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INTRODUCTION TO CELLULAR
RESPIRATION
Photosynthesis and Cellular Respiration Provide Energy
For Life
 Energy is necessary for life processes (growth, transport,
manufacture, movement, reproduction, etc.)
 Energy that supports life on Earth is captured from sun
and used for plant, algae, protist, and bacterial
photosynthesis
 Photosynthesis produces ___________ and __________.
 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
Sunlight energy
ECOSYSTEM
Photosynthesis
in chloroplasts
CO2
Glucose
+
+
H2O
O2
Cellular respiration
in mitochondria
ATP
(for cellular work)
Heat energy
Breathing Supplies Oxygen to Our Cells For Use in Cellular
Respiration and Removes Carbon Dioxide
 Breathing and cellular respiration are closely related
– Breathing is necessary for exchange of CO2 produced during cellular
respiration for atmospheric O2
– Cellular respiration uses O2 and produces CO2
O2
Breathing
CO2
Lungs
CO2
Bloodstream
Muscle cells carrying out
Cellular Respiration
Glucose + O2
CO2 + H2O + ATP
O2
Cellular Respiration Banks Energy in ATP
Molecules
 Cellular respiration is an exergonic process that transfers
energy from the bonds in glucose to ATP
 Cellular respiration produces 38 ATP/glucose molecule
C6H12O6
Glucose
+ 6
O2
Oxygen
6 CO2
Carbon
dioxide
+ 6
H2O
Water
+
ATPs
Energy
 Other foods (organic molecules) can be used as a source of
energy as well
Cells Tap Energy From Electrons “falling” From Organic
Fuels to Oxygen
 When the bonds of glucose are broken, electrons are
ultimately transferred to oxygen
 Oxygen is electronegative, and pulls e- towards it
 Cellular respiration is the controlled breakdown of
organic molecules
 Energy is released in small amounts, and stored in ATP
NADH
NAD+
+
ATP
2e–
Controlled
release of
energy for
synthesis
of ATP
H+
2e–
H+
H 2O
1

2
O2
Cells Tap Energy From Electrons “falling” From Organic
Fuels to Oxygen
 The cellular respiration equation explained:
– Glucose loses its hydrogen (and electrons) atoms and is ultimately converted
to CO2
– At the same time, O2 gains hydrogen atoms (and electrons) and is converted
to H2O
– Loss of electrons is called oxidation
– Gain of electrons is called reduction
– The reducing agent = The molecule carrying the hydrogens
(e-) (NADH, FADH2)
– The oxidizing agent= The molecule that receives the
hydrogens (e-) (NAD+, FAD)
Loss of hydrogen atoms
(oxidation)
C6H12O6
+ 6 O2
6 CO2 + 6 H2O + Energy
(ATP)
Glucose
Gain of hydrogen atoms
(reduction)
Enzymes are necessary to Oxidize Glucose and Other Foods
The enzyme that removes hydrogen from an organic
molecule is called dehydrogenase
Oxidation
Dehydrogenase
Reduction
NAD+
+ 2H
2
H+
+ 2
e–
+
NADH + H
(carries
2 electrons)
Cells tap energy from electrons “falling” from
organic fuels to Oxygen
– Dehydrogenase requires a
coenzyme called NAD+
(nicotinamide adenine
dinucleotide) to carry e– Another coenzyme that functions
like NAD+ is FAD
– They “carry” e- from glucose to a
series of proteins found along the
cristae of the mitochondrion
called the electron transport
chain or ETC
Copyright © 2009 Pearson Education, Inc.
