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Cellular Respiration
Process whereby cells breakdown glucose and other food molecules to release energy.
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• The efficiency of cellular respiration
– Provides a high % of energy in a controlled manner
Figure 6.2B
Burning glucose in an experiment
Energy released from glucose
(as heat and light)
100%
Energy released from glucose
banked in ATP
“Burning” glucosein cellular respiration
About 40%
Gasoline energy converted to movement
Burning gasolinein an auto engine
25%
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• When you exercise
BIOLOGY AND SOCIETY: FEELING THE “BURN”
– Muscles need energy in order to perform work• Enzymes in muscle cells help a cell use glucose and
oxygen to produce ATP
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• Aerobic metabolism
– When enough oxygen reaches cells to support energy needs
• Anaerobic metabolism
– When the demand for oxygen outstrips the body’s ability to deliver it
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• Anaerobic metabolism
– Without enough oxygen, muscle cells break down glucose to produce lactic acid
– Lactic acid is associated with the “burn” associated with heavy exercise
– If too much lactic acid builds up, your muscles give out
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• Physical conditioning allows your body to adapt to increased activity
– The body can increase its ability to deliver oxygen to muscles
• Long-distance runners wait until the final sprint to exceed their aerobic capacity
Figure 6.1
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
ENERGY FLOW AND CHEMICAL CYCLING IN THE BIOSPHERE
• Fuel molecules in food represent solar energy
– Energy stored in food can be traced back to the sun
• Animals depend on plants to convert solar energy to chemical energy
– This chemical energy is in the form of sugars and other organic molecules
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Figure 6.3
Sunlightenergy
Ecosystem
Photosynthesis(in chloroplasts)
Glucose
Oxygen
Carbon dioxide
Cellular respiration(in mitochondria)
Water
for cellular work
Heat energy
Energy and Food• A large amount of
energy is stored within the chemical bonds of food.
• Burning 1g glucose (C6H12O6) releases 3811 C of heat.
• Calorie - amount of energy needed to raise the temperature of 1g of H2O 1ºC.
• Cells do not burn glucose , but gradually break it down to release the energy.
• Cellular respiration
CELLULAR RESPIRATION: AEROBIC HARVEST OF FOOD ENERGY
– The main way that chemical energy is harvested from food and converted to ATP
– This is an aerobic process—it requires oxygen
• Cellular respiration and breathing are closely related
– Cellular respiration requires a cell to exchange gases with its surroundings
– Breathing exchanges these gases between the blood and outside air
The Relationship Between Cellular Respiration and Breathing
Figure 6.4
Breathing
Lungs
Musclecells
Cellularrespiration
Cellular Respiration
Three Steps
I. GlycolysisII. Krebs CycleIII. Electron Transport
Chain
• A common fuel molecule for cellular respiration is glucose
– This is the overall equation for what happens to glucose during cellular respiration
The Overall Equation for Cellular Respiration
Unnumbered Figure 6.1
Glucose Oxygen Carbondioxide
Water Energy
Cellular respiration can produce up to 38 ATP molecules for each glucose molecule consumed
• ATP molecules are the key to energy coupling
• ATP molecules store energy during the process of cellular respiration
• ATP power nearly all forms of cellular work
ATP the cell’s chemical energy
The Role of ATP
• Cellular money
• Cells “earn” ATP in exergonic reactions
• Cells “spend” ATP in endergonic reactions
P P P
ribose
adenine
• Hydrolysis breaks a phosphate group bond from the ATP molecules releasing energy
• The exergonic reaction supplies energy for cellular work
Figure 5.4A
Phosphategroups
Adenine
Ribose
Adenosine triphosphate
Hydrolysis
Adenosine diphosphate(ADP)
Energy
Energy Coupling
• Phosphorylation – How ATP powers cellular work
Figure 5.4B
Reactants
Po
ten
tia
l en
erg
y o
f m
ole
cule
s
Products
Protein Work
• The ATP cycle
Figure 5.4C
Energy from exergonic reactions
Deh
yd
rati
on
syn
thes
is
Hyd
roly
sis
Energy for endergonic reactions
• During cellular respiration, hydrogen and its bonding electrons change partners
– Hydrogen and its electrons go from sugar to oxygen, forming water
The Role of Oxygen in Cellular Respiration
• Why does electron transfer to oxygen release energy?
– When electrons move from glucose to oxygen, it is as though they were falling
– This “fall” of electrons releases energy during cellular respiration
Figure 6.5
Releaseof heatenergy
Cell with Mitochondria (red spots)
Mitochondria
Site of Krebs cycle and Electron Transport Chain
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• An overview of cellular respiration
Figure 6.8
High-energy electrons carried by NADH
GLYCOLYSIS
Glucose Pyruvicacid
KREBSCYCLE
ELECTRONTRANSPORT CHAIN
AND CHEMIOSMOSIS
MitochondrionCytoplasmic
fluid
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Stage 1: Glycolysis
• A molecule of glucose is split into two molecules of pyruvic acid
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• Glycolysis breaks a six-carbon glucose into two three-carbon molecules
– These molecules then donate high energy electrons to NAD+, forming NADH
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• Glycolysis makes some ATP directly when enzymes transfer phosphate groups from fuel molecules to ADP
Figure 6.9
Enzyme
Cell with Mitochondria (red spots)
Mitochondria
Site of Krebs cycle and Electron Transport Chain
• An overview of cellular respiration
Figure 6.8
High-energy electrons carried by NADH
GLYCOLYSIS
Glucose Pyruvicacid
KREBSCYCLE
ELECTRONTRANSPORT CHAIN
AND CHEMIOSMOSIS
MitochondrionCytoplasmic
fluid
Stage 2: The Krebs Cycle• The Krebs cycle completes the breakdown
of sugar
• The Krebs cycle extracts the energy of sugar by breaking the acetic acid molecules all the way down to CO2
– The cycle uses some of this energy to make ATP
– The cycle also forms NADH and FADH2
II. Krebs CycleProcess whereby pyruvate is broken down into CO2 in a
series of energy releasing reactions.
