ENERGETICS

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ENERGETICS
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Laws of Thermodynamics

• 1 Energy can be transferred and transformed,
  but not created or destroyed. (Conservation of
  energy)
• 2 Every energy transfer /transformation
  increases the entropy (disorder) of the universe.

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Coupled Reactions
Living organisms appear to cheat the
thermodynamic laws because they develop order,
however, they are essentially open systems and
receive and release energy by coupling reactions
of metabolism.
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Metabolism

• All the chemical processes in the body can be
  categorized as either anabolic (energy-requiring
  in order to build up) or catabolic
  (energy-releasing for breakdown).
• They work in concert with each other to meet the
  needs of the organism.

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Respiration

• The process of extracting stored energy from
  glucose to form ATP
• C6H12O6 6O2 ?6CO2 6H20
• ATP(energy)

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Aerobic Respiration

• Consists of 3 phases
• Glycolysis
• Krebs Cycle
• Oxidative Phosphorylation aka Electron Transport
  Chain

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Glycolysis

• Literally means sugar-breaking
• Glucose is broken down in a series of reactions,
  each by an enzyme. Magnesium ions (Mg2) are
  cofactors that aid enzyme action.
• Takes place in the cytoplasm.

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The final product from the breakdown of glucose
is pyruvic acid. In order to start the
reactions some activation energy is supplied in
the form of 2 ATP molecules.
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Glycolysis Summary

• 2 ATP supply energy.
• 2 NADH (coenzyme) are produced as electrons are
  released during the breakdown.
• 4 ATP are produced.
• 2 pyruvic acid molecules (3 C) result.
• Net gain of 2 ATP.

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Crossroads

• Depending on the presence of oxygen, determines
  what happens to the pyruvic acid next.
• Without oxygen, the process of fermentation will
  occur. We will explore that process later.
• But we can extract more energy, if O2 is present,
  lets take a look!

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• Pyruvic acid (pyruvate) binds to coenzyme A to
  form acetyl CoA, releasing CO2 and electrons
  (picked up by NADH) just prior to entering the
  cycle. (2 C)

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Krebs Cycle

• This cycle of reaction occurs in the matrix of
  the mitochondrion.
• Although the Krebs cycle does not use oxygen
  directly, the molecules required to keep it
  running, do require it in order to be recycled.

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Krebs Cycle

• In the course of the cycle, the initial molecule
  (Acetyl CoA) is, first combined with a 4C
  compound (Oxaloacetate) to form a 6C compound
  (Citric Acid) and then subsequently broken
  apart, piece by piece w/ more energy and CO2
  released.

Krebs cycle aka Citric Acid Cycle.
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Watch the cycle in motion.
Please note that this animation is
oversimplified, but you should see the basic
breakdown of the molecule and the subsequent
results.
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Krebs Cycle - Intermediate Reactions

• The breakdown reactions can generally be
  categorized as one of the three
• Phosphorylation
• Redox
• Isomerization
• also Glycolysis intermediate reactions

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A Closer Look

• Phosphorylation changes the shape of the
  molecule, thus allowing work to be performed.

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A Closer Look

• Redox reactions release energy when electrons
  move closer to electronegativeatoms.
• The loss of electrons is called oxidation.
• The addition of electrons is called reduction.
• More generally Xe- Y -gt X Ye-
• X, the electron donor, is the reducing agent and
  reduces Y.
• Y, the electron recipient, is the oxidizing agent
  and oxidizes X.
• If the degree of electron sharing changes it is
  also considered a redox reaction.

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A Closer Look

• An example of redox is when hydrogen atoms are
  stripped from glucose and passed to a coenzyme,
  like NAD (nicotinamide adenine dinucleotide).
• Enzymes strip two hydrogen atoms from glucose,
  pass two electrons and one proton to NAD and
  release H.
• This changes the oxidized form, NAD, to the
  reduced form NADH.

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A Closer Look

• Isomerization molecule changes shape but
  retains the same molecular formula.

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Krebs Cycle Summary

• The released energy is picked up by 1 ATP, 3 NADH
  and 1 FADH2.
• 1 molecule of CO2 is released. The CO2 is
  considered waste and we exhale it.
• Since two molecules of pyruvate, from the 1
  glucose molecule, go through this cycle, the
  amounts above are actually doubled.