STAGES OF CELLULAR
RESPIRATION
AND FERMENTATION
Cellular respiration occurs in three main stages
 Stage 1: Glycolysis
– Occurs in the cytoplasm
– What happens ?: A single molecule of glucose is
enzymatically cut in half through a series of steps
to produce two molecules of pyruvate
– In addition to Pyruvate, other products are:
–
–
Two molecules of NADH (when two molecules of NAD+
are reduced)
Two molecules of ATP, produced by substrate-level
phosphorylation
Substrate-level Phosphorylation
 Substrate level phosphorylation is when an enzyme
transfers a phosphate group from a substrate
molecule to ADP, forming ATP
Enzyme
P
Enzyme
+
ADP
ATP
P
Substrate
P
Product
ENERGY INVESTMENT
PHASE
Glucose
ATP
Steps 1 – 3 A fuel molecule is energized,
using ATP.
Step
1
ADP
P
Glucose-6-phosphate
P
Fructose-6-phosphate
P
Fructose-1,6-bisphosphate
2
ATP
3
ADP
P
Step 4 A six-carbon intermediate splits
Into two three-carbon intermediates.
4
P
Step 5 A redox reaction
generates NADH.
Glyceraldehyde-3-phosphate
(G3P)
P
NAD+
NAD+
5
P
NADH
5
NADH
+ H+
ENERGY PAYOFF PHASE
P
+ H+
P
P
ADP
P
P 1,3-Bisphosphoglycerate
ADP
6
6
ATP
ATP
P
P 3-Phosphoglycerate
7
Steps 6 – 9 ATP and pyruvate
are produced.
7
P
P
2-Phosphoglycerate
8
H2 O
P
P
ADP
Phosphoenolpyruvate
(PEP)
ADP
9
ATP
8
H2 O
9
ATP
Pyruvate
Pyruvate is chemically groomed for the citric acid cycle
Grooming Step:
 Location: mitochondrial matrix
 Purpose: to prepare pyruvate for entry into the Kreb’s cycle
 What Happens?: There are three steps
– 1. The removal of a carboxyl group released as CO2
(decarboxylation)
– 2. Oxidization of the remaining 2-carbon compound
to form acetate
– 3. Coenzyme A binds to the 2-carbon fragment
forming acetyl coenzyme A
• Products are CO2 , Acetyl CoA, and NADH
NADH + H+
NAD+
2
CoA
Pyruvate
Acetyl coenzyme A
1
3
CO2
Coenzyme A
Cellular respiration occurs in three main stages
 Stage 2: The Kreb’s Cycle (citric acid cycle)
– Location: mitochondrial matrix
– Purpose: Breaks down pyruvate into CO2 and supplies ETC
with electrons (via NADH, FADH2)
– What Happens?: 2-C acetate combines with 4-C
oxaloacetate forming 6-C citrate
– 6-C citrate then passes through a series of redox reactions
that regenerate oxaloacetate (4-C molecule )
– Glucose is completely oxidized in this phase
– For one turn of the cycle products are 3 NADH, 1 FADH2
, 1 ATP (by SLP), 2 CO2
Acetyl CoA
CoA
CoA
CITRIC ACID CYCLE
2 CO2
3 NAD+
FADH2
3 NADH
FAD
3 H+
ATP
ADP + P
CoA
Acetyl CoA
CoA
2 carbons enter cycle
Oxaloacetate
1
Citrate
NADH +
H+
NAD+
5
NAD+
2
NADH + H+
CITRIC ACID CYCLE
CO2 leaves cycle
Malate
ADP + P
FADH2
4
ATP
FAD
Alpha-ketoglutarate
3
CO2 leaves cycle
Succinate
NADH + H+
Step 1
Acetyl CoA stokes the furnace.
NAD+
Steps 2 – 3
NADH, ATP, and CO2 are generated
during redox reactions.
Steps 4 – 5
Redox reactions generate FADH2
and NADH.
