Chapter 7Chapter 7
How Cells Release How Cells Release Chemical energyChemical energy
Overview of Overview of Carbohydrate Breakdown PathwayCarbohydrate Breakdown Pathway
Plants and all other photoautotrophs get Plants and all other photoautotrophs get energy from the sun, heterotrophs get by energy from the sun, heterotrophs get by eating plants and one anothereating plants and one another
ATP is a common energy currency that ATP is a common energy currency that drives metabolic reactions in cellsdrives metabolic reactions in cells
Pathways of Carbohydrate Pathways of Carbohydrate BreakdownBreakdown
Starts withStarts with glycolysis in the cytoplasmglycolysis in the cytoplasm–– Convert glucose and other sugars to pyruvateConvert glucose and other sugars to pyruvate
Comparison of main pathwaysComparison of main pathways
Fermentation Fermentation pathwaypathway
Aerobic Aerobic RespirationRespiration
Produces ATP under Produces ATP under anaerobic conditionsanaerobic conditions
Ends in cytoplasm, do Ends in cytoplasm, do not use oxygen, yields 2 not use oxygen, yields 2 ATP per molecule of ATP per molecule of glucoseglucose
Produces ATP by Produces ATP by using oxygenusing oxygen
Ends in mitochondria, Ends in mitochondria, uses oxygen, yields up uses oxygen, yields up to 36 ATP per glucose to 36 ATP per glucose moleculemolecule
Oxygen acts as the Oxygen acts as the final acceptor of final acceptor of electrons used during electrons used during these reactionsthese reactions
Overview of Aerobic RespirationOverview of Aerobic Respiration
Three main stages of aerobic respiration:Three main stages of aerobic respiration:1. Glycolysis1. Glycolysis
2. Krebs cycle2. Krebs cycle
3. Electron transfer phosphorylation3. Electron transfer phosphorylation
Summary equation:Summary equation:
CC66HH1212OO66 + 6O+ 6O22 →→ 6CO6CO22 + 6 H+ 6 H22OOglucose
Cytoplasm
GLYCOLYSIS
KrebsCycle ATP
ATP
6CO2
4 ATP(2net)
32 ATP
2 NADH
8 NADH, 2 FADH2
2 pyruvate
oxygen
2 ATP
glucose
ATPATP
2 ATP
Electron TransferPhosphorylation
Mitochondrion
The first stage, glycolysis, occurs in the cell’s cytoplasm. Enzymes convert a glucose molecule to 2 pyruvate for a net yield of 2 ATP. During the reactions, 2 NAD+ pick up electrons and hydrogen atoms, so 2 NADH form.
The second stage, the Krebs cycle and a few steps before it, occurs inside mitochondria. The 2 pyruvates are broken down to CO2, which leaves the cell. During the reactions, 8 NAD+ and 2 FAD pick up electrons and hydrogen atoms, so 8 NADH and 2 FADH2 form. 2 ATP also form.
