Power of Photosynthesis: The Energy Cycle Explained

1. I’ve Got the Power!! http://www.johnkyrk.com/glycolysis.html

2. Photosynthesis Let the sun shine….. Hooray for photosynthesis!!!!

3. The equations… • Cellular respiration-highly exergonic • C6H12O6 + O2  CO2 + H2O + ATP!! • Energy released thru oxidation of glucose • Photosynthesis-highly endergonic • Light + CO2  C6H12O6 + O2 • Light energy used to reduce CO2

4. Stroma • ATP produced in stroma • Calvin cycle • Thylakoid membrane • Photosystems embedded • ETCs • ATP synthase • Thylakoid space • H+ conc. gradient

5. Overview Produce energy Required for dark reactions “fix” CO2 into glucose Highly endergonic

6. Light independent reactions • Occur in thylakoid space & membrane • Light strikes chlorophyll • E- are boosted to higher energy level & travel down an ETC • Released energy captured to form ATP & NAPH • Water molecules borken apart to replace lost e- • Light independent reactions-carbon fixing • Uses energy captured in ATP & NADPH to reduce CO2 to sugar • Occurs in stroma

8. Absorption pigments • Light energy must be absorbed to be of any benefit • Pigments absorb certain wavelengths of light, which causes altered structure • Chloroplasts contain several pigments • Chlrophyll-absorbs violet, blue, red • Carotenoids-absorb blue & green • Phycocyanins-absorb green

9. What happens when chlorophyll absirbs light? • An e- becomes energized & moves to higher orbital • This is unstable-e- will normally release energy & move back to its original orbital • In photosynthesis, e- is captured by ETC

10. What is a photosystem? • Located in thylakoid membrane • Composed of a reaction center(chlorophyll), ,accessory(antennae) pigments, & an ETC • PSI- • evolved 1st, • cotains a dimer of chlorophyll, • can operate independently of PSII, • its ETC makes NADPH • PSII • Supllies e- to PSI • ETC produces ATP (photophosphorylation) • Accessory pigments absorb light & pass it chlorophyll • Only chlorophyll loses e- to ETCs

12. Light causes e- to become energized in PSII Jump to higher level

13. Water is split to replace e-

14. E- captured by cytochromes in ETC Energy used to push H+ from stroma to space Gradient used to produce ATP in stroma

15. E- end up in PSI, which has also lost e- To its ETC

16. PSI ETC gives its e- to NAD-an e- shuttle, it carries e- to calvin cycle

18. Cyclic e- flow-used when no NADP is available-(calvin cycle uses ATP faster than NADPH) This ETC shuts down No NADPH or O2

21. RuBP carboxylase CO2 is reduced RuBP is regenerated Reverse reactions of glycolysis Totals-1 glucose molecule Requires: 6CO2 18 ATP 12 NADPH How many ATP do we get From 1 glucose in cell resp? G3P In stroma

24. C4 plants • During hot weather, stoma close to avoid water loss • Causes build up of O2 which favors photorespiration-rubisco not selective • This inhibits calvin cycle • C4 plants have 2 adaptations to combat this • Bundle sheath cells in leaf interior-less PSII, so less O2 produced • PEP carboxylase-high affinity for CO2 despite O2 levls • Result is maintenance of high level of CO2, with a lower level of O2

25. CAM plants • Crusculacean Acid Metabolism • Open stomata at night-store CO2 as CA • During day, stomata closed-convert CA back to CO2 & photosynthesize

29. Terminal phosphates Break off fairly easily Due to instability of Molecule-provide Enough energy for most Cellular reactions

31. ADP  AMP + Pi

32. Coupled reactions-energy released from exergonic reactions drives endergonic reactions Nuclear fusion H Light energy He +   EXERGONIC + O2 CO2 + H2O  ENDERGONIC

33. This reaction is endergonic Sometimes the breakdown Of ATP is coupled to An endergonic reaction This compound is Phosphorylated & Has energy This bond is Broken & the Energy released Drives the reaction

34. ATP is formed through the oxidation (breakdown) of glucose in a series of step wise reactions

35. Redox (oxidation-reduction) Reactions • e- pass from one atom/molecule to another • H+ may also be lost or gained as a result • Molecule which loses the e- (H+) is oxidized • Molecule which gains e- (H+) is reduced • Must always occur together • The transfer of an e- to a more electronegative atom releases energy Na + Cl Na+ Cl- Na is oxidized Cl is reduced

36. 6CO2 + 6H2O • During cellular respiration….. • Glucose is oxidized, oxygen is reduced • e- shift from glucose to highly electronegative O2 • Energy released a little at a time C6H12O6 + 6O2

38. No matter what food is taken in It can be fed into this process At some point!

39. The Reactions…….

40. So what’s really important aboutglycolysis? • Takes place in cytoplasm • With or without oxygen • Every living thing on the planet does it • Starts with 6C glucose • Ends with 2, 3C pyruvates • Gross 4 ATP • Net 2ATP, & 2 NADH

41. Nicotinamide adenine diphosphate, aka NAD, is an electron shuttle

42. So what happens next?That depends on whether or not O2 is present!!! • W/ O2, Kreb’s cycle & ETC • W/O O2, fermentation

43. Fermentation Hooray for Fermentation! • In the presence of O2, NADH carries its e- to the ETC • NAD is regenerated for use during glycolysis • W/o this regeneration, glycolysis would stop!! • If no O2 is present, fermentation regenerates NAD, & keeps glycolysis active

44. Used by anaerobic microorganisms (bacteria, yeast), & to make human foods

45. Used by human muscles during vigorous exercise (oxygen debt) • Allows muscles to continue working w/o oxygen • Build-up forces muscles to slow down until intake of O2 catches up • Lactic acid eventually breaks down

47. Outer membrane permeable to most small molecules • Inner membrane only permeable to ATP & pyruvate • Matrix-enzymes, water, Pi-parts of Kreb’s & ETC • Cristae-kreb cycle enzymes, ATP synthetase, ETC embedded in folds

48. Intermediate Step-what’s important…link between glycolysis & Kreb’smoves pyruvate into mitochondria (sometimes ACTIVE transport)happens twice per glucose (2 pyruvate)start w/ 2 pyruvateend with 2 acetyl CoAnet 2 NADH, 2 CO2 (by-product) To Krebs cycle oxidized

49. Series of redox Reactions which Completely finishes The oxidation of glucose

50. So Dunbar, help us out here! What’s important? • Each glucose requires 2 turns of cycle (2 pyruvates) • Takes place in matrix & cristae • Oxaloacetate is regenerated • Start w/ 2 acetyl CoA • End w/ oxaloacetate • Net, per glucose • 2 ATP • 6 NADH • 2 FADH2 (another e- shuttle) • 4 CO2 (by-product) • TOTALS SO FAR • 4 ATP • 10 NADH • 2 FADH2 • 6 CO2