Transcript Bio 226: Cell and Molecular Biology

Plant Respiration
Releases 50% of fixed CO2
Provides energy for all sinks,
source leaves at night & helps
source during day!
Plant Respiration
Similar, but more complex than in animals
Making precursors, recycling products, releasing energy
are also important
Plant Respiration
1. Glycolysis in cytosol
2. Pyruvate oxidation in mito
3. Krebs cycle in mito
4. Electron transport &
chemiosmosis in mito
Plant Respiration
1. Glycolysis in cytosol
• 1 glucose -> 2 pyruvate
• Yields 2 NADH & 2 ATP
per glucose
Unique features in plants
1. May start with DHAP
from cp instead of glucose
Unique features in plants
1.May start with DHAP from cp instead of glucose
2.May yield malate cf pyr
• PEP ->OAA by PEPC, then reduced to malate
Plant Respiration
2.May yield malate cf pyr
• PEP ->OAA by PEPC, then reduced to malate
• Get more ATP/NADH in mito
Unique features in plants
2.May yield malate cf pyr
• PEP ->OAA by PEPC, then reduced to malate
• Get more ATP/NADH in mito
• Replaces substrates
Plant Respiration
1.Glycolysis in cytosol
• 1 glucose -> 2 pyruvate
• Yields 2 NADH & 2 ATP
per glucose
Anaerobic plants ferment
pyr to regenerate NAD+
Form EtOH
Plant Respiration
1.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
Plant Respiration
3. Krebs cycle
• Similar, but
more complex
Key role is making
intermediates &
recycling products
Plant Respiration
3. Krebs cycle
• Similar, but
more complex
Key role is making
intermediates &
recycling products
Many ways to feed in
other substrates to burn
Plant Respiration
3. 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
Plant Respiration
Many ways to feed in other substrates to burn or replace
intermediates used
for biosynthesis
Needed to keep
cycle going
Plant Respiration
Many ways to feed in other substrates to burn or replace
intermediates used
for biosynthesis
Needed to keep
cycle going
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
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
Plant Respiration
Pentose phosphate shunt in cytosol or cp
• 6 glucose-6P + 12NADP++ 7 H2O -> 5 glucose-6P + 6 CO2
+ 12 NADPH +12 H+ : makes NADPH & intermediates
Plant Respiration
Pentose phosphate shunt in cytosol or cp
makes NADPH & intermediates
Uses many Calvin Cycle enzymes
Plant Respiration
Pentose phosphate shunt in cytosol or cp
makes NADPH & intermediates
Uses many Calvin Cycle enzymes
Makes nucleotide &
phenolic precursors
Plant Respiration
Uses many Calvin Cycle enzymes
Makes nucleotide & phenolic precursors
Gets Calvin cycle started at dawn
ATP generation
2 stages
1) e- transport
2) chemiosmotic ATP synthesis
Three steps transport H+ across membrane
1) NADH dehydrogenase pumps 4 H+/ 2 e2) Cyt bc1 pumps 4 H+/ 2 e3) Cyt c oxidase pumps 2 H+/ 2 e- and adds 2 H+ to O to
form H2O
e- transport
Plants have additional enzymes!
•NADH dehydrogenase in matrix that transfers e- from
NADH to UQ w/o pumping H+
Additional e- transport enzymes!
•NADH dehydrogenase in matrix that transfers e- from
NADH to UQ w/o pumping H+ Insensitive to rotenone
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
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
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+
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
Additional e- transport enzymes!
•NADPH dehydrogenase in intermembrane space that
transfers e- from NADPH to UQ w/o pumping H+
Insensitive to rotenone
• "imports" e- from cytoplasmic NADPH
Additional e- transport enzymes!
•Alternative oxidase on matrix side of IM transfers efrom UQ to O2 w/o pumping H+
•Insensitive to Cyanide, Azide
or CO
•Sensitive to SHAM
(salicylhydroxamic acid)
Additional e- transport enzymes!
•Alternative oxidase on matrix side of IM transfers efrom UQ to O2 w/o pumping H+
•Insensitive to Cyanide, Azide or CO
•Sensitive to SHAM (salicylhydroxamic acid,)
•Also found in fungi, trypanosomes & Plasmodium
Additional e- transport enzymes!
