3110_Chap23(Wold)-CalvinCycle.pdf

3110_Chap23(Wold)-CalvinCycle.pdf - BIOC 3110 Marc S Wold...

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BIOC 3110 Marc S. Wold, PhD Lecture 23 Chapter 23: The Calvin Cycle 1 Rain forests are the primary site of carbon fixation. The Calvin Cycle fixes carbon dioxide into sugar. Outline Calvin Cycle synthesizes hexose from CO 2 and H 2 O Calvin Cycle is regulated by environmental conditions Variations in the Calvin Cycle (C3, C4 and CAM plants) Melvin Calvin Nobel Prize in Chemistry 1961 Photosynthesis is composed of two parts: The light reactions -light into chemical energy The Calvin Cycle -chemical energy used to reduce CO 2 to make glucose These notes are for the person, educational and noncommercial use of students enrolled in BIOC 3110 at the University of Iowa. Illustrations are copyrighted material from Biochemistry, A Short Course , 3 Ed. By Tymoczko, Berg, Stryer, W.H. Freeman & Co, 2015. Explanatory text and content were developed by Marc Wold © 2017. These notes are not available for reproduction, distribution, or revision without the prior written permission of the instructor. See problems # 4-14, 17, 19 and 21 at the end of Chapter 23.
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Overview of light reactions in photosynthesis Photosynthesis uses energy from light to boost electrons (e - ) from a low-energy state to a high-energy state. High energy e- are used to: Generate NADPH (reducing power) Generate proton gradient which drives ATP synthesis NADPH and ATP produced in stroma 2
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Overview of Calvin Cycle Calvin Cycle occurs in the stroma of chloroplasts 3 Stages – Fixation – Reduction – Regeneration One CO 2 fixed per cycle 3
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Overview of Calvin Cycle 3 Stages Fixation – CO 2 + ribulose 1,5 bisphosphate è two 3-phosphoglycerate Reduction two 3-phosphoglycerate reduced to make fructose 6-phosphate Requires 2 ATP + 2 NADPH Regeneration Regenerate ribulose 1,5 bisphosphate C 3 plants carry out Calvin Cycle using CO 2 drawn directly from air 4
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Stage 1: Fixation CO 2 is fixed by ribulose 1,5- bisphosphate carboxylase/oxidase (rubisco) Fixation of CO 2 is highly exergonic! ( G°’=-51.9 kJ mol -1 ) Rate limiting step 5 Composed of 8 large and 8 small subunits. Located on stromal surface of thylakoid Each large subunit has active site Lysine in active site binds CO 2 to form carbamate which coordinates essential magnesium
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6 History - Why Rubisco? R ib u lose 1,5- bis phosphate c arboxylase/ o xygenase Originally purified as an abundant protein from plant leaves in 1947 by Sam Wildman.
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