Bre’ona Fergerson and Jaelon Harris
Cellular Respiration Outline
9.1 Catabolic pathways yield energy by oxidizing organic fuels.
To keep working a cell must regenerate the ATP that it uses
The breakdown of glucose and other organic fuels are exergonic (accompanied by the release of
energy)
What is Cellular Respiration?
It is the process in a cell’s mitochondria when food (sugar) is broken down using oxygen to produce
energy. There are two main types of cellular respiration processes, aerobic and anaerobic.
Aerobic respiration
and Anaerobic Respiration
 Aerobic respiration is the consumption of oxygen as a reactant along with organic fuel.
Just think of it like this: Aerobic means “air” so this process needs air (oxygen) in order for it to work.
Equation:
Anaerobic Respiration is when a different substance is used in replace of oxygen as a
reactant to harvest chemical energy. (*Also known as fermentation)
o For example, sometimes a plant or an animal doesn’t have enough oxygen to respire,
but they still need energy to live so they perform respiration without oxygen to
produce energy.
Redox Reactions
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In redox reactions the cell taps the energy stored in the food molecules, which causes one
substance to partially or totally shift electrons to another substance. The substance that
receives the electrons is reduced (becomes more negative) and the substance losing the
electrons is oxidized (becomes more positive).
During cellular respiration, glucose is oxidized to CO₂ and O₂ is reduced to H₂O.
When electrons transfer from organic compounds to oxygen they lose potential energy;
Electrons from the organic compound are usually first passed to NAD+ which reduces it to
NADPH; the NADPH then passes the electrons to and Electron Transport Chain that connects
them to O₂ in energy releasing steps. This energy is then used to make ATP.
Stages of Cellular Respiration: A Preview
 Glycolysis-The breakdown of enzymes by enzymes releasing energy and pyruvic acid; it
produces 2 molecules of ATP.
 Citric Acid Cycle (Kreb’s Cycle)- the sequence of reactions in which most living cells
generate energy during the process of aerobic respiration;takes place in mitochondria,
consuming O₂, producing CO₂ and H₂O as waste products and converting ADP to energyrich ATP.
Bre’ona Fergerson and Jaelon Harris
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Glycolysis and the citric acid cycle supply electrons (through either NADH or FADH₂) to the
electron transport chain, which drives oxidative phosphorylation (metabolic pathway that
cells use to oxidize nutrients which causes the release of energy which is used to reform ATP).
Oxidative phosphorylation then generates ATP.
9.2 Glycolysis harvests chemical energy by oxidizing glucose to pyruvate
9.3 The citric acid cycle completes the energy-yielding oxidation of organic molecules
 In eukaryotic cells, the importation of the pyruvate into the mitochondrion and its conversion
to acetyl CoA links glycolysis to the citric acid cycle .
9.4 During oxidative phosphorylation, chemiosmosis couples electron transport to ATP
synthesis
Introduction
 Glycolysis (Concept 9.2) and the citric acid cycle(Concept 9.3)
o Glycolysis ⇒ 2 ATP (through substrate level phosphorylation)
o Citric Acid Cycle ⇒ 2 ATP (through substrate level phosphorylation)
 Concept 9.4: Oxidative Phosphorylation
o Oxidative Phosphorylation= Electron Transport Chain + Chemiosmosis ⇒ generating
34 ATP
 The most efficient and productive way in which cell harvest the energy from
glucose and other nutrient
Bre’ona Fergerson and Jaelon Harris
2 parts of process
 Electron Transport Chain
 Chemiosmosis
o NADH and FADH2 serve as electron carriers
o 34 ATP are produced
Electron Transport Chain
o Location
 cristae= the folded inner membrane of the mitochondria (in eukaryotes)
 Plasma membrane (in prokaryotes)
Series of protein are embedded in the cristae
o 4 large protein complex (Complex I - IV)
o Cytochrome= electron carriers between ubiquinone and oxygen
Electrons are passed down from one protein complex(less electronegative) to next protein
complex(more electron negative) through the series of redox reaction
o As ETC progresses, reduction potentials increase until O2
o
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The Pathway of Electron Transport
 NADH and FADH2 donate their electrons to ETC
o NADH (produced from Glycolysis and Citric Acid Cycle)
o FADH2 (produced from Citric Acid Cycle)
 FADH2 has less energy b/c it is added later in the chain
 Electrons are transferred along the ETC through the series of redox reaction ⇒ released
energy
o Using that energy, H+ are pumped from matrix to intermembrane space ⇒ establish
Proton Motive Force
o Proton Motive Force= high [H+] gradient in intermembrane space and low [H+]
gradient in matrix
 Stored energy which can be used to make ATP through chemiosmosis
 At the end of ETC, oxygen serves as final electron acceptor by converting into water
Cytochromes are electron carriers between ubiquinone and oxygen.
ATP Synthase
 What?
o Protein complex ⇒ made up of multiple polypeptides
 Location
o the inner membrane of the Mitochondrion
 4 Components
o Stator
o Rotor
o internal rod
o Knob
 How it works?
