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Chapter 6
How Cells Harvest Chemical Energy
How Is a Marathoner Different from a Sprinter?
The different types of muscle fibers
Slow- twitch (red) fibers
Fast- twitch (white) fibers

Slow- twitch (red) fibers
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
Aerobic
Lots of mitochondria
Myglobin (carries O2- red color)
Long muscle contractions
Cellular respiration
Fast- twitch (white) fibers
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Anerobic
Less mitochondria
Less myoglobin (pale)
Quick bursts
Produces less ATP
Cellular respiration
The aerobic harvesting of
energy from sugars by cells
Yields CO2, H2O and a
large amount of ATP
6.1 Photosynthesis and cellular respiration provide
energy for life
Cellular respiration
•
•
•
•
consumes O2
during the oxidation of glucose
to CO2 and H2O
makes ATP
Photosynthesis
• uses solar energy
• And CO2 and H2O
• To produce glucose and O2
Sunlight energy
ECOSYSTEM
CO2
Photosynthesis in
chloroplasts
Glucose
+
+
H2O
O2
Cellular respiration in
mitochondria
ATP
(for cellular work)
Heat energy
6.2 Breathing supplies oxygen to our cells and removes
carbon dioxide
O2
CO2
Breathing
Lungs
CO2
Bloodstream
O2
Muscle cells carrying out
Cellular Respiration
Glucose + O2
CO2 + H2O + ATP
6.3 Cellular respiration banks energy in
ATP molecules
 Cells “burn” organic molecules
 Through several reactions
 Generating 38 ATP molecules
 40% efficient (car =25%)
 Working muscle cell requires 10
million molecules of ATP/s
Where does the energy come from???
Glucose and oxygen are rearranged
Bonds broken in glucose release chemical bond
energy
The cell stores the energy in the bonds of ATP
C6H12O6 + 6 O2
Glucose Oxygen gas
6 CO2
+ 6 H 2O
Carbon dioxide
Water
+
ATPs
Energy
6.4 The human body uses energy from ATP for all
its activities
Maintenance:
Blood pumping
Breathing
Maintain temp
Digestion
Energy= Kcal
Average person
requires 2,2000 Kcal
for maintenance and
voluntary actives
6.5 Cells tap energy from electrons “falling” from
organic fuels to oxygen



Oxygen is very electronegative
Electrons lose potential energy during their “fall”
to oxygen
Cellular respiration is a “controlled fall” of
electrons, like stepping down a staircase



Electron transfer = energy
Hydrogen (1e,1p) movements = electron transfer =
energy
Redox Reaction (oxidation-reduction): movement of
electrons from one molecule to another


Oxidation- loss of electrons from one substance
Reduction- addition of electrons to another substance
C6H12O6
Glucose
Loss of hydrogen atoms
(oxidation)
+ 6 O2
6 CO2
Gain of hydrogen atoms
(reduction)
+
6 H2 O
+
Energy
(ATP)
NADH
NAD+
+
ATP
2e

H+

NADH passes
electrons to an
electron
transport chain

As electrons
“fall” from
carrier to carrier
and finally to O2
Energy is
released in
small quantities
Controlled release of
energy for synthesis of
ATP
2 H+
2
H
+
2e
1 O2
2
H2O
H 2O
STAGES OF CELLULAR RESPIRATION AND
FERMENTATION
6.6 Overview: Cellular respiration
occurs in three main stages
1. Glycolysis
2. Citric Acid Cycle
3. Oxidative Phosphorylation


Stage 1: Glycolysis
 Occurs in the cytoplasm
 Breaks down glucose
 into pyruvate
 producing a small amount of ATP

Stage 2: The citric acid cycle
 Takes place in the mitochondria
 Completes the breakdown of
glucose,
 producing a small amount of ATP
 Supplies the third stage of cellular
respiration with electrons

Stage 3: Oxidative phosphorylation
 Occurs in the mitochondria
 Uses the energy released by
“falling” electrons
 to pump H+ across a membrane
 Harnesses the energy of the H+
gradient through chemiosmosis,
producing ATP
Cellular Respiration Video
NADH
High-energy electrons
carried by NADH
NADH FADH2
and
OXIDATIVE
PHOSPHORYLATION
(Electron Transport
and Chemiosmosis)
CITRIC
ACID
CYCLE
GLYCOLYSIS
Glucose
Pyruvate
Mitochondrion
Cytoplasm
ATP
Substrate-level
phosphorylation
CO2
ATP
CO2
Substrate-level
phosphorylation
ATP
Oxidative
phosphorylation

