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Cellular respiration (glycolysis, TCA and ETC)
1. NSB 211: DIGESTIVE SYSTEM NUTRITION
AND METABOLISM
TOPIC;
â˘CELLULAR RESPIRATION
Lecturer: Dr. G. Kattam Maiyoh
11/20/13
GKM/NSB 211: DIGESTIVE SYSTEM NUTRITION
AND METABOLISM/2013
2. Learning Objectives
⢠Explain why cells need breakdown
biomolecules (E.G. glucose)
⢠Describe the basic steps in;
â Glycolysis,
â The TCA cycle,
â The electron transport chain (ETC)
⢠Summarize the energy yield of all above steps
cellular respiration
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3. Overview of Cellular Respiration
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4. Overview of Cellular Respiration
⢠Cellular respiration is the step-wise release of
energy from carbohydrates and other
molecules; energy from these reactions is
used to synthesize ATP molecules.
⢠This is an aerobic process that requires oxygen
(O2) and gives off carbon dioxide (CO2), and
involves the complete breakdown of glucose
to carbon dioxide and water.
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5. ⢠Metabolism refers to all the chemical reactions
of the body
â some reactions produce the energy stored in
ATP that other reactions consume
â all biological molecules will eventually be
broken down and recycled or excreted from
the body
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6. Catabolism and Anabolism
⢠Catabolic reactions breakdown complex
organic compounds
â providing energy (exergonic)
â glycolysis, Krebs cycle and electron transport
⢠Anabolic reactions synthesize complex
molecules from small molecules
â requiring energy (endergonic)
⢠Exchange of energy requires use of ATP
(adenosine triphosphate) molecule.
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7. ATP Molecule & Energy
a
b
⢠Each cell has about 1 billion ATP molecules that last for less than
one minute
⢠Over half of the energy released from ATP is converted to heat
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8. Mechanisms of ATP Generation
⢠Phosphorylation is the addition of phospahate
group.
â bond attaching 3rd phosphate group contains stored
energy
⢠Mechanisms of phosphorylation
â within animals
⢠substrate-level phosphorylation in cytosol
⢠oxidative phosphorylation in mitochondria
â in chlorophyll-containing plants or bacteria
⢠photophosphorylation.
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9. Phosphorylation in Animal Cells
⢠In cytoplasm (1)
⢠In mitochondria (2, 3 & 4)
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10. ⢠(Insert Fig. 7.4a)
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Sld 38
11. Carbohydrate Metabolism--In Review
⢠In GI tract
â polysaccharides broken down into simple sugars
â absorption of simple sugars (glucose, fructose &
galactose)
⢠In liver
â fructose & galactose transformed into glucose
â storage of glycogen (also in muscle)
⢠In body cells --functions of glucose
â oxidized to produce energy
â conversion into something else
â storage energy as triglyceride in fat
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12. Glucose Movement into Cells
⢠In GI tract and kidney tubules,
Na+/glucose symporters
⢠Most other cells, GluT facilitated
diffusion transporters move
glucose into cells
⢠Glucose 6-phosphate forms
immediately inside cell (requires
ATP) thus, glucose hidden in cell
⢠Concentration gradient favorable
for more glucose to enter
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13. Glucose Catabolism
⢠Cellular respiration
â 4 steps are involved
â glucose + O2 produces
H2O + energy + CO2
⢠Anaerobic respiration
â called glycolysis (1)
â Results in formation of acetyl CoA (2)
is transitional step to Krebs cycle
⢠Aerobic respiration
â Krebs cycle (3) and electron transport chain (4)
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14. ⢠Each step of cellular respiration
requires a separate enzyme.
⢠Some enzymes use the oxidationreduction coenzyme NAD+
(nicotinamide adenine
dinucleotide).
⢠When a metabolite is oxidized,
NAD+ accepts two electrons plus a
hydrogen ion (H+) and NADH
results; NAD+ can also reduce a
metabolite by giving up
electrons.
⢠FAD (flavin adenine dinucleotide)
is sometimes used instead of
NAD+.
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15. 6 CH OPO 2â
2
3
5
O
H
4
OH
H
OH
3
H
H
2
H
1
OH
OH
glucose-6-phosphate
Glycolysis takes place in the cytosol of cells.
