Photosynthesis

Photosynthesis (in a nutshell) The energy originally from sunlight is transformed and used to combine CO2 and H2O into Glucose (C6H12O6) or other plant molecules (cellulose, amino acids, etc.)

Structures Photosynthesis occurs only in plants and a small number of single-celled organisms (like algae). To be able to photosynthesize, you must have a specific organelle: the Chloroplast.

Chloroplasts Inside each chloroplast are what look like stacks of green pancakes. Each pancake is called a thylakoid. The stacks of thylakoids are known as grana. The empty space inside the chloroplast is called the stroma.

Chlorophyll Each chloroplast’s thylakoids are lined with a special sun-absorbing pigment. This pigment is known as chlorophyll. It is what allows the plant to absorb sunlight which is used to power photosynthesis It also is what makes the plant green. Chloroplasts use red & blue light and reflect green

Photosynthesis Photosynthesis has two components: A) Photosystem II 1. The absorption of sunlight and water (H2O) 2. The removal of hydrogen atoms from water using the energy of sunlight 3. The use of this hydrogen to power ATP production in each thylakoid’s ATP Synthase. B) The Calvin Cycle 1. The absorption of CO2 2. The use of ATP to power the production of G3P from CO2 and Rubisco (5 carbon molecule) in the stroma. 3. The use of G3P to make sugars, amino acids, fats, and all other components of the plant.

Photosynthesis

Click for explanations Photosystem II 1. Sunlight (primarily red & blue wavelengths) is absorbed by chlorophyll pigments in the chloroplasts. Water (H2O) is absorbed by the chloroplast 2. The sunlight is used to separate hydrogen from oxygen. Oxygen is released as O2. H+ is stored in each thylakoid. 3. The hydrogen absorbed by the thylakoid is used to power ATP Synthase, which makes ATP from ADP and Pi Be sure to remark that this is only showing a partial picture of PSII. For example far more ATP would be produced than is shown. It is important for students to know that this is a grossly simplified version of PSII and should be taken with a grain of salt. CK Click for explanations

Calvin Cycle The Calvin Cycle is powered by ATP (not shown) 1. CO2 is absorbed. Carbon is separated from oxygen. O2 is released. 2. The remaining carbon atom is combined with 5-carbon Rubisco (from the previous cycle) Once again, this is very simplified. In reality, 3 CO2 molecules would bind to 3 Rubisco molecules per cycle, and multiple cycles would occur at the same time. This too is simplified for understanding and technical inaccuracies should be taken with a grain of salt. 3. The 6-carbon molecule is split into two 3-carbon molecules (G3P). One G3P is used to make sugars or other plant molecules. The other is paired with 2 carbon atoms to re-make Rubisco. G3P’s on their way to becoming glucose. Rubisco, re-created and ready to bind to the carbon in CO2 Click for explanations

Photosynthesis (PSII & Calvin) Instructors: point out the following components one by one – splitting of water, release of O2, production of ATP from ATP Synthase, binding of Carbon from CO2 to Rubisco, splitting of 6-carbon molecule into two 3-carbon G3P’s, and the re-creation of Rubisco.

Research Regulation of photosynthesis in developing leaves of soybean chlorophyll-deficient mutants Cai-Zhong Jiang, et al, Iowa State Univ This team used soybeans that were missing one gene (out of two genes total) for chlorphyll production. These plants were lighter green than the control. Why?

Research Jiang created the plants through genetic crosses. ¼ of the plants were dark green (normal), ½ were light green, and ¼ were yellow. The yellow plants always died. Why were some yellow? Why did the yellow always die?

Research Jiang’s team also found that plants with half as much chlorophyll produced half as much Rubisco. Why might this be? Why would this be good for a plant?