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Cell Respiration
Biology AP Todeschini
Photosynthesis and Respiration
• There is a reciprocal relationship
between chemoheterotrophs and
photoautotrophs
All Animals Must Eat to Obtain Energy
Controlled Energy Conversion
• Metabolic reactions are tightly controlled in multi-step metabolic pathways.
• FYI, if this didn’t happen your body would burst into flames…
Catabolic Reactions
• “Destroy” = Break down food (few organic
molecules) into (many) simpler molecules
• This is an exergonic reaction
• This reaction releases energy
• Two famous catabolic processes for food
• Fermentation
• Cellular Respiration (more efficient)
• How is food broken down? How does
breakdown release energy?
Redox Reactions
• Chemical reactions
where electrons are
transferred from one
atom to another
• OIL RIG = Oxidation Is
Loss; Reduction Is Gain
Visualizing Terminology (practice)
X reduces Y
X becomes oxidized
Xe-
+
Y

X
Ye-
+
Y becomes reduced
Y oxidizes X
Na becomes oxidized
Na+ becomes reduced
Cl becomes reduced
Cl- becomes oxidized
Na
+
Cl
↔
Na+
Na reduces Cl
Cl oxidizes Na
+
ClNa+ oxidizes Cl-
*Note Reaction is reversible…
Cl- reduces Na+
Redox Energetics
• One reactant gains energy – reduced
• One reactant loses energy – oxidized
• How do you know if overall reaction is exergonic or endergonic?
• Cellular Respiration (Exergonic, Catabolic)
• C6H12O6 + 6O2  6CO2 + 6H2O
+ Energy
• Photosynthesis (Endergonic, Anabolic)
Energy + 6CO2 + 6H2O  C6H12O6 + 6O2
• Methane combustion (burning natural gas)
• CH4 + 2O2  CO2 + 2H2O + Energy
Redox w/ Cellular Respiration
• Cellular Respiration breaks down glucose
• Glucose is oxidized  loses electrons
• Release energy in a controlled manner
• Oxidize glucose little by little
How many electrons?
• Strip electrons a few at a time
• Use electron carriers (NADH) via ETC
• Biochemical pathway with several enzymes
If release energy all at once…
http://www.youtube.com/watch?v=txkRCIPSsjM
Electron Shuttles
• Compounds the store electrons from food
• Exist in oxidized and reduced forms
• In cells electrons come with protons
• Transfer electrons and protons to other
areas of the cell to continue metabolism
General Overview of Cell Respiration
• Cellular respiration has three stages:
1.
2.
3.
Glycolysis (breaks down glucose into two molecules of
pyruvate)
The citric acid cycle (completes the breakdown of
glucose)
Oxidative phosphorylation (accounts for most of the
ATP synthesis)
• Anaerobic Respiration stops with glycolysis
• Aerobic respiration will occur in a mitochondria with
oxygen present(in eukaryotes only).
• The point of all of it is to make ATP
Fig. 9-6-1
Electrons
carried
via NADH
Glycolysis
Pyruvate
Glucose
Cytosol
ATP
Substrate-level
phosphorylation
Fig. 9-6-2
Electrons carried
via NADH and
FADH2
Electrons
carried
via NADH
Citric
acid
cycle
Glycolysis
Pyruvate
Glucose
Mitochondrion
Cytosol
ATP
ATP
Substrate-level
phosphorylation
Substrate-level
phosphorylation
Fig. 9-6-3
Electrons carried
via NADH and
FADH2
Electrons
carried
via NADH
Citric
acid
cycle
Glycolysis
Pyruvate
Glucose
Oxidative
phosphorylation:
electron transport
and
chemiosmosis
Mitochondrion
Cytosol
ATP
ATP
ATP
Substrate-level
phosphorylation
Substrate-level
phosphorylation
Oxidative
phosphorylation
Glycolysis (in cytoplasm)
• All respiration begins with glycolysis in
the cytoplasm
• Glucose (6C) is cleaved into 2 molecules
of pyruvate (3C)
• This requires 2 ATP. It produces 4
• 2NAD+ are reduced to 2 NADPH
Glycolysis
• Substrate level phosphorylation
• When ATP is produced by
enzymatic phosphate transfer
from another organic phosphate
• Occurs in glycolysis and citric
acid(Kreb’s) cycle
• Glycolysis is hypothesized to be
most ancient metabolic
pathway because it happens in
all organisms
• What’s next???
