Background information before Photosynthesis 1. ATP cycle 2. Redox reactions 3. Electron Transport Chain (ETC) 4. Coenzymes (NADP)

ATP Cycle Adenosine Triphosphate is an energy carrying molecule. Adenosine Triphosphate is an energy carrying molecule. Adenosine + Phosphate + Phosphate + Phosphate Adenosine + Phosphate + Phosphate + Phosphate When there is a demand for energy in our cells, enzymes break the last bond (+) releasing useable energy, producing: When there is a demand for energy in our cells, enzymes break the last bond (+) releasing useable energy, producing: Adenosine + Phosphate + Phosphate + Phosphate Adenosine + Phosphate + Phosphate + Phosphate (ADP + Phosphate + energy release) (ADP + Phosphate + energy release) Dephosphorylation – Exergonic reaction Dephosphorylation – Exergonic reaction

ATP Cycle After cellular respiration, a lot of energy is release from the break down of glucose. 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. 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- attachment of a phosphate group Phosphorylation - Endergonic Phosphorylation - Endergonic This breaking down and building up of ATP is called the ATP cycle 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 Other reactions where ATP is formed: Glycolysis and the Light Reaction of photosynthesis

ATP Cycle

What is ATP? What is ATP? What is ATP? What is ATP? ATP cartoon ATP cartoon ATP cartoon ATP cartoon

Redox Reactions Reduction is gaining electrons/hydrogen (and usually some energy) Reduction is gaining electrons/hydrogen (and usually some energy) Oxidation is losing electrons/hydrogen (and usually some energy. Oxidation is losing electrons/hydrogen (and usually some energy. OIL RIG OIL RIG During most chemical reactions, electrons are being lost or gained by atoms that make up molecules. 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 Molecules that gain electrons are said to be reduced and molecules that lose electrons are said to be oxidized

Electron Transport Chain - a series of redox reactions that transport electrons - a series of redox reactions that transport electrons 2e - 2e - Coe Energy Coenzyme + ADP + P = ATP

Electron Transport Chain When a coenzyme grabs 2 electrons, it has been reduced. When a coenzyme grabs 2 electrons, it has been reduced. When the coenzyme releases the electrons, it has been oxidized, and energy is released. 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. 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 If some protons are waiting at the bottom of the ETC, they join with the electrons to form Hydrogen atoms

Coenzymes Coenzymes are organic molecules that act as electron carriers, or Hydrogen carriers. Coenzymes are organic molecules that act as electron carriers, or Hydrogen carriers. The coenzyme that functions in photosynthesis is Nicotinamideadeninedinucleotidephosphate The coenzyme that functions in photosynthesis is Nicotinamideadeninedinucleotidephosphate Ok, it is really 4 words, and we can call it NADP Ok, it is really 4 words, and we can call it NADP NADP + 2H NADPH 2 NADP + 2H NADPH 2

Photosynthesis Divided into 2 stages, the Light Reaction and the Dark Reaction Divided into 2 stages, the Light Reaction and the Dark Reaction Balanced chemical equation: Balanced chemical equation: 6 CO H 2 O + Light C 6 H 12 O 6 + 6O 2 + 6H 2 O 6 CO H 2 O + Light C 6 H 12 O 6 + 6O 2 + 6H 2 O DR LR DR LR DR DR LR DR LR DR

Chloroplast

Light Reaction Can only take place in the presence of light energy Can only take place in the presence of light energy Happens in the thylakoid disks Happens in the thylakoid disks Consists of 3 reactions that are happening at the same time and are interdependent. Consists of 3 reactions that are happening at the same time and are interdependent. 1. Photosystem 1 (PS1) 2. Photosystem 2 (PS2) 3. Photolysis

Electromagnetic Spectrum

Products of the Light Reaction The “Light Reaction” is considered the power phase The “Light Reaction” is considered the power phase The products of the Light Reaction are The products of the Light Reaction are 1. ATP – provide a source of energy for the Dark Reaction (and some phosphates) 2. NADPH 2 – provide H for the Dark Reaction (and a little energy)

Photosystem 1 Photosystem 1 Chlorophyll of PS1 absorbs energy and becomes “excited” (EM spectrum?) Chlorophyll of PS1 absorbs energy and becomes “excited” (EM spectrum?) Chlorophyll loses 4 electrons Chlorophyll loses 4 electrons This creates a problem: “chlorophyll ain’t chlorophyll no more” This creates a problem: “chlorophyll ain’t chlorophyll no more” PS2 to the rescue! PS2 to the rescue!

Photosystem 2 Chlorophyll of PS2 absorbs light energy Chlorophyll of PS2 absorbs light energy Chlorophyll loses 4 electrons Chlorophyll loses 4 electrons These electrons move along an ETC and replace the electrons lost in PS1 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. 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 …. For every pair of electrons moved, enough energy is released to synthesize 1 ATP, therefore …. One problem solved……. One problem solved……. One problem created…… One problem created……

PS2 continued Chlorophyll of PS1 has been restored Chlorophyll of PS1 has been restored Chlorophyll of PS2 is missing electrons Chlorophyll of PS2 is missing electrons Have no fear! Have no fear! Photolysis to the rescue! Photolysis to the rescue!

Photolysis - breakdown of water, in the presence of sunlight. - breakdown of water, in the presence of sunlight. 2 H 2 O + sunlight = 4 Hydrogen atoms + 2 oxygen atoms. 2 H 2 O + sunlight = 4 Hydrogen atoms + 2 oxygen atoms. 4 H separate into 4 electrons (-) and 4 protons (+) 4 H separate into 4 electrons (-) and 4 protons (+) 2 O join to form O 2 (atmospheric oxygen gas) 2 O join to form O 2 (atmospheric oxygen gas)

What happens to the products of Photolysis? 4 electrons – replace those lost from PS2 4 electrons – replace those lost from PS2 4 protons - join with the original electrons lost from PS1 to form 4 hydrogen atoms 4 protons - join with the original electrons lost from PS1 to form 4 hydrogen atoms O 2 is released into the atmosphere O 2 is released into the atmosphere The 4 hydrogen atoms are picked up by the coenzyme (hydrogen carrier) NADP The 4 hydrogen atoms are picked up by the coenzyme (hydrogen carrier) NADP 2 NADP + 4 H = 2NADPH 2 2 NADP + 4 H = 2NADPH 2 2NADPH 2 carry hydrogen atoms to the Dark Reaction 2NADPH 2 carry hydrogen atoms to the Dark Reaction

How many ATP are produced in the Light Reaction? 2 ATP come from the ETC 2 ATP come from the ETC A third ATP is produced when sunlight provides the energy needed to attach a phosphate to an ADP molecule…..this is called A third ATP is produced when sunlight provides the energy needed to attach a phosphate to an ADP molecule…..this is called Photophosphorylation Photophosphorylation

End products of the Light Reaction 2 NADPH 2 – carry hydrogen atoms to the Dark Reaction (and some energy) 2 NADPH 2 – carry hydrogen atoms to the Dark Reaction (and some energy) 3 ATP – provide energy for the Dark Reaction (and some phosphates) 3 ATP – provide energy for the Dark Reaction (and some phosphates)

Light Reaction Summary