My AP Biology Thoughts Unit 3 Cellular EnergeticsWelcome to My AP Biology Thoughts podcast, my name is Saarim Rizavi and I am your host for episode #79 called Unit 3 Cellular Energetics: The Calvin Cycle. Today we will be discussing the second stage of photosynthesis known as the Calvin Cycle (or the light-independent reactions). We will be talking about what the calvin cycle is in the first place and I will give a brief overview of the whole process. Then, I will go into the specific reactions of the calvin cycle and the three main steps of the calvin cycle which include carbon fixation, reduction, and regeneration. Finally, to end it off, I will place and discuss the calvin cycle in the scope of the broader topic of cellular energetics and just the overall importance of the calvin cycle to the environment. Before I begin, I would like to give credit to a couple of websites and resources that were used to create this podcast which include sciencing.com, national geographic, khan academy, biology libretexts, and Ms. Ribecca’s AP Biology Cellular Energetics Videos. So thank you to them for making this podcast possible. Segment 1: Introduction to The Calvin Cycle Calvin cycle is named Calvin cycle because it was named after Melvin C. Calvin who discovered it and won a Nobel Prize in Chemistry for it What is the Calvin Cycle? A process that plants and algae use to turn carbon dioxide from the air into sugar (glucose) Every living thing on Earth depends on the Calvin cycle either directly or indirectly to survive The calvin cycle takes place in the stroma - the inner space of the chloroplasts Function - to create three carbon sugars which can be used to build other sugars such as glucose, starch, and cellulose that is then used by plants to function and survive Steps of Calvin Cycle (quick overview) Carbon fixation - organic carbon in the form of carbon dioxide in the air is incorporated into organic molecules Inorganic carbon converted to organic compounds by living organisms Reduction - the organic molecules produced in the first stage accept electrons and are reduced Regeneration - the reduced organic molecules use energy from ATP to make RuBP to start the cycle all over again Cycle is powered by ATP and NADPH from light dependent reactions Segment 2: More About The Calvin Cycle“Preliminary step” In plants, carbon dioxide enters the leaves through the stomata, which is located on the underside of plant leaves The CO2 diffuses through intercellular space until it reaches the mesophyll cells - CO2 then diffuses into the stroma of the chloroplast Stroma - besides the CO2, there’s an enzyme called rubisco and three molecules of ribulose bisphosphate (RuBP) - RuBP = 5 carbon acceptor molecule Carbon Fixation A reaction between carbon dioxide and RUBP occurs and produces a 6 carbon compound that splits into 2 molecules of a three carbon compound known as 3-PGA, which has 3 carbons and one phosphate 3 molecules of carbon dioxide react with 3 molecules of RuBP to produce 6 molecules of the 3 carbon molecules, 3-PGA - reaction catalyzed by rubisco A turn of the calvin cycle involves only 1 RuBP and 1 carbon dioxide molecule forming 2 molecules of 3-PGA - it takes 3 turns of the calvin cycle to produce 6 molecules of 3-PGA Reduction The 3-PGA molecules created through fixation are converted into molecules of simple sugar, known as G3P The 6 molecules of 3 PGA use 6 molecules of ATP and 6 molecules of NADPH, which store the light reactions, to generate 6 molecules of G3P, a 3 carbon sugar Reduction reaction because the 3-PGA molecules gain electrons - the PGA is basically reduced to G3P ATP - energy is released with the loss of the terminal phosphate group converting it to ADP NADPH - both energy and a hydrogen atom are lost, converting it into NADP+; NADPH donates electron to a 3 carbon intermediate to make G3P One turn o