The third and final stage, electron transfer phosphorylation, occurs inside mitochondria. 10 NADH and 2 FADH2 donate electrons and hydrogen ions at electron transfer chains.Electron flow through the chains sets up H+ gradients that drive ATP formation. Oxygen
Overview of aerobic respirationOverview of aerobic respiration
Glycolysis Glycolysis ––Glucose Breakdown StartsGlucose Breakdown Starts
First step First step –– Conversion of glucose to Conversion of glucose to pyruvatepyruvateEnzymes of glycolysis use two ATP to Enzymes of glycolysis use two ATP to convert one molecule of glucose to two convert one molecule of glucose to two molecules of threemolecules of three--carbon pyruvate carbon pyruvate
Reactions transfer electrons and hydrogen Reactions transfer electrons and hydrogen atoms to two NADatoms to two NAD++ (reduces to NADH) (reduces to NADH)
2 ATP is formed by substrate2 ATP is formed by substrate--level level phosphorylationphosphorylation
Products of GlycolysisProducts of Glycolysis
Net yield of glycolysis:Net yield of glycolysis:–– 2 pyruvate, 2 ATP, and 2 NADH per glucose2 pyruvate, 2 ATP, and 2 NADH per glucose
Pyruvate may: Pyruvate may: –– Enter fermentation pathways in cytoplasm Enter fermentation pathways in cytoplasm
–– Enter mitochondria and be broken down Enter mitochondria and be broken down further in aerobic respirationfurther in aerobic respiration
ATP
ATP
glucose
ADP
ADP
P
Pglucose–6–phosphate
fructose–1,6–bisphosphate
Glycolysis
ATP Requiring Steps
p
ATP
2 ADP
2 NAD+ + 2 Pi
2 PGA
NADH
2 PGAL
ATP
2 pyruvate
2 PEP
2 ADP
to second stage Net 2 ATP + 2 NADH
2 ATP producedby substrate-levelphosphorylation
2 ATP producedby substrate-levelphosphorylation
2 reduced coenzymes
ATP Generating steps
Second Stage of Aerobic Second Stage of Aerobic RespirationRespiration
Krebs CycleKrebs CycleBreak down of pyruvate to Carbon dioxideBreak down of pyruvate to Carbon dioxide
The second stage of aerobic respiration The second stage of aerobic respiration takes place in the inner compartment of takes place in the inner compartment of mitochondria mitochondria
It starts with acetylIt starts with acetyl--CoA formation and CoA formation and proceeds through the Krebs cycleproceeds through the Krebs cycle
outer mitochondrialcompartment (inbetween the twomembranes)
inner mitochondrialcompartment
inner membrane
outer membrane(next to cytoplasm)
KrebsCycle
2 acetyl–CoA Breakdown of 2 pyruvate to 6CO2 yields 2 ATP. Also, 10 coenzymes are reduced (8 NADH, 2 FADH2). The coenzymes carry hydrogenions and electrons to sites of the third stage of aerobic respiration.
INNER COMPARTMENT
OUTER COMPARTMENT
2 pyruvate(glycolysis)
glucose
b The second stage starts after membrane proteins transport pyruvate from the cytoplasm, across both mitochondrial membranes, to the innercompartment. Six carbon atoms enter these reactions (in two pyruvate), and six leave (in six CO2). Many coenzymes form.
a An inner membrane divides a mitochondrion’s interior into two compartments. The second and third stages of aerobic respiration take place at this membrane.
FADH2
NADH
ATPCO2
AcetylAcetyl--CoA FormationCoA Formation
Two pyruvates from glycolysis are Two pyruvates from glycolysis are converted to two acetylconverted to two acetyl--CoA CoA
Two COTwo CO22 leave the cellleave the cell
AcetylAcetyl--CoA enters the Krebs cycle CoA enters the Krebs cycle
Krebs CycleKrebs Cycle
In each turn of the Krebs cycle, one acetylIn each turn of the Krebs cycle, one acetyl--CoA is converted to two molecules of COCoA is converted to two molecules of CO22
After two cyclesAfter two cycles–– Two pyruvates are dismantledTwo pyruvates are dismantled
–– Glucose molecule that entered glycolysis is Glucose molecule that entered glycolysis is fully broken downfully broken down
Energy ProductsEnergy Products
Reactions transfer electrons and hydrogen Reactions transfer electrons and hydrogen atoms to NADatoms to NAD++ and FADand FAD–– Reduced to NADH and FADHReduced to NADH and FADH22
