Download CELLULAR RESPIRATION: AEROBIC HARVESTING OF ENERGY

Chapter 6
How Cells Harvest Chemical Energy
Introduction
  In eukaryotes, cellular respiration
–  harvests energy from food,
–  yields large amounts of ATP, and
–  Uses ATP to drive cellular work.
  A similar process takes place in many prokaryotic
organisms.
PowerPoint Lectures for
Campbell Biology: Concepts & Connections, Seventh Edition
Reece, Taylor, Simon, and Dickey
Lecture by Edward J. Zalisko
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Figure 6.0_1
Chapter 6: Big Ideas
Cellular Respiration:
Aerobic Harvesting
of Energy
Fermentation: Anaerobic
Harvesting of Energy
Stages of Cellular
Respiration
CELLULAR RESPIRATION:
AEROBIC HARVESTING
OF ENERGY
Connections Between
Metabolic Pathways
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6.1 Photosynthesis and cellular respiration
provide energy for life
6.1 Photosynthesis and cellular respiration
provide energy for life
  Life requires energy.
  In cellular respiration
  In almost all ecosystems, energy ultimately comes
from the sun.
–  glucose is broken down to carbon dioxide and water
and
  In photosynthesis,
–  the cell captures some of the released energy to make
ATP.
–  some of the energy in sunlight is captured by
chloroplasts,
  Cellular respiration takes place in the mitochondria
of eukaryotic cells.
–  atoms of carbon dioxide and water are rearranged, and
–  glucose and oxygen are produced.
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Figure 6.1
Figure 6.1_1
Sunlight energy
Sunlight energy
ECOSYSTEM
ECOSYSTEM
Photosynthesis
in chloroplasts
CO2
Photosynthesis
in chloroplasts
Glucose
CO2
O2
H 2O
H 2O
Cellular respiration
in mitochondria
Glucose
O2
Cellular respiration
in mitochondria
(for cellular
ATP
work)
(for cellular
ATP
work)
Heat energy
6.2 Breathing supplies O2 for use in cellular
respiration and removes CO2
Heat energy
Figure 6.2
O2
Breathing
  Respiration, as it relates to breathing, and cellular
respiration are not the same.
CO2
Lungs
–  Respiration, in the breathing sense, refers to an
exchange of gases. Usually an organism brings in
oxygen from the environment and releases waste CO2.
CO2
O2
Bloodstream
–  Cellular respiration is the aerobic (oxygen requiring)
harvesting of energy from food molecules by cells.
Muscle cells carrying out
Cellular Respiration
Glucose + O2
CO2 + H2O + ATP
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6.3 Cellular respiration banks energy in ATP
molecules
Figure 6.3
  Cellular respiration is an exergonic process that
transfers energy from the bonds in glucose to form
ATP.
  Cellular respiration
–  produces up to 32 ATP molecules from each glucose
molecule and
C6H12O6
6
Glucose
Oxygen
O2
6 CO2
Carbon
dioxide
6
H 2O
ATP
Water
+ Heat
–  captures only about 34% of the energy originally stored
in glucose.
  Other foods (organic molecules) can also be used
as a source of energy.
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6.4 CONNECTION: The human body uses energy
from ATP for all its activities
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 kilocalorie (kcal) is
–  About 75% of these calories are used to maintain a
healthy body.
–  The remaining 25% is used to power physical activities.
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979
Dancing (fast)
510
Bicycling (10 mph)
490
Swimming (2 mph)
408
Walking (4 mph)
341
Walking (3 mph)
245
Dancing (slow)
Sitting (writing)
–  used to measure the nutritional values indicated on food
labels.
6.5 Cells tap energy from electrons falling
from organic fuels to oxygen
kcal consumed per hour
by a 67.5-kg (150-lb) person*
Running (8–9 mph)
Driving a car
–  the same as a food Calorie, and
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Figure 6.4
Activity
–  the quantity of heat required to raise the temperature of
1 kilogram (kg) of water by 1oC,
204
  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?
