Download Background Stuff-Light Reaction

Background information
before Photosynthesis
1.
2.
3.
4.
ATP cycle
Redox reactions
Electron Transport Chain (ETC)
Coenzymes (NADP)
ATP Cycle
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Adenosine Triphosphate is an energy carrying
molecule.
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Adenosine + Phosphate + Phosphate + Phosphate
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When there is a demand for energy in our cells,
enzymes break the last bond (+) releasing useable
energy, producing:
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Adenosine + Phosphate + Phosphate + Phosphate
(ADP + Phosphate + energy release)
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Dephosphorylation – Exergonic reaction
ATP Cycle
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After cellular respiration, a lot of energy is release from the
break down of glucose.
This energy can be used to attach free phosphates to ADP to
produce ATP. In fact there is enough energy released to require
the formation of 36 ATP molecules.
Phosphorylation- attachment of a phosphate group
Phosphorylation - Endergonic
This breaking down and building up of ATP is called the ATP
cycle
Other reactions where ATP is formed: Glycolysis and the Light
Reaction of photosynthesis
ATP Cycle
ATP Cycle
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What is ATP?
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ATP cartoon
Redox Reactions
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Reduction is gaining electrons/hydrogen (and usually
some energy)
Oxidation is losing electrons/hydrogen (and usually
some energy.
OIL RIG
During most chemical reactions, electrons are being
lost or gained by atoms that make up molecules.
Molecules that gain electrons are said to be reduced
and molecules that lose electrons are said to be
oxidized
Electron Transport Chain
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- a series of redox reactions that transport
electrons
2eEnergy
Coe
Coe
Coe
Coe
Coenzyme
+ ADP + P = ATP
Electron Transport Chain
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When a coenzyme grabs 2 electrons, it has
been reduced.
When the coenzyme releases the electrons, it
has been oxidized, and energy is released.
Using this energy to attach a phosphate to ADP
is called Oxidative Phosphorylation.
If some protons are waiting at the bottom of
the ETC, they join with the electrons to form
Hydrogen atoms
Coenzymes
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Coenzymes are organic molecules that act as
electron carriers, or Hydrogen carriers.
The coenzyme that functions in photosynthesis
is Nicotinamideadeninedinucleotidephosphate
Ok, it is really 4 words, and we can call it
NADP
NADP + 2H
NADPH2
Photosynthesis
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Divided into 2 stages, the Light Reaction and
the Dark Reaction
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Balanced chemical equation:
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6 CO2 + 12 H2O + Light
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DR
LR
C6H12O6 + 6O2 + 6H2O
DR
LR
DR
Chloroplast
Light Reaction
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1.
2.
3.
Can only take place in the presence of light
energy
Happens in the thylakoid disks
Consists of 3 reactions that are happening at
the same time and are interdependent.
Photosystem 1 (PS1)
Photosystem 2 (PS2)
Photolysis
Electromagnetic Spectrum
Products of the Light Reaction
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1.
2.
The “Light Reaction” is considered the
power phase
The products of the Light Reaction are
ATP – provide a source of energy for the
Dark Reaction (and some phosphates)
NADPH2 – provide H for the Dark Reaction
(and a little energy)
Photosystem 1
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Chlorophyll of PS1 absorbs energy and
becomes “excited” (EM spectrum?)
Chlorophyll loses 4 electrons
This creates a problem: “chlorophyll ain’t
chlorophyll no more”
PS2 to the rescue!
Photosystem 2
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Chlorophyll of PS2 absorbs light energy
Chlorophyll loses 4 electrons
These electrons move along an ETC and replace the
electrons lost in PS1
As they move along the ETC, energy is given off and
used to produce ATP.
For every pair of electrons moved, enough energy is
released to synthesize 1 ATP, therefore ….
One problem solved…….
One problem created……
PS2 continued
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Chlorophyll of PS1 has been restored
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Chlorophyll of PS2 is missing electrons
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Have no fear!
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Photolysis to the rescue!
Photolysis
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- breakdown of water, in the presence of
sunlight.
2 H2O + sunlight = 4 Hydrogen atoms + 2
oxygen atoms.
4 H separate into 4 electrons (-) and 4 protons
(+)
2 O join to form O2 (atmospheric oxygen gas)
What happens to the products of
Photolysis?
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4 electrons – replace those lost from PS2
4 protons - join with the original electrons
lost from PS1 to form 4 hydrogen atoms
O2 is released into the atmosphere
The 4 hydrogen atoms are picked up by the
coenzyme (hydrogen carrier) NADP
2 NADP + 4 H = 2NADPH2
2NADPH2 carry hydrogen atoms to the Dark
Reaction
How many ATP are produced in the
Light Reaction?
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2 ATP come from the ETC
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A third ATP is produced when sunlight
provides the energy needed to attach a
phosphate to an ADP molecule…..this is called
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Photophosphorylation
End products of the Light Reaction
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2 NADPH2 – carry hydrogen atoms to the Dark
Reaction (and some energy)
3 ATP – provide energy for the Dark Reaction
(and some phosphates)
Light Reaction Summary