PHOTOSYNTHESIS Bio 11 Mr. McIntyre

Simple Photosynthesis Overview Simplified Chemical summary: 6CO2 + 6H2O + energy (sun)  C6H12O6 + 6O2

Properties of Light http://www.phschool.com/science/biology_place/biocoach/photosynth/electro.html

Structure of a Leaf Label the diagram provided by Mr. A. Take this test...

Stoma This structure allows for the plant to exchange gasses with its environment. What gasses?? Stoma Guard cells

Chloroplast structure http://Animation: Show first 20 sec for chloroplast anatomy#

Photosynthesis: An Overview of the Light and ‘Dark’ Reactions Occurs in Photoautotrophs (organisms that can make their own using energy from the sun). Photosynthesis takes place in the chloroplasts. Photosynthesis includes two processes… http://simple animation LIGHT REACTIONS (aka photophosphorylation) Requires sunlight Occurs in the granna of chloroplasts Produces ATP and NADPH (used to power the Calvin cycle) ‘DARK’ REACTIONS (a misnomer) (aka Calvin cycle) Doesn’t require sunlight (happens 24/7). Occurs in the stroma of chloroplasts Produces glucose

Micrograph of Chloroplast take a quiz! http://indycc1.agri.huji.ac.il/~zacha/chloroplast.jpg

Photosystems Photosystems are arrangements of chlorophyll and other accessory pigments packed into thylakoids. Many prokaryotes have only one photosystem, Photosystem I. Eukaryotes have Photosystem I plus Photosystem II. Photosystem I uses chlorophyll a, in the form referred to as P700. It absorbs light at 700 nm. Photosystem II uses a form of chlorophyll a known as P680. It absorbs light at 680 nm. The accessory pigments (chlorophyll b, carotenes, and xanthophylls) play an indirect role in the formation of glucose through photosynthesis. These pigments provide chlorophyll a with the energy that they have captured from the sun. These pigments capture varying wavelengths of light and thus allow the plant to receive sun energy across a greater spectrum Accessory pigments absorb energy that chlorophyll a does not absorb. Graphic: http://kvhs.nbed.nb.ca/gallant/biology/photosystem.jpg

Phosphorylation Phosphorylation: The chemical addition of a phosphate group (phosphorous and oxygen) to a compound. i.e. adding Pi to ADP to get ATP Photophosphorylation is addition of a phosphate using the sun’s energy! There are two types of photophosphorylation; cyclic and non-cyclic

Cyclic Photophosphorylation (In bacterial photosynthesis) A single photosystem is involved. A photon of light strikes a pigment molecule in the P700 antenna system. The energy eventually reaches a molecule of P700 (specialized chlorophyll A - the ‘reaction centre’). This electron is ejected from the photosystem. The energized electron leaves P700 and is passed to an acceptor molecule; Ferrodoxin (fd). The electron is then passed through the cytochrome b6f complex. This complex pumps protons (H+) into the space between bacterium’s cell membrane and capsule. This creates a proton gradient. Protons can only exit the thylakoid space via ATP synthase. ATP synthase uses the energy flow of protons (proton motive force) to make ATP (Phosphorylaion). Animation 1: Development of Proton Motive Force (proton gradient) Animation 3: ATP synthase Animation 2: Formation of ATP from Proton motive force

…Cyclic Photophosphorylation The electron is then passed through the plastocyanin (pC). The electron is passed back to the reaction centre. The electron’s energy is gradually lost during this process. The de-energized electron returns to the chlorophyll A molecule to be energized again. We call this process cyclic photophosphorylation because electrons return to the photosystem and are then again energized. The process is a cycle! The energy released during this electron transport generates a proton gradient which is used to produce ATP. Animation: (non) cyclic photophosphorylation animation

NON-cyclic photo-phosphorylation Hmmmm…

Non-Cyclic Photophosphorylation Happens in PLANTS. Two photosystems are involved. A photon hits Photosystem II (PS II or P680). This energy is relayed to the reaction centre via accessory pigments. A high energy electron is emitted. …meanwhile, an enzyme in PS II splits water. The oxygen is released as a byproduct. Electrons from water are used to replace those lost by PS II. The electron excited in PS II then travels to plastoquinone (Q), then to the b6f complex (proton pump). The proton pump uses this energy to pump protons across the thylakoid membrane, from the stroma into the thylakoid space. These protons can only exit the thylakoid via ATP synthase. The flow of protons through ATP synthase is used to make ATP. Proton pump PC Fd Q NADP Reductase Animation: (non) cyclic photophosphorylation animation

