How Cells Acquire Energy Chapter 6. Fig. 6.3a, p. 94 leafs upper surfacephotosynthetic cells two...
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Transcript of How Cells Acquire Energy Chapter 6. Fig. 6.3a, p. 94 leafs upper surfacephotosynthetic cells two...
How Cells Acquire Energy
Chapter 6
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)
Organelles of photosynthesis
Chloroplasts
Photosynthesis Equation
12H2O + 6CO2 6O2 + C2H12O6 + 6H2Owater carbon
dioxideoxygen glucose water
LIGHT ENERGY
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
Electromagnetic Spectrum
Shortest Gamma rays
wavelength X-rays
UV radiation
Visible light
Infrared radiation
Microwaves
Longest Radio waves
wavelength
Visible Light
• Wavelengths humans perceive as different colors
• Violet (380 nm) to red (750 nm)
• Longer wavelengths, lower energy
Pigments
• Light-absorbing molecules
• Absorb some wavelengths and transmit others
• Color you see are the wavelengths NOT absorbed
Wavelength (nanometers)
chlorophyll b
chlorophyll a
• 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
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
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
Photosystems and Electron Transporters
water-splitting complex thylakoidcompartment
H2O 2H + 1/2O2
P680
acceptor
P700
acceptor
pool of electron
transporters
stromaPHOTOSYSTEM II
PHOTOSYSTEM I
• 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
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
Cyclic Electron Flow
electron acceptor electron transport system
e–
e–
e–
e–ATP
Machinery of Noncyclic Electron Flow
photolysis
H2O
NADP+ NADPH
e–
ATP
ATP SYNTHASE
PHOTOSYSTEM IPHOTOSYSTEM II ADP + Pi
e–
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
• Synthesis part of
photosynthesis
• Can proceed in the dark
• Take place in the stroma
• Calvin-Benson cycle
Light-Independent Reactions
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
animation
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