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Cellular Respiration
Energy and Organisms
• Organisms are classified based on the kind of energy they use.▫ Autotrophs
Use the energy from sunlight to make organic molecules (sugar)
Use the energy in the organic molecules to make ATP
▫ Heterotrophs Obtain organic molecules by eating the autotrophs
Use the energy in the organic molecules to make ATP
• Autotrophs use photosynthesis.▫ To use the energy from light to make organic molecules
• All organisms use cellular respiration.▫ To harvest the energy from organic molecules and use it to make
ATP
Review: Structure of Mitochondrion
• Double membranous organelle found in almost all living cells.
• The inner membrane is folded to form little selves called cristae.
• The inner space filled with gel-like is called the matrix.
• The transition reaction and krebs cycle occur in the matrix while ETC occurs in cristae.
Review Oxidation and Reduction
• In oxidation
– A substance loses electrons, or is oxidized
• In reduction
– A substance gains electrons, or is reduced
Overview of Aerobic Cellular
Respiration
Figure 9.6
Electrons
carried
via NADH
GlycolsisGlucose Pyruvate
ATP
Substrate-level
phosphorylation
Electrons carried
via NADH and
FADH2
Citric
acid
cycle
Oxidative
phosphorylation:
electron
transport and
chemiosmosis
ATPATP
Substrate-level
phosphorylationOxidative
phosphorylation
MitochondrionCytosol
Cellular Respiration
• Is the process that releases energy by breaking down glucose and other food molecules in the presence of oxygen.
6O2+C6H12O6 6CO2 + 6H20+ Energy
Glycolysis
• The breakdown of glucose into pyruvic acid
• As glucose is metabolized, enough energy is released to
• Occurs in the cytoplasm
Glycolysis Citricacidcycle
Oxidative
phosphorylation
ATP ATP ATP
2 ATP
4 ATP
used
formed
Glucose
2 ATP + 2 P
4 ADP + 4 P
2 NAD+ + 4 e- + 4 H + 2 NADH + 2 H+
2 Pyruvate + 2 H2O
Energy investment phase
Energy payoff phase
Glucose 2 Pyruvate + 2 H2O
4 ATP formed – 2 ATP used 2 ATP
2 NAD+ + 4 e– + 4 H +2 NADH
+ 2 H+
Figure 9.8
Glycolysis
Krebs Cycle• Also known as the citric
acid cycle or the tricarboxylic acid (TCA) cycle
• The breakdown of pyruvicacid▫ Released as carbon
dioxide• Occurs in the
mitochondrial matrix
ATP
2 CO2
3 NAD+
3 NADH
+ 3 H+
ADP + P i
FAD
FADH2
Citric
acid
cycle
CoA
CoA
Acetyle CoA
NADH
+ 3 H+
CoA
CO2
Pyruvate(from glycolysis,2 molecules per glucose) ATP ATP ATP
Glycolysis Citricacidcycle
Oxidative
phosphorylatio
n
Figure 9.11
Krebs Cycle
Electron Transport Chain
• NADH and FADH2 release the electrons they received during glycolysis and the Kreb’s cycle to the electron transport chain (ETC).
• The proteins of the ETC transfer the electrons and use the energy released to pump protons.▫ Protons are pumped from the matrix to
the intermembrane space.▫ Creates a concentration gradient
Electron Transport Chain
Oxidative
phosphorylation.
electron transport
and chemiosmosis
Glycolysis
ATP ATP ATP
Inner
Mitochondrial
membrane
H+
H+H+
H+
H+
ATPP i
Protein complex
of electron
carners
Cyt c
I
II
III
IV
(Carrying electrons
from, food)
NADH+
FADH2
NAD+
FAD+ 2 H+ + 1/2 O2
H2O
ADP +
Electron transport chain
Electron transport and pumping of protons (H+),
which create an H+ gradient across the membrane
Chemiosmosis
ATP synthesis powered by the flow
Of H+ back across the membrane
ATP
synthase
Q
Oxidative phosphorylation
Intermembrane
space
Inner
mitochondrial
membrane
Mitochondrial
matrix
Figure 9.15
Total Yields for Aerobic Cellular
Respiration per Glucose MoleculeElectron shuttles
span membraneCYTOSOL 2 NADH
2 FADH2
2 NADH 6 NADH 2 FADH22 NADH
Glycolysis
Glucose
2
Pyruvate
2
Acetyl
CoA
Citric
acid
cycle
Oxidative
phosphorylation:
electron transport
and
chemiosmosis
MITOCHONDRION
by substrate-level
phosphorylation
by substrate-level
phosphorylation
by oxidative phosphorylation, depending
on which shuttle transports electrons
from NADH in cytosol
Maximum per glucose:About
36 or 38 ATP
+ 2 ATP + 2 ATP + about 32 or 34 ATP
or
Figure 9.16
Anaerobic Cellular Respiration
• Metabolizing glucose in the absence of oxygen is called anaerobic respiration.
▫ Involves the incomplete oxidation of glucose
▫ Fermentation is an anaerobic pathway that uses an organic molecule as the final electron acceptor.
Anaerobic Cellular Respiration
• Anaerobic respiration usually starts with glycolysis.▫ Glucose is metabolized into pyruvic acid.▫ 2 ATP are made.
• The fermentation reactions oxidize NADH to regenerate the NAD+ that is needed in glycolysis.▫ In the process, pyruvic acid is reduced to
either lactic acid or ethanol or another organic molecule.
Anaerobic Cellular Respiration
Alcoholic Fermentation
• Starts with glycolysis▫ Glucose is metabolized to pyruvic acid.▫ A net of 2 ATP is made.
• The equation for alcoholic fermentation after glycolysis is:▫ Pyruvic acid+NADH alcohol+CO2+NAD+
• During alcoholic fermentation▫ Pyruvic acid is reduced to form ethanol.▫ Carbon dioxide is released.
• Yeasts do this▫ Leavened bread▫ Sparkling wine
Lactic Acid Fermentation
• Starts with glycolysis
▫ Glucose is metabolized to pyruvic acid.
▫ A net of 2 ATP is made.
• During lactic acid fermentation
▫ Pyruvic acid is reduced to form lactic acid.
▫ No carbon dioxide is released.
• Muscle cells have the enzymes to do this, but brain cells do not.
▫ Muscle cells can survive brief periods of oxygen deprivation, but brain cells cannot.
▫ Lactic acid “burns” in muscles.
Lactic Acid Fermentation
• The equation for lactic acid fermentation after glycolysis is:
▫ Pyruvic acid+ NADH lactic acid + NAD+
2 ADP + 2 P1 2 ATP
GlycolysisGlucose
2 NAD+ 2 NADH
2 Pyruvate
2 Acetaldehyde2 Ethanol
(a) Alcohol fermentation
2 ADP + 2 P1 2 ATP
GlycolysisGlucose
2 NAD+ 2 NADH
2 Lactate
(b) Lactic acid fermentation
H
H OH
CH3
C
O –
OC
C O
CH3
H
C O
CH3
O–
C O
C O
CH3O
C O
C OHH
CH3
CO22
Figure 9.17
Metabolizing Other Molecules
• Cells will use the energy in carbohydrates first.
▫ Complex carbohydrates are metabolized into simple sugars.
• Cells can use the energy in fats and proteins as well.
▫ Fats are digested into fatty acids and glycerol.
▫ Proteins are digested into amino acids.
• Cells must convert fats and proteins into molecules that can enter and be metabolized by the enzymes of glycolysis or the Kreb’scycle.
