how cells harvest chemical energy chapter 6 cellular respiration
TRANSCRIPT
How Cells Harvest Chemical Energy
Chapter 6
Cellular Respiration
Energy Flow and Chemical Cyclingin 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
ATPNAD+
NADH
H+
H+2e–
2e–
Electron transport
chain
Controlledrelease ofenergy forsynthesis
of ATP
+
O2
H2O
12
Stages of Cellular Respiration:
1. Glycolysis
2. Citric Acid Cycle
3. Oxidative Phosphorylation
Mitochondrion
CO2 CO2
NADH
ATP
High-energy electronscarried by NADH
NADH
CITRIC ACID
CYCLE
GLYCOLYSIS
PyruvateGlucose
andFADH2
Substrate-levelphosphorylation
Substrate-levelphosphorylation
OXIDATIVEPHOSPHORYLATION(Electron Transportand Chemiosmosis)
Oxidativephosphorylation
ATPATP
CytoplasmInnermitochondrialmembrane
1. Glycolysis
Occurs in the cytoplasm Does not require
oxygen to generate ATP
Then, enters aerobic or anaerobic reactions
Glycolysis
6 Carbon oxidizes glucose into 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
Glucose
NAD+
+2
2 ADP
NADH2
P2
2
ATP2 +
H+
2 Pyruvate
ADP
ATP
Substrate
Enzyme
Product
Enzyme
P
P
P
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 cycle1. Acetyl-CoA enters the cycle and binds to a four-carbon
molecule, forming a six-carbon molecule
2. Two carbons are removed as CO2 and their electrons donated to NAD+
In addition, an ATP is produced
3. The four-carbon molecule is recycled and more electrons are extracted, forming NADH and FADH2
The Krebs cycle
Note: a single glucose molecule produces two turns of the cycle, one for each of the two pyruvate molecules generated by glycolysis
CITRIC ACID CYCLE
NAD+
NADH
3 H+
CO2
3
3
2
CoA
CoA
Acetyl CoA
PADP +ATP
FADH2
FAD
Cytoplasm
Glucose
FADH2
Mitochondrion
Maximum per glucose:
OXIDATIVEPHOSPHORYLATION(Electron Transportand Chemiosmosis)
CITRIC ACIDCYCLE
Electron shuttleacross membrane
2 NADH
2 NADH
2 NADH
6 NADH 2(or 2 FADH2)
2 AcetylCoA
GLYCOLYSIS2
Pyruvate
About38 ATP
about 34 ATP
by substrate-levelphosphorylation
by oxidative phosphorylation
2 ATP
by substrate-levelphosphorylation
2 ATP
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+
ATP
H+
Intermembranespace
O2
H2O
12
Innermitochondrialmembrane
H+NAD+
H+
H+
H+
H+
H+
H+
H+
H+
H+
H+
H+
H+
Mitochondrialmatrix
Electronflow
Electroncarrier
Proteincomplexof electroncarriers
NADH
FADH2FAD
ATPsynthase
PADP +
Chemiosmosis
+ 2
OXIDATIVE PHOSPHORYLATION
Electron Transport Chain
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
Glucose
FADH2
Mitochondrion
Maximum per glucose:
OXIDATIVEPHOSPHORYLATION(Electron Transportand Chemiosmosis)
CITRIC ACIDCYCLE
Electron shuttleacross membrane
2 NADH
2 NADH
2 NADH
6 NADH 2(or 2 FADH2)
2 AcetylCoA
GLYCOLYSIS2
Pyruvate
About38 ATP
about 34 ATP
by substrate-levelphosphorylation
by oxidative phosphorylation
2 ATP
by substrate-levelphosphorylation
2 ATP
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 aspeanuts
ProteinsFatsCarbohydrates
Glucose
OXIDATIVEPHOSPHORYLATION(Electron Transportand Chemiosmosis)
CITRICACID
CYCLE
AcetylCoA
GLYCOLYSIS
Pyruvate
Amino acidsGlycerolSugars Fatty acids
Amino groups
G3P
ATP
Do plants perform cellular respiration??