Cellular Respiration - Download Now DOC by 6BBeI5




Coenzyme – A coenzyme is a chemical that helps an enzyme do it job.

NAD+ and FAD – Are coenzymes that collect energy in the form of H+ (hydrogen
ions) and e- (electrons) when the covalent bonds of the glucose molecule are
broken. Energy is obtained from the glucose molecule in the form of H+ and e-.
Electrons are harmful to cells and therefore must never be free within cells.
NAD+ picks up the H+ and e- to become NADH. FAD picks up two H+ ions to become

Cofactor - A cofactor is a non-protein chemical attached to a protein that is
necessary for it to function properly.

CoA (coenzyme A) – A cofactor attached to an enzyme (protein) that helps it do
its job. Coenzyme A is present in all living cells and functions as an acyl group
carrier. It is important in the oxidation of pyruvate.

Substrate Level ATP - An ATP molecule that was made during directly from one
of the cellular respiration reactions. It is called a substrate-level phosphorylation.
Phosphorylation means that phosphorus is added to GDP or ADP during the reaction
to make GTP or ATP.

Oxidation - Reduction Reactions: A compound is reduced when H+ ions are added
to it and it is oxidized when H is taken away, especially by the action of oxygen.
CELLULAR RESPIRATION - Using Glucose To Make Energy. Energy is
collected as NADH, FADH2, and ATP

  1. The function of cellular respiration is to produce energy, and to form smaller
     molecules that are used to build larger molecules in our bodies. Cellular
     respiration is therefore a series of chemical reactions that place in the body
     (biochemical reactions), (see diagram below)
  2. Cellular respiration begins in the cytoplasm and the products of this process
     are transported into the mitochondrion where the process of cellular
     respiration is completed. (see diagram below)
  3. The portion of cellular respiration that takes place in the cytoplasm does not
     use oxygen (anaerobic respiration) but the portion of the process that takes
     place in the mitochondrion does require oxygen (aerobic respiration).(see
     diagram below)

                                                                 A. Glycolysis
                                                                 in the

                                                               C. Pyruvate, which is a 3 carbon
                                                               compound is transported into the
                                                               mitochondria and decarboxylated
                                                               to a 2-carbon compound. The
                                                               decarboxylated carbon is
                                                               released as a molecule of CO2
                                                               that we breathe out.

                                                                B. The end product of
                                                                glycolysis is Pyruvate
                                                                and it goes into the
                                                                mitochrondia and is used
                                                                for Aerobic Respiration.
       CELLULAR RESPIRATION take place in four distinct steps:

I. GLYCOLYSIS is the first phase of cellular respiration and it takes place in
the cytoplasm of the cell.
   1. Glycolysis is when glucose a 6-carbon compound is split into two 3-carbon
   2. Glycolysis is the most primitive phase of cellular respiration.
   3. Glycolysis is an anaerobic process because no oxygen is needed for it to take
      place. Remember oxygen is required for that phase of cellular respiration
      that takes place in the mitochondrion.
   4. Glycolysis occurs in the cytoplasm.
   5. Glycolysis is that activation phase of respiration. It prepares the cell for
      the process of energy extraction from the glucose molecule.
   6. The end product of glycolysis is pyruvate, a 3-carbon compound. When the
      6-carbon glucose molecule was split into two 3-carbon compounds, these
      compounds underwent structural changes and became pyruvate.
   7. In the process of the 3-carbon compounds undergoing a structural change to
      pyruvate, 2 NADH and 2 ATP were formed. ATP is the chemical form in
      which energy exists in the cell.

II. OXIDATION OF PYRUVATE is the second phase of cellular respiration.
The pyruvate that was the end product of glycolysis is transported into the
matrix of the mitochondria to begin the aerobic phase of the respiratory

   1. Oxidation of pyruvate means that once pyruvate is transported into the
      mitochondrion, it is decarboxylated. That means that one of the 3 carbons
      of pyruvate is changed to CO2 (carbon dioxide), so that a 2-carbon compound
      is left.

   2. The 2-carbon compound that is left is known as Acetyl CoA. Two molecules
      of NADH are produced when pyruvate, a 3-carbon compound is
      decarboxylated to become a 2-carbon compound.

