Presentation on theme: "Pathways that Harvest and Store Chemical Energy 6."— Presentation transcript:
Pathways that Harvest and Store Chemical Energy 6
Concept 6.1 ATP, Reduced Coenzymes, and Chemiosmosis Play Important Roles in Biological Energy Metabolism Five principles governing metabolic pathways: 1. Chemical transformations occur in a series of intermediate reactions that form a metabolic pathway. 2. Each reaction is catalyzed by a specific enzyme. 3. Most metabolic pathways are similar in all organisms.
Concept 6.1 ATP, Reduced Coenzymes, and Chemiosmosis Play Important Roles in Biological Energy Metabolism 4. In eukaryotes, many metabolic pathways occur inside specific organelles. 5. Each metabolic pathway is controlled by enzymes that can be inhibited or activated.
What are the energy processing strategies that autotrophs use to obtain free energy? Use energy from the environment to convert inorganic molecules into organic compounds where free energy is stored They are the producers for all food chains on Earth! Examples: photosynthetic and chemosynthetic
How do photosynthetic organisms obtain free energy? Use visible light energy to convert water and CO2 in to organic compounds (sugar precursor molecules) and oxygen gas (waste) Ex: ALL plants, phytoplankton (cyanobacteria and protists)
Are plants the only photosynthetic organisms? NO! Most of the oxygen in the atmosphere was produced by cyanobacteria and photosynthetic protists (phytoplankton)
Water and CO2 are both required for photosynthesis...How do they get to the sites of photosynthesis?
Photosynthesis is a two part process Light Reactions (light dependent) Carbon Fixation (Calvin Cycle; Dark reaction; Light Independent)
Photosynthesis is described as an endergonic redox process Why endergonic? What substance is oxidized? To what is it oxidized? What substance is reduced? To what is it reduced?
What is light? Light is energy! Photons of specific wavelengths of light are used in the light reactions
What are the major photosynthetic pigments? Is this the only photosynthetic pigment? In plants, two chlorophylls absorb light energy chlorophyll a and chlorophyll b. PROTEINS! Accessory pigments—additional pigments that can absorb other wavelengths of light energy
Why are plants green? Chloroplasts cannot absorb all wavelengths of light equally and they reflect green
The Chloroplast Chloroplasts are adapted to separate the light reactions from carbon fixation The light reactions occur in the thylakoid membranes Carbon fixation takes place in the stroma
Figure 6.15 An Overview of Photosynthesis
How do photosynthetic prokaryotic organisms carry out photosynthesis? Internal folding of the plasma membrane and presence of chlorophyll provides a specialized site for photosynthesis to occur
Overview of the Light Reactions Occurs: in photosystems (membrane proteins and pigment proteins) in the thylakoid membranes of chloroplasts Uses: Water, light, NADP+, and ADP Produces: O2 (waste), NADPH, and ATP
Figure 6.18 The Molecular Structure of Chlorophyll (Part 1)
Figure 6.18 The Molecular Structure of Chlorophyll (Part 2)
79 What happens when chlorophyll absorbs light energy?
Chlorophyll molecules in photosystems produce high energy electrons when exposed to photons Excited Electrons move through electron transport chains between photosystems This releases free energy used to move protons across the thylakoid membrane
Non-cyclic electron flow
Figure 6.19 Noncyclic Electron Transport Uses Two Photosystems
What is the role of water in the light reactions? Water is decomposed at PSII to supply chlorophyll with replacement electrons This produces waste O2
How is ATP produced in non-cyclic electron flow? Chemiosmosis! The high concentration of H+ in the thylakoid space passively diffuse through ATP synthase enzyme
How is NADPH produced? Why is it considered a “final electron acceptor” Electrons in the ETC are used to reduce NADP+ to NADPH NADPH “accepts” the electrons at the end of the ETC
Figure 6.20 Cyclic Electron Transport Traps Light Energy as ATP
Summary of the Light Dependent Reactions: Location? Reactants (4)? Products (4)? **The ATP and NADPH produced are needed for the light independent reactions to take place**
Overview of the Calvin Cycle Occurs: in the stroma of the chloroplast Uses: CO2, NADPH, and ATP Produces: Organic Molecules (G3P), NADP+, and ADP
How can we describe the process of carbon fixation? The ATP and NADPH produced during the L.D. reactions will be used to drive the incorporation of CO2 in to an organic sugar building block called G3P
Figure 6.22 RuBP Is the Carbon Dioxide Acceptor
What is the first step of the Calvin Cycle? What is the name of the enzyme that catalyzes this reaction? This is carbon fixation. Carbon dioxide is incorporated into the Calvin Cycle by the enzyme RuBisCo. This reaction turns a 5-Carbon RuBP molecule into two 3-Carbon PGA molecules
How are ATP and NADPH used in the Calvin Cycle? The energy in ATP and the electrons in NADPH are used to reduce the PGA molecules into 3- Carbon G3P molecules. A total of 12 G3P molecules are produced
G3P is the 3-Carbon organic compound produced during the calvin cycle. What are the possible fates of the G3P molecules produced? 10 of the 12 molecules produced are used to regenerate RuBP…Why? 2 G3P molecules exit the stroma and can be combined to… Make sugars and be used in C.R. Excess glucose stored as starch Make lipids, amino acids, or nucleotides
Why is photosynthesis the most important biological reaction on Earth? The C—H bonds generated by the Calvin cycle provide almost all the energy for life on Earth. Autotrophs and Heterotrophs rely on this chemical energy to support their own growth and reproduction!
Photosynthesis Determines Global Productivity
Summary of the Calvin Cycle: Location: Reactants: Products: