerobic respiration of glucoseII. TCA cycleIII. Electron carriersIV. Electron transport systemV. Oxidative phosphorylation
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97
Growth substrates
Oxidized products
Reoxidation of NADH
Oxidized electron carriers
Reduced electron carriers
re-oxidation1. Fermentation2. Aerobic respiration3. Anaerobic respiration TB
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98I. Aerobic respiration of glucose
one way to get more energy out of glucose than by fermentation
glucose + 6 O2 6 CO2 + 6 H2O
Respiration: ~36 to 38 ATP / glucose
Fermentation: ~2 ATP / glucose
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99A. Respiration1. Oxidation of an organic energy source in the presence of an external terminal electron acceptor
glucose + 6 O2 6 CO2 + 6 H2O
organic energy source
"external" terminal electron acceptor
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1001. terminal electron acceptor:
the last molecule to receive theelectrons during catabolism
2. "external" terminal electron acceptor:
terminal electron acceptor that is NOT derived from the energy source
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101B. Aerobic respiration 1. Terminal electron acceptor is O2
Anaerobic respiration "external" terminal electron acceptor is NOT O2 eg. NO3
- (nitrate), Fe3+, SO4
-, CO2, CO3
2-, succinate or another organic molecule
O2
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102B. Aerobic respiration (continued) 2. Reoxidation of reduced electron carriers with O2 occurs via intermediate electron carriers arranged as electron transport chains (respiratory chains).
3. ATP synthesis occurs mainly by oxidative phosphorylation
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103 C. Aerobic respiration of glucose complete oxidation of glucose to CO2
higher energy yield than fermentation
Respiration: 36 to 38 ATP
Fermentation: 2 ATP
C6H12O6glucose
6 CO2 + 6 H2 O2 C3H6O3
6 O2
lactic acid
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104D. Oxidative phosphorylation (electron transport phosphorylation)
ATP synthesis at the expense of a proton gradient (proton motive force) produced across a membrane by an electron transport system
H+
H+
ADP + Pi
ATPH+
H+
H+H+H+
H+
H+
H+
Cytoplasmic membrane in prokaryotesInner mitochondrial membrane in eukaryotes
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105
NADH
glucose
pyruvate
protonmotive force
membraneoutsideacCoA
NADH
E. Overview: aerobic glucose respiration
TCA NADH
NADH
NADH
FADH2
GTP
2H + + 1/2O2
H2O
ADP + Pi
ATP
H+
NAD+ 2 H+
2 H+
H+
e-
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106
Glucose respiration 1. Glycolysis 2. Conversion of pyruvate (3C) to acetyl CoA (2C) 3. Oxidation of acetyl CoA in TCA cycle 4. Reoxidation the intermediate electron acceptors 5. ATP synthesis by oxidative phosphorylation
II. Glucose respiration to CO2 and the TCA cycle glucose
pyruvate
TCA CO2
CO2
CO2 acCoA2
NADH
NADH
1
NAD+
4
3
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107
2 CoA + 2 NAD+ 2 NADH
2 acetyl CoA (2C)2 CO2
2 pyruvate (3C)
glucose
glycolysis
A. Conversion of pyruvate to acetyl CoA• pyruvate oxidation produces NADH• decarboxylation makes CO2
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108B. Oxidation of acetyl CoA in the TCA cycle (tricarboxylic acid cycle)
also called the citric acid cycle
• two carbons are oxidized to CO2 per acetyl CoA • 3 NADHs and 1 FADH2 are made per acetyl CoA• one GTP is made by substrate level phosphorylation
TCA
acetyl CoA
CO2
CO2
NADH
FADH2
GTP
NADH
NADH
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109
acetyl CoA (2C)
(6C)
(5C)(4C)
CH2COO-
HOCH2COO-
CH2COO-
oxaloacetate citrate COO-
O=CH CH2
COO-
OCH3C~SCoA
1. Acetyl CoA (C2) condenses with oxaloacetate (C4) to form citrate (C6).
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110
acetyl CoA (2C)
NAD+
NADHCO2
CO2
NADH
NAD+
pyruvate (3C) CO2
CoA + NAD+ NADH
FADH2
FAD
NAD+NADH
GTP GDP + Pi
CoA*SLP
(6C)
(5C)(4C)
2. Redox reactions, decarboxylations, SLP
citrateoxaloacetate
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111
acetyl CoA (2C)
citrate
isocitrate
NADH
NAD+ CO2
succinyl CoA
succinate
fumarate
malate
oxaloacetate
NADHCO2
NAD+
GTP GDP + Pi
CoASLP
FADH2
FAD -ketoglutarate
NAD+NADH
(6C)
(5C)(4C)
3. The TCA Cycle
aconitate
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1124. In the TCA cycle, there are 4 redox reactions (3 NADH and 1 FADH2) and two decarboxylations.
