Transcript Chapter 7: Cellular Respiration and Fermentation

Chapter 9: Cellular Respiration
AP Biology
Oxidation and Reduction
• E is gained by the transfer of e’s
• The relocation of e-’s releases the
stored E and the E ultimately
makes ATP
Redox Reactions
• Oxidation: the loss of e-’s
from a substance
• Reduction: the gain of e-’s
by a substance
• E must be added to pull e-’s
from an atom
Redox Reactions
• A redox reaction that
relocates an e- from a less
electronegative atom to a
more electronegative atom
loses potential E
Hydrogen
• In most redox reactions, it is
not only the e- that is
transferred but in most
biological reactions the whole
hydrogen atom is transferred
Carbohydrates and Fats
• Contain high levels of hydrogen
and their electrons
• There is a barrier that keeps sugar
from combining immediately with
O2
• This barrier is reduced inside the
body with the help of enzymes
Cellular Respiration
C6H12O6 + 6O2  6H2O + 6CO2 + E
Introduction
• Cellular Respiration is a
catabolic pathway.
–Does not directly perform
cellular work???
–Redox reactions!!
–Importance of Hydrogen??
Introduction
• Does glucose react instantaneously?
Spontaneously?
• Activation barrier/ Enzymes(lots of
them)
– Lowers activation energy
– Allows breakdown to proceed
spontaneously
Cellular Respiration
• What is a potential problem with the
breakdown of glucose as a spontaneous
reaction??
– Hint: TNT, Gasoline
• How does the cell prevent this problem?
– Does not release energy all at once
– Multi- step process catalyzed by specific enzymes
Cellular Respiration
• With each step, electrons are released with a
proton (hydrogen atom)
• Each hydrogen is transferred to a coenzyme
(NAD+)
• And eventually to Oxygen
Nicotinamide Adenine Dinucleotide
• NAD+
• Derivative of the vitamin niacin
• Coenzyme
– Oxidizing agent
• Will be reduced to NADH
– (2 electrons and Hydrogen)
– Dehydrogenase-removes two hydrogen from
substrate
Nicotinamide Adenine Dinucleotide
Glycolysis:
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Occurs in the cytoplasm
Net gain of 2 ATP and 2 NADH
Start: 6 carbon glucose
End: 2- 3 carbon pyruvate molecules
Ten steps- two phases
– Energy investment phase
– Energy payoff phase
Glycolysis:
• Energy investment stage:
• Glucose phosphorylated by ATP(2)
– Unstable
– Splits
• Each 3 carbon molecule is phosphorylated
again
– Inorganic phosphate comes from cytosol not ATP
Glycolysis:
• Energy Payoff Phase:
• Each 3 carbon molecule reduces NAD+ to
NADH
• Each 3 carbon molecule gives up its 2
phosphates to ADP to form 4 ATP.
Glycolysis: Summary
• Reactants:
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Glucose
NAD+
ATP (2)
ADP (2)
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Products:
Pyruvate (2)
NADH (2)
ATP (4)
Mitochondria Structure
• Double membrane organelle
– Outer membrane: very permeable
– Inner membrane:
• selectively permeable
– pyruvate (yes)
– NADH (no)
• contains electron transport proteins
• Cristae- inner foldings
– Increase surface area
• similar to plasma membrane of bacteria
Mitochondria Structure
• Double membrane organelle
– Matrix: inside inner membrane
• Protein rich solution: enzymes
• In between cristae
Citric Acid Cycle:
– Krebs Cycle
• Tricarboxylic Acid Cycle
– Matrix
– Reactants:
• 2 molecules of pyruvate
• Each makes a circuit through the cycle
– One glucose = two pyruvate = two turns of the cycle
– Products:
• For each pyruvate
– 3 NAD+
– 1 FAD+
– 1 ADP + P
3 NADH
1 FADH2
1 ATP
Oxidation of Pyruvate:
• Pyruvate must first be converted to
Acetyl CoA
– Pyruvate dehydrogenase
– Each pyruvate molecule loses one Carbon and two
Oxygen- Acetyl group
– Acetyl group attaches to CoA molecule forming
acetyl CoA
– Reduction of NAD+ molecule to NADH
• 2 total- one for each pyruvate
Cyclic Nature of Citric Acid Cycle
• CoA transfers 2 carbon molecule
– Transfers 2 carbon acetyl group to 4 carbon oxaloacetate
– Results = 6 carbon citrate
– Start of cycle
Cyclic Nature of Citric Acid Cycle
• Citrate- goes through a series of oxidation reactions
– Priming/ rearrangement stage
• Prepares the 6 carbon citrate for energy extraction
– Oxidized by NAD+
– Carbon dioxide
Cyclic Nature of Citric Acid Cycle
• Citrate also loses 2 carbon atoms (CO2) eventually
returning to 4 carbon oxaloacetate again
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Energy Extraction/ Acetyl group stage
More reduction of NAD+
Reduction of FAD
ATP produced- substrate level phosphorylation
Cycle starts over again
Important Features
• NAD+ and FAD+ are reduced by the oxidation of
an organic compound (transfer of H atom).
