Cell Energy: ATP and Photosynthesis

1. NOTES – Cell Energy Part 2 (Photosynthesis)

2. Cell Energy Part 1 (ATP) Review • Cells use ATP molecules for their energy needs • As ATP is used up, more is made by the cell • Cells need a continuous input of energy in order to keep making ATP

3. How fast is the ATP cycle? • A working muscle cell recycles all of its ATP about once each minute • That’s about 10 million molecules of ATP consumed & regenerated per second, per cell! (600 million molecules per minute!) • If ATP was not continuously regenerated, you would need to consume an amount roughly equal to your bodyweight every day to meet the energy needs of your cells!

4. From high energy food molecules Glucose (C6H12O6) - basic food molecule used by most cells to power the ATP cycle Simple sugar (carbohydrate) Made by plants, algae, and some bacteria during the process of photosynthesis Glucose molecules can be linked together to form larger carbohydrates, like starch and cellulose Where does the “continuous input of energy” come from?

5. Cellulose is the main ingredient in plant cell walls and is the most abundant organic compound on Earth - plants produce roughly 100 billion tons of cellulose per year! Paper and cotton are almost 100% cellulose Cows and termites have cellulose-digesting microorganisms living in their digestive systems that enable them to break down cellulose-rich foods like grass (cows) and wood (termites) – you don’t have any! Did you know?

6. Historical Photosynthesis Experiments – Jan van Helmont (1643) • How will the growth of the plant affect the mass of the soil? • Concluded that the mass of a plant comes from the water • He turned out to be wrong, but plants do need water, and he put an end to the idea that the mass of the plant comes from the soil itself

7. Historical Photosynthesis Experiments – Joseph Priestly (1771) • Candles and mice produce “injured air” • Plants make the air better again! • Plants are capable of using something in the injured air (carbon dioxide) to produce whatever it is that candles and mice take away (oxygen)

8. Historical Photosynthesis Experiments – Jan Ingenhousz (1779) Put a water plant in the light = bubbles Put a water plant in the dark = no bubbles Ingenhousz literally put the “photo” in photosynthesis (photo means light) Plants only photosynthesize in the light Ingenhousz also discovered that plants in the dark will “injure” the air, just like candles and mice

9. More discovery eventually leads to a basic understanding of photosynthesis… Jean Senebier (1796) – green plants consume CO2 and release O2 in the presence of light Nicolas-Théodore de Saussure (1796) – increase in mass of plant could not be due to CO2 alone, but also to the uptake of H2O, leading to the basic equation for photosynthesis H2O + CO2 + light energy  C6H12O6 + O2

10. Scientist’s Contributions Summary • A good understanding of how photosynthesis actually works did not come until the second half of the 20th century (1950+)

11. Photosynthesis uses the energy of sunlight to convert water and carbon dioxide into oxygen and high-energy sugars Photosynthesis takes place in a chloroplast There are 2 stages to photosynthesis: Light Reactions Light and H2O converted to ATP, NADPH, and O2 Light-Independent Reactions (aka Calvin Cycle or Dark Reactions) ATP, NADPH, and CO2 converted to C6H12O6 Photosynthesis Overview

12. A closer look at the chloroplast • Thylakoid – membrane sac, filled with chlorophyll, site of light reactions • Granum – a stack of thylakoids • Stroma – fluid that surrounds the grana, site of light-independent reactions

13. Thylakoids contain a green pigment called chlorophyll When visible light shines on a plant, chlorophyll absorbs some colors and reflects others Chlorophyll molecules reflect most of the light in the green part of the visible spectrum, which is why plant leaves appear green How do chloroplasts absorb light energy?

14. A closer look at the light reactions Photosynthesis begins with the light reactions The light reactions convert light energy into the chemical energy of ATP and NADPH molecules Requires: Light energy (absorbed by chlorophyll) H2O (taken up through plant roots) ADP + P and NADP+ (present in chloroplast) Produces: ATP and NADPH (provides energy for light-independent reactions) O2 (not needed, released into air)

15. Light Reactions – What happens? (Simple Version)

16. Light Reactions – What happens? • Light is absorbed by chlorophyll adding energy to 2 electrons (e-), which are captured by an e- carrier molecule • H2O is split (photolysis) into 2 H+ ions, 2 e-, and one O atom • The O atom immediately bonds with another O atom to make O2, which is released • The 2 e- replace the ones lost by chlorophyll

17. Light Reactions – What happens? • The 2 high-energy e- from chlorophyll move down an electron transport chain which uses their energy to pump H+ across the membrane (active transport) into the thylakoid, creating a high concentration of H+ inside the thylakoid • The e- are re-energized by additional sunlight, and are combined with NADP+ and an H+ ion to make NADPH • H+ ions diffuse out of the thylakoid providing energy to a special protein which converts ADP + P into ATP

18. Light Reactions – What happens?(complex version) http://www.fw.vt.edu/dendro/forestbiology/photosynthesis.swf

19. A closer look at the Calvin Cycle (light-independent reactions) Photosynthesis ends with the light-independent reactions (Calvin Cycle) Requires: ATP and NADPH (from light reactions) CO2 (taken in from air through stomata) Produces: C6H12O6 (used by plant for energy and synthesis of other molecules)

20. Calvin Cycle – What happens? (Simple Version)

21. Calvin Cycle – What happens? • 6 CO2 molecules are combined with 6 5-carbon sugars to make 12 3-carbon sugars • ATP and NADPH are broken down into ADP + P and NADP+ releasing energy • The released energy is used to turn 2 3-carbon sugars into a 6-carbon sugar (glucose) • The remaining 10 3-carbon sugars are turned into the 6 5-carbon sugars to be used in the next cycle • The ADP + P and the NADP+ are recycled in another round of light reactions

22. Calvin Cycle – What happens? (Complex Version)

23. Making glucose • To make one molecule of glucose requires: • 6 H2O molecules, 6 CO2 molecules • 18 ATP molecules, 12 NADPH molecules • Equation: • 6 H2O + 6 CO2 + light energy  C6H12O6 + 6 O2 • Neither matter nor energy is created or destroyed • Matter is rearranged, energy changes forms

24. What happens to glucose after photosynthesis? • 50% is used to produce ATP during cell respiration • Extra is stored as starch molecules • 50% is used as carbon skeletons to synthesize all the major organic molecules of the cell (proteins, lipids, nucleic acids, carbohydrates)

25. How important is photosynthesis? • ~ 160 billion metric tons (352,000,000,000,000 lbs) of carbohydrate per year • No other chemical process on Earth matches this output • Without photosynthesis, there would be no energy for almost all organisms

26. Photosynthesis Summary • Photosynthesis converts light energy into chemical energy • At the end of photosynthesis, some of the original input energy is stored in glucose • Photosynthesis takes place in the chloroplast • Photosynthesis occurs in two stages: (1) Light Reactions and (2) Calvin Cycle • 6 H2O + 6 CO2 + light energy  C6H12O6 + 6 O2