Download Cellular Respiration

How Cells Harvest
Chemical Energy
Chapter 6
Cellular Respiration
Energy Flow and Chemical Cycling
in the Biosphere
 Fuel molecules in food


represent solar energy
traced back to the sun
 Animals depend on plants:


to convert solar energy to
chemical energy
In form of sugars and other
organic molecules
Gas Exchange in the Body
 Cellular respiration and
breathing are closely related


Cellular respiration requires a cell
to exchange gases with its
surroundings
Breathing exchanges these
gases between blood and
outside air
Cellular respiration
 Cellular respiration is an exergonic
process that transfers energy from the
bonds in glucose to ATP
–
–
produces 38 ATP molecules from each
glucose molecule
Other foods (organic molecules) can be
used as a source of energy as well
Cellular Respiration
 Release of energy from molecules
accompanied by the use of this energy
to synthesize ATP molecules
 Metabolic pathway
 Main method that chemical energy is
harvested from food and converted to
ATP
 Aerobic

Requires oxygen and gives off carbon
dioxide
Where Is the Energy in Food?
 The process of aerobic respiration requires
oxygen and carbohydrates
C6H12O6 + 6 O2  6 CO2 + 6 H2O + energy
 The products are carbon dioxide, water, and
energy (heat or ATP)
How do we get the energy??
 Energy contained in the arrangement of
electrons in chemical bonds in organic
molecules
 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
–
Oxygen has a strong tendency to attract electrons
ATP
 Adenosine triphosphate (ATP)



Nucleotide with the base
adenine and the sugar ribose
Main energy carrier in cells
Formed during reactions that
breakdown organic
compounds to CO2 and water



Requires ample oxygen
Occurs within the
mitochondrion
Hydrolyzes phosphates to
release energy

form adenosine
diphosphate (ADP)
Redox Reaction (O-R)
 Chemical reaction that
transfers electrons from
one substance to another
 electrons retain their
potential energy
– Glucose loses its
hydrogen atoms and is
ultimately converted to
CO2
– O2 gains hydrogen atoms
and is converted to H2O
Oxidation
Reduction
Redox Reaction
 Electrons pass from atoms or molecules to one
another as part of many energy reactions

Oxidation
 When
an atom or molecule loses an electron
 Glucose is oxidized

Reduction
 When
an atom or molecule gains an elections
 Oxygen is reduced
Other important players……
 Enzymes are necessary to oxidize glucose
and other foods
–
Dehydrogenase
–
–
enzyme that removes hydrogen from an organic
molecule
requires a coenzyme called NAD+
–
–
–
–
(nicotinamide adenine dinucleotide)
shuttle electrons
NAD+ can become reduced when it accepts electrons
and oxidized when it gives them up
Reduced to NADH
The Finale….
 First step is transfer of electrons from
organic molecule to NAD+
 Other electron carrier molecules
represent the electron transport chain


Undergoes series of redox reactions
Release energy to make ATP
NADH
NAD+
+
ATP
2e–
Controlled
release of
energy for
synthesis
of ATP
H+
2e–
H+
H 2O
1

2
O2
Stages of Cellular Respiration:
1.
2.
3.
Glycolysis
Citric Acid Cycle
Oxidative Phosphorylation
NADH
Mitochondrion
High-energy electrons
carried by NADH
NADH
FADH2
and
OXIDATIVE
GLYCOLYSIS
Glucose
PHOSPHORYLATION
(Electron Transport
and Chemiosmosis)
CITRIC ACID
CYCLE
Pyruvate
Cytoplasm
Inner
mitochondrial
membrane
CO2
CO2
ATP
ATP
Substrate-level
phosphorylation
Substrate-level
phosphorylation
ATP
Oxidative
phosphorylation
1. Glycolysis
 Occurs in the cytoplasm
 Does not require
oxygen to generate
ATP
 Then, enters aerobic or
anaerobic reactions
Glucose
Glycolysis
 6 Carbon oxidizes glucose into
2 ADP
+
2 molecules


Pyruvate
3 Carbon
breaking of the bond yields
energy that is used to
phosphorylate ADP to ATP
 in addition, electrons and
hydrogen are donated to NAD+
to form NADH
2 NAD+
2 P
2 NADH

