Photosystems & Light Reactions AP Biology Ms. Day Chapter 10 (Part 2) Photosystems & Light Reactions AP Biology Ms. Day

Recall…Fill in the letters of the leaf anatomy B E C D

Recall…Fill in the letters of the leaf anatomy A=Spongy mesophyll B=Palisade m mesophyll E= Air space C= Stoma D= guard cell

Recall… How is water formed in cellular respiration? Label the parts of water as it is formed +_____

Recall… How is water formed in cellular respiration? e-’s + 2H+’s  H20 +2e - ½ x 2

A B ?H K I + J M L G E D  F C

G3P(pGAL) An overview of photosynthesis http://www.wwnorton.com/college/biology/discoverbio3/full/content/index/animations.asp 8.1a - Photosynthesis: The Flow of Energy Process 8.1b - Photosynthesis: Overview of Reactions https://www.youtube.com/watch?v=YeD9idmcX0w H2O CO2 Light LIGHT REACTIONS CALVIN CYCLE Chloroplast GLUCOSE (sugar) NADPH NADP  ADP + P O2 ATP G3P(pGAL) Starch

Convert solar energy to chemical energy The Light Reactions Occur in the grana (& thylakoids) Convert solar energy to chemical energy Chlorophyll absorbs solar energy Split water release oxygen gas (a by-product) produce ATP (using chemiosmosis) Forms NADPH from NADP+ (an e- acceptor) Temporarily stores high energy e-’s “Electron shuttle bus”

Light Reactions (in detail) The light reactions convert solar energy to the chemical energy of ATP and NADPH

Spectrophotometer Machine that sends light through pigments  measures fraction of light transmitted and absorbed at each wavelength Produces an absorption spectrum

An absorption spectrum graph plotting light absorption versus wavelength White light Refracting prism Chlorophyll solution Photoelectric tube Galvanometer Slit moves to pass light of selected wavelength Green The high transmittance (low absorption) reading indicates that chlorophyll absorbs very little green light. The low transmittance (high absorption) reading chlorophyll absorbs most blue light. Blue 1 2 3 4 100

The absorption spectra of three types of pigments in chloroplasts

Chlorophyll a The main photosynthetic pigment (primary pigment) Accessory Pigments Absorb different wavelengths of light pass energy to chlorophyll a

Excitation of Chlorophyll by Light When a pigment absorbs light It goes from a ground state (stable) to an excited state (unstable)

Photosystems Reaction centers used in Light Reactions Made of light harvesting proteins (complexes) Funnel (move) energy of photons (light pieces) to the middle of reaction center INSIDE thylakoid membrane 2 DIFFERENT CENTERS Photosystem II (PSII) Photosystem I (PSI)

(INTERIOR OF THYLAKOID) Primary election acceptor Photon Thylakoid Light-harvesting complexes Reaction center Photosystem STROMA Thylakoid membrane Transfer of energy Special chlorophyll a molecules Pigment THYLAKOID SPACE (INTERIOR OF THYLAKOID) e– When a reaction-center “special” chlorophyll a molecule absorbs energy An electron gets bumped up to a primary electron acceptor http://www.bio.miami. edu/~cmallery/255/2 55phts/photosynthesi s.swf

2 Different Photosystems BOTH found in thylakoid phospholipid membrane 2 types photosystems II (PII) Uses chlorophyll a called P680 1ST photosystem in membrane photosystems I (PI) Uses chlorophyll a called P700 2ND photosystem in membrane

2 types of e- flow Non-cyclic photophosphorylation

Recall… What are the 3 events in Chemiosmosis? Create a proton gradient A difference in amts ( [ ]’s) of H+ ions on either side of a membrane Uses energy from e-’s falling down an ETC to PUSH H+ ions AGAINST [ ] gradient Create a proton motive force H+ ions use facilitated diffusion to move down ATP synthase (H  L [ ] ) ATP synthase makes ATP ATP synthase spins from motive force so ADP + Pi  ATP

Non cyclic light reactions & Chemiosmosis

Noncyclic Electron Flow Steps 1. PII  excited e- to primary e- acceptor 2. Photolysis- water splits by enzyme e-s are replaced from lost chl a P680 H20  2 H+ + 2e- + ½ O2 (2 O’s combine and O2 is released) 3. Electron Transport Chain proteins in thylakoid membrane pass e-s (become reduced) Flow of e-’s is exergonic  releases energy to make ATP Proteins used = Cytochromes, PC, and PQ complexes

4. Chemiosomosis – the process that forms ATP during light reactions Protons (H+) are pumped ACTIVELY into thylakoid space (lumen) from stroma by electron transport system #1 AGAINST [ H+ ] gradient  LESS acidic Protons (H+) from split water build up in thylakoid space (lumen) MORE acidic H+’s then DIFFUSE down ATP synthase channels in stroma

5. Photosystem I – P700 absorbs energy  e- becomes excited goes down electron transport chain #2 6. NADP+ becomes reduced using NADP+ reductase NADP+ + 2H+ + 2e-  NADPH from split from PSI water

Non cyclic light reactions & Chemiosmosis PHOTOLYSIS

Antennae pigments

Non Cyclic Electron Flow (Overview) Light  P680  ATP made  P700  NADPH made O2 released In Out 2 light events Water Oxygen gas ADP+ Pi ATP NADP+ NADPH

Noncyclic Electron Flow Animations http://www.stolaf.edu/people/giannini/flashanimat /metabolism/photosynthesis.swf http://highered.mcgraw- hill.com/sites/0072437316/student_view0/chapter 10/animations.html# 2nd animation http://www.science.smith.edu/departments/Biolo gy/Bio231/ltrxn.html http://www.sumanasinc.com/webcontent/animati ons/content/harvestinglight.html

Tutorials (Light Reactions) http://faculty.nl.edu/jste/noncyclic_photophosphorylation.ht m http://www.bio.miami.edu/~cmallery/255/255phts/255phts. htm http://www.biology.arizona.edu/biochemistry/problem_sets/ photosynthesis_1/photosynthesis_1.html

Cyclic Electron Flow Under certain conditions Photoexcited electrons take an alternative path (shorter pathway) Why use this pathway? Sugar production (Calvin Cycle) uses a lot more ATP than NADPH Sometimes, autotrophs run low on ATP needs to replenish ATP levels and uses cycle e- flow

Why is it “cyclic”? This process is cyclic since electrons return to the reaction center (PS1) Water is NOT required and oxygen is NOT produced ONLY PS1 and P700 is used and PART of the ETC #1

Cyclic Electron Flow Steps Photon hits PS1 e-s from PSI P700 travel BACK to cytochrome complex (ETC#1) in P680 electron transport chain ATP is produced using ATP synthase and H+ diffusion…NO NADPH!!!

In cyclic electron flow Only photosystem I is used Only ATP is produced NO NADPH

NON CYCLIC

CYCLIC

NON CYCLIC CYCLIC

CYCLIC PHOTOPHOSPHORALYTION Overview IN OUT 1 light event ADP + P ATP NO OXYGEN and NO NADPH like non-cyclic photophosphorylation

Noncyclic Electron Flow Animations https://www.youtube.com/watch?v=NG- YnMFkK78 https://www.youtube.com/watch?v=wJDlxp17rY4 http://highered.mcgraw- hill.com/sites/0072437316/student_view0/chapter 10/animations.html# 1st animation EXCELLENT REVIEW OF CELLULAR RESPIRATION and PHOTOSYNTHESIS (14 min) https://www.youtube.com/watch?v=5PqoGW7sZoU