Stage 1: Glycolysis

Occurs in the cytoplasm
Breaks down glucose into pyruvate
Producing a small amount of ATP
Universal
Anaerobic (no O2 required)
Doesn’t occur in a membrane-bound organelle
Ancient metabolic system
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6.7 Glycolysis

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1st Stage: “Splitting of Sugar”
Harvests chemical energy by oxidizing glucose
to pyruvate
Glucose (6C) 2 Pyruvate Molecules (3C ea)
Nine step process
Cell reduces 2 NAD+ into 2 NADH
2 ATP via substrate level phosphorylationenzyme tranfers phosphate group from
substrate molecule to ADP, forming ATP
An Overview of Glycolysis
2 NAD
+
2 NADH
+
H
+2
Glucose
2 Pyruvate
2 ADP
+
2
P
2
ATP


Substrate-Level Phosphorylation
a phosphate group is transferred (by an enzyme) from an
organic molecule (substrate) to ADP
Enzyme
P
P
P
Adenosine
ADP
P
Organic molecule
(substrate)
ATP
P

The 1st Phase: ATP is used to energize a glucose
molecule, which is then split in two
Steps 1– 3
A fuel molecule is
energized, using ATP.
Glucose
ATP
ADP
PREPARATORY
PHASE
(energy investment)
Step 4
A six-carbon intermediate
splits into two threecarbon intermediates.
Figure 6.7C
P
Glucose-6-phosphate
P
Fructose-6-phosphate
P
Fructose-1,6-diphosphate
ATP
ADP
P
Glyceraldehyde-3-phosphate
(G3P)

The 2nd Phase: ATP, NADH, and pyruvate are formed
P
P
Step 5
A redox reaction
generates NADH.
6
9
Steps 6–9
ATP and pyruvate
are produced.
ENERGY
PAYOFF
PHASE
NAD+
NAD+
NADH
+H
P
P
P
+
1,3 P Diphosphoglycerate
NADH
+H
ADP
6
ATP
ADP
P
P
6
ATP
P
P 3 7-Phosphoglycerate
7
P
P
8
8
H2O
H2O
P
ADP
ATP
2-Phosphoglycerate
P
9
ADP
Phosphoenolpyruvate
(PEP)
9
ATP
Pyruvate
What’s the payoff from Glycolyis?

For each molecule of glucose:

2 NADH molecules- stored energy not available in
anaerobic environment (without O2)
2 Pyruvate molecules- to be used later
4 ATP molecules
BUT… The first phase uses 2 ATP molecules
Net Gain= 2 ATP Molecules
Not enough energy fro most organisms
Yeasts, bacteria
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6.8 Pyruvate is chemically groomed for the citric
acid cycle

Prior to the citric acid cycle

Enzymes process pyruvate:
1.
Carbon atom removed and released in CO2
2.
Compound is oxidized and NAD+ is reduced to
NADH
3.
Coenzyme A joins compound

Produces Acetyl Coenzyme A (acetyl CoA)

A higher energy molecule for the citric acid cycle
Pyruvate is chemically groomed for the citric
NADH
High-energy electrons
acid cycle
carried by NADH
NADH FADH2
and
NAD+
+ H+
NADH
OXIDATIVE
PHOSPHORYLATION
(Electron Transport
CoA
and Chemiosmosis)
CITRIC
ACID
CYCLE
GLYCOLYSIS
Glucose
Pyruvate
Pyruvate
Acetyl CoA
(acetyl coenzyme A)
2
CO2
Cytoplasm
Mitochondrion
Coenzyme A
1
ATP
Substrate-level
phosphorylation
CO2
3
ATP
CO2
Substrate-level
phosphorylation
ATP
Oxidative
phosphorylation
6.9 STAGE 2: The citric acid cycle
Takes place in
the mitochondria
Completes
the breakdown of glucose,
producing
a small amount of ATP
Supplies
the third stage of cellular respiration with
electrons
Krebs
Cylcle
Completes
the oxidation of organic fuel, generating
many NADH and FADH2 molecule
The two-carbon
acetyl part of acetyl CoA is oxidized
The Citric Acid Cycle
CoA
Acetyl CoA
Oxaloacetate
CoA
2 carbons enter cycle
+ H+
Citrate
NADH
NAD+
CO2 leaves cycle
CITRIC ACID CYCLE
NAD+
+
NADH + H
Malate
ADP + P
FADH2
ATP
Alpha-ketoglutarate
FAD
CO2 leaves cycle
Succinate
+
NADH + H
Step
Step
1: 1
Acetyl CoA stokes
the furnace.
and
NAD+
Steps 2-3: Steps
NADH, ATP, and CO2 are generated
during redox reactions.
Steps 4-5
and
Steps
Redox reactions generate
FADH2 and NADH.
What’s the payoff from The Citric Acid Cycle?

