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Glucose breakdown is exergonic! Energy is given off as heat and ATP.
Redox reactions
Occurs in matrix
Net result:
4 carbon dioxide
2 ATP
6 NADH
2 FADH2
H pumped into
inner-membrane space
Oxygen is final
electron acceptor
Occurs on inner mitochondrial membrane – produces energy that drives
oxidative phosphorylation
Noncyclic electron flow
Calvin cycle – end product is G3P (sugar) which will later be metabolized
Into larger carbs
Photorespiration: An
Evolutionary Relic?
• In photorespiration
– O2 substitutes for CO2 in the active site of the
enzyme rubisco
– The photosynthetic rate is reduced
– Energetically less efficient
– Early atmosphere contained little oxygen
• Enzyme rubisco could not distinguish between O2 or CO2 and
thus today this continues
• Or free radical preventer?
C4 Plants
• C4 plants minimize the cost of photorespiration
(reduce uptake/use of O2)
– By incorporating CO2 into four carbon compounds in
mesophyll cells
– Increasing CO2 levels
• These four carbon compounds
– Are exported to bundle sheath cells where O2
concentration is low, and then release CO2 used in
the Calvin cycle.
Mesophyll
cell
Mesophyll cell
Photosynthetic
cells of C4 plant
leaf
CO
CO
2 2
• C4 leaf anatomy and the C4 pathway
PEP carboxylase
Bundlesheath
cell
PEP (3 C)
ADP
Oxaloacetate (4 C)
Vein
(vascular tissue)
Malate (4 C)
ATP
C4 leaf anatomy
BundleSheath
cell
Pyruate (3 C)
CO2
Stoma
CALVIN
CYCLE
Sugar
Vascular
tissue
Figure 10.19
• CAM plants (cacti)
– Open their stomata at night, incorporating CO2
into organic acids
• During the day, the stomata close
– And the CO2 is released from the organic acids
for use in the Calvin cycle
• Helps eliminate high water loss form
stomata during heat of day (transpiration)
• The CAM pathway is similar to the C4
pathway
Pineapple
Sugarcane
C4
Mesophyll Cell
Organic acid
Bundlesheath
cell
(a) Spatial separation
of steps. In C4
plants, carbon fixation
and the Calvin cycle
occur in different
Figure 10.20 types of cells.
CALVIN
CYCLE
Sugar
CAM
CO2
CO2
1 CO2 incorporated Organic acid
into four-carbon
organic acids
(carbon fixation)
2 Organic acids
release CO2 to
Calvin cycle
CALVIN
CYCLE
Sugar
Night
Day
(b) Temporal separation
of steps. In CAM
plants, carbon fixation
and the Calvin cycle
occur in the same cells
at different times.
• Overview of cell signaling
EXTRACELLULAR
FLUID
1 Reception
CYTOPLASM
Plasma membrane
2 Transduction
3 Response
Receptor
Activation
of cellular
response
Relay molecules in a signal transduction pathway
Signal
molecule
Figure 11.5
• G-protein-linked receptors
Signal-binding site
Segment that
interacts with
G proteins
G-protein-linked
Receptor
Plasma Membrane
Activated
Receptor
Signal molecule
Inctivate
enzyme
GDP
CYTOPLASM
G-protein
(inactive)
Enzyme
GDP
GTP
Activated
enzyme
GTP
GDP
Pi
Figure 11.7
Cellular response
GTP replaced with GDP, now inactive
• Receptor tyrosine kinases
Signal-binding sites
Signal
molecule
Signal
molecule
Helix in the
Membrane
Tyr
Tyrosines
Tyr
Tyr
Tyr
Tyr
Tyr
Tyr
Tyr
Tyr
Tyr
Tyr
Tyr
Tyr
Tyr
Tyr
Tyr
Tyr
Receptor tyrosine
kinase proteins
(inactive monomers)
CYTOPLASM
Tyr
Dimer
Activated
relay proteins
Figure 11.7
Tyr
P Tyr
P Tyr
Tyr P
Tyr P
Tyr
P Tyr
Tyr P
Tyr
Tyr
Tyr
Tyr
6
ATP
Activated tyrosinekinase regions
(unphosphorylated
dimer)
6 ADP
Fully activated receptor
tyrosine-kinase
(phosphorylated
dimer)
P Tyr
P Tyr
P Tyr
Tyr P
Tyr P
Tyr P
Inactive
relay proteins
Cellular
response 1
Cellular
response 2
• Ion channel receptors
Signal
molecule
(ligand)
Gate
closed
Ions
Ligand-gated
ion channel receptor
Plasma
Membrane
Gate open
Think if these receptors as
having allosteric activators/inhibitors
Cellular
response
Gate close
Figure 11.7