61
28
*Not including kcal needed for
body maintenance
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6.5 Cells tap energy from electrons falling
from organic fuels to oxygen
6.5 Cells tap energy from electrons falling
from organic fuels to oxygen
  When the carbon-hydrogen bonds of glucose are
broken, electrons are transferred to oxygen.
  Energy can be released from glucose by simply
burning it.
–  Oxygen has a strong tendency to attract electrons.
  The energy is dissipated as heat and light and is
not available to living organisms.
–  An electron loses potential energy when it “falls” to
oxygen.
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6.5 Cells tap energy from electrons falling
from organic fuels to oxygen
6.5 Cells tap energy from electrons falling
from organic fuels to oxygen
  On the other hand, cellular respiration is the
controlled breakdown of organic molecules.
  The movement of electrons from one molecule to
another is an oxidation-reduction reaction, or redox
reaction. In a redox reaction,
  Energy is
–  gradually released in small amounts,
–  captured by a biological system, and
–  stored in ATP.
–  the loss of electrons from one substance is called
oxidation,
–  the addition of electrons to another substance is called
reduction,
–  a molecule is oxidized when it loses one or more
electrons, and
–  reduced when it gains one or more electrons.
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6.5 Cells tap energy from electrons falling
from organic fuels to oxygen
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Figure 6.5A
  A cellular respiration equation is helpful to show the
changes in hydrogen atom distribution.
Loss of hydrogen atoms
(becomes oxidized)
  Glucose
–  loses its hydrogen atoms and
C6H12O6
–  becomes oxidized to CO2.
Glucose
6 O2
6 CO2
6 H 2O
+ Heat
Gain of hydrogen atoms
(becomes reduced)
  Oxygen
ATP
–  gains hydrogen atoms and
–  becomes reduced to H2O.
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6.5 Cells tap energy from electrons falling
from organic fuels to oxygen
Figure 6.5B
  Enzymes are necessary to oxidize glucose and
other foods.
 
Becomes oxidized
2H
NAD+
–  is an important enzyme in oxidizing glucose,
–  accepts electrons, and
–  becomes reduced to NADH.
2H
NAD+
2 H+
Becomes reduced
2
NADH
H+
(carries
2 electrons)
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6.5 Cells tap energy from electrons falling
from organic fuels to oxygen
  There are other electron carrier molecules that
function like NAD+.
Figure 6.5C
NADH
ATP
NAD+
2
Controlled
release of
energy for
synthesis
of ATP
H+
El
ec
–  They form a staircase where the electrons pass from
one to the next down the staircase.
tr
o
n
tr
an
–  These electron carriers collectively are called the
electron transport chain.
sp
or
tc
ha
in
–  As electrons are transported down the chain, ATP is
generated.
2
1 O
2 2
2 H+
H 2O
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6.6 Overview: Cellular respiration occurs in
three main stages
STAGES OF CELLULAR
RESPIRATION
  Cellular respiration consists of a sequence of steps
that can be divided into three stages.
–  Stage 1 – Glycolysis
–  Stage 2 – Pyruvate oxidation and citric acid cycle
–  Stage 3 – Oxidative phosphorylation
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6.6 Overview: Cellular respiration occurs in
three main stages
6.6 Overview: Cellular respiration occurs in
three main stages
  Stage 1: Glycolysis
  Stage 2: The citric acid cycle
–  occurs in the cytoplasm,
–  takes place in mitochondria,
–  begins cellular respiration, and
–  oxidizes pyruvate to a two-carbon compound, and
–  breaks down glucose into two molecules of a threecarbon compound called pyruvate.
–  supplies the third stage with electrons.
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6.6 Overview: Cellular respiration occurs in
three main stages
Figure 6.6
  Stage 3: Oxidative phosphorylation
–  involves electrons carried by NADH and FADH2,
CYTOPLASM
NADH
–  shuttles these electrons to the electron transport chain
embedded in the inner mitochondrial membrane,
Electrons
carried by NADH
Glycolysis
–  involves chemiosmosis, and
Glucose
Pyruvate
Pyruvate
Oxidation
NADH
Citric Acid
Cycle
FADH2
Oxidative
Phosphorylation
(electron transport
and chemiosmosis)
–  generates ATP through oxidative phosphorylation
associated with chemiosmosis.
