Light Energy Conversion into Glucose: The Process of Photosynthesis

1. How does light energy get converted into glucose?10/19 Photosynthesis • Without photosynthesis, almost everything on our planet quickly dies!!!Important enough? • Photosynthesis has light-dependent and light-independent parts. • Photosynthesis occurs in a chloroplast. • Different photosynthetic pigments absorb light energy at different wavelengths. • Light energy is contained in photons, which are used to increase the energy of electrons taken from water leaving oxygen (O2)behind. • Energy from the light-dependent reactions drives a series of light-independent reactions called the Calvin Cycle that convert CO2 into glucose….”Carbon Fixation”

2. Photosynthesis is a two part process:#1: Photons of light make ATP and NADPH#2: ATP/NADPH are used to “fix” CO2 • Light-Dependent Reactions: • Convert photons to proton pumps and NADPH • ATP synthesized via ATP-synthase • Light-Independent Reactions: • Convert CO2 into glucose as long as sufficient ATP and NADPH is present • Reactions stop moment ATP and NADPH runs out • Chloroplast is location of photosynthesis in cell • Similarity to mitochondria: structures and DNA • “Color” of a plant represents light wavelengths that are “not” absorbed for photosynthesis • Green color/light wavelengths poorly used

3. Big Picture of Photosynthesis:

4. Summary of the light and dark reactions of photosynthesis that capture energy (photons of light) and permit the fixation of carbon dioxide. ATP synthesis when H+ escape the thylakoid H+ pumped INTO thylakoid “NAPDH” not NADH as in mitochondria ATP and NADPH were generated by P680 and P700 photo-systems above.

5. Photosynthesis occurs in coin-like thylakoids that create stacks (granum) that sit inside chloroplasts. • Membranes of a chloroplast: 3 lipid bilayers • 3 membranes: OuterInnerThylakoid • Chlorophyll is a lipid-soluble pigment found in the thylakoid membrane (a and b forms) • Collection of photons of light (energy) • Chloroplasts contain DNA of bacterial origins • Chlorophylls transfer energy to electrons that run through a series of cytochrome reactions • Original electrons taken from H2O, making H+ and oxygen (O2) • Path similar to electron transport in mitochondria • Energy drives proton pumps (H+ into thylakoids) • H+ escape linked to ATP-synthase • Electrons finally make NADPH

6. Accessory “antenna” pigments feed energy from photons into P680 and P700 which excite the electrons.

7. Light energy is absorbed mostly by chlorophyll a and b. Accessory pigments such as Beta-Carotene feed their energy directly to the chlorophylls. Double bonds help stabilize electrons by creating a resonance hybrid structure.

8. Energy in specific light wavelengths is absorbed by specific pigments. Color is what is left behind.Key Absorbencies: Chloro a=430/670 Chloro b=450/650

9. Photons increase the energy in electrons that initiate Photosystem II(P680) and pass into Photosystem I(P700) when an additional photon is received. This pathway is similar to the electron transport pathway of a mitochondria. Atrazine is a herbicide that blocks P680.

10. The reactions of the Calvin Cycle convert CO2 into glucose using energy from ATP and NADPH.This is “Light-Independent” “Carbon Fixation”Triose Sugar leaves and goes to gluconeogenesis. Carbon dioxide is “fixed” to pre-existing carbohydrates that are “occasionally removed”. 3X5-Carbon(R-1,5-BP )+3 CO2 6X3-Carbon(3-PG)skim some carbohydrates/recycle the rest

11. Reversal of the part of glycolysis (Gluconeogenesis) using NADPH instead of NADH

12. Carbon fixation attaches CO2 onto pre-existing ribulose 1,5 bisphosphates to create glyceraldehyde-1,3-bisphosphate and dihydroxyacetone phosphate that can feed substrates back into Fructose 1,6-bisphosphate by the action of aldolase.into gluconeogenesis

13. What sorts of delay occur in a cell with respect to the time needed to produce ATP from PCr, glucose and fatty acids when you begin exercise, when you sustain it for a minute and sustain it for 15 minutes? How does this describe the runner surge 15 minutes into a workout? When would your time of exhaustion onset and duration differ if you had a genetic defect (higher than normal Km) for each enzyme? 1) Enolase 2) Fumarase 3) Fatty acyltransferase (“carnitineacylecarnitinetranslocase” move FA to matrix) , 4) Creatinekinase, 5) Lactate dehydrogenase

14. These are some nice animations for help with understanding the reactions that make chemiosmosis, oxidative phosphorylation and photosynthesis possible (you may wish to look around for others): • Glycolysis: • http://www.youtube.com/watch?v=EfGlznwfu9U • Mitochondrial Reactions: • http://www.youtube.com/watch?v=VCpNk92uswY • http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/C/CellularRespiration.html • http://vcell.ndsu.nodak.edu/animations/etc/movie.htm • Calvin Cycle and Photosynthesis: • http://www.youtube.com/watch?v=OYSD1jOD1dQ&feature=related

15. A Good Mitochondrial Review Question: ATP transport is mediated by an Antiportthat gets inserted into the inner mitochondrial membrane. The rest is driven simply by relative concentrations differences! ADP wants In because it accumulates in cytosol during cellular work (ATPADP), ATP wants Out of mitochondria because it is created inside (↑[ATP]).Proton gradients are used to bring Pi and Pyruvate to the matrix! Symports