• 1 ATP molecule is formed by substrate level
phosphorylation during each turn of cycle (net
per glucose = 2 ATP)
• For each turn of the cycle, 3 Carbon atoms are
lost to Carbon Dioxide
– All 6 carbons exit the system by the end of the Kreb
cycle.
Oxidative Phosphorylation
• Electron transport is coupled with ATP synthesis via
chemiosmosis.
• Over all drop in ΔG as electrons are transferred from
NADH to Oxygen
– Releases energy in manageable amounts
• Create proton motive force
– Drives the production of ATP
Electron Transport Chain
• Inner Mitochondrial membrane
• Series (I - IV) of protein complexes
– Complexes one – three have increasing affinity
for electrons
• Prosthetic groups: non-protein components
essential to certain enzymes
• Redox (downhill) reactions
• Does not directly make ATP- eases the fall
Prosthetic Groups:
• FMN- flavin mono nucleotide– Gets reduced by NADH at complex I
• CoQ- Ubiquinone– very hydrophobic
– very mobile
– Carries between complex I/II and complex III
Prosthetic Groups:
• Iron/Sulfur cluster– gets reduced by FADH2 at complex II
– Transfer electrons between cytochromes
• Cytochromes- transfers electrons to oxygen
– Heme- Fe atom- carries electrons
Chemiosmosis
• The formation of a hydrogen ion gradient
drives the cellular process of ATP synthesis
– Proton motive force
Chemiosmosis
• Final protein complex = F0F1 protein
– Catalyzed by ATP synthase
– Oxidative phosphorylation: synthesis of ATP
from ADP and Pi
– 3 to 4 H+ to generate 1 ATP
Animation
• http://www.science.smith.edu/d
epartments/Biology/Bio231/etc.
html
Fermentation
 If a cell runs out of O2, all the ecarriers are stuck in reduced form,
halting system
• Pyruvate produced by glycolysis
acts as alternative acceptor of H
from NADH, keeping glycolysis
going to allow small ATP
production
Alcoholic Fermentation
• Yeasts break down sugar into
pyruvate.
• Each pyruvate is dismantled into a
molecule of CO2 and a 2C compound
acetaldehyde
• Acetaldehyde is reduced by accepting
2H's from NADH and H+ forming 2C
alcohol ethanol (ethyl alcohol)
Lactic Acid Fermentation
• Occurs during strenuous exercise
• Pyruvate from glycolysis is reduced
by accepting hydrogens from NADH
and H+
• Pyruvate converted into 3C
compound, lactate
Metabolic Energy Systesm:
• Phosphagen pathway- high powered
activities that last around 10 secs
• Glycolytic pathway- moderately powered
activities that last two minutes
• Oxidative pathway- low powered pathways
that last more than several minutes
Respiration W/O O2
 Anaerobic respiration: uses nitrate
or sulfate as final electron acceptor
 Fermentation: the anaerobic
breakdown of food molecules in
which the final e- acceptor is an
organic molecule