   3. Oxidation of pyruvate is the step between glycolysis and Krebs cycle.
4. The Acetyl CoA that is produced from the oxidation of pyruvate is used in
   Krebs cycle, which is the very next step in cellular respiration.

5. The products of the oxidation of pyruvate are 2 CO2 and 2 NADH (because
   there were two molecules of pyruvate to be oxidized.

III. KREBS CYCLE is the third phase of cellular respiration. It takes place in
the matrix of the mitochondria. Krebs cycle is also known as the tricarboxylic
acid cycle or the Citric Acid Cycle.
1. Krebs cycle, gets its name from its discoverer Hans Krebs.
2. Krebs cycle is the main pathway for respiration.

3. Krebs cycle is said to be a cycle because the starting compound is reproduced
   after the series of reactions that make up the cycle is complete. Krebs cycle,
   therefore, begins and ends with the same compound, a tricarboxylic acid.
4. The first of the series of reactions that make up Krebs cycle is when Acetyl
   CoA, the 2-carbon compound from the oxidation of pyruvate combines with a 4-
   carbon compound called oxaloacetate to make a 6-carbon compound. The CoA
   portion of the 2-carbon compound is a coenzyme that returns to the oxidation
   of pyruvate step to make more Acetyl CoA.
5. The 6-carbon compound is oxidized to produce 2 NADH and is decarboxylated
   to produce 2 CO2 and a 5-carbon compound called alpha-ketoglutaratic acid.
6. The 5-carbon compound is oxidized (similar to the oxidation of pyruvate
   reaction) to produce 2 NADH and is decarboxylated to produce 2 CO2 and a 4-
   carbon compound called succinyl-CoA. However, this reaction is called the
   oxidation of alpha-ketoglutaratic acid or just alpha-ketoglutarate.

7. All six of the glucose molecule that began the cycle are now oxidized and
   reduced to CO2. From this point on the reactions in the Krebs cycle will
   function to reproduce the beginning 4-carbon compound.

8. In the next reaction, the 4-carbon succinlyl-CoA compound loses its CoA to
   become succinate. This is an exothermic reaction, which is a reaction that
   releases energy. This energy is used to form 2 GTP, which becomes or is
   equivalent in energy to 2 ATP. ATP was not formed when Acetyl-CoA was
   formed because the energy was used to combine the 2-carbon compound to the
   4-carbon at the beginning of Krebs cycle to make the 6-carbon compound.
9. The 4-carbon succinate compound is oxidized to another 4-carbon compound
   called fermarate and two molecules of FADH2 are formed. 2 FADH2 were
   formed because there wasn’t enough energy to reduce NAD+.
10. The 4-carbon fermarate compound is changed to malate by adding in a molecule
    of water to form another 4-carbon compound called malate.

11. The 4-carbon malate is oxidized to produce the 4-carbon oxaloacetate that at
    the beginning of Krebs cycle combined with the 2-carbon acetyl CoA.
12. With the reformation of the 4-carbon oxaloacetate compound the cycle will go
    through the same process to reproduce oxaloacetate again.
13. The end result of Krebs cycle is 2 ATP, 6 NADH, 2 FADH2, and 6 CO2.


     2 NADH and 2 ATP - Glycolysis
     6 NADH and 2 ATP and 2 FADH2 and 6 CO2 – Krebs cycle

15. The process moves into the IV phase of cellular respiration. In this phase the
    NADH and FADH2 must move onto the Electron Transport Chain to get rid of
    its electrons.

16. The H+ ions, which all move to one side of the inner mitochondrial membrane
   causing a steep gradient of H+ ions. flow to the other side of the membrane
   through the ATPase pump. The energy from the flow of H+ ions passing
   through the pump causes a phosphate ion to combine with ADP to make ATP.

  Oxidation Phosphorylation - Oxidative phosphorylation is the final metabolic
  pathway of cellular respiration (IV phase), after glycolysis and the citric acid
  cycle by which respiratory enzymes in the mitochondria synthesize ATP from
  ADP and inorganic phosphate during the oxidation of NADH and FADH2 by
  molecular oxygen.

