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C4 and CAM photosynthesis
Adaptations that reduce PR & water loss Both fix CO2 with a different enzyme later release CO2 to be fixed by rubisco use energy to increase [CO2] at rubisco C4 isolates rubisco spatially (e.g. corn) CAM isolates rubisco temporally (e.g. cacti)
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Crassulacean acid metabolism (CAM)
Can tell by d13C rubisco discriminates against 13C, so C3 plants have d13C of -280/00 if it can choose CAM & C4 have d13C of -140/00 because although use up most CO2 in leaf 13C diffuses more slowly Can tell if sugar came from C3 or C4/CAM by d13C Also tells about stomatal opening &water use efficiency
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Photosynthesis in the real world
Sun leaves: thicker, more PSII, protein & xanthophyll light compensation pt: more cells = more mito Shade leaves: thinner, more PSI & chl, > chlb/chla
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Plants and Temperature
Affects enzymes: too slow if cold, denature if too hot Rubisco activase is very T sensitive; way to limit PR?
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Plants and Temperature
Affects enzymes Affects membranes Fluidity: must be correct Too stiff, may leak if too cold Denature if too warm
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Plants and Temperature
PSII sets Topt & upper limit for C4 plants Topt for C3 also depends on photorespiration Limiting factor varies at lower T depending on which enzymes fall behind -> rubisco usually limits C3
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Plants and Temperature
Heat dissipation Long wave-length radiation Sensible heat loss Conduction & convection to cool air Evaporation
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Plant Respiration Recovers energy stored by photosynthesis C6H12O6 + 6 O2 <=> 6 CO2 + 6 H2O + energy Occurs in all plant tissues: even source leaves in light! Releases 50% of fixed CO2
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Plant Respiration Releases 50% of fixed CO2 Provides energy for all sinks, source leaves at night & helps source during day!
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Plant Respiration Similar, but more complex than in animals Making precursors, recycling products, releasing energy are also important
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Plant Respiration Glycolysis in cytosol Pyruvate oxidation in mito Krebs cycle in mito Electron transport & chemiosmosis in mito
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Plant Respiration Glycolysis in cytosol 1 glucose -> 2 pyruvate Yields 2 NADH & 2 ATP per glucose Unique features in plants May start with DHAP from cp instead of glucose
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Unique features in plants
May start with DHAP from cp instead of glucose May yield malate cf pyr PEP ->OAA by PEPC, then reduced to malate
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Plant Respiration May yield malate cf pyr PEP ->OAA by PEPC, then reduced to malate Get more ATP/NADH in mito
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Unique features in plants
May yield malate cf pyr PEP ->OAA by PEPC, then reduced to malate Get more ATP/NADH in mito Replaces substrates
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Plant Respiration Glycolysis in cytosol 1 glucose -> 2 pyruvate Yields 2 NADH & 2 ATP per glucose Anaerobic plants ferment pyr to regenerate NAD+ Form EtOH
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Plant Respiration Glycolysis in cytosol 1 glucose -> 2 pyruvate Yields 2 NADH & 2 ATP per glucose Anaerobic plants ferment pyr to regenerate NAD+ Form EtOH Less toxic than lactate because diffuses away
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Plant Respiration Krebs cycle Similar, but more complex Key role is making intermediates & recycling products
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Plant Respiration Krebs cycle Similar, but more complex Key role is making intermediates & recycling products Many ways to feed in other substrates to burn
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Plant Respiration Krebs cycle Similar, but more complex Key role is making intermediates & recycling products Many ways to feed in other substrates to burn or replace intermediates used for biosynthesis
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Plant Respiration Many ways to feed in other substrates to burn or replace intermediates used for biosynthesis Needed to keep cycle going
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Plant Respiration Many ways to feed in other substrates to burn or replace intermediates used for biosynthesis Needed to keep cycle going Malic enzyme is key: lets cell burn malate or citrate from other sources
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Plant Respiration Many ways to feed in other substrates to burn or replace intermediates used for biosynthesis Needed to keep cycle going Malic enzyme is key: lets cell burn malate or citrate from other sources PEPCarboxylase lets cell replace Krebs intermediates used for synthesis
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Plant Respiration Pentose phosphate shunt in cytosol or cp 6 glucose-6P + 12NADP++ 7 H2O -> 5 glucose-6P + 6 CO NADPH +12 H+ : makes NADPH & intermediates
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Plant Respiration Pentose phosphate shunt in cytosol or cp makes NADPH & intermediates Uses many Calvin Cycle enzymes
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Plant Respiration Pentose phosphate shunt in cytosol or cp makes NADPH & intermediates Uses many Calvin Cycle enzymes Makes nucleotide & phenolic precursors
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Plant Respiration Uses many Calvin Cycle enzymes Makes nucleotide & phenolic precursors Gets Calvin cycle started at dawn
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ATP generation 2 stages 1) e- transport 2) chemiosmotic ATP synthesis
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Three steps transport H+ across membrane
1) NADH dehydrogenase pumps 4 H+/ 2 e- 2) Cyt bc1 pumps 4 H+/ 2 e- 3) Cyt c oxidase pumps 2 H+/ 2 e- and adds 2 H+ to O to form H2O
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e- transport Plants have additional enzymes! NADH dehydrogenase in matrix that transfers e- from NADH to UQ w/o pumping H+
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e- transport Plants have additional enzymes! NADH dehydrogenase in matrix that transfers e- from NADH to UQ w/o pumping H+ Insensitive to rotenone
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Additional e- transport enzymes!
