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Intensive Biology
Chapter 6: Cellular Respiration
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Cellular Respiration
Cells do lots of work - anabolism, transport, movement, growth, reproduction, etc. They need energy to fuel this
work. Cells store potential energy in the arrangement of the atoms in macromolecules. Cells use energy in the
form of ATP.
A cell must regenerate its supply of ATP.
Working muscles use ATP at a rate of 10 million molecules per second.
Cellular respiration converts the potential energy stored in macromolecules to the usable energy of ATP.
Metabolism – all chemical activity of a cell
Anabolism = synthesis = building larger molecules – endothermic reactions = require energy
Catabolism = decomposition = breaking down molecules – exothermic reactions = release energy
Oxidation - partial or complete loss of electron(s) (NADH to NAD+)
Reduction - partial or complete gain of electron(s) (NAD+ to NADH)
Reducing agent (compounds that get oxidized)- electron donor C6H12O6, FADH2, NADH
Oxidizing agent (compounds that get reduced)- electron acceptor Oxygen, FADH+, NAD+
In general, organic molecules that have an abundance of C-H bonds are a source of electrons with the potential
to fall (move) closer to Oxygen.
Potential Energy = Bonds = Position of Electrons
An electron loses potential energy when it shifts from a less electronegative atom (atom that doesn’t like
electrons as much) toward a more electronegative atom (atom that likes electrons more).
A redox reaction relocates electrons closer to oxygen (or another oxidizing agent) releasing chemical energy that
can be put to work.
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Aerobic respiration – in presence of oxygen.
Anaerobic respiration – absence of oxygen (glycolysis + fermentation)
Summary equation for aerobic cellular respiration
----------Oxidation----------
C6H12O6 + 6O2 --------- 6CO2 + 6H2O + Energy
 ------------Reduction-------
Cellular respiration converts the potential energy stored in macromolecules to the usable energy of ATP.
In effect, they "cash in the large denomination of energy banked in glucose for the small change of ATP, which
is more practical for the cell to spend on its work."
ELECTONS TRAVEL DOWNHILL VIA
Food ------------NADH -------------Electron Transport Chain-----------Oxygen
TWO WAYS ATP IS GENERATED:
6.7 Two mechanisms generate ATP
• Cells use the energy
released by “falling”
electrons to pump
H+ ions across a
membrane
– The energy of the
gradient is
harnessed to make
ATP by the process
of chemiosmosis
High H+
concentration
ATP synthase
uses gradient
energy to
make ATP
Membrane
Electron
transport
chain
ATP
synthase
Energy from
Low H+
concentration
Figure 6.7A
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• ATP can also be
made by
transferring
phosphate groups
from organic
molecules to ADP
– This process
is called
substrate-level
phosphorylation
Enzyme
Adenosine
Organic molecule
(substrate)
Adenosine
New organic molecule
(product)
Figure 6.7B
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
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Cellular Respiration Overview
I. Glycolysis - occurs outside of the mitochondrion in cytosol.
II. Transition Reactions - occurs in the Mitochondrial Matrix
III. Krebs Cycle (Citric Acid Cycle) - occurs in the Mitochondrial Matrix
IV. Electron Transport Chain (Oxidative Phosphorylation) - built into membrane of the cristae
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I. GLYCOLYSIS
Glycolysis harvests chemical energy by breaking down glucose to pyruvate (pyruvic acid)
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WHERE IT OCCURS:
OVERALL PROCESS:
GLYCOLYSIS
END PRODUCTS:
WHAT YOU START WITH:
FERMENTATION:
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FERMENTATION
Glycolysis in and of itself is not a very effective means of tapping all the energy stored in glucose. Most of the
energy is still stuck in the 2 molecules of pyruvate.
Under aerobic conditions (oxygen is present) the pyruvate will enter the Krebs Cycle.
Under anaerobic conditions (no oxygen present) glycolysis would quickly deplete the cell of NAD+.
However, if there is no oxygen present, a cell may use the process of fermentation.
FERMENTATION = glycolysis plus reactions that regenerate NAD+
Alcohol fermentation -
Lactic Acid Fermentation -
In absence of oxygen, get regeneration of NAD+ thru fermentation
Realize that some animals (particularly many bacteria) live in anaerobic environments or habitats with
very little oxygen. Glycolysis is their main way to get ATP. Glycolysis only produces 2 ATP's by itself (for
every molecule of glucose), but when coupled with the Krebs Cycle and Electron Transport Chain, each
molecule of glucose decomposed can produce 36-38 ATP's! That's a huge difference.
In presence of oxygen, potential energy of 2NADH gets shuttled over to electron transport chain. Further, the 2
pyruvate molecules can get broken down to tap their potential energy in the Krebs cycle.
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II. INTERMEDIATE STAGE
Transition (Intermediate) Reactions
Before pyruvate enters Krebs Cycle, it must
enter
the mitochondria via a transport protein.
Then the pyruvate:
1.
2.
3.
The 2 acetylCoA molecules can now enter the
Krebs Cycle.
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III. THE KREBS CYCLE (Citric Acid Cycle)
Keep in mind that:
• for every glucose molecule split during glycolysis, two acetyl CoA molecules are produced; therefore,
• it takes two turns of Krebs Cycle to complete the breakdown of glucose.
WHERE IT OCCURS:
OVERALL PROCESS:
KREB CYCLE
END PRODUCTS:
WHAT YOU START WITH:
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IV. ELECTRON TRANSPORT CHAIN
Every NADH that enters the electron transport chain will yield approximately 3 ATP molecules.
Every FADH2 that enters the electron transport chain will yield approximately 2 ATP molecules.
ETC: TWO MAJOR EVENTS:
1. Passing of electrons
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2. Pumping of H+ ions
Those H+ ions can then diffuse down their concentration
gradient through ATP Synthase a protein complex
embedded in the inner membrane which uses the energy
of the H+ gradient to drive ATP synthesis.
This process of harnessing the energy of H+ ions
diffusion down there concentration gradient to power the
synthesis of ATP is called Chemiosmosis
ETC
START WITH:
END PRODUCTS:
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