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Photosynthesis – the Light and Dark Reactions
Outermembrane
Innermembrane
Stroma
Thylakoids
Granum
Light-dependent reactions take place in the thylakoid membrane
The light reactions change the electromagnetic energy from light into chemical energy in the form of ATP and NADPH
Photosynthesis takes place in chloroplasts
Overview Movie – Click Me
THE EM Spectrum
PS Pigments
Photosynthesis is a two-step process ATP and NADPH are used in the stroma (cytoplasm of
the chloroplast) to fuel the Dark Reaction
• They provide chemical energy for the reactions
Light Reaction Dark Reaction( Calvin Cycle)
Ribose
Adenine
Phosphate groups
Ribose
Adenine
ATP consists of adenine, ribose, and three phosphate groups.
High energy bonds
ATP
+ EnergyADP
Water
P P P P P Pi
Inorganicphosphate
+ H2O + +
Figure 6.1b
Energy is released when ATP is ripped apart
Reduction
Oxidation
NADPH(electron carrier
Or charged battery)
NAD+(empty battery)
NAD+Is an energy carrying molecule in plants
that must be recharged in the Light Reaction
Photosynthesis takes place in ChloroplastsChlorophyll and accessory (helper) pigments capture electromagnetic energy by absorbing photons of light
MOVIE CLICK ME
The Light Reactions Lead to the Formation of ATP and NADPH
ATP is the primary product of Photosystem II
NADPH is formed after electron excitation in Photosystem I
Photon
Chlorophyll molecules
Reactioncenter
Photon
Light Reaction – Step 1
Chlorophyll molecules transmit energy from excited electrons to a reaction center.
Higher
Lower
En
erg
y o
f el
ectr
on
Chlorophyll
Photon
e–
Carrier #1
#2Electrontransport chain Carrier #3
In photosystem II, excited electrons feed anelectron transport chain.
Energy put to work
PQ
H+
2e–
H+
NAD NADPH
Oxidation of H2O provides electrons
2 H2O --> 4 H+ + 4 e- + O2
Photosystem II is the only known protein complex that can
rip apart (oxidize) water
All of the earth’s oxygen originates this way!!!!!!!!!!!
The energy from light is captured and converted in chloroplasts
This energy is passed through an electron transport chain in chloroplasts that convert that energy to a more usable chemical
form = ATP and NADPH
PHOTOSYSTEM II -- a Funky 3D Visualization
Photo-system II
Cytochromecomplex
Photo-system I
H+H+H+H+
H+
H+
H+
H+
H+
H+
H+
Stroma
Stroma
Granum
Found in membranefacing inside of grana
ATP synthase
Found in membrane facing stroma
Equally common in both types of membrane
Hey Bleecker! Where’s the ATP come From??Well – the secret lies in these little ATPase Enzymes also found
in the membrane
H+H+
H+H+
H+
THE STRUCTURE OfEnzyme ATP SYNTHASE
Inside Thylakoid
Chloroplast Stroma
H+
ADP + Pi ATP
Rod
F1 unit
FO unit
H2O torn apart donates loads of Hydrogen which is useful to make ATP+
Here’s a little movie summarizing ATP synthesisH shown as (+) moves through the enzyme, creating a
whirling, which is energy to crunch ADP+P ATP
THE DARK REACTION
Uses NADPH and ATP produced in the LIGHT REACTION to produce GLUCOSE
Requires 9 ATP for every 6 NADP
Short Movie Intro – Click ME
The Dark Reaction is a
Cycle
DA’ MAIN PLAYERS!
CO2 is source of carbon (comes from the atmosphere)
RUBP is the 5 carbon starting point where C from CO2 is inserted
Rubisco is the enzyme that helps produce glucose and keep the Dark Reaction going
PGA or phosphoglyceraldehyde (3C) is eventually glued together into glucose or becomes RUBP
What is the Result of the DARK REACTION (BESIDES BRAIN-PAIN FOR BIO 11 STUDENTS??)
Plant produces GLUCOSE molecules using the energy of ATP and NADPH
The Carbon came from CO2 gas from the atmosphere
Glucose = potential chemical energy is prodcuced, making
plants the PRIMARY PRODUCERS
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