Cellular respiration occurs in three main stages
 Stage 3: Oxidative phosphorylation (aka the ETC)
– Location: cristae of mitochondrion
– Purpose: to generate a proton gradient that will be used to form ATP
– What Happens?: Electrons are supplied by NADH & FADH2 , then
–
–
–
–
shuttled through the ETC. As e- are transported from protein to
protein, H+ are concentrated in the intermembrane space
The potential energy of this proton gradient is used to make ATP by
chemiosmosis
The concentration gradient drives H+ through ATP synthases
producing ATP
The ETC + chemiosmosis = oxidative phosphorylation
Products: 34-38 ATP/glucose
Intermembrane
space
Protein
complex
of electron
carriers
H+
H+
H+
H+
H+
H+
H+
Electron
carrier
H+
H+
ATP
synthase
Inner
mitochondrial
membrane
FADH2
Electron
flow
NADH
Mitochondrial
matrix
FAD
NAD+
H+
1

2
O2 + 2 H+
H+
H+
H2O
Electron Transport Chain
OXIDATIVE PHOSPHORYLATION
ADP + P
ATP
H+
Chemiosmosis
Electron shuttle
across membrane
Cytoplasm
2 NADH
Mitochondrion
2 NADH
(or 2 FADH2)
6 NADH
2 NADH
GLYCOLYSIS
Glucose
2
Pyruvate
2 Acetyl
CoA
+ 2 ATP
by substrate-level
phosphorylation
Maximum per glucose:
CITRIC ACID
CYCLE
+ 2 ATP
by substrate-level
phosphorylation
About
38 ATP
2 FADH2
OXIDATIVE
PHOSPHORYLATION
(Electron Transport
and Chemiosmosis)
+ about 34 ATP
by oxidative phosphorylation
Fermentation enables cells to produce ATP without oxygen
 Fermentation is an anaerobic (without oxygen) energy-
generating process
– Includes glycolysis, and the regeneration of NAD+
– Purpose: to produce ATP in the absence of oxygen
– What Happens?: NADH is oxidized to NAD+ when pyruvate is
reduced to lactate
– Pyruvate serves as an “electron sink,” a place to dispose of the electrons
generated by oxidation reactions in glycolysis
– Your muscle cells and certain bacteria can oxidize NADH through
lactic acid fermentation
Copyright © 2009 Pearson Education, Inc.
2 ADP
+2 P
Glycolysis
2 ATP
GLYCOLYSIS
Glucose
2 NAD+
2 NADH
Lactic Acid
Fermentation
2 Pyruvate
2 NADH
Steps to
regenerate
NAD+
2 NAD+
2 Lactate
Lactic acid fermentation
Fermentation enables cells to produce ATP without oxygen
 The baking and winemaking industry have used alcohol
fermentation for thousands of years
– Happens in yeast cells (single-celled fungi)
– They convert pyruvate to CO2 and ethanol while oxidizing NADH back
to NAD+
2 ADP
+2 P
Glycolysis
2 ATP
GLYCOLYSIS
Glucose
2 NAD+
2 NADH
2 Pyruvate
2 NADH
Steps to
regenerate
NAD+ with a
release of CO2
2 CO2
released
2 NAD+
2 Ethanol
Alcohol fermentation
Alcohol
Fermentation
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 the quantity of heat required to
raise the temperature of 1 kilogram (kg) of water by 1oC
INTERCONNECTIONS BETWEEN
MOLECULAR BREAKDOWN
AND SYNTHESIS
Cells use many kinds of organic molecules as fuel for cellular
respiration
 Although glucose is considered the primary source
of sugar for respiration and fermentation, there are
actually three sources of molecules for generation of
ATP
– Carbohydrates (disaccharides)
– Proteins (after conversion to amino acids)
– Fats
Food, such as
peanuts
Carbohydrates
Fats
Glycerol
Sugars
Proteins
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
GLUCOSE SYNTHESIS
Acetyl
CoA
Pyruvate
G3P
Glucose
Amino
groups
Amino acids
Proteins
Fatty acids Glycerol
Fats
Cells, tissues, organisms
Sugars
Carbohydrates
Cellular
respiration
generates
has three stages
oxidizes
uses
ATP
produce
some
(a)
C6H12O6
energy for
produces
many
(b)
(d)
to pull
to
electrons down
(c)
by process called
uses
H+ diffuse
through
ATP synthase
uses
(e)
pumps H+ to create
(f)