ATP forms by substrateATP forms by substrate--level level phosphorylationphosphorylation–– Direct transfer of a phosphate group from a Direct transfer of a phosphate group from a
reaction intermediate to ADPreaction intermediate to ADP
Net ResultsNet Results
Second stage of aerobic respiration results inSecond stage of aerobic respiration results in
Six COSix CO22, two ATP, eight NADH, and two FADH, two ATP, eight NADH, and two FADH22
for every two pyruvates for every two pyruvates
Adding the yield from glycolysis, the total isAdding the yield from glycolysis, the total is
–– Twelve reduced coenzymes and four ATP for Twelve reduced coenzymes and four ATP for each glucose moleculeeach glucose molecule
Coenzymes deliver electrons and hydrogen to Coenzymes deliver electrons and hydrogen to the third stage of reactionthe third stage of reaction
NADH
NADH
FADH2
ATP
KrebsCycle
KrebsCycle
NADH
NADH
coenzyme A
coenzyme A
acetyl–CoA
oxaloacetate citrate
pyruvate
Acetyl–CoAFormation
CO2
CO2NAD+
NAD+
NAD+
FAD
NAD+
CO2
ADP + P i
Third Stage: Aerobic RespirationThird Stage: Aerobic Respiration’’s s Big Energy PayoffBig Energy Payoff
Coenzymes deliver electrons and hydrogen ions Coenzymes deliver electrons and hydrogen ions to electron transfer chains in the inner to electron transfer chains in the inner mitochondrial membrane mitochondrial membrane Energy released by electrons flowing through Energy released by electrons flowing through the transfer chains moves Hthe transfer chains moves H++ from the inner to from the inner to the outer compartmentthe outer compartmentHH++ gradient builds up across the inner gradient builds up across the inner membranemembraneHH++ ions flow by concentration gradient back to ions flow by concentration gradient back to the inner compartment through ATP synthasesthe inner compartment through ATP synthases
The Aerobic Part of Aerobic The Aerobic Part of Aerobic RespirationRespiration
At the end of electron transfer chain At the end of electron transfer chain oxygen and Hoxygen and H++ , forming water, forming water
Overall, aerobic respiration yields up to 36 Overall, aerobic respiration yields up to 36 ATP for each glucose moleculeATP for each glucose molecule
KrebsCycle
Glycolysis
glucose
youarehere
Electron TransferPhosphorylation
NADHFADH2
ATPADP + P i
H+
H+H+
H+H+H+
H+H+H+
H+ H+ H+
INNERMITOCHONDRIAL
MEMBRANE
OUTERCOMPARTMENT
INNERCOMPARTMENT
H2O
1/2 O2
H+
glucose
Glycolysis
2 pyruvate
KrebsCycle
Electron TransferPhosphorylation
(2 net)
2 NADH
ATP
2 FADH2
6 NADH
2 acetyl-CoA
32
ADP + P i
H+
ATP
2 NADH
2 NADH
ATP
ATP
H+ H+ H+ H+
2 NAD+
2 CO2
4 CO2
2
oxygen
INNER MITOCHONDRIALCOMPARTMENT
OUTER MITOCHONDRIALCOMPARTMENT
CYTOPLASM
water
2
Anaerobic Anaerobic EnergyEnergy--Releasing PathwaysReleasing Pathways
Fermentation PathwayFermentation PathwayBegins with glycolysis and ends in the Begins with glycolysis and ends in the cytoplasmcytoplasmDo not use oxygen or electron transfer Do not use oxygen or electron transfer chainschainsTwo ATP is formed from glycolysisTwo ATP is formed from glycolysisFinal steps do not produce ATP; only Final steps do not produce ATP; only regenerate oxidized NADregenerate oxidized NAD++ required for required for glycolysis to continueglycolysis to continue
FermentationPathway
Glycolysis
glucose
you arehere
Anaerobic PathwaysAnaerobic Pathways
Alcoholic fermentationAlcoholic fermentation
End product:End product: Ethyl alcohol (or ethanol)Ethyl alcohol (or ethanol)
Pyruvate(3 carbon) is broken downPyruvate(3 carbon) is broken down
Enzyme splits pyruvate into two Enzyme splits pyruvate into two -- carbon carbon acetaldehyde and carbon dioxideacetaldehyde and carbon dioxide
Alcoholic fermentationAlcoholic fermentation
Role of Yeast in fermentationRole of Yeast in fermentation
They are unicellular fungiThey are unicellular fungi
Sacchromyces cerevisiae Sacchromyces cerevisiae (Baker(Baker’’s yeast)s yeast)
Cells release carbon dioxide in Cells release carbon dioxide in fementation and dough expandsfementation and dough expands
Other strains are used in the production of Other strains are used in the production of winewine
