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Chapter 08
Cellular
Respiration
Cellular
Respiration
Outline
Glycolysis
Transition Reaction
Citric Acid Cycle
Electron Transport System
Fermentation
Metabolic Pool
Catabolism
Anabolism
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Cellular
Respiration
Cellular Respiration
A cellular process that requires oxygen and
gives off carbon dioxide
Usually involves breakdown of glucose to
carbon dioxide and water
Energy extracted from glucose molecule:
- Released step-wise
- Allows ATP to be produced efficiently
Oxidation-reduction enzymes include NAD+
and FAD as coenzymes
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Glucose Breakdown:
Summary Reaction
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Cellular
Respiration
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NAD+ and FAD
NAD+ (nicotinamide adenine dinucleotide)
Called a coenzyme of oxidation-reduction it
can
- Oxidize a metabolite by accepting electrons
- Reduce a metabolite by giving up electrons
Each NAD+ molecule used over and over again
FAD (flavin adenine dinucleotide)
Also a coenzyme of oxidation-reduction
Sometimes used instead of NAD+
Accepts two electrons and two hydrogen ions
(H+) to become FADH2
NAD+ Cycle
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Cellular Respiration:
Overview of 4 Phases
Cellular
Respiration
Glycolysis:
Occurs in cytoplasm
Glucose broken down to two molecules of pyruvate
ATP is formed
Transition reaction:
Both pyruvates are oxidized
Electron energy is stored in NADH
Two carbons are released as CO2
Citric acid cycle:
Electron energy is stored in NADH and FADH2
ATP is formed
Four carbons are released as CO2
Electron transport chain:
Extracts energy from NADH & FADH2
Produces 32 or 34 molecules of ATP
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Glucose Breakdown:
Overview of 4 Phases
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Glucose Breakdown:
Glycolysis
Cellular
Respiration
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Occurs in cytoplasm outside mitochondria
Energy Investment Steps:
Two ATP are used to activate glucose
Glucose splits into two G3P molecules
Energy Harvesting Steps:
Two electrons (as hydrogen atoms) are picked
up by two NAD+
Four ATP produced by substrate-level
phosphorylation
Net gain of two ATP
Both G3Ps converted to pyruvates
Glycolysis:
The Balance Sheet
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Substrate-level Phosphorylation
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Glycolysis
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Glycolysis
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Cellular
Respiration
Glucose Breakdown:
The Preparatory (Prep) Reaction
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End product of glycolysis, pyruvate, enters
the mitochondrial matrix
Pyruvate converted to 2-carbon acetyl group
Attached to Coenzyme A to form acetyl-CoA
Electron picked up (as hydrogen atom) by
NAD+
CO2 released, and transported out of
mitochondria into the cytoplasm
Mitochondrion:
Structure & Function
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Preparatory Reaction
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Glucose Breakdown:
The Citric Acid Cycle
Cellular
Respiration
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A.K.A. Krebs cycle
Occurs in matrix of mitochondria
Both acetyl (C2) groups received from the
preparatory reaction:
Join with an enzyme CoA molecule to make acetylCoA
Acetyl (C2) group transferred to oxaloacetate (C2) to
make citrate (C6)
Each acetyl oxidized to two CO2 molecules
Remaining 4 carbons from oxaloacetate converted
back to oxaloacetate (thus “cyclic”)
NADH, FADH2 capture energy rich electrons
ATP formed by substrate-level phosphorylation
The Citric Acid Cycle
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Citric Acid Cycle:
Balance Sheet
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Cellular
Respiration
Electron Transport Chain
Location:
Eukaryotes: cristae of the mitochondria
Aerobic Prokaryotes: plasma membrane
Series of carrier molecules:
Pass energy rich electrons along
Complex arrays of protein and cytochromes
- Cytochromes are respiratory molecules
- Complex carbon rings with metal atoms in
center
Receives electrons from NADH & FADH2
Produce ATP by oxidative phosphorylation
