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Chapter Chapter 66How Cells Harvest Chemical Energy
Copyright © 2009 Pearson Education, Inc.
PowerPoint Lectures for
Biology: Concepts & Connections, Sixth Edition
Campbell, Reece, Taylor, Simon, and Dickey
Lecture by Richard L. Myers
6.1 Photosynthesis and cellular respiration provide energy for life
� Energy is necessary for life processesEnergy is necessary for life processesEnergy is necessary for life processesEnergy is necessary for life processes– These include growth, transport,
manufacture, movement, reproduction, and othersand others
– Energy that supports life on Earth is captured from sun rays reaching Earth through plant, algae, protest, and bacterial photosynthesis
Copyright © 2009 Pearson Education, Inc.
6.1 Photosynthesis and cellular respiration provide energy for life
� Energy in sunlight is used in photosynthesis to make glucose from CO2 and H2O with release of O2
� Other organisms use the O2 and energy in � Other organisms use the O2 and energy in sugar and release CO2 and H2O� Together, these two processes are responsible for the majority of life on Earth
Copyright © 2009 Pearson Education, Inc.
Sunlight energy
ECOSYSTEM
Photosynthesisin chloroplasts
Glucose
H2O
CO2
O2
++++ ++++
The connection betweenphotosynthesis andcellular respiration
Cellular respirationin mitochondria
(for cellular work (ل
ATP
Heat energy
6.2 Breathing supplies oxygen to our cells for use in cellular respiration and removes carbon dioxide
� Breathing and cellular respiration are closely related– BreathingBreathingBreathingBreathing is necessary for exchange of CO2– BreathingBreathingBreathingBreathing is necessary for exchange of CO2produced during cellular respiration for
atmospheric O2
– Cellular respiration Cellular respiration Cellular respiration Cellular respiration uses O2 to help harvest energy from glucose and produces CO2 in the process
Copyright © 2009 Pearson Education, Inc.
Breathing
Lungs
BloodstreamCO2O2
CO2O2
Cellular Respiration
Muscle cells carrying out
CO2 + H2O + ATP
Glucose + O 2
The connection between breathing and cellular respi ration
INTRODUCTION TO
CELLULAR RESPIRATION
Copyright © 2009 Pearson Education, Inc.
6.3 Cellular respiration banks energy in ATP molecules
� Cellular respiration is an exergonicexergonicexergonicexergonicprocess that transfers energy from the bonds in glucose to ATP– Cellular respiration produces 38 38 38 38 ATP ATP ATP ATP molecules from each glucose moleculemolecules from each glucose molecule– Other foods (organic molecules) can be used as a source of energy as well
Copyright © 2009 Pearson Education, Inc.
C6H12O6 + 6 O2 6 CO2 + 6 H2O + ATPs
Summary equation for cellular respiration
Glucose Oxygen Carbon dioxide Water Energy
6.4 CONNECTION: The human body uses energy from ATP for all its activities
� The average adult human needs about 2,200 kcal of energy per day– A kilocaloriekilocaloriekilocaloriekilocalorie (kcalkcalkcalkcal) is the quantity of heat
required to raise the temperature of 1 required to raise the temperature of 1 kilogram (kg) of water by 1oC
– This energy is used for body maintenance and for voluntary activities
Copyright © 2009 Pearson Education, Inc.
Energy Consumed by Various Activities (in kcal).
6.5 Cells tap energy from electrons “falling” from organic fuels to oxygen
� The energy necessary for life is contained in the arrangement of electrons in chemical bonds in organic molecules� An important question is how do cells extract this energy?
Copyright © 2009 Pearson Education, Inc.
� When the carbon-hydrogen bonds of glucose arebroken, electrons are transferred to oxygen and hydrogen – oxygen bonds of water formed.– Oxygen has a strong tendency to attract electrons
6.5 Cells tap energy from electrons “falling” from organic fuels to oxygen
� A cellular respiration equation is helpful to A cellular respiration equation is helpful to A cellular respiration equation is helpful to A cellular respiration equation is helpful to show the changes in hydrogen atom show the changes in hydrogen atom show the changes in hydrogen atom show the changes in hydrogen atom distributiondistributiondistributiondistribution– Glucose loses its hydrogen atoms and is ultimately – Glucose loses its hydrogen atoms and is ultimately
converted to CO2
– At the same time, O2 gains hydrogen atoms and is converted to H2O
– Loss of electrons is called oxidationoxidationoxidationoxidation– Gain of electrons is called reductionreductionreductionreduction
Copyright © 2009 Pearson Education, Inc.