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A Closer Look
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Summary so far
Glucose Molecule ATP NADH FADH2
Net gain of 4 4-22 glycolysis 2 Krebs
2 Krebs
10 total 2 glycolysis 8 Krebs
2 pyruvate
6 Carbon dioxide
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Electron Transport Chainaka Electron Transport
System

• Occurs in the cristae of mitochondrion.
• Electrons from NADH FADH2 are passed (like a
  hot potato) through a chain of cytochrome
  molecules.
• This regenerates NAD and FAD so that they can be
  reused in glycolysis and Krebs cycle.

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ETC or ETS

• Oxygen is needed to accept the electrons,
  together with H ions, at the end of the chain,
  forming water.
• More importantly, a lot of ATP is generated
  through this process called oxidative
  phosphorylation.

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A Closer Look

• Electrons carried by NADH are transferred to the
  first molecule in the electron transport chain,
  flavoprotein.
• The electrons carried by FADH2 have lower free
  energy and are added to a later point in the
  chain.

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Oxidative Phosphorylation

• The maximum output from
• ox-phos is 3 ATP/NADH and 2 ATP/FADH2
• Calculate how many ATP can be produced during
  this process from the 1 molecule of glucose.

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Chemiosmosis

• A major part of oxidative phosphorylation, this
  basic process also occurs in chloroplasts.
• The energy lost from electrons passing through
  the ETS, is used to phosphorylate
• ADP to ATP. (coupling reactions)

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• Chemiosmosis involves coupled reactions, where
  the products of one reaction are used in another
  reaction.
• In this case, the initial products are H ions,
  which are released from NADH and FADH2.
• These protons are pumped out of the fluid matrix,
  across the cristae, to the intermembrane space of
  the mitochondrion.

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• A pH and electrical gradient is formed as the
  protons accumulate, forming a reservoir of
  potential energy.
• The protons flow back into the matrix through
  channel proteins called ATP synthases.
• This flow generates the energy to produce ATP.

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• At the end of the ETS, the moving electrons,
  which first served to provide the H ions
  (protons) when the bonds of NADH and FADH2 were
  broken, are transferred to oxygen and coupled
  with the pumped H ions (back in the matrix),
  form water.

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A Closer Look
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http//www.youtube.com/watch?v3y1dO4nNaKY
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How efficient is respiration in generating ATP?
Complete oxidation of glucose releases 686 kcal
per mole. Formation of each ATP requires at least
7.3 kcal/mole. Efficiency of respiration is 7.3
kcal/mole x 38 ATP/glucose/686 kcal/mole glucose
40. The other approximately 60 is lost as
heat. Cellular respiration is remarkably
efficient in energy conversion.
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Whew!

• Now you can see why cell respiration leads to
  some of the top 40 ways you know youve been
  traumatized by AP Biology.
• In the end, if you remember nothing else,
  remember what results after each phase or cycle.

Its not quite over yet, remember we said that
there is an alternative path if no oxygen was
present? Well.
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FERMENTATION

• How Glycolysis keeps going if there is no oxygen.

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When there is no Oxygen why is Fermentation
necessary?

• W/O O2, glycolysis is the ONLY chemical reaction
  to release energy from glucose.

Cells need to continuously carry out glycolysis,
but eventually the NAD can be used up.
If all the NAD is used up, then glycolysis jams
or stops.
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• Why would it be disastrous for the cell if
  glycolysis stops?

It would run out of energy.
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What does Fermentation do in order to help
glycolysis continue?

• In Fermentation, chemical reactions occur that
  free up the NAD, thus regenerating it for use in
  glycolysis.
• The electron energy released from NADH (What NAD
  is called when it carries the high energy
  electrons)
• is put back into pyruvic acid. This chemical
  reaction results in a new product.
• Fermentation ONLY occurs if there is no oxygen.

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Products of Fermentation

• In animals, the new product formed is
  lactic acid.
• This often forms in muscles when they cant get
  the oxygen they need fast enough.
• Lactic acid accumulating in muscles is painful,
  but this chemical can later be broken down to
  extract energy when enough oxygen is present.

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Products of Fermentation

• In yeast, the new products formed are alcohol and
  carbon dioxide.
• People put both these products to use to make
  wines and cause bread dough to rise.

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Fermentation Review

• In your notes write your answers in your own
  words.

How does fermentation help a cell release energy
from glucose?
Compare and contrast lactic acid fermentationand
alcoholic fermentation.
What would happen to fermenting wine if there was
an air leak in the fermentation tank?