  Chemiosmosis - the diffusion of ions across a selectively-permeable membrane.
  More specifically, to cellular respiration it is the generation of ATP by the
  movement of H+ ions across the inner mitochondrial membrane through the
  ATPase pump.
 IV. ELECTRON TRANSPORT CHAIN is the fourth phase of cellular
respiration. This process requires oxygen and is therefore the aerobic portion
of cellular respiration.

1. The body uses energy in the form of ATP but at the end of glycolysis and
   the Krebs cycle most of the energy from the glucose molecule (C-C-C-C-C-C)
   is in the form of NADH and FADH2. This energy is not directly useful, so
   the electron transport chain is used to convert this energy into useful ATP.
2. The electron transport chain is made up of three protein complexes (NADH
   dehydrogenase, cytochrome b-c, and cytochrome oxidase) and two carrier
   molecules (coenzyme Q and cytochrome C) that transport the high-energy
   electrons down the chain. NADH will unload its e- and H+ at complex I while
   FADH2 will unload its e- and H+ at complex II.
3. Therefore, NADH unloads the H+ and e- that it collects at the beginning of
   the electron transport chain and produces 3 ATP molecules for each NADH
   because the electrons flow through all three complexes. FADH2 enters the
   electron transport chain at the second complex and therefore generates
   only 2 ATP molecules for every FADH2 molecules that enters the chain.
4. Remember, that electrons cannot be free in the cell. Oxygen is at the end
   of electron transport chain and so, is the final acceptor of the electrons.
   After oxygen accepts electrons, it adds on H+ and makes water (H2O). This
   is referred to as metabolic water because it is made during the metabolic
   process of making energy.

5. Electrons are transferred down the Electron Transport Chain according to
   electronegativity. In case of the electron transport chain, this is the
   attraction of the three complexes and carrier molecules for the electrons.

6. Both the electron transport chain and the ATP synthase pump are embedded
   in the inner membrane (cristae) of the mitochondria. Therefore, the
   transport chain reactions and chemiosmosis takes place on the surface of
   the inner mitochondrial membrane. Energy is transferred from electron
   transport chain to the ATP synthase pump by the movement of the protons
   (H+ ions) across the mitochondrial membrane, this is chemiosmosis.
 The Electron Transport Chain Reactions are known as Oxidative Phosphorylation
                               and Chemiosmosis

                  NADH dehydrogenase                                             here.
                  complex I,                                                     3 ATPs are
                                                                                 made when
cytochrome b-c
complex II                                                                       here

                                                                                 2 ATPs
                      cytochrome oxidase                                         made when

                                                                                 Water is
                                                                                 made when
   The Oxygen that that we breathe in
   diffuses into the cells and is used in
                                                                                 flow to
   cellular respiration to accept the
                                                                                 oxygen and
   electrons that are generated during
   the process.
                                                                                 is added.
                             A Close-up Look at Chemiomosis

-NADH will unload its e- and H+ at complex I while FADH2 unloads its e- and H+ at complex II

- Notice in this diagram as indicated by the arrows and in the diagram below that the H+ are all
transferred to one side of the complexes.

- Also notice that these H+ are transported back to the opposite side of the complexes through the
ATP synthase protein complex as indicated by the        arrow in the diagram above. This
phenomenon is also depicted in the diagram below.

Why is the manner in which the H+ ion is transferred so important to the
formation of ATP?

   -   This is important because ATP is made from the energy that is generated from the flow of
       hydrogen ions moving from one side of the complexes to the other. The energy, which
  can be liken to the energy generated from a MACK truck passing you at a high speed
  while you are standing on the side of the road with a stack of papers in your arms. What
  will happen to the papers and why? That’s correct the energy generated from the truck
  will scatter the papers and cause them to flow from your arms. That is the same concept
  with making ATP. ADP and Phosphorus in associated with ATP synthase protein. The
  energy from H+ passing through the ATP synthase pump causes the ADP and Pi to join
  together to make ATP (see the diagram below)

   2 NADH and 2 ATP – Glycolysis
  2 NADH + 2 ATP = 8 ATP -
Each NADH from glycolysis is trapped outside the mitochondria, so NADH passes
its electrons through the mitochondria membranes. Total ATP from glycolysis =
4ATP from 2 NADH + 2 ATP (substrate level phosphorylation) = 6 ATP
2 NADH produces 4 ATP instead of six because 2 ATP were required to
phosphorylate the glucose molecule so that it could undergo cellular respiration.