Four oxidative steps in the TCA cycle
isocitrate -ketoglutarate -ketoglutarate succinyl CoAsuccinate fumarate (FADH2) malate oxaloacetate2 decarboxylations (CO2 removed)
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113d. There is one substrate level phosphorylation in the TCA cycle.
GTP is made and is easily converted to ATP
succinyl CoA succinate
GDP + Pi GTP CoA
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114e. Sum of reactions for pyruvate oxidation and TCA cycle
pyruvate 3 CO2
4 NADH1 FADH2
1 GTP by SLP
must be reoxidized
TCA
pyruvate acCoA
NADH
NADH
NADH
NADH
FADH2
GTP
15 ATP equivalents per pyruvate
CO2
CO2
CO2
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115III. Reoxidation of NADH and FADH2 with O2 occurs via intermediate electron carriers arranged as electron transport chains in the membrane.
TB
Q2H
NADH + H+
NAD+
2H e– e–
e–
e–
1/2 O2 + 2H+ H2O
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116
1. NADH dehydrogenasesProtein complexes that acceptprotons and electrons from NADH.
A. Intermediate electron carriers
TB
2H
NADH + H+
NAD+
[2H] = 2 protons + 2 electrons
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1172. Flavoproteins
Proteins with FAD or FMN (flavin adenine dinucleotide or flavin mononucleotide) as a prosthetic group.
Flavoproteins carry protons and electrons.
TB
2H
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118FMN and FAD (isoalloxazine ring)
N
N N
NH
O
OH3C
H3C
R
Oxidized form
Flavin couples
FAD / FADH2
FMN / FMNH2
FMN and FAD are functionally equivalent, but have a different R-group TB
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119Iron-sulfur center
S
S
FeFe
S-cys-E
S-cys-E
E-cys-S
E-cys-S
E-cys-S = the sulfur of a cys residue ofthe protein is bonded to the iron
2Fe2S
TB
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120Iron-sulfur center
S
Fe
S
SS
Fe
FeFe
S-cys-E
E-cys-S
S-cys-E
4Fe4S
E-cys-S
TB
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1214. QuinonesSmall molecules (nonprotein)
Quinones can diffuse within the membrane.
Quinones carry both protons andelectrons.
TB
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122
O
Quinone
CH3O
CH3OO
R
Q
HOCH3O
CH3OOH
R
QH2
Oxidized Reduced
TB
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123Diffusion of quinones within the cell membrane.
cytoplasmTB
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1245. CytochromesProteins that contain the heme prosthetic group.
Cytochromes carry electrons only.
TBcytochrome
bc1
cytochrome c
cytochromeaa3
e–
e–e–
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125Cytochrome
N NNN
Fe
protein
heme
Fe3+/Fe2+ The iron carries the electronsTB
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126B. Electron Transport ChainsA series of electron carriers arranged within a membrane.Many different electron transport chains are known and they all function similarly.
TB
• electron transport chains can oxidize intermediate electron carriers like NADH and FADH2 and create proton gradients (PMF)
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127
Q
cytoplasm
NADH dehydrogenase
flavoprotein
iron-sulfurprotein
quinone
cytochromebc1
cytochrome c
cytochromeaa3
1. Electron transport chain of E. coli.
TB
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128
Q
cytoplasmNADH + H+
NAD
2H2H 2e– e–
e–
e–
1/2 O2 + 2H+H2O
a. In aerobic respiration, the electron transport chain is used to reoxidize NADH with O2.
2H = 2 protons and 2 electrons
TB
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129
Q
cytoplasmNADH + H+
NAD
2H2H 2e– e–
e–
e–
2H+ 2H+
222H+
1/2 O2 + 2H+H2O
b. Oxidation via electron transport allows proton pumping. A proton gradient (PMF) is formed across the membrane.
