CHNG 2804 Biological Systems

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CHNG 2804 Biological Systems

• Biothermodynamics
• John Kavanagh

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This Lecture

• Laws of Thermodynamics
• Energy
• Work and Cells
• Calculations
• Energy released during catabolism
• Energy required by anabolism

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Thermodynamics and Biological Systems

• The laws of thermodynamics apply to biological
  systems
• 1st Law Conservation of Energy
• 2nd Law Generation of Entropy

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First Law of Thermodynamics

• Conservation of Energy
• Energy can not be created or destroyed, merely
  transformed from one form to another.
• Can be written in a number of simplified forms
  for open/closed systems etc.
• Can be expanded to include the production of
  energy due to the disappearance of mass in
  nuclear reactions.

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Second Law of Thermodynamics

• Can be written in a number of ways.
• It is not possible to device a process whose
  sole result is the transfer of heat from a low
  temperature object to a high temperature object
• No apparatus can operate so that its only effect
  is to convert heat into work without also causing
  a change in the state of another body

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Second Law of Thermodynamics

• Energy spontaneously tends to flow only from
  being concentrated in one place to becoming
  diffused or dispersed and spread out
• For any real processes the change in entropy of
  the system and its surroundings must be greater
  than or equal to zero
• You probably already understand it intuitively,
  but this law actually tells us the upper limit of
  an engines efficiency.
• http//www.secondlaw.com/

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Energy

• Energy is defined as the ability to do work.
• In the lecture on yeast metabolism we saw
  examples of how cells obtain there energy.
• What do cells use the energy for?

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Types of work done by cells

• Chemical Work
• Anabolism
• The formation of many molecules needed by the
  cell requires energy.
• Mechanical Work
• Change physical locations of organisms, cells and
  internal structures
• Transport Work
• Movement of molecules and ions into and out of
  cells against electrical and concentration
  gradients

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How do cells obtain their energy?

• In the previous lecture we looked at the two of
  the metabolic pathways used to obtain energy from
  glucose.
• Cells do not combust their carbohydrate fuels
• The pathways we covered in the last lectures are
  common to many organisms
• They are not the only pathways used by
  microorganisms to obtain energy

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Simplified View of Glucose Catabolism
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Simplified View of Glucose Catabolism
2 Pyruvate
Anaerobic Glycolysis
Aerobic Oxidation
Anaerobic Alcoholic Fermentation
2 NADH
2 NADH
Citric Acid Cycle
2 NAD
2 NAD
2 Lactate
6 O2
2 CO2 2 Ethanol
2 NADH
Oxidative Phosphorylation
2 NAD
6 CO2 6 H2O
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Glycolysis

• Overall reaction
• glucose 2 ADP 2 Pi 2 NAD ?
• 2 pyruvate 2 ATP 2 NADH 2 H 2 H2O
• http//www.gwu.edu/mpb/glycolysis.htm

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TCA Cycle
Pyruvate
Acetyl-CoASH
NAD
NADH H
CO2
NADH H
Acetyl-CoA
Acetyl-CoASH
NAD
Oxaloacetate
Citrate
Isocitrate
H2O
Malate
NAD
H2O
CO2
Fumarate
NADH H
FADH2
a-Ketoglutarate
FAD
CoASH
Succinate
NAD
CO2
Pi
GTP
NADH H
ADP
Succinyl-S-CoA
GDP
ATP
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Overall Reaction

• Pyruvate 4 NAD FAD ADP Pi H2O ? 4 NADH
  4H FADH2 ATP 3 CO2
• http//www.gwu.edu/mpb/citric.htm
• In eukaryotes, the reactions of the TCA cycle
  occur in the mitochondria

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How do cells store/transfer there energy?

• ATP is commonly referred to as the universal
  currency of cellular energy
• Problems
• The TCA cycle requires aerobic conditions but
  molecular oxygen does take part in any of the
  reactions
• Little ATP has been generated, for each mole of
  glucose only 4 ATP have been generated (2 during
  glycolysis and 2 in the TCA cycle)

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The Electron Transport Chain

• The Electron Transport Chain is composed of a
  series of electron carriers.
• Located in
• Mitochondria (Eucaryotes)
• Bacterial plasma membrane
• Starts with When NADH and FADH2
• Electrons are passed from more negative reduction
  potentials to more positive reduction potentials

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The Electron Transport Chain

• e- eventually combine with H and O2 to form
  water
• NADH and FADH2 have sufficiently different
  electro potentials to oxygen that ATPs can be
  generated
• The process by which ATP is generated from NADH
  and FADH2 is called Oxidative Phosphorylation
• ATP yield
• up to 3 ATP for each NADH
• up to 2 ATP for each FADH2
• may be less.

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Energy Calculations
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Modified Standard State

• For calculations of Standard Gibbs Free Energies
  it is necessary for substances to be in their
  standard states.
• For solutions this is approximated as 1M
• H ions are important for many Biochemical
  reactions
• Commonly the H is near 10-7 (pH 7)
• Some Biochemistry Textbooks use a pH of 7 as a
  standard state
• The Modified Standard Gibbs Free Energy is given
  as DGo

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ATP Generation

• Oxidation of Glucose
• Maximum 38 ATP (Check for yourself in tutorial)
• Glucose 38Pi 38 ADP 6O2
• gt
• 6CO2 6H2O 38ATP
• 38 ATPs can provide the cell with
• DGo -1160.6 kJ/mol
• (The maximum ATP yield is often given as 36
  ATP/glucose as the yield of NADH depends on where
  it is produced)

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ATP Generation

• Fermentation of Glucose
• 2 ATPs (Check for yourself in tutorial)
• Glucose 2 Pi 2 ADP
• gt
• 2CO2 2C2H5OH 2 ATP
• 2 ATPs can provide the cell with
• DGo -61.0 kJ/mol

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Chemical Oxidation

• Glucose 6O2 gt 6CO2 6H2O
• DGo -2870.2 kJ/mol
• Efficiency of Glycolysis TCA cycle
• 1160.6/ 2870.2 40.4
• Efficiency of Glycolysis Alcoholic Fermentation
  Path
• 60.1 / 2870.2 2.1

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ATP Yields

• In the previous calculations we assumed maximum
  yields of ATP from NADH and FADH2
• The yields are often less dependent on cell type,
  and where the NADH is formed.
• Consult Biochemistry Texts

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ATP Yields
http//www.chem.mtu.edu/drshonna/cm4710/lectures/
chapter5.pdf http//www.columbia.edu/cu/biology/co
urses/c2005/ppts/lec09_04.ppt
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Summary

• Laws of Thermodynamics
• Energy
• Work and Cells
• Calculations
• Energy released during catabolism