•Alternative oxidase on matrix side of IM transfers efrom UQ to O2 w/o pumping H+
•Also found in fungi, trypanosomes & Plasmodium
•Energy lost as heat:
can raise Voodoo lilies
25˚ C
Additional e- transport enzymes!
•Alternative oxidase on matrix side of IM transfers efrom UQ to O2 w/o pumping H+
• Plants also have an uncoupler protein: lets H+ in w/o
doing work!
Additional eAdditional
e- transport
transport enzymes!
enzymes!
Why so
Why
so many
many ways
ways to
to reduce
reduce ATP
ATP synthesis
synthesis efficiency?
efficiency?
Additional eAdditional
e- transport
transport enzymes!
enzymes!
Why so
Why
so many
many ways
ways to
to reduce
reduce ATP
ATP synthesis
synthesis efficiency?
efficiency?
• Regenerate
Regenerate NAD+
NAD+ needed
needed for
for precursor
precursor synthesis
synthesis
• Generate
Generate heat
heat
• Burn
Burn off
off excess
excess energy
energy captured
captured by
by photosynthesis
photosynthesis
• Prevalence
Prevalence says
says they're
they're doing
doing something
something important!
important!
Regulating Respiration
Regulated by demand for ATP,
NADPH and substrates
Glycolysis is allosterically regulated at 3 irreversible steps
Hexokinase is allosterically inhibited by its product: G-6P
Allosteric site has lower affinity than active site
Glycolysis is allosterically regulated at 3 irreversible steps
Hexokinase is allosterically inhibited by its product: G-6P
Pyr kinase is allosterically inhibited by ATP & citrate
Regulating Glycolysis
Main regulatory step is Phosphofructokinase
Rate-limiting step
Committed step
Regulating Glycolysis
Main regulatory step is
Phosphofructokinase
Inhibited by Citrate, PEP & ATP
Stimulated by
ADP
Regulating Pyruvate DH
Mainly by a kinase
•Inhibited when Pi added
Regulating Pyruvate DH
Mainly by a kinase
•Inhibited when Pi added
•NADH, Acetyl CoA, ATP
NH4+ inhibit PDH &
activate kinase
Regulating Pyruvate DH
Mainly by a kinase
•Inhibited when Pi added
•NADH, Acetyl CoA, ATP
NH4+ inhibit PDH &
activate kinase
•Activated when no Pi
•ADP, pyruvate inhibit
kinase
REGULATING THE KREBS CYCLE
Krebs cycle is allosterically regulated at 4 enzymes
1) citrate synthase
2) Isocitrate dehydrogenase
3) a-ketoglutarate dehydrogenase
4) Malate dehydrogenase
REGULATING THE KREBS CYCLE
Krebs cycle is allosterically regulated at 4 enzymes
1) citrate synthase
2) Isocitrate dehydrogenase
3) a-ketoglutarate dehydrogenase
4) Malate dehydrogenase
All are inhibited by NADH
& products
Environmental factors
1) Temperature
• Rate ~ doubles for each 10˚ C increase up to ~ 40˚
• At higher T start to denature
Environmental factors
1) Temperature
• Rate ~ doubles for each 10˚ C increase up to ~ 40˚
• At higher T start to denature
2) pO2
• Respiration declines if pO2 <5%
Environmental factors
1) Temperature
• Rate ~ doubles for each 10˚ C increase up to ~ 40˚
• At higher T start to denature
2) pO2
• Respiration declines if pO2 <5%
• Problem for flooded roots
Environmental factors
1) Temperature
• Rate ~ doubles for each 10˚ C increase up to ~ 40˚
• At higher T start to denature
2) pO2
• Respiration declines if pO2 <5%
• Problem for flooded roots
3) pCO2
• Inhibits respiration at 3%
Environmental factors
1) Temperature
• Rate ~ doubles for each 10˚ C increase up to ~ 40˚
• At higher T start to denature
2) pO2
• Respiration declines if pO2 <5%
• Problem for flooded roots
3) pCO2
• Inhibits respiration at 3%
• No obvious effects at 700 ppm, yet biomass reduced