TB
2H+
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H+
H+H+
H+
H+H+H+
H+
H+
H+
+ + + + + + + + + +
+ + + + + + + + + +
- - - - - - - - - - - -
- - - - - - - - - - - -
++
++
++
----
-
- OH-
ENERGY
PMF
about -20 kJ/mol
In prokaryotes, H+ are pumped out of the cell.The outside becomes slightly acidic and positively charged relative to the inside.
2. Proton motive force (PMF) an energized state of the membrane created by a proton gradient
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1313. Results of the electron transport chain
a. intermediate electron carriers (e.g. NADH and FADH2) are reoxidizedb. electrons are ultimately transferred to O2, making water c. proton motive force (PMF) is created, which can be used for ATP synthesis
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132V. Oxidative phosphorylation (electron transport phosphorylation)
ATP synthesis driven by PMF
The F1F0 ATPase synthesizes ATP using the PMF.
TB
A. ChemiosmosisUse of an ion gradient (like PMF) to drive ATP synthesis
(Peter Mitchell, 1961):
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133
H+
H+
H+
H+H+H+
H+
H+
Energy is released when the H+ gradient is dissipated. The energy can do work (make ATP, rotate flagella, take up nutrients).
ENERGY
ADP + Pi
ATP2 to 4H+
ATP synthase
B. ATP synthesis using PMF
PMF
-20 kJ/mol
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134F1F0 ATPase
ADP + Pi ATP
H+H+
H+
H+H+ H+
cytoplasm
TB
F1: catalyzesATP
synthesis
Fo
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135C. How many ATPs can be synthesized when NADH and FADH2 are reoxidized through an electron transport chain (respiratory chain)?
NADH ~ 3 ATPFADH2 ~ 2 ATP
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136
glucose respiration (bacteria): 38 ATP per glucose
glucose fermentation: 2 ATP per glucose
D. Comparison of glucose fermentation and respiration in bacteria
glycolysis: 2 ATP (net) 2 ATP
2 acCoA (2) x TCA cycles:(2) x 3 NADH (2 x 3 x 3 ATP) 18 ATP(2) x 1 FADH2 (2 x 1 x 2 ATP) 4 ATP(2) x 1 GTP 2 ATP
Total: 38 ATP
2 NADH (2 x 3 ATP) 6 ATP 2 pyr 2 acCoA: 2 NADH 6 ATP
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137Study objectives for lecture 91. Understand respiration. Contrast fermentation and respiration.2. Understand oxidative phosphorylation. Contrast oxidative phosphorylation and substrate level phosphorylation.3. Describe the overall process of glucose respiration and the five steps presented in class.4. Memorize and understand the reaction of pyruvate conversion to acetyl CoA.5. Understand the TCA cycle. Know that the TCA cycles begins with the reaction of acetyl CoA and oxaloacetate to make citrate. How does the TCA cycle help cells produce energy?6. Memorize ALL the steps in the TCA cycle. Know which steps involve redox reactions, substrate level phosphorylation, decarboxylation. You do not need to memorize the structures.7. In respiration, glucose is oxidized completely to CO2. How is this done? Where is CO2 released? What happens to the electrons? What is the role of oxygen in respiration? How is energy conserved as ATP? How do cells derive energy from glucose in respiration? In fermentation?
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1388. What are electron transport chains? What is their role in metabolism?9. Compare and contrast the electron carriers used in electron transport chains. Understand the particular features of each electron carrier. You do not need to memorize the structures.10. Which electron carrier is nonprotein?11. Can cytochromes carry protons?12. Describe how electron transport chains are used to synthesize ATP. Understand how electron transport in the membrane generates proton motive force. Recall that proton motive force can be used to produce ATP.
Continued on next slide
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1391. Describe oxidative phosphorylation. Define chemiosmosis.2. Know the general structure of the F1/F0 ATPase. What is its function?3. How is the reoxidation of intermediate electron carriers related to ATP synthesis?4. Which method allows production of more ATP: aerobic respiration or fermentation?5. Starting with glucose, describe how ATP is made from glucose in fermentation and respiration. 6. Describe how glycolysis, the TCA cycle, electron transport chains, and ATP synthesis are connected in respiration.