Mitochondrion
ATP
Substrate-level
phosphorylation
ATP
Substrate-level
phosphorylation
ATP
Oxidative
phosphorylation
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Figure 6.6_1
6.7 Glycolysis harvests chemical energy by
oxidizing glucose to pyruvate
CYTOPLASM
NADH
Electrons
carried by NADH
Glycolysis
Pyruvate
Oxidation
Pyruvate
Glucose
NADH
  In glycolysis,
FADH2
Oxidative
Phosphorylation
(electron transport
and chemiosmosis)
Citric Acid
Cycle
–  a single molecule of glucose is enzymatically cut in half
through a series of steps,
–  two molecules of pyruvate are produced,
–  two molecules of NAD+ are reduced to two molecules of
NADH, and
Mitochondrion
–  a net of two molecules of ATP is produced.
ATP
ATP
ATP
Substrate-level
phosphorylation
Substrate-level
phosphorylation
Oxidative
phosphorylation
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Figure 6.7A
6.7 Glycolysis harvests chemical energy by
oxidizing glucose to pyruvate
Glucose
2 ADP
2 NAD+
2 P
  ATP is formed in glycolysis by substrate-level
phosphorylation during which
–  an enzyme transfers a phosphate group from a
substrate molecule to ADP and
2 NADH
2
ATP
2 H+
–  ATP is formed.
  The compounds that form between the initial
reactant, glucose, and the final product, pyruvate,
are called intermediates.
2 Pyruvate
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Figure 6.7B
6.7 Glycolysis harvests chemical energy by
oxidizing glucose to pyruvate
Enzyme
P
  The steps of glycolysis can be grouped into two
main phases.
Enzyme
–  In steps 1–4, the energy investment phase,
ADP
–  energy is consumed as two ATP molecules are used to
energize a glucose molecule,
ATP
P
P
Substrate
Product
–  which is then split into two small sugars that are now primed
to release energy.
–  In steps 5–9, the energy payoff,
–  two NADH molecules are produced for each initial glucose
molecule and
–  ATP molecules are generated.
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Figure 6.7Ca_s1
ENERGY
INVESTMENT
PHASE
Glucose
Steps 1 – 3 A fuel
ATP
molecule is energized,
using ATP.
ADP
Step
1
Figure 6.7Ca_s2
Step
1
Glucose 6-phosphate
P
2
P
Glucose 6-phosphate
P
Fructose 6-phosphate
P
Fructose
1,6-bisphosphate
2
P
Fructose 6-phosphate
ATP
ATP
3
3
ADP
ADP
P
Fructose
1,6-bisphosphate
P
Step 4 A six-carbon
intermediate splits
into two three-carbon
intermediates.
P
4
P
P
Figure 6.7Cb_s1
Step 5
A redox reaction
generates NADH.
ENERGY
INVESTMENT
PHASE
Glucose
Steps 1 – 3 A fuel
ATP
molecule is energized,
using ATP.
ADP
NAD+
NAD+
5
P
NADH
H+
P
ENERGY
PAYOFF
PHASE
P
P
P
5
P
NADH
H+
P
P
Figure 6.7Cb_s2
Step 5
A redox reaction
generates NADH.
NAD+
5
P
NADH
H+
5
P
NADH
H+
P
P
ADP
Steps 6 – 9
ATP and pyruvate
are produced.
ENERGY
PAYOFF
PHASE
P
P
NAD+
1,3-Bisphosphoglycerate
Glyceraldehyde
3-phosphate (G3P)
P
1,3-Bisphosphoglycerate
P
3-Phosphoglycerate
ADP
6
6
ATP
ATP
P
7
7
P
P
8
H 2O
8
H 2O
P
2-Phosphoglycerate
P
ADP
Phosphoenolpyruvate (PEP)
ADP
9
9
ATP
P
ATP
Pyruvate
7
6.8 Pyruvate is oxidized prior to the citric acid
cycle
6.8 Pyruvate is oxidized prior to the citric acid
cycle
  The pyruvate formed in glycolysis is transported
from the cytoplasm into a mitochondrion where
  Two molecules of pyruvate are produced for each
molecule of glucose that enters glycolysis.