NADH dehydrogenase in matrix that transfers e- from NADH to UQ w/o pumping H+ Insensitive to rotenone Helps burn off excess NADH from making precursors
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Additional e- transport enzymes!
NADH dehydrogenase in matrix that transfers e- from NADH to UQ w/o pumping H+ Insensitive to rotenone Helps burn off excess NADH from making precursors Much lower affinity for NADH than complex I
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Additional e- transport enzymes!
NADH dehydrogenase in matrix that transfers e- from NADH to UQ w/o pumping H+ Insensitive to rotenone Helps burn off excess NADH from making precursors Much lower affinity for NADH than complex I Energy is released as heat
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Additional e- transport enzymes!
NADH dehydrogenase in matrix that transfers e- from NADH to UQ w/o pumping H+ Insensitive to rotenone Helps burn off excess NADH from making precursors Energy is released as heat NADH dehydrogenase in intermembrane space that transfers e- from NADH to UQ w/o pumping H+
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Additional e- transport enzymes!
NADH dehydrogenase in intermembrane space that transfers e- from NADH to UQ w/o pumping H+ Insensitive to rotenone "imports" e- from cytoplasmic NADH Much lower affinity for NADH than complex I Energy is released as heat
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Additional e- transport enzymes!
Alternative oxidase on matrix side of IM transfers e- from UQ to O2 w/o pumping H+
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Additional e- transport enzymes!
Alternative oxidase on matrix side of IM transfers e- from UQ to O2 w/o pumping H+ Insensitive to Cyanide, Azide or CO
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Additional e- transport enzymes!
Alternative oxidase on matrix side of IM transfers e- from UQ to O2 w/o pumping H+ Insensitive to Cyanide, Azide or CO Sensitive to SHAM (salicylhydroxamic acid)
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Additional e- transport enzymes!
Alternative oxidase on matrix side of IM transfers e- from UQ to O2 w/o pumping H+ Insensitive to Cyanide, Azide or CO Sensitive to SHAM (salicylhydroxamic acid) Also found in fungi, trypanosomes & Plasmodium
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Additional e- transport enzymes!
Alternative oxidase on matrix side of IM transfers e- from UQ to O2 w/o pumping H+ Also found in fungi, trypanosomes & Plasmodium Energy lost as heat: can raise Voodoo lilies 25˚ C
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Additional e- transport enzymes!
Alternative oxidase on matrix side of IM transfers e- from UQ to O2 w/o pumping H+ Plants also have an uncoupler protein: lets H+ in w/o doing work!
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Additional e- transport enzymes!
Alternative oxidase on matrix side of IM transfers e- from UQ to O2 w/o pumping H+ Plants also have an uncoupler protein: lets H+ in w/o doing work! Why so many ways to reduce ATP synthesis efficiency?
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Additional e- transport enzymes!
Why so many ways to reduce ATP synthesis efficiency? Regenerate NAD+ needed for precursor synthesis
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Additional e- transport enzymes!
Why so many ways to reduce ATP synthesis efficiency? Regenerate NAD+ needed for precursor synthesis Generate heat
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Additional e- transport enzymes!
Why so many ways to reduce ATP synthesis efficiency? Regenerate NAD+ needed for precursor synthesis Generate heat Burn off excess energy captured by photosynthesis
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Additional e- transport enzymes! Additional e- transport enzymes!
Why so many ways to reduce ATP synthesis efficiency? Regenerate NAD+ needed for precursor synthesis Generate heat Burn off excess energy captured by photosynthesis Prevalence says they're doing something important! Additional e- transport enzymes! Why so many ways to reduce ATP synthesis efficiency? Regenerate NAD+ needed for precursor synthesis Generate heat Burn off excess energy captured by photosynthesis Prevalence says they're doing something important!
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