2
ATP
+
2 H+
2 Pyruvate
Enzyme
Enzyme
P
ADP
+
P
Substrate
P
Product
ATP
Anaerobic verse aerobic?
 Absence of oxygen


Fermentation
Make lactate or ethanol
 Presence of oxygen



Oxidative respiration
Pyruvate transported to mitochondria
Oxidize pyruvate to form acetyl-coA
When pyruvate is oxidized:
 A single carbon cleaved off by the
enzyme pyruvate dehydrogenase




This carbon leaves as part of a CO2
molecule
hydrogen and electrons are removed
from pyruvate
 donated to NAD+ to form NADH
Remaining two-carbon fragment of
pyruvate is joined to a cofactor called
coenzyme A (CoA)
Final compound called acetyl-CoA
Acetyl-CoA
 The fate of acetyl-CoA depends on the
availability of ATP in the cell

Insufficient ATP
 The

acetyl-CoA heads to the Krebs cycle
Plentiful ATP
 The
acetyl-CoA is diverted to fat synthesis for energy
storage
2. Citric Acid Cycle
 “Krebs Cycle”
 occurs within the
mitochondrion
 Breaks down
pyruvate into carbon
dioxide
 electrons passed to
an electron transport
chain in order to
power the production
of ATP
Stages of Citric Acid Cycle
 acetyl (two-carbon) compound enters the citric
acid cycle
Acetyl-CoA enters the cycle and binds to a four-carbon
molecule, forming a six-carbon molecule
Two carbons are removed as CO2 and their electrons
donated to NAD+
1.
2.

3.
In addition, an ATP is produced
The four-carbon molecule is recycled and more
electrons are extracted, forming NADH and FADH2
Acetyl CoA
CoA
CoA
The
Krebs
cycle
CITRIC ACID CYCLE
Note: a single
glucose molecule
produces two turns
of the cycle, one for
each of the two
pyruvate molecules
generated by
glycolysis
2 CO2
3 NAD+
FADH2
3 NADH
FAD
3 H+
ATP
ADP + P
Cytoplasm
Electron shuttle
across membrane
2 NADH
Mitochondrion
2 NADH
(or 2 FADH2)
6 NADH
2 NADH
GLYCOLYSIS
Glucose
2
Pyruvate
2 Acetyl
CoA
CITRIC ACID
CYCLE
+ 2 ATP
by substrate-level
phosphorylation
+ 2 ATP
by substrate-level
phosphorylation
Maximum per glucose:
About
38 ATP
2 FADH2
OXIDATIVE
PHOSPHORYLATION
(Electron Transport
and Chemiosmosis)
+ about 34 ATP
by oxidative phosphorylation
3. Oxidative Phosphorylation
 Electron transport chain

Shuttle molecules NADH and FADH take electrons
to oxygen
 Final


acceptor
Forms H2O
Carriers bind and release electrons in redox
reactions
 Pass
electrons down the “energy staircase”
 Use energy released from the transfers to transport H+
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
3. Oxidative Phosphorylation
 Chemiosmosis




Uses energy stored in a hydrogen ion
gradient to drive ATP synthesis
H+ concentration gradient stores potential
energy
ATP synthase drives hydrogen ions
through
Generates ATP
Cytoplasm
Electron shuttle
across membrane
2 NADH
Mitochondrion
2 NADH
(or 2 FADH2)
6 NADH
2 NADH
GLYCOLYSIS
Glucose
2
Pyruvate
2 Acetyl
CoA
CITRIC ACID
CYCLE
+ 2 ATP
by substrate-level
phosphorylation
+ 2 ATP
by substrate-level
phosphorylation
Maximum per glucose:
About
38 ATP
2 FADH2
OXIDATIVE
PHOSPHORYLATION
(Electron Transport
and Chemiosmosis)
+ about 34 ATP
by oxidative phosphorylation
Fermentation
 Occurs when O2 is
not available
 Animal cells and
bacteria convert
pyruvate to lactate
 Other organisms
convert pyruvate to
alcohol and CO2
Glucose Is Not the Only Food
Molecule
 Cells also get energy from foods other than sugars
 The other organic building blocks undergo
chemical modifications that permit them to enter
cellular respiration
Food, such as
peanuts
Carbohydrates
Fats
Glycerol
Sugars
Proteins
Fatty acids
Amino acids
Amino
groups
Glucose
G3P
GLYCOLYSIS
Pyruvate
Acetyl
CoA
ATP
CITRIC
ACID
CYCLE
OXIDATIVE
PHOSPHORYLATION
(Electron Transport
and Chemiosmosis)
DO PLANTS PERFORM
CELLULAR RESPIRATION??