Glucose enters the Glycolysis pathway by conversion
to glucose-6-phosphate.
Initially there is energy input corresponding to
cleavage of two ~P bonds of ATP.
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16. 6 CH2OH
5
H
4
OH
O
H
OH
H
2
3
H
OH
glucose
6 CH OPO 2â
2
3
5
O
ATP ADP
H
H
1
OH
Mg2+
4
H
OH
OH
3
H
1
H
2
OH
Hexokinase H
OH
glucose-6-phosphate
1. Hexokinase catalyzes:
Glucose + ATP ď glucose-6-P + ADP
The reaction involves nucleophilic attack of the C6
hydroxyl O of glucose on P of the terminal phosphate
of ATP.
ATP binds to the enzyme as a complex with Mg++.
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17. Glycolysis & Fate of Pyruvic Acid
⢠Breakdown of six-carbon
glucose molecule into 2 threecarbon molecules of pyruvic
acid
â 10 step process occurring in
cell cytosol
â produces 4 molecules of
ATP after input of 2 ATP
â utilizes 2 NAD+ molecules
as hydrogen acceptors
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18. 10 Steps of Glycolysis
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20. If O2 shortage in a cell
â˘Pyruvic acid is reduced to lactic acid so that
NAD+ will be still available for further
glycolysis
â˘This process is known as fermentation
â˘Lactic acid rapidly diffuses out of cell to
blood
â˘Liver cells remove it from blood & convert it
back to pyruvic acid
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21. Why does fermentation occur?
Pyruvate is reduced to lactate when
oxygen is not available because
fermentation uses NADH and
regenerates NAD+.
In this way NAD+ is now free to pick up
more electrons during early steps of
glycolysis; this keeps glycolysis going.
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22. Two types of Anaerobic Respiration
Fermentation-yeast
Lactic Acid or lactate-muscles
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23. Advantages and Disadvantages of
Fermentation
⢠Fermentation can provide a rapid burst of ATP
in muscle cells, even when oxygen is in limited
supply.
⢠Lactate, however, is toxic to cells.
⢠Initially, blood carries away lactate as it forms;
eventually lactate builds up, lowering cell pH,
and causing muscles to fatigue.
⢠Oxygen debt occurs, and the liver must
reconvert lactate to pyruvate.
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24. Efficiency of Fermentation
⢠Two ATP produced during fermentation are
equivalent to 14.6 kcal; complete oxidation of
glucose to CO2 and H2O represents a yield of
686 kcal per molecule of glucose.
⢠Thus, fermentation is only 2.1% efficient
compared to cellular respiration.
⢠(14.6/686) x 100 = 2.1%
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26. Transition Reaction
⢠The transition reaction connects glycolysis to
the citric acid cycle, and is thus the transition
between these two pathways.
⢠Pyruvate is converted to a C2 acetyl group
attached to coenzyme A (CoA), and CO2 is
released.
⢠During this oxidation reaction, NAD+ is
converted to NADH + H+; the transition
reaction occurs twice per glucose molecule.
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27. Formation of Acetyl Coenzyme A
⢠Pyruvic acid enters the
mitochondria with help of
transporter protein
⢠Decarboxylation
â pyruvate dehydrogenase converts 3
carbon pyruvic acid to 2 carbon
fragment (CO2 produced)
â pyruvic acid is oxidized so that NAD+
becomes NADH
⢠2 carbon fragment (acetyl group) is
attached to Coenzyme A to form
Acetyl coenzyme A which enter
Krebs cycle
â coenzyme A is derived from
pantothenic acid (B vitamin).
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28. Krebs Cycle (Citric Acid Cycle)
⢠Citric acid cycle â a cyclical oxidationreduction & decarboxylation reactions
occurring in matrix of mitochondria
⢠Gives off CO2 and produce one ATP per cycle;
occurs twice per glucose molecule
⢠It finishes the same as it starts (4C)
â acetyl CoA (2C) enters at top & combines with a
4C compound
â 2 decarboxylation reactions peel 2 carbons off
again when CO2 is formed
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30. THE TCA
The names of the various enzymes in
the previous slide are indicated in the
figure below
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31. What happens in the cycle?
⢠During the cycle, oxidation occurs when NAD+
accepts electrons in three sites and FAD
accepts electrons once.