–  the citric acid cycle and
  Pyruvate does not enter the citric acid cycle, but
undergoes some chemical grooming in which
–  oxidative phosphorylation will occur.
–  a carboxyl group is removed and given off as CO2,
–  the two-carbon compound remaining is oxidized while a
molecule of NAD+ is reduced to NADH,
–  coenzyme A joins with the two-carbon group to form
acetyl coenzyme A, abbreviated as acetyl CoA, and
–  acetyl CoA enters the citric acid cycle.
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Figure 6.8
6.9 The citric acid cycle completes the oxidation of
organic molecules, generating many NADH
and FADH2 molecules
NAD+
NADH
  The citric acid cycle
H+
2
CoA
Pyruvate
Acetyl coenzyme A
1
CO2
3
–  is also called the Krebs cycle (after the German-British
researcher Hans Krebs, who worked out much of this
pathway in the 1930s),
–  completes the oxidation of organic molecules, and
–  generates many NADH and FADH2 molecules.
Coenzyme A
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Figure 6.9A
6.9 The citric acid cycle completes the oxidation of
organic molecules, generating many NADH
and FADH2 molecules
Acetyl CoA
CoA
CoA
  During the citric acid cycle
2 CO2
Citric Acid Cycle
–  the two-carbon group of acetyl CoA is added to a fourcarbon compound, forming citrate,
–  citrate is degraded back to the four-carbon compound,
3 NAD+
FADH2
3 NADH
FAD
–  two CO2 are released, and
–  1 ATP, 3 NADH, and 1 FADH2 are produced.
3 H+
ATP
ADP
P
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6.9 The citric acid cycle completes the oxidation of
organic molecules, generating many NADH
and FADH2 molecules
Figure 6.9B_s1
Acetyl CoA
CoA
CoA
2 carbons enter cycle
Oxaloacetate
1
  Remember that the citric acid cycle processes two
molecules of acetyl CoA for each initial glucose.
  Thus, after two turns of the citric acid cycle, the
overall yield per glucose molecule is
Citric Acid Cycle
–  2 ATP,
–  6 NADH, and
–  2 FADH2.
Step 1
Acetyl CoA stokes
the furnace.
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Figure 6.9B_s2
Acetyl CoA
Figure 6.9B_s3
CoA
Acetyl CoA
CoA
CoA
2 carbons enter cycle
Oxaloacetate
CoA
2 carbons enter cycle
Oxaloacetate
1
1
Citrate
Citrate
NADH
NAD+
NADH
2
Citric Acid Cycle
H+
NAD+
5
NAD+
Alpha-ketoglutarate
CO2 leaves cycle
NADH
2
Citric Acid Cycle
CO2 leaves cycle
3
H+
CO2 leaves cycle
Malate
FADH2
H+
Alpha-ketoglutarate
4
3
FAD
NAD+
CO2 leaves cycle
NAD+
Succinate
ADP
Step 1
Acetyl CoA stokes
the furnace.
P
NADH
ADP
H+
Steps 2 – 3
ATP
NADH, ATP, and CO2
are generated during redox reactions.
Step 1
Acetyl CoA stokes
the furnace.
P
Steps 2 – 3
ATP
NADH, ATP, and CO2
are generated during redox reactions.
NADH
H+
Steps 4 – 5
Further redox reactions generate
FADH2 and more NADH.
6.10 Most ATP production occurs by oxidative
phosphorylation
6.10 Most ATP production occurs by oxidative
phosphorylation
  Oxidative phosphorylation
–  involves electron transport and chemiosmosis and
  Electrons from NADH and FADH2 travel down the
electron transport chain to O2.
–  requires an adequate supply of oxygen.
  Oxygen picks up H+ to form water.
