How Cells Acquire Energy Chapter 7

 Photoautotrophs  Carbon source is carbon dioxide  Energy source is sunlight  Heterotrophs  Get carbon and energy by eating autotrophs or one another Carbon and Energy Sources

Photoautotrophs  Capture sunlight energy and use it to carry out photosynthesis  Plants  Some bacteria  Many protistans

Linked Processes Photosynthesis  Energy-storing pathway  Releases oxygen  Requires carbon dioxide Aerobic Respiration  Energy-releasing pathway  Requires oxygen  Releases carbon dioxide

Chloroplast Structure two outer membranes inner membrane system (thylakoids connected by channels) stroma Figure 7.3d, Page 116

Photosynthesis Equation 12H 2 O + 6CO 2 6O 2 + C 2 H 12 O 6 + 6H 2 O WaterCarbon Dioxide OxygenGlucoseWater LIGHT ENERGY In-text figure Page 115

Where Atoms End Up Products6O 2 C 6 H 12 O 6 6H 2 O Reactants12H 2 O6CO 2 In-text figure Page 116

Two Stages of Photosynthesis sunlightwater uptakecarbon dioxide uptake ATP ADP + P i NADPH NADP + glucose P oxygen release LIGHT- INDEPENDENT REACTIONS LIGHT- DEPENDENT REACTIONS new water In-text figure Page 117

Electromagnetic Spectrum Shortest Gamma rays wavelength X-rays UV radiation Visible light Infrared radiation Microwaves LongestRadio waves wavelength

Visible Light  Wavelengths humans perceive as different colors  Violet (380 nm) to red (750 nm)  Longer wavelengths, lower energy Figure 7.5a Page 118

Photons  Packets of light energy  Each type of photon has fixed amount of energy  Photons having most energy travel as shortest wavelength (blue-violet light)

Pigments  Color you see is the wavelengths not absorbed

Variety of Pigments Chlorophylls a and b CarotenoidsAnthocyanins

Chlorophylls Wavelength absorption (%) Wavelength (nanometers) chlorophyll b chlorophyll a Main pigments in most photoautotrophs Figure 7.6a Page 119 Figure 7.7 Page 120

Accessory Pigments percent of wavelengths absorbed wavelengths (nanometers) beta-carotene phycoerythrin (a phycobilin) Carotenoids, Phycobilins, Anthocyanins

Pigments in Photosynthesis  Bacteria  Pigments in plasma membranes  Plants  Pigments and proteins organized into photosystems that are embedded in thylakoid membrane system

Arrangement of Photosystems water-splitting complexthylakoid compartment H2OH2O2H + 1/2O 2 P680 acceptor P700 acceptor pool of electron carriers stromaPHOTOSYSTEM II PHOTOSYSTEM I Figure 7.10 Page 121

 Pigments absorb light energy, give up e -, which enter electron transfer chains  Water molecules split, ATP and NADH form, and oxygen is released  Pigments that gave up electrons get replacements Light-Dependent Reactions

Photosystem Function: Harvester Pigments  Most pigments in photosystem are harvester pigments  When excited by light energy, these pigments transfer energy to adjacent pigment molecules  Each transfer involves energy loss

Photosystem Function: Reaction Center  This molecule (P700 or P680) is the reaction center of a photosystem

Pigments in a Photosystem reaction center Figure 7.11 Page 122

Electron Transfer Chain  Adjacent to photosystem  As electrons pass along chain, energy they release is used to produce ATP

Cyclic Electron Flow  Electrons  are donated by P700 in photosystem I to acceptor molecule  flow through electron transfer chain and back to P700  Electron flow drives ATP formation  No NADPH is formed

Synthesis of ATP (chemiosmotic phosphorylation) photolysis H2OH2O NADP + NADPH e–e– ATP ATP SYNTHASE PHOTOSYSTEM IPHOTOSYSTEM II ADP + P i e–e– first electron transfer chain second electron transfer chain Figure 7.13a Page 123

Chemiosmotic Model of ATP Formation  Electrons within the membrane of the chloroplast attract H+ protons  The H+ protons are pumped inside the chloroplast membranes  The Protons are allowed to pass out of the membrane through the CF1 particle that is rich in ADP + P plus phosphorylating enzymes.

Chemiosmotic Model for ATP Formation ADP + P i ATP SYNTHASE Gradients propel H + through ATP synthases; ATP forms by phosphate-group transfer ATP H + is shunted across membrane by some components of the first electron transfer chain PHOTOSYSTEM II H2OH2O e–e– acceptor Photolysis in the thylakoid compartment splits water Figure 7.15 Page 124

 Synthesis part of photosynthesis  Can proceed in the dark  Take place in the stroma  Calvin-Benson cycle Light-Independent Reactions

Calvin-Benson Cycle  Overall reactants  Carbon dioxide  ATP  NADPH  Overall products  Glucose  ADP  NADP + Reaction pathway is cyclic and RuBP (ribulose bisphosphate) is regenerated

Calvin- Benson Cycle CARBON FIXATION 6CO 2 (from the air) 66 RuBP PGA unstable intermediate 6 ADP 6 12 ATP NADPH PGAL glucose P PGAL 2 PiPi 12 ADP 12 P i 12 NADP P i PGAL Figure 7.16 Page 125

 In Calvin-Benson cycle, the first stable intermediate is a three-carbon PGA  Because the first intermediate has three carbons, the pathway is called the C3 pathway The C3 Pathway

Photorespiration in C3 Plants  On hot, dry days stomata close  Inside leaf  Oxygen levels rise  Carbon dioxide levels drop  The plant is in trouble because it does not enough Carbon dioxide to undergo photosynthesis  The plant still needs energy so it taps its own store of glucose

C4 Plants  Carbon dioxide is fixed twice  In mesophyll cells, carbon dioxide is fixed to form four-carbon oxaloacetate  Oxaloacetate is stored as a crystal  When times get bad (drought conditions), the plant can now convert the crystalline form of oxaloacetate back to Carbon dioxide and undergo photosynthesis.

Summary of Photosynthesis Figure 7.21 Page 129 light 6O 2 12H 2 O CALVIN- BENSON CYCLE C 6 H 12 O 6 (phosphorylated glucose) NADPHNADP + ATP ADP + P i PGA PGAL RuBP P 6CO 2 end product (e.g., sucrose, starch, cellulose) LIGHT-DEPENDENT REACTIONS 6H 2 O LIGHT-INDEPENDENT REACTIONS

Satellite Images Show Photosynthesis Photosynthetic activity in spring Atlantic Ocean Figure 7.20 Page 128