..Non-Cyclic Photophosphorylation The electron then goes to plastocyanin (PC) and then to PS I. Remember, the electron has lost energy because…the proton pump used it up! It’s now de-energized! …A photon hits PS I (P 700). Energy is passed from accessory pigments to reaction centre which ejects a high energy electron. The de-energized electron replaces the electron lost from PS I. Proton pump Fd PC Q NADP Reductase Animation: (non) cyclic photophosphorylation animation

…Non-Cyclic Photophosphorylation The electron is then passes to ferrodoxin (Fd) and then to NADP reductase, which uses the newly energized electron to reduce NADP to NADPH. The ATP and NADPH produced during non-cyclic photophosphorylation go to the Calvin cycle to provide energy and raw materials to make SUGAR! Proton pump PC Fd Q NADP Reductase Animation: (non) cyclic photophosphorylation animation

NON-cyclic photo-phosphorylation… Does this make sense now?

animation: non-cyclic photophosphorylation Watch the animation, then answer this question: Where do the protons come from that go through ATP synthase? animation: non-cyclic photophosphorylation

Examine the formula that summarizes photosynthesis… sunlight CO2 + H2O C6H12O6 + O2 You should know… Where the O2 byproduct comes from… Infer… Where the carbon in glucose comes from… Where the hydrogen in glucose comes from… Where the oxygen in glucose comes from…

The Calvin Cycle In Photosynthesis, ATP and NADPH are produced in photophosphorylation, aka the Light Reactions. This happens in the thylakoid. The next series of reactions, the Calvin cycle, happens in the stroma. This is where sugars are manufactured. Melvin Calvin discovered this cycle in 1940.

… The Calvin Cycle The end product of photosysnthesis isn’t really glucose; it’s PGAL (phosphoglyceraldehyde). PGAL can be used to manufacture glucose, or other sugars, fatty acids or amino acids. The Calvin Cycle has three phases: 1st phase: Carbon Fixation 2nd phase: Reduction 3rd phase: Regeneration of the Carbon acceptor molecule (RuBP)

1st Phase: Carbon Fixation The Calvin Cycle 1st Phase: Carbon Fixation 1. Three five-carbon sugar molecules called ribulose bisphosphate, or RuBP, are the acceptors that bind 3 CO2 molecules (dissolved in the stroma). This reaction is catalyzed by the enzyme rubisco. 2. Three unstable 6-C molecules are produced (not shown) which quickly break down to give six molecules of the three-carbon phosphoglyceric acid (PGA). 3 x CO2 1 2 6 x PGA 3-C 3 x RuBP (5-C) Rubisco Animation: Calvin cycle

2nd Phase Reduction The Calvin Cycle 3. The six PGA molecules are converted into six phosphoglyceraldehyde (PGAL) molecules, a three-carbon sugar phosphate, by adding high-energy phosphates group from ATP molecules, then breaking the phosphate bond and adding hydrogen from NADPH. 4. Six molecules of PGAL are produced. However, only one of the six molecules exits the cycle as an output (to make sugar, etc.) while... 3 x CO2 1 2 6 x PGA (3-C) 3 x RuBP (5-C) Rubisco 6 x ATP 3 6 x ADP 6 x NADPH 6 x NADP 6 x Pi 6 x PGAL (3-C) 4 Animation: Calvin cycle PGAL

3rd Phase: Regeneration of the Carbon acceptor molecule (RuBP) The Calvin Cycle 3rd Phase: Regeneration of the Carbon acceptor molecule (RuBP) 5. ...the remaining five enter a complex process that regenerates more RuBP to continue the cycle.... 6. In this process, ATP is used to convert the five PGAL’s to three RuBP’s. 7. Summary... 9 ATP used 6 NADPH used 1 PGAL produced RuBP regenerated 3 x CO2 1 2 6 x PGA (3-C) 3 x RuBP (5-C) Rubisco 6 x ATP 3 3 x ADP 6 x ADP 3 x ATP 6 x NADPH 6 6 x NADP 6 x Pi 6 x PGAL (3-C) 5 x PGAL (3 C) 5 4 Animation: Calvin cycle 1 x PGAL (3-C)

Overview of light dependent reactions