o Hydrogen ions flow down between the stator and rotor and causes the rotor and rod to
rotate
o The spinning rod causes changes in the stationary knob, activating three catalytic sites
that make up the knob
Bre’ona Fergerson and Jaelon Harris
o
It catalyzes the addition of inorganic phosphate to ADP, generating ATP
Chemiosmosis: The Energy-Coupling Mechanism
 Chemiosmosis = Proton Motive Force ⇒ ATP(through ATP synthase)
o Chemiosmosis= energy stored in form of hydrogen ion gradient across a membrane to
synthesize ATP
o H+ flow from high concentration gradient (intermembrane space) to low concentration
gradient (matrix) through ATP synthase
o ATP synthase generates 34 ATP
 In total, cellular respiration generate 38 ATP
o Glycolysis⇒ 2 ATP (Substrate Level Phosphorylation)
o Citric Acid Cycle⇒ 2 ATP (Substrate Level Phosphorylation)
o ETC + Chemiosmosis⇒ 34 ATP (Oxidative Phosphorylation)
https://www.youtube.com/watch?v=kN5MtqAB_Yc
Chemiosmosis is energy stored in form of hydrogen ion gradient across a membrane to synthesize
ATP
9.5 Fermintation and anaerobic respiration enables cells to produce ATP without Oxygen.
Fermentation
 At the end of Glycolysis, pyruvate, ATP, and NADH are produced
 Pyruvate can undergo 2 different pathway (depending whether or not O2 is present)
o O2 is present⇒ Aerobic cellular respiration
o No O2 is present⇒ Fermentation
 2 Types of Fermentation
o Alcohol Fermentation
o Lactic Acid Fermentation
 Purpose: regeneration of NAD+, which can be reused in Glycolysis
Types of Fermentation
1. Alcohol Fermentation(Pyruvate⇒ ethanol)
o 2 Steps
o
o
o
 Pyruvate⇒ Acetaldehyde (by releasing CO2)
 Acetaldehyde⇒ Ethanol (reduced by NADH)
Final electron acceptor: Acetaldehyde
Produce 2 ATP (substrate level phosphorylation)
Ex. yeast
Type of Fermentation
2. Lactic Acid Fermentation
o One Step
 Pyruvate⇒ lactate (reduced by NADH)
o Final electron acceptor: Pyruvate
o Produce 2 ATP (substrate level Phosphorylation)
o Example
 Fungi
Bre’ona Fergerson and Jaelon Harris
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bacteria (used to make cheese and yogurt)
human muscle cells
Comparing Fermentation and Aerobic Respiration
Aerobic Respiration
Environment
o O2 is present
 Final Electron Acceptor
o Oxygen
 Net ATP Production (38 ATP)
o Glycolysis⇒ 2 ATP
o Citric Acid Cycle⇒ 2 ATP
o ETC + Chemiosmosis⇒ 34 ATP
 Types of organism that use Aerobic Respiration
o Obligate Aerobic= organism that can survive with O2
Fermentation
 Environment
o No O2
 Final electron acceptor
o Organic molecule (Pyruvate or Acetaldehyde)
 Net ATP Production (4 ATP)
o 2 ATP (Glycolysis)
o 2 ATP (Fermentation)
 Type of Organism that use fermentation
o Obligate Anaerobe= organism that cannot survive in the presence of O2
Both
 Common pathway
o Glycolysis (to oxidize glucose)
 Type of Organism that can use either pathway
o Facultative Anaerobe= organism that can use either use either fermentation or
aerobic respiration
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9.6 Glycolysis and the citric acid cycle connect to many other metabolic pathways
Catabolic Pathway
 Breakdown complex molecules into monomers(used as fuels⇒ generate ATP)
o Carbohydrates
 (enter) Glycolysis and Citric Acid Cycle
o Proteins⇒ Amino acid ⇒ Deamination(removal of amino group) need to occur first
 Converted into intermediates of Glycolysis and Citric Acid Cycle
o
Fat (broken down into) ⇒ Glycerol + Fatty Acid
 Glycerol(converted into)⇒Glyceraldehyde-3-Phosphate (intermediate of Glycolysis)
 Fatty Acid ⇒ beta oxidation(breakdown FA into acetyl CoA) ⇒ (enter) Citric Acid Cycle
Bre’ona Fergerson and Jaelon Harris
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(produce) NADH and FADH2⇒ generate ATP (through Oxidative
Phosphorylation)
Anabolic Pathway
 Monomers⇒ Complex molecules (consume ATP)
o Amino Acid⇒ Protein (build up muscle)
o Pyruvate⇒ Glucose
o Acetyl CoA⇒ Fatty Acid
 Connection between Glycolysis and Citric Acid Cycle
o Dihydroxyacetone Phosphate (from glycolysis) ⇒ (converted into) precursor of fat ⇒ used
in Citric Acid Cycle
Feedback Mechanisms⇒ Regulation
 Feedback Inhibition= end product of pathway inhibits the enzyme that is used for early
reaction step
o Ex. increase ATP⇒ slow down respiration; Decrease ATP⇒ speed up respiration (by
regulating Enzyme activity)
o Enzyme pathway regulates: Phosphofructokinase(enzyme for step 2 glycolysis)
 Allosteric enzyme(has sites for specific activator and inhibitor to bind
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Activator: AMP⇒ speed up Glycolysis
Inhibitor: ATP and Citrate⇒ slow down Glycolysis
Chapter Questions
1. What is the reducing agent in the following reaction?
2. The immediate energy source that drives ATP synthesis by ATP synthase during oxidative
phosphorylation is the?
3. What metabolic pathway is common to both fermentation and cellular respiration of a
glucose molecule?
4. In mitochondria, exergonic redox reactions do what?
5. The final electron acceptor of the electron transport chains of mitochondria, which of the
following changes occur?
6. When electrons flow along the electron transport chains of mitochondria, what changes
occur?
7. Cells do not catabolize carbon dioxide because?
8. Which of the following is a true distinction between fermentation and cellular respiration
9. Most CO2 from catabolism is released during?
Answers
1. NADPH
2. Hᐩ concentration across the membrane holding ATP synthase
3. Glycolysis
4. Provide the energy that establishes the proton gradient.
5. Oxygen
6. The pH of the matrix increases
7. CO₂ is already completely oxidized
8. NADH is oxidized by the electron transport chain in respiration only
9. The citric acid cycle
Bre’ona Fergerson and Jaelon Harris