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Each turn of the cycle:
1 ATP molecule via substrate level phosphorylation
3 NADH
1FADH2
For each molecule of glucose (2 turns: 2 Acetyl CoA)
6 NADH
2FADH2
2 ATP
So far the cell has produced:







For 1 molecule of glucose:
4 ATP (substrate-level phosphorylation)
10 NADH
2 FADH2
To used the energy banked in NADH and FADH2
The cell must shuttle their electrons to the Electron
Transport Chain
Where energy from the oxidation of organic fuel will
power the oxidative phosphorylation of ADP to
ATP
6.10 Most ATP production occurs by oxidative
phosphorylation



Electrons from NADH and FADH2
 Travel down the electron transport chain to
oxygen, which picks up H+ to form water
Energy released by the redox reactions
 Is used to pump H+ into the space between the
mitochondrial membranes
 Creates an H+ gradient
In chemiosmosis, the H+ diffuses back through the
inner membrane through ATP synthase complexes
 Driving the synthesis of ATP
Electron Transport Chain
NADH
NAD+
+
H+
ATP
2e
Controlled release of energy for
synthesis of ATP
H+
+
H
2e
H2O
H 2O
1
2
O2

http://www.youtube.com/watch?v=9UM78eqy1oc
H+
Protein
complex
H+
H+
H+
+
H
.
H+
H+
Electron
carrier
ATP
H+ synthase
+
H
Intermembrane
space
Inner
mitochondrial
membrane
Electron flow
Mitochondrial
matrix
FADH2 FAD
NAD+
NADH
H+
1 O + 2H+
2
2
H+
+
+
H
H2O
ADP
Electron Transport Chain
OXIDATIVE PHOSPHORYLATION
P
+
ATP
H
Chemiosmosis
6.12 : Each molecule of glucose yields many molecules of ATP:
Oxidative phosphorylation, using electron transport and
chemiosmosis
Electron shuttle
across membrane
Mitochondrion
2 NADH
2 NADH
6 NADH 2 FADH2
2 NADH
GLYCOLYSIS
Glucose
2
Pyruvate
+ 2 ATP
by substrate-level
phosphorylation
Cytoplasm
(or 2 FADH2)
CITRIC ACID
CYCLE
2 Acetyl
CoA
+ 2 ATP
by substrate-level
phosphorylation
Maximum per glucose:
About
38 ATP
OXIDATIVE
PHOSPHORYLATION
(Electron Transport
and Chemiosmosis)
+ about 34 ATP
by oxidative
phosphorylation
6.13 Fermentation is an anaerobic alternative to
cellular respiration
 Under anaerobic conditions, many kinds of
cells can use glycolysis alone to produce small
amounts of ATP
 2 ATP per glucose
 Lactic Acid
Fermentation
 Alcohol
Fermentation
INTERCONNECTIONS BETWEEN MOLECULAR
BREAKDOWN AND SYNTHESIS

6.14 Cells use many kinds of organic molecules as fuel for
cellular respiration
Food, such as
peanuts
Fats
Carbohydrates
Sugars
Proteins
Glycerol Fatty acids
Amino acids
Amino groups
Glucose
G3P
Pyruvate
GLYCOLYSIS
Acetyl
CoA
ATP
CITRIC
ACID
CYCLE
OXIDATIVE
PHOSPHORYLATION
(Electron Transport
and Chemiosmosis)
ATP needed to drive biosynthesis
ATP
CITRIC
ACID
CYCLE
Acetyl CoA
GLUCOSE SYNTHESIS
Glucose
Pyruvate
G3P
Amino
groups
Amino acids
Proteins
Fatty acids Glycerol
Fats
Cells, tissues, organisms
Sugars
Carbohydrates
6.16 The fuel for respiration ultimately comes from
photosynthesis



All organisms can harvest energy from organic molecules
Plants, but not animals
Can also make these molecules from inorganic sources by the
process of photosynthesis