      2 NADH and 2 CO2 – Oxidation of Pyruvate
   2 NADH = 6 ATP

     6 NADH and 2 ATP and 2 FADH2 and 6 CO2 – Krebs cycle
   6 NADH = 18 ATP; 2 FADH2 = 4 ATP; Substrate level phosphorylation = 2 ATP
   Total = 24 ATP
   Grand Total = 6 ATP + 6 ATP +18 ATP + 4 ATP + 2 ATP = 36 ATP


  - TO MAKE THIS HAPPEN an enzyme catalyzes each and every reaction that

occurs in the body of an organism. Catalyze means to make the reaction go fast. A

different enzyme catalyzes each reaction. See examples from the cellular

respiration reactions below. First examples are some enzymes from gylcolysis

beginning with the formation of the two 3C carbons that are reduced to pyruvate.

The second example shows the enzymes of the Kreb cycle.
    Some Enzymes from Glycolysis   converts one
                                   isomeric substance
                                   into another. A
                                   isomerase also
                                   adds a phosphate

                                        transfer e- and H+
                                        from a substrate to
                                        an acceptor such as
                                        NAD to make
                                        NADH and FAG to
                                        make FADH2

                                        Mutases switch
                                        functional groups
                                        around within the
                                        same molecule

                                        Enolase catalyzes
                                        the removal of a
                                        water molecule
                                        from a substrate

                                       A kinase transfers
                                       a phosphate group
                                       from a donor such
                                       as ADP and ATP
                                       to an acceptor

      Enzymes for the Kreb cycle are in red. Compare the reactions
      with the definitions above.

                                           e- and H+ taken out here. Two
                                           molecules of CO2 generated
                                           which means that 2C of
                                           glucose were oxidized (C-C-
                                                                                  Notice that water is taken out,
                                                                                  the molecule is rearranged and
                                                                                  then water is added in again so
                                                                                  that more e- and H+ can be
                                                                                  taken out.

                                                                                              A dehydrogenase
                                                                                              takes out e- and H+
                           A dehydrogenase                                                    and transfers them
                           takes out e- and H+                                                to NAD. Two
                           and transfers them                                                 more molecules of
                           to NAD.                                                            CO2 generated

                          More water is
                          added here

                                                                                       e- and H+ taken out here.
                                                                                       Two more molecules of
                                                                                       CO2 generated
                                                                                       (count=6) All of the
                                                                                       glucose molecule is
                                                                                       degraded at this point.

Succinate dehydrogenase           Substrate level ATP; GTP
takes H+ ions from the            converted to ATP                         FROM THIS POINT ON
succinate molecule and            (equivalent compounds)                   THE 4C RECEIVING
transfers it to FAD                                                        COMPOUND IS
                                                                           REGENERATED TO
                                                                           RECEIVE ANOTHER 2C
Gluconeogenesis (abbreviated GNG) is a metabolic pathway that generates glucose
from non-carbohydrate substrates such as the monomers such as glycerol from
fats, and lactate from carbohydrates. It mostly uses protein. Gluconeogenesis
and glycogenolysis (degradation of glycogen) are the two main mechanisms that
animals use to keep blood glucose levels from dropping too low (hypoglycemia)).

Gluconeogenesis is a ubiquitous process, that is it is present in plants, animals,
fungi, bacteria and other microorganisms. In animals, it takes place mainly in the
liver and, to a lesser extent, in the cortex of kidneys. This process occurs during
periods of fasting, starvation, low-carbohydrate diets, or intense exercise.
(Wikipedia Free Encyclopedia),

                                                                   Gluconeogenesis takes
                                                                  place at night when we
                                                                  sleep if glucose is

                                                                  Gluconeogenesis is
                                                                  almost a reversal of
                                                                  glycolycis but not quite
                                                                  because some of the
                                                                  reactions of glycolysis
                                                                  requires too much
                                                                  energy to reverse.
                                                                  Those reactions are
                                                                  indicated by the
                                                                  reactions labeled with
                                                                  the enzymes that
                                                                  catalyze the reactions
                                                                  in both metabolic

  PROTEINS          CARBOHYDRATES                    FATS

     Amino                     Sugars            Glycerol   Fatty






                          Acetyl CoA


                    Oxidative Phosphorylation
                    (Electron Transport Chain)

                   Cellular Respiration
Summary of Main Events

Glycolysis – Takes place in the cytoplasm – known as Anaerobic Respiration

   1. A six 6-carbon sugar compound is split into two, 3-carbon pyruvate

   2. 2 NADH and a net gain of 2 ATP are produced.