⢠A gain of one ATP per every turn of the cycle;
it turns twice per glucose.
⢠During the citric acid cycle, the six carbon
atoms in glucose become CO2.
⢠The transition reaction produces two CO2, and
the citric acid cycle produces four CO2 per
molecule of glucose.
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32. Products of the Krebs Cycle
⢠Energy stored in bonds is released step by step to form several
reduced coenzymes (NADH & FADH2) that store the energy
⢠In summary: each Acetyl CoA
molecule that enters the Krebs
cycle produces yields;
â 2 molecules of CO2
⢠one reason O2 is needed
â 3 molecules of NADH + H+
â one molecule of ATP
â one molecule of FADH2
⢠Remember, each glucose
produced 2 acetyl CoA molecules
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33. Citric acid cycle inputs and outputs per
glucose molecule
â˘Inputs:
â˘2 acetyl groups
â˘6 NAD+
â˘2 FAD
â˘2 ADP + 2 P
â˘Outputs:
½ of the above per cycle
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â˘4 CO2
â˘6 NADH
â˘2 FADH2
â˘2 ATP
34. The Electron Transport Chain
⢠Involves a series of integral
membrane proteins in the
inner mitochondrial
membrane capable of
oxidation/reduction
⢠Each electron carrier is
reduced as it picks up
electrons and is oxidized as it
gives up electrons
⢠Small amounts of energy is
released in small steps
⢠Energy used to form ATP by
chemiosmosis
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35. Chemiosmosis
⢠Small amounts of energy
released as substances are
passed along inner
membrane
⢠Energy used to pump H+ ions
from matrix into space
between inner & outer
membrane
⢠High concentration of H+ is
maintained outside of inner
membrane
⢠ATP synthesis occurs as H+
diffuses through a special H+
channel in inner membrane
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36. Steps in Electron Transport
⢠Carriers of electron transport chain are clustered into 3 complexes
that each act as proton pump (expel H+)
⢠Mobile shuttles pass electrons between complexes
⢠Last complex passes its electrons (2H+) to a half of O2 molecule to
form a water molecule (H2O)
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37. Proton Motive Force & Chemiosmosis
â˘
â˘
Buildup of H+ outside the inner membrane creates + charge
â electrochemical gradient potential energy is called proton motive force
ATP synthase enzyme within H+ channel uses proton motive force to synthesize
ATP from ADP and P
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38. Energy yields from Glycolysis -TCA
⢠Glycolysis and the citric acid cycle accounts for
four ATP.
⢠ETC accounts for 32 or 34 ATP, and the grand
total of ATP is therefore 36 or 38 ATP.
⢠Cells differ as to the delivery of the electrons
from NADH generated outside the
mitochondria.
⢠If they are delivered by a shuttle mechanism to
the start of the electron transport system, 6 ATP
result; otherwise, 4 ATP result.
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39. ⢠Most ATP is produced by the electron
transport system and chemiosmosis.
⢠Per glucose molecule, ten NADH and two
FADH2 take electrons to the electron transport
system; three ATP are formed per NADH and
two ATP per FADH2.
⢠Electrons carried by NADH produced during
glycolysis are shuttled to the electron
transport chain by an organic molecule.
7-39
40. A Summary of the Energy Yield of
Aerobic Metabolism
Figure 25.7
41. Thank you for listening !!
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Hinweis der Redaktion
Glycolysis takes place in the cytoplasm of almost all cells.
The electrons received by NAD+ are high-energy electrons that are usually carried to the electron transport system. NAD+ can be used over and over again. FAD accepts two electrons and two hydrogen ions (H+) to become FADH2.
Oxidation of 2 PGA by removal of water results in 2 high-energy PEP (phosphoenolpyruvate) molecules. In the final step, removal of high-energy phosphate from PEP by 2 ADP produces 2 ATP and 2 pyruvate molecules. There are four ATP molecules produced, and 2 invested in the first step of glycolysis for a net gain of 2 ATP.
The inputs of fermentation include glucose, 2 ATP, and 4 ADP + 2 P. Outputs are 2 lactate, or 2 alcohol and 2 CO2, and 4 ATP (net 2 ATP).
On each occasion, NAD+ accepts two electrons and one hydrogen to become NADH. FAD accepts two electrons and two hydrogen ions to become FADH2.