Metabolism Part 2

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MetabolismPart 2
I teach a simplified version of Glycolysis and
Tricarboxylic Acid Cycle (Kreb Cycle). I dont
want to you spend any time memorizing chemical
structures, I simply want you to understand the
concepts behind the 2 cycles. Once you
understand the concepts behind the cycles then
you will better understand them in more detail.
(Which you will get in other classes, not this
one.)
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Glycolysis

• Here are a couple of important definitions for
  you to know before we begin.
• Oxidation this means that a molecule has lost
  electrons
• Reduction this means that a molecule has gained
  electrons
• Glycolysis is the is the process of breaking
  glucose down into 2 molecules of pyruvate (also
  referred to as pyruvic acid).
• Glucose is a sugar that is composed of 6 carbons
  (6 Cs) and multiple oxygen (O) and hydrogen (H).
• Pyruvate is a molecule that is composed of 3 Cs,
  O, and H.
• Simply put, Glycolysis is the formation of 2
  molecules of pyruvate through the oxidation of
  glucose. (A 6C molecule is split into 2, 3
  carbon molecules.

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Glucose
OH
OH
OH
OH
O
H
C
C
C
C
C
C
H
H
OH
Lose 1 H2O
Lose 1 H2O
C
C
C
C
C
C
Pyruvate
Pyruvate
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• In the process of forming pyruvate some H and O
  molecules are lost as water.
• 2 molecules of ATP are used in the process of
  splitting glucose.
• By the time the process is finished, 4 ATP are
  made.
• The Net Energy that is produced by this process
  is 2 ATP.

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• Before pyruvate can then enter the Tricarboxylic
  Acid Cycle (TCA Cycle) it has to be changed
  slightly. It changes from a 3 C molecule to a 2
  C molecule.
• The first CO2 is released and Coenzyme A is added
  on. If the acetyl CoA is not added, the molecule
  cant fit into the TCA cycle because it is not
  the right shape.

H
H
O
O
C
C
C
C
C
H
H
OH
H
O
S-CoA
H
CO2 is lost
Acetyl CoA
Pyruvate
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TCA Cycle

• Now the Acetyl CoA can fit into the TCA cycle and
  continue its journey.
• Remember that each glucose gives us 2 molecules
  of pyruvate. Each pyruvate is converted to
  Acetyl CoA. During the conversion process 1CO2
  is lost from each pyruvate. So, from the
  original 6 Cs of glucose we now have 4 remaining.
  We have also lost some H and O as water during
  Glycolysis, as well as some additional O as CO2.

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• The TCA results in the complete oxidation of
  acetyl CoA to CO2. In other words, all 4 Cs and
  the O from the acetyl CoA are lost as CO2 by the
  time it is finished with the TCA cycle.
• 1 ATP is made per Acetyl CoA molecule that enters
  the TCA Cycle. So a total of 2 ATP are made
  during the TCA Cycle per molecule of glucose.
• Once the C and O are gone, there are still a few
  H left. Normally a H molecule is a composed of 1
  proton and 1 neutron and 0 electrons. During the
  TCA Cycle, the H molecules are left with 1
  electron each.
• These H molecules with their corresponding
  electrons are the most important part of aerobic
  metabolism!

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• Special taxis called, NAD and FAD, come and pick
  up the molecules of H with their corresponding
  electrons and take them to the Electron Transport
  Chain.
• NAD can carry 1 H with its corresponding
  electron and FAD can carry 2 Hs with their
  corresponding electrons.

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Electron Transport Chain

• The carrier molecules NAD and FAD bring the Hs
  to cell membrane (in prokaryotes) or the
  mitochondrial membrane (in eukaryotes).
• The Hs and their corresponding electrons are
  released into the cell membrane at the sight of a
  proton that specializes in pumping the Hs
  outside of the cell membrane.
• The electrons are passed through a series of
  proteins (via oxidation and reduction reactions)
  inside of the cell membrane, called the Electron
  Transport Chain.

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Outside the Cell
Cell Wall
H
H
H
H
H
H
H
H
ATP Synthase
H
e-
Cell Memrane
e-
e-
e-
e-
H
oxygen
NAD-H
H
NAD
e-

oxygen
H


H2O
Inside the Cell
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• Once the electrons have moved through the
  electron transport chain they are transported to
  a molecule called, the Terminal Electron
  Acceptor. In the case of Aerobic Respiration,
  the Terminal Electron Acceptor is oxygen.
• Excess Hs (now called protons because they are
  no longer carrying an electron) outside the cell
  membrane create potential energy because there is
  a high positive charge on one side of membrane.
• These protons are then pumped back inside the
  cell through the enzyme ATP Synthase. The
  movement of the protons through ATP Synthase
  powers the enzyme to make ATP.
• Then the protons, electrons and terminal electron
  acceptor combine to form water.
• Net result 34 ATP 4 ATP from glycolysis and
  kreb cycle 38 ATP in prokaryotes. In addition,
  H2O and CO2 are given off as the by products of
  respiration/metabolism.

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Summary of Glycolysis
Start with End With Net ATP Generated
Glycolysis 1, 6C glucose 2 ATP 2, 3C pyruvate 4 ATP 2 ATP
TCA Cycle 2, 3C Pyruvate Co2, ATP, H with e-s 2 ATP
Electron Transport Chain H with e-s H2O, ATP 34 ATP Total38 ATP
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Anaerobic Respiration

• Anaerobic Respiration is essentially the same as
  aerobic respiration. The main difference is that
  the terminal electron acceptor is a compound
  other than O2. It is usually some compound that
  contains nitrogen, sulfur, or carbon.
• Ie. Nitrate, nitrite, sulfate, or carbonate
• It does not generate as many ATP as aerobic
  respiration.

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Fermentation

• Anaerobic Respiration and Fermentation are not
  the same thing.
• Anaerobic Respiration still utilizes the TCA
  cycle but fermentation only utilizes glycolysis.
• After pyruvate is generated through glycolysis,
  it is then converted to some acid or alcohol by
  product.
• Fermentation does not require oxygen to occur.
• Fermentation does not require the TCA cycle.
• It uses organic compounds as the terminal
  electron acceptor.
• It produces only small amounts of ATP.
• Examples of end products are lactic acid or
  ethanol

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• This completes the lecture material for Unit 1.
• I will be happy to stay after lab and answer any
  questions regarding the material for Test 1 or to
  conduct a review.
• I will post a review sheet Monday morning, Sept.
  25.