• Only occurs if O2 is present (aerobic respiration).
• Takes place within the mitochondria of the cell.
• Each pyruvate that goes through the cycle produces 1 ATP, 4 NADH, 1 FADH2 and 3 CO2 (2 X that amount for each glucose molecule).
• An overview of cellular respiration
Figure 6.8
High-energy electrons carried by NADH
GLYCOLYSIS
Glucose Pyruvicacid
KREBSCYCLE
ELECTRONTRANSPORT CHAIN
AND CHEMIOSMOSIS
MitochondrionCytoplasmic
fluid
Stage 3: Electron Transport• Electron transport releases the energy your
cells need to make the most of their ATP
• The molecules of electron transport chains are built into the inner membranes of mitochondria
– The chain functions as a chemical machine that uses energy released by the “fall” of electrons to pump hydrogen ions across the inner mitochondrial membrane
– These ions store potential energy
• When the hydrogen ions flow back through the membrane, they release energy
– The ions flow through ATP synthase– ATP synthase takes the energy from this flow
and synthesizes ATP
The Versatility of Cellular Respiration• Cellular respiration can “burn” other kinds of
molecules besides glucose
– Diverse types of carbohydrates– Fats– Proteins
• Pathways of molecular breakdown
Figure 6.16
Food, such as peanuts
Polysaccharides Fats Proteins
Sugars Glycerol Fatty acids Amino acids
Amino groups
Glucose G3PPyruvic
acid
GLYCOLYSIS
AcetylCoA
KREBSCYCLE
ELECTRONTRANSPORT CHAIN
AND CHEMIOSMOSIS
• The path that electrons take on their way down from glucose to oxygen involves many stops
NADH and Electron Transport Chains
Figure 6.6
1/2
(from food via NADH)
2 H 2 e
Energy forsynthesis
of
Electro
n tran
spo
rt chain 2 e
2 H1/2
• Cellular respiration is an example of a metabolic pathway
– A series of chemical reactions in cells• All of the reactions involved in cellular respiration can be grouped into three
main stages
– Glycolysis– The Krebs cycle– Electron transport
The Metabolic Pathway of Cellular Respiration
FERMENTATION: ANAEROBIC HARVEST OF FOOD ENERGY
• Some of your cells can actually work for short periods without oxygen
– For example, muscle cells can produce ATP under anaerobic conditions
• Fermentation
– The anaerobic harvest of food energy
• Human muscle cells can make ATP with and without oxygen
– They have enough ATP to support activities such as quick sprinting for about 5 seconds
– A secondary supply of energy (creatine phosphate) can keep muscle cells going for another 10 seconds
– To keep running, your muscles must generate ATP by the anaerobic process of fermentation
Fermentation in Human Muscle Cells
• Various types of microorganisms perform fermentation
– Yeast cells carry out a slightly different type of fermentation pathway
– This pathway produces CO2 and ethyl alcohol
Fermentation in Microorganisms
• The food industry uses yeast to produce various food products
Figure 6.16
SUMMARY OF KEY CONCEPTS• Chemical Cycling Between Photosynthesis and Cellular Respiration
Visual Summary 6.1
Sunlight
Heat
PhotosynthesisCellular
respiration
• The Overall Equation for Cellular Respiration
Visual Summary 6.2
Oxidation:Glucose loses electrons(and hydrogens)
Glucose Carbon dioxide
Electrons(and hydrogens) Energy
Oxygen
Reduction:Oxygen gainselectrons (andhydrogens)
• The Metabolic Pathway of Cellular Respiration
Visual Summary 6.3
Glucose Oxygen Water Energy
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• Long-distance runners have many slow fibers in their muscles
– Slow fibers break down glucose for ATP production aerobically (using oxygen)
– These muscle cells can sustain repeated, long contractions
How is a Marathoner Different from a Sprinter?
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• Sprinters have more fast muscle fibers
– Fast fibers make ATP without oxygen - -anaerobically
– They can contract quickly and supply energy for short bursts of intense activity
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• The dark meat is an example of slow fiber muscle
– Leg muscles support sustained activity
• The white meat consists of fast fibers
– Wing muscles allow for quick bursts of flight
• Biosynthesis of macromolecules from intermediates in cellular respiration
Figure 6.17
ATP needed todrive biosynthesis
PolyscaccharidesFatsProteins
KREBSCYCLE
AcetylCoA
Pyruvicacid G3P Glucose
GLUCOSE SYNTHESIS
Aminogroups
Amino acids Fatty acids Glycerol Sugars
Cells, tissues, organisms