Fermentation
• NADH is oxidized back into NAD+
• Pyruvate must be reduced into another
compound(waste product)
• Ethanol(yeast)
• Lactic acid(animals)
• Glycolysis can continue indefinitely, but costly
After Glycolysis
• In presence of oxygen Aerobic Respiration
 Mitochondrialots of ATP(very efficient)
• No oxygen  Anaerobic
Fermentationcytoplasmlactic
acid(animals) or ethanol(microorganisms)
• Anaerobic respiration produces 2 ATP per glucose
making it much less efficient than aerobic which
produces ~38 total per glucose.
Citric Acid Cycle (Kreb’s Cycle)
• Following glycolysis, aerobic respiration
in eukaryotes will take place in the
mitochondrion.
• The products of glycolysis are
transported through the mitochondrial
membranes into the mitochondrial
matrix.
• This is where the citric acid cycle
occurs.
• Prokaryotes that carry out aerobic
respiration utilize specializing portions
of their cell membrane.
First Acetyl-CoA
(intermembrane space)
• While being transported
into the mitochondrion,
pyruvate is converted into
acetyl group (-CH2CH3) and
a molecule of CO2
• The CO2 is waste product.
• The acetyl group is attached
to a molecule of CoEnzymeA (CoA). This is the carbon
input into the citric acid
acid cycle.
• Another NAD+ is reduced to
NADH
Citric Acid Cycle(matrix)
• The acetyl group from
pyruvate is attached to
oxaloacetate, forming citric
acid(aka citrate)
• The carbons from the
acetyle group are oxidized
into 2CO2
• 3 molecules of NAD+ are
reduced into NADH
• 1 molecule of FAD is
reduced into FADH2
• 1 ATP is produced
• The citrate is converted back
into oxaloacetate.
*this happens 2X per glucose
Oxidative Phosphorylation (intermembrane space)
• Electrons are from NADH and FADH2
are transported through a series of
proteins found in the folds of the
cristae (electron transport chain).
• H+ are pumped into and build up in
the intermembrane space and will
eventually flow across ATP synthase
to generate ATP.
• Oxygen is the “final electron
acceptor”. It will “grab” the
electrons and H+ to forms water, a
harmless waste product.
Chemiosmosis
• Ultimately how ATP is produced.
• H+ protons can only diffuse back into the matrix
through the ATP synthase channel.
• The free energy that is released is used to catalyze
ATP formation from ADP and free phosphate
groups(“oxidative phosphorylation”)
https://www.youtube.com/watch?v=JnQqbMg74Hk
It’s not all about glucose…
• All macromolecules can be used as substrates for
respiration.
• Different components enter at different points.
• If an animal is starving it will digest molecules in
the following order:
• Carbsfatsproteins(as a last resort)
• A fat gram will produce 2X as much ATP as a
gram of carbohydrate
• Gluconeogenesis is a way the body can create
substrates for respiration, costly
Overview of all Steps
Glycolysis(cytoplasm) Transition Step(cytoplasm)
Inputs
Inputs
• Glucose (6C)
• 2 pyruvate (3C)
• 2 NAD+
• 2 NAD+
• 2 ATP
Outputs
Outputs
• 2 Acetyl-CoA (2C from
pyruvate)
• 2 Pyruvate (3C)
• 2NADH
• 4 ATP
• 2CO2
• 2 NADH
Citric Acid
Cycle(mitochondria matrix)
Inputs
• 2 Acetyl-CoA (2C from
pyruvate)
• 6 NAD+
• 2 FAD
• 2 ADP
Outputs
• 4 CO2
• 6 NADPH
• 2 FADH2
• 2 ATP
ETC(inner membrane)
Inputs
• 20 NADH
• 2 FADH2
• O2
Outputs
• ~32-34 ATP
• H2O
• 20 NAD+
• 2 FAD+