   3. ATP is produced by substrate level phosphorylation.

   4. Oxygen is not involved in glycolysis only after pyruvate is transported into
      the mitochondria. Therefore, glycolysis is known as anaerobic (without
      oxygen) respiration

                                      Aerobic Respiration

Decarboxylation of Pyruvate – Takes place in the matrix of the mitochondria

   1. Pyruvate is reacted with coenzyme A (CoA). Carbon dioxide is released and
      NADH is formed. The result is a 2-carbon acetyl group that links with
      coenzyme A forming Acetyl-CoA.

Krebs Cycle – Takes place in the matrix of the mitochondria

   2. The 2-carbon compound reacts with a 4-carbon molecule to form a 6-carbon
      compound named citrate.

   3. More Carbon dioxide is removed in the Krebs cycle, and the hydrogen ions
      are harvested in NADH and FADH.

   4. One ATP is generated by substrate level phosphorylation.
Electron Transport Chain – Takes place on the surface of cristae in the

   1. Hydrogen ions are actively transported between the membranes of the

   2. The result is an electrochemical gradient that provides the energy for the production of

   3. Electrons are passed down a chain of mostly protein compounds.

   4. Oxygen that you breathe in is the ultimate acceptor of hydrogen ions and electrons and
      water is made.

Questions You Should Know the Answer to:
   1. What are phospholipids composed of?
   2. In isomerization reactions, how are the reactants and the products the same
      and how are they different?
   3. Why is FADH2 produced in Krebs cycle; why not all NADH?
   4. How are ATP and ADP molecules different?
   5. What is the final product of the electron transport chain?
   6. Account for the 36 ATP produced during cellular respiration.
   7. Explain why 36 ATP are produced under ideal conditions.
   8. Explain why it is essential for muscle cells to convert pyruvate into lactic
      acid during anaerobic respiration. Lactic acid accumulation causes fatigue
      and pain and very little energy is obtained from the process.

   1. Phospholipids are composed of glycerol backbone, phosphorylated alcohol,
      and fatty acids.
   2. Isomerization is when a compound changes its form but retains the same
      general formal, for example glucose is isomerized to fructose in glycolysis.
   3. Because enough energy to reduce NADH was not released.
   4. ADP has less stored energy.
   5. A molecule of water.
6. The following chart accounts for the 36 ATP in cellular respiration:
                            Number of ATP Produced
                           2 ATP
                                                         =4 (-2 from moving into
                           2 NADH x3

 Oxidation of Pyruvate     2 NADH x3                     =6

                           6 NADH x3                     =18

    Citric Acid Cycle      2 FADH2 x2                    =4

                           2 ATP                         =2

                                                                   TOTAL: 36 ATP

  7. ATP will be used or increased depending on the conditions of the cell. For
     example, if there isn't enough oxygen, the cell changes to anaerobic
     respiration. Sometimes our body will produce more ATP because our body
     needs more energy. Some ATP is used in other life functions like going to
     form fats and proteins.
  8. It is essential that muscle cells during anaerobic respiration, convert
     pyruvate to lactic acid incase there isn't any more oxygen produced. When
     there isn't oxygen present, NADH can't be recycled, therefore glycolysis
     can't continue. In order to produce energy, our bodies need to rely on
     another system. The lactic acid system, which doesn't require oxygen, can
     still produce energy.

  1. LINKS
  2. Diagram of the electron transport chain
  3. http://members.tripod.com/beckysroom/etc-1.jpg
  4. Diagram of how the phases of respiration are interrelated
  5. http://en.wikipedia.org/wiki/File:CellRespiration.svg#file

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