C6H12O6 + 6 O2
Loss of hydrogen atoms
6 CO2 + 6 H2O + Energy(ATP)
Rearrangement of hydrogen atoms (with their electro ns)in the redox reactions of cellular respiration
(Oxidation)
GlucoseGain of hydrogen atoms
(ATP)
A cellular respiration equation A cellular respiration equation A cellular respiration equation A cellular respiration equation
(Reduction)
6.5 Cells tap energy from electrons “falling” from organic fuels to oxygen
� Enzymes are necessary to oxidize glucose and other foods– The enzyme that removes hydrogen from an organic molecule is called dehydrogenasedehydrogenasedehydrogenasedehydrogenase– Dehydrogenase requires a coenzyme called – Dehydrogenase requires a coenzyme called NADNADNADNAD++++ (nicotinamide adenine dinucleotide) to shuttle electrons– NAD+ can become reduced when it accepts electrons and oxidized when it gives them up
Copyright © 2009 Pearson Education, Inc.
Oxidation
Dehydrogenase
pair of redox reactions, occurring simultaneously
adenine dinucleotideadenine dinucleotideadenine dinucleotideadenine dinucleotide
2 H+ + 2 e–
Reduction اختزال NAD+ + 2 H NADH + H+
(carries2 electrons)
adenine dinucleotideadenine dinucleotideadenine dinucleotideadenine dinucleotide
6.5 Cells tap energy from electrons “falling” from organic fuels to oxygen
� The transfer of electrons to NAD+
results in the formation of NADH, the reduced form of NAD+
– In this situation, NAD+ is called an electron acceptor, but it eventually becomes oxidized (loses an electron) and is then called an electron donor
Copyright © 2009 Pearson Education, Inc.
6.5 Cells tap energy from electrons “falling” from organic fuels to oxygen
� There are other electron “carrier” molecules that function like NAD+ .called FAD– They form a staircase where the electrons
pass from one to the next down the pass from one to the next down the staircase
– These electron carriers collectively are called the electron transport chainelectron transport chainelectron transport chainelectron transport chain, and as electrons are transported down the chain, ATP is generated
Copyright © 2009 Pearson Education, Inc.
ATPNAD+
NADH
H+2e–
Controlledrelease ofenergy forsynthesis
of ATP
+
H+2e–
of ATP
O2
H2O
1−−−−2In cellular respiration, electrons fall
down an energy staircase and finally reduce O2
STAGES OF CELLULAR
RESPIRATION
AND FERMENTATION
Copyright © 2009 Pearson Education, Inc.
6.6 Overview: Cellular respiration occurs in three main stages
Stage Stage Stage Stage 1111: : : : GlycolysisGlycolysisGlycolysisGlycolysis
Stage Stage Stage Stage 2222: : : : The citric acid cycleThe citric acid cycleThe citric acid cycleThe citric acid cycle
Copyright © 2009 Pearson Education, Inc.
Stage Stage Stage Stage 3333: : : : Oxidative phosphorylationOxidative phosphorylationOxidative phosphorylationOxidative phosphorylation
6.6 Overview: Cellular respiration occurs in three main stages
� Stage Stage Stage Stage 1111: Glycolysis: Glycolysis: Glycolysis: Glycolysis– Glycolysis begins respiration by breaking glucose, a six-carbon molecule, into two
C-C-C-C-C-C
GlycolysisIn Cytoplasm
Glucose
molecule, into two molecules of a three-carbon compound called pyruvate
Copyright © 2009 Pearson Education, Inc.
C-C-C C-C-C
In Cytoplasm
Pyruvate Pyruvate
Glucose
NAD+
+2
2 ADP
NADH2
P2
� In glycolysis, a single molecule of glucose is enzymatically cut in half through a series of steps to produce two molecules of pyruvate
6.7 Glycolysis harvests chemical energy by oxidizing glucose to pyruvate
2
ATP2 +
H+
2 Pyruvate
An overview of glycolysis
– In the process, two molecules of NAD+ are reduced to two molecules of NADH– At the same time, two molecules of ATP are produced by substrate-level phosphorylation
6.6 Overview: Cellular respiration occurs in three main stages
� Stage Stage Stage Stage 2222: The citric acid cycle: The citric acid cycle: The citric acid cycle: The citric acid cycle- The citric acid cycle completes the oxidation of organic
molecules supplies the third stage with electrons generating many NADH and FADH2
-It breaks down pyruvate into carbon dioxide-This stage occurs in the mitochondria.--This stage occurs in the mitochondria.-
Copyright © 2009 Pearson Education, Inc.
