Respiration

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Respiration Metabolism

• Chapter 5

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What happens to Glucose from Photosynthesis?

• Burned for energy
• Converted to sucrose for transport
• Starch/Cellulose (polysaccharides)
• Amino Acids (proteins)
• Lipids (fats)

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Why does the plant need to have an active
respiration system to generate ATP and NADPH when
photosynthesis produces them?
1. The plant needs ATP and NADPH at night.
2. The location of photosynthetic ATP and
NADPH may not be convenient.
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Respiration
C6H12O6 6O2 ----gt 6CO2 6H2O Energy
Process occurs in several locations Requires
numerous reactions Uses e- transport chain
different from Z scheme
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The generation of ATP in the mitochondria is
similar to that of the chloroplasts. A proton
gradient is generated and H ion transport from
the mitochondrial matrix and into the
intermembrane space of the mitochondria (somewhat
equivalent to stroma). The transport is linked
to an ATP generating ATP synthase.
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Three Steps of Respiration

• Glycolysis (cytoplasm)
• Krebs Cycle (mitochondria)
  a.k.a. TCA cycle
• Electron Transport Chain
• (mitochondria)

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R e s p i r a t i o n
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How does glucose or CH2O get into glycolysis?
1. Starch phosphorylase produces a
Glucose-1-P. 2. Starch hydrolysis produce a
Glucose. 3. Sucrose is inverted or sucrose
synthase produces a UDP-glucose fructose.
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Glycolysis
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Krebs Cycle
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Electron Transport
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Pathways of Respiration That Are Unique to Plants
1. External NADPH Dehydrogenase - Facilitates
transfer of reducing energy to ubiquinone in
mitochondrial membrane but only 6 H gradient is
achieved.
2. Rotenone-insensitive NADH Dehydrogenase -
Rotenone blocks the first step of electron
transfer in nearly all all living cells.
However, this alternative dehydrogenase
facilitates transfer of internal NADH to
ubiquinone.
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Pathways of Respiration That Are Unique to Plants
3. Cyanide-Resistant Respiration - CN-, CO, and
N3-, inhibit cytochrome c oxidase. In animals,
they completely inhibit respiration but in plants
an alternative oxidase accepts electrons from
ubiquinone. However, only 3 or less H ions are
extruded so only 1 or less ATPs are formed. The
function of this pathway is thought to be
thermogenesis to handle overflow energy.
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Interrelationship between CH2O, fats, and proteins
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Alcoholic Fermentation
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Lactic Acid Fermentation
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Factors Affecting Respiration Rate
1. Radiation It is not known whether
mitochondria generate much ATP in the light but
the TCA cycle may be necessary to generate some
carbon skeletons. Sun leaves respire more than
shade leaves.
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Factors Affecting Respiration Rate
2. Temperature As temperature increases from 5
to 25ºC, many respiratory reaction rates
increase exponentially.
Rate at (t 10)ºC
Q10
Q10 often equals 2.0.
Rate at (t)ºC
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Factors Affecting Respiration Rate
3. Oxygen Availability Usually at 250 µM in
cytosol and cytochrome c oxidase has a Km of 1
µM. Of course, under flooding stress,
intercellular spaces lack air and oxygen
deficiency can result.
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Factors Not Covered in This Session
1. Glyoxylate Cycle Conversion of lipids to
sucrose. 2. Climacteric A rise in respiration in
senescing tissues.