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Cellular
Respiration
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Electron Transport Chain
The fate of the hydrogens:
Hydrogens from NADH deliver enough energy
to make 3 ATPs
Those from FADH2 have only enough for 2
ATPs
“Spent” hydrogens combine with oxygen
Recycling of coenzymes increases efficiency
Once NADH delivers hydrogens, it returns (as
NAD+) to pick up more hydrogens
However, hydrogens must be combined with
oxygen to make water
If O2 not present, NADH cannot release H
No longer recycled back to NAD+
Electron Transport Chain
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Organization of Cristae
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Glucose Catabolism:
Overall Energy Yield
Cellular
Respiration
Net yield per glucose:
From glycolysis – 2 ATP
From citric acid cycle – 2 ATP
From electron transport chain – 32 ATP
Energy content:
Reactant (glucose) 686 kcal
Energy yield (36 ATP) 263 kcal
Efficiency 39%; balance is waste heat
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Overall Energy Yielded
per Glucose Molecule
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Cellular
Respiration
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Fermentation (1)
When oxygen limited:
Spent hydrogens have no acceptor
NADH can’t recycle back to NAD+
Glycolysis stops because NAD+ required
Fermentation:
“Anaerobic” pathway
Can provide rapid burst of ATP
Provides NAD+ for glycolysis
NADH combines with pyruvate to yield NAD+
Fermentation
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Cellular
Respiration
Fermentation (2)
Pyruvate reduced by NADH to:
Lactate
- Animals & some bacteria
- Cheese & yogurt; sauerkraut
Ethanol & carbon dioxide
- Yeasts
- Bread and alcoholic beverages
Allows glycolysis to proceed faster than O2 can be
obtained
Anaerobic exercise
Lactic acid accumulates
Causes cramping and oxygen debt
When O2 restored, lactate broken down to
acetyl-CoA and metabolized
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Products of Fermentation
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Efficiency of Fermentation
InLine Figure 143
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Metabolic Pool:
Catabolism (1)
Cellular
Respiration
Foods:
Sources of energy rich molecules
Carbohydrates, fats, and proteins
Catabolism (breakdown side of metabolism)
Breakdown products enter into respiratory
pathways as intermediates
Carbohydrates
- Converted into glucose
- Processed as above
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The Metabolic Pool Concept
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Metabolic Pool:
Catabolism (2)
Cellular
Respiration
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Breakdown products enter into respiratory
pathways as intermediates (cont.)
Proteins
- Broken into amino acids (AAs)
- Some AAs used to make other proteins
- Excess AAs deaminated (NH2 removed) in liver
 Results
in poisonous ammonia (NH3)
 Quickly converted to urea
- Different R-groups from AAs processed
differently
- Fragments enter respiratory pathways at many
different points
Metabolic Pool:
Anabolism (1)
Cellular
Respiration
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All metabolic reactions part of metabolic pool
Intermediates from respiratory pathways can be
used for anabolism
Anabolism (build-up side of metabolism):
Carbs:
- Start with acetyl-CoA
- Basically reverses glycolysis (but different pathway)
Fats
- G3P converted to glycerol
- Acetyls connected in pairs to form fatty acids
- Note – dietary carbohydrate RARELY converted to fat in
humans!
Metabolic Pool:
Anabolism (2)
Cellular
Respiration
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Anabolism (cont.):
Proteins:
- Made up of combinations of 20 different amino
acids
- Some amino acids (11) can be synthesized from
respiratory intermediates
 organic
acids in citric acid cycle can make amino
acids
 Add NH2 – transamination
- However, other amino acids (9) cannot be
synthesized by humans
 Essential
amino acids
 Must be present in diet or die
Cellular
Respiration
Review
Glycolysis
Transition Reaction
Citric Acid Cycle
Electron Transport System
Fermentation
Metabolic Pool
Catabolism
Anabolism
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Ending Slide Chapter 08
Cellular
Respiration