  Energy released by these redox reactions is used
to pump H+ from the mitochondrial matrix into the
intermembrane space.
  In chemiosmosis, the H+ diffuses back across the
inner membrane through ATP synthase
complexes, driving the synthesis of ATP.
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Figure 6.10
Figure 6.10_1
H+
H+
Intermembrane
space
H+
H+
H+ Mobile
electron
carriers
Protein
complex
of electron
carriers
H+
H+
III
H+ ATP
synthase
Mitochondrial
matrix
NAD+
H+
H+
H+
H+
III
H+ ATP
synthase
IV
I
II
II
FADH2
Electron
flow
NADH
H+
H+
H+ Mobile
electron
carriers
Protein
complex
of electron
carriers
IV
I
Inner mitochondrial
membrane
H+
H+
FAD
2 H+
1
2 O2
FADH2
Electron
flow
NADH
H 2O
H+
ADP
P
FAD
2 H+
NAD+
1
O
2 2
H 2O
H+
ATP
ADP
H+
Electron Transport Chain
P
ATP
H+
Chemiosmosis
Chemiosmosis
Electron Transport Chain
Oxidative Phosphorylation
Oxidative Phosphorylation
6.11 CONNECTION: Interrupting cellular respiration
Figure 6.11
can have both harmful and beneficial effects
Rotenone
  Three categories of cellular poisons obstruct the
process of oxidative phosphorylation. These
poisons
Cyanide,
carbon monoxide
H+
H+
H+
ATP
synthase
H+ H+ H+
1.  block the electron transport chain (for example,
rotenone, cyanide, and carbon monoxide),
DNP
2.  inhibit ATP synthase (for example, the antibiotic
oligomycin), or
FADH2
NAD+
NADH
3.  make the membrane leaky to hydrogen ions (called
uncouplers, examples include dinitrophenol).
Oligomycin
H+
H+
FAD
1
O
2 2
2 H+
H 2O
ADP
P
ATP
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6.11 CONNECTION: Interrupting cellular respiration
6.11 CONNECTION: Interrupting cellular respiration
  Brown fat is
  In brown fat,
can have both harmful and beneficial effects
–  a special type of tissue associated with the generation
of heat and
–  more abundant in hibernating mammals and newborn
infants.
can have both harmful and beneficial effects
–  the cells are packed full of mitochondria,
–  the inner mitochondrial membrane contains an
uncoupling protein, which allows H+ to flow back down
its concentration gradient without generating ATP, and
–  ongoing oxidation of stored fats generates additional
heat.
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6.12 Review: Each molecule of glucose yields
many molecules of ATP
6.12 Review: Each molecule of glucose yields
many molecules of ATP
  Recall that the energy payoff of cellular respiration
involves
  The total yield is about 32 ATP molecules per
glucose molecule.
1.  glycolysis,
2.  alteration of pyruvate,
  This is about 34% of the potential energy of a
glucose molecule.
3.  the citric acid cycle, and
  In addition, water and CO2 are produced.
4.  oxidative phosphorylation.
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Figure 6.12
CYTOPLASM
Electron shuttles
across membrane
2 NADH
Mitochondrion
2 NADH
or
2 FADH2
6 NADH
2 NADH
Glycolysis
2
Pyruvate
Glucose
Pyruvate
Oxidation
2 Acetyl
CoA
Citric Acid
Cycle
2 FADH2
FERMENTATION: ANAEROBIC
HARVESTING OF ENERGY
Oxidative
Phosphorylation
(electron transport
and chemiosmosis)
Maximum
per glucose:
+2
+2
ATP
ATP
by substrate-level
phosphorylation
by substrate-level
phosphorylation
+ about
28 ATP
About
32 ATP
by oxidative
phosphorylation
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6.13 Fermentation enables cells to produce ATP
without oxygen
6.13 Fermentation enables cells to produce ATP
without oxygen
  Fermentation is a way of harvesting chemical energy
that does not require oxygen. Fermentation
  Your muscle cells and certain bacteria can oxidize
NADH through lactic acid fermentation, in which
–  takes advantage of glycolysis,
–  NADH is oxidized to NAD+ and
–  produces two ATP molecules per glucose, and
–  pyruvate is reduced to lactate.
