how cells acquire energy chapter 6. fig. 6.3a, p. 94 leafs upper surfacephotosynthetic cells two...
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How Cells Acquire Energy
Chapter 6
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Fig. 6.3a, p. 94
leaf’s upper surface photosynthetic cells
two outer layers of membrane
inner membrane system (thylakoids, all interconnecting bychannels) stroma
(see next slide)
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Organelles of photosynthesis
Chloroplasts
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Photosynthesis Equation
12H2O + 6CO2 6O2 + C2H12O6 + 6H2Owater carbon
dioxideoxygen glucose water
LIGHT ENERGY
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Two Stages of Photosynthesis
sunlight water uptake carbon dioxide uptake
ATP
ADP + Pi
NADPH
NADP+
glucoseP
oxygen release
LIGHT INDEPENDENT-
REACTIONS
LIGHT DEPENDENT-REACTIONS
new water
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Electromagnetic Spectrum
Shortest Gamma rays
wavelength X-rays
UV radiation
Visible light
Infrared radiation
Microwaves
Longest Radio waves
wavelength
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Visible Light
• Wavelengths humans perceive as different colors
• Violet (380 nm) to red (750 nm)
• Longer wavelengths, lower energy
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Pigments
• Light-absorbing molecules
• Absorb some wavelengths and transmit others
• Color you see are the wavelengths NOT absorbed
Wavelength (nanometers)
chlorophyll b
chlorophyll a
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• Light-catching part of molecule often has alternating single and double bonds
• These bonds contain electrons that are capable of being moved to higher energy levels by absorbing light
Pigment Structure
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Excitation of Electrons
• Excitation occurs only when the quantity of energy in an incoming photon matches the amount of energy necessary to boost the electrons of that specific pigment
• Amount of energy needed varies among pigment molecules
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Pigments in Photosynthesis
• Bacteria– Pigments in plasma membranes
• Plants– Pigments embedded in thylakoid membrane
system– Pigments and proteins organized into
photosystems– Photosystems located next to electron
transport systems
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Photosystems and Electron Transporters
water-splitting complex thylakoidcompartment
H2O 2H + 1/2O2
P680
acceptor
P700
acceptor
pool of electron
transporters
stromaPHOTOSYSTEM II
PHOTOSYSTEM I
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• Pigments absorb light energy, give up e- which enter electron transport systems
• Water molecules are split, ATP and NADH are formed, and oxygen is released
• Pigments that gave up electrons get replacements from splitting water
Light-Dependent Reactions
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Electron Transport System
• Adjacent to photosystem • Acceptor molecule donates electrons
from reaction center
• As electrons flow through system, energy they release is used to produce ATP and, in some cases, NADPH
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Cyclic Electron Flow
electron acceptor electron transport system
e–
e–
e–
e–ATP
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Machinery of Noncyclic Electron Flow
photolysis
H2O
NADP+ NADPH
e–
ATP
ATP SYNTHASE
PHOTOSYSTEM IPHOTOSYSTEM II ADP + Pi
e–
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Energy ChangesP
ote
nti
al
to t
ran
sfer
en
erg
y (v
oid
s)
H2O 1/2 O2 + 2H+
(PHOTOSYSTEM II)
(PHOTOSYSTEM I)
e–
e–
e–e–
secondtransport
system
NADPHfirst
transport
system
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• Synthesis part of
photosynthesis
• Can proceed in the dark
• Take place in the stroma
• Calvin-Benson cycle
Light-Independent Reactions
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Calvin- Benson Cycle
CARBON FIXATION
6 CO2 (from the air)
6 6RuBP
PGA
unstable intermediate
6 ADP
6
12
12ATP
ATP
NADPH
10
12PGAL
glucoseP
PGAL2
Pi
12 ADP12 Pi
12NADP+
12
4 Pi
PGAL
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animation
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Summary of Photosynthesislight
6O212H2O
CALVIN-BENSON CYCLE
C6H12O6
(phosphorylated glucose)
NADPHNADP+ATPADP + Pi
PGA PGAL
RuBP
P
6CO2
end product (e.g. sucrose, starch, cellulose)
LIGHT-DEPENDENT REACTIONS