Alcoholic FermentationAlcoholic Fermentation
Anaerobic PathwaysAnaerobic Pathways
Lactate fermentationLactate fermentation
End product:End product: LactateLactate
Conversion of pyruvate into three carbon Conversion of pyruvate into three carbon lactate (lactic acid)lactate (lactic acid)
Fermenters such as Fermenters such as lactobacillus lactobacillus acidophillusacidophillus can ferment milk, butter milk, can ferment milk, butter milk, cheese, yogurtcheese, yogurt
glucoseGlycolysis
2
pyruvate
NADH
2 NAD+
2ATP
ATP4
NADH
2 NAD+
2
LactateFermentation
lactate
The TwitchersThe Twitchers
SlowSlow--twitch and fasttwitch and fast--twitch skeletal muscle twitch skeletal muscle fibers can support different activity levels fibers can support different activity levels
Aerobic respiration and lactate Aerobic respiration and lactate fermentation proceed in different fibers of fermentation proceed in different fibers of musclesmuscles
These pathways yeilds ATP for musclesThese pathways yeilds ATP for muscles
Alternative Energy SourcesAlternative Energy Sources
Complex Carbohydrate break downComplex Carbohydrate break downThey are broken down into simple sugars like They are broken down into simple sugars like glucoseglucoseGlucose gets converted to glucoseGlucose gets converted to glucose--66--phosphate.phosphate.If the body doesnIf the body doesn’’t need glucose for t need glucose for energy,glucoseenergy,glucose--66--phosphate can be converted phosphate can be converted to glycogen for storageto glycogen for storageWhen blood sugar drops, glycogen is converted When blood sugar drops, glycogen is converted to glucoseto glucose--66--phosphate and and enters the phosphate and and enters the glycolysis pathwayglycolysis pathway
Alternative Energy Sources;Alternative Energy Sources;Energy from FatsEnergy from Fats
Most fat in the body are triglyceridesMost fat in the body are triglyceridesEnzymes convert fat into glycerol and fatty Enzymes convert fat into glycerol and fatty acidacidGlycerol is converted into PGAL, an Glycerol is converted into PGAL, an intermediate of glycolysisintermediate of glycolysisThe carbon back bones of the fatty acid The carbon back bones of the fatty acid tail is broken apart, and fragments are tail is broken apart, and fragments are converted into acetyl CoA, which can enter converted into acetyl CoA, which can enter the Krebs cyclethe Krebs cycle
Energy from ProteinsEnergy from Proteins
Enzymes split proteins into amino acid Enzymes split proteins into amino acid subunitssubunits
The amino group is removed and The amino group is removed and becomes ammonia, then ureabecomes ammonia, then urea
Urea is excretedUrea is excreted
Carbon Back bones can enter at several Carbon Back bones can enter at several different points of Krebs cycledifferent points of Krebs cycle
FOOD
fats COMPLEX CARBOHYDRATES PROTEINS
glucose, other simple sugars amino acids
Glycolysis
glycerolfatty acids
pyruvate
acetyl-coA
NADH
KrebsCycle
NADH, FADH2
PGALacetyl-coA
oxaloacetateor anotherintermediateof the Krebs
Electron TransferPhosphorylation
LifeLife’’s Unitys Unity
Photosynthesis and aerobic respiration are Photosynthesis and aerobic respiration are interconnected on a global scale interconnected on a global scale
In its organization, diversity, and continuity In its organization, diversity, and continuity through generations, life shows unity at through generations, life shows unity at the bioenergetic and molecular levelsthe bioenergetic and molecular levels
Driven by energy input from the sun, electrons and hydrogen are used to form ATP. ATP energy drives the synthesis of glucose from hydrogen, electrons (delivered by coenzymes), and carbon dioxide’s atoms.
Photosynthesis Aerobic Respiration
Energy input from two ATPinitiates three stages ofreactions. Many ATP form during thecomplete breakdown ofglucose to carbon dioxideand water.
energy out (heat)
chemical energy in many ATP available to drive nearly all cellular tasks
carbondioxide,water
glucose(storedchemicalenergy)
oxygen
energy out (heat)
sunlightenergy in