–  reduces
NAD+
to NADH.
  The trick of fermentation is to provide an anaerobic
path for recycling NADH back to NAD+.
Animation: Fermentation Overview
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11
Figure 6.13A
Glucose
2 ADP
2 P
  Lactate is carried by the blood to the liver, where it
is converted back to pyruvate and oxidized in the
mitochondria of liver cells.
2 NAD+
Glycolysis
6.13 Fermentation enables cells to produce ATP
without oxygen
2 ATP
2 NADH
  The dairy industry uses lactic acid fermentation by
bacteria to make cheese and yogurt.
2 Pyruvate
  Other types of microbial fermentation turn
2 NADH
–  soybeans into soy sauce and
–  cabbage into sauerkraut.
2 NAD+
2 Lactate
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Figure 6.13B
Glucose
2 ADP
2 P
  The baking and winemaking industries have used
alcohol fermentation for thousands of years.
2 ATP
2 NAD+
Glycolysis
6.13 Fermentation enables cells to produce ATP
without oxygen
2 NADH
  In this process yeasts (single-celled fungi)
–  oxidize NADH back to NAD+ and
–  convert pyruvate to CO2 and ethanol.
2 Pyruvate
2 NADH
2 CO2
2 NAD+
2 Ethanol
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6.13 Fermentation enables cells to produce ATP
without oxygen
6.14 EVOLUTION CONNECTION: Glycolysis
evolved early in the history of life on Earth
  Obligate anaerobes
  Glycolysis is the universal energy-harvesting
process of life.
–  are poisoned by oxygen, requiring anaerobic conditions,
and
–  live in stagnant ponds and deep soils.
  Facultative anaerobes
  The role of glycolysis in fermentation and
respiration dates back to
–  life long before oxygen was present,
–  include yeasts and many bacteria, and
–  when only prokaryotes inhabited the Earth,
–  can make ATP by fermentation or oxidative
phosphorylation.
–  about 3.5 billion years ago.
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6.14 EVOLUTION CONNECTION: Glycolysis
evolved early in the history of life on Earth
  The ancient history of glycolysis is supported by its
–  occurrence in all the domains of life and
CONNECTIONS BETWEEN
METABOLIC PATHWAYS
–  location within the cell, using pathways that do not
involve any membrane-bounded organelles.
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6.15 Cells use many kinds of organic molecules
as fuel for cellular respiration
6.15 Cells use many kinds of organic molecules
as fuel for cellular respiration
  Although glucose is considered to be the primary
source of sugar for respiration and fermentation,
ATP is generated using
  Fats make excellent cellular fuel because they
–  carbohydrates,
–  contain many hydrogen atoms and thus many energyrich electrons and
–  yield more than twice as much ATP per gram than a
gram of carbohydrate or protein.
–  fats, and
–  proteins.
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Figure 6.15
6.16 Food molecules provide raw materials for
biosynthesis
Food, such as
peanuts
  Cells use intermediates from cellular respiration for
the biosynthesis of other organic molecules.
Carbohydrates
Sugars
Fats
Proteins
Glycerol Fatty acids
Amino acids
Amino
groups
Glucose
G3P
Pyruvate
Glycolysis
Pyruvate
Oxidation
Acetyl CoA
Citric
Acid
Cycle
Oxidative
Phosphorylation
ATP
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13
Figure 6.16
ATP needed
to drive
biosynthesis
Citric
Acid
Cycle
6.16 Food molecules provide raw materials for
biosynthesis
ATP
Pyruvate
Oxidation
Acetyl CoA
Glucose Synthesis
Pyruvate
G3P
Glucose
Amino
groups
Amino acids
Proteins
Fatty acids Glycerol
Fats
Sugars
  Metabolic pathways are often regulated by
feedback inhibition in which an accumulation of
product suppresses the process that produces the
product.
Carbohydrates
Cells, tissues, organisms
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