Citric Acid Cycle
Pyruvate Electrons
CO2
6.6 Overview: Cellular respiration occurs in three main stages
� Stage Stage Stage Stage 3333: Oxidative phosphorylation: Oxidative phosphorylation: Oxidative phosphorylation: Oxidative phosphorylation– At this stage, electrons are shuttled through the electron transport chain– As a result, ATP is generated through oxidative phosphorylation
associated with chemiosmosis– This stage occurs in the inner mitochondrion membrane
Copyright © 2009 Pearson Education, Inc.
PyruvateCitric Acid
CycleElectrons
CO2
Electron Transport Chain
O2
H2O ATP
Oxidative Phosphorylation
Mitochondria
Chemiosmosis
MitochondrionNADH
High-energy electronscarried by NADH
NADH
CITRIC ACIDCYCLE
GLYCOLYSIS
PyruvateGlucose
andFADH2
OXIDATIVEPHOSPHORYLATION(Electron Transportand Chemiosmosis)
An overview of cellular respiration
CO2 CO2ATP
Substrate-level phosphorylation Substrate-level phosphorylation
and Chemiosmosis)
Oxidative phosphorylation
ATPATP
CytoplasmInner mitochondrial
Membrane
6.13 Fermentation enables cells to produce ATP without oxygen
� FermentationFermentationFermentationFermentation is an anaerobic (without oxygen) energy-generating process – It takes advantage of glycolysis, producing two producing two producing two producing two
ATPATPATPATP molecules and reducing NAD+ to NADHATPATPATPATP molecules and reducing NAD+ to NADH
– The trick is to oxidize the NADH without passing its electrons through the electron transport chain to oxygen
Copyright © 2009 Pearson Education, Inc.
6.13 Fermentation enables cells to produce ATP without oxygen
دون الحاجة الى ا�وكسجين ATPيجعل التخمر الخ�يا قادرة على انتاج
� Your muscle cells and certain bacteria can oxidize NADH through lactic acid lactic acid lactic acid lactic acid fermentationfermentationfermentationfermentation
� NADH is oxidized to NAD+ when pyruvate is reduced to lactate
� In a sense, pyruvate is serving as an “electron sink,” a place to dispose of the electrons generated by oxidation reactions in glycolysis
Copyright © 2009 Pearson Education, Inc.
Glucose جلوكوز
NADH
NAD+
2
22 ADPP
ATP2
2 Pyruvate بايروفيت 2
GLY
CO
LYS
ISي
وزوك
جلل
حلت
Lactic acid fermentation تخمر الحامض اللبني
++++ 2
NADH2
NAD+2
2 Pyruvate بايروفيت 2
2 Lactate $كتيت 2
6.13 Fermentation enables cells to produce ATP without oxygen
� The baking and winemaking industry have used alcohol alcohol alcohol alcohol fermentationfermentationfermentationfermentation for thousands of years
� Yeasts are single-celled fungi that not only can use respiration for energy but can ferment under anaerobic conditions� They convert pyruvate to CO2 and ethanol while oxidizing NADH back to NAD+
Copyright © 2009 Pearson Education, Inc.
2 ADPP
ATP2 GLY
CO
LYS
IS
NADH
NAD+
2
2
2 Pyruvate
Glucose
++++ 2
NADH2
NAD+2
2 Pyruvate
2 Ethanol
Alcohol fermentation CO22Released
INTERCONNECTIONS BETWEEN
MOLECULAR BREAKDOWN
AND SYNTHESIS
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6.15 Cells use many kinds of organic molecules as fuel for cellular respiration
تستخدم الخ�يا العديد من المركبات العضوية كوقود للتنفس الھوائي
�Although glucose is considered to be the primary source of sugar for respiration and fermentation, there are actually three sources of molecules for generation of ATP
–Carbohydrates Carbohydrates Carbohydrates Carbohydrates (disaccharides)–Proteins Proteins Proteins Proteins (after conversion to amino acids)–FatsFatsFatsFats
Copyright © 2009 Pearson Education, Inc.
Food, such aspeanuts
ProteinsFatsCarbohydrates
Amino acids GlycerolSugarsأحماض امينية Fatty acids
Amino groups
GlucoseOXIDATIVE
PHOSPHORYLATION(Electron Transportand Chemiosmosis)
CITRIC ACIDCYCLE
Acetyl CoA
GLYCOLYSIS
Pyruvate
Amino groups
G3P
ATP
Pathways that break down various food molecules