Cell Respiration

1. Cell Respiration Topic 8.2 Chap. 7 in Falcon Book

2. 8.2 Cell Respiration • Oxidation (8.2.1) • Loss of electrons from an element • Oxygen is gained • Hydrogen is lost • OIL – Oxidation is Loss of energy • Reduction • Gain of electrons from an element • Oxygen is lost • Hydrogen is gained • RIG – Reduction is Gain of energy

3. Electron acceptors • NAD+ and FAD are hydrogen acceptors • NAD+ is reduced to NADH + H+ • NAD+ +2H NADH + H+ • FAD is reduced to FADH2 • FAD + 2H  FADH2

4. Cell Respiration • Occurs in the mitochondria of animal cells • Reactants are glucose and oxygen • Products are water and carbon dioxide • Aerobic respiration occurs in three steps: • Glycolysis • Krebs Cycle (aka Citric Acid Cycle) • Oxidative Phosphorylation (aka Electron Transport Chain)

5. Glycolysis • Occurs in the cytoplasm, just outside of the mitochondria • Begins with phosphorylation: • 2 ATP lose a phosphate to glucose (a six carbon sugar) and thus become ADP • The added phosphates makes the sugar unstable, thus allowing it to be broken down more easily

6. After phosphorylation is lysis six carbon glucose is broken down into two three-carbon molecules called G3P Glyceraldehyde-3- phosphate G3P is oxidized results in the production of two pyruvate (pyruvic acid) molecules and two NADH molecules 2 2 NAD+ 2 2

7. Substrate level phosphorylation of ATP 4 ADP  4 ATP

8. G3P G3P

9. Glycolysis Summary • 2 ATP used at start • Total of 4 ATP’s produced. Net gain of 2 • 2NADH are produced • 2 Pyruvates are produced • Phosphorylation, lysis, oxidation • Controlled by enzymes, increase in ATP levels will result in end product inhibition and slow or stop process.

10. 8.2 • Anaerobic Respiration (no oxygen present) • pyruvate will be converted to lactic acid (animals) or ethanol and carbon dioxide (yeast) • Aerobic Respiration (oxygen present) • pyruvate will go into the mitochondria to participate in the Kreb’s Cycle

11. 8.2 • The fluid filled matrix contains the enzymes necessary for the Krebs cycle to take place

12. Link Reaction • Once inside the matrix of the mitochondria (via active transport) each pyruvate is decarboxylated (CO2 is removed) • The remaining two-carbon molecule (acetyl) reacts with reduced co-enzyme A (carbohydrate metabolism only), and at the same time NADH + H+ is formed

14. Krebs Cycle • Each acetyl group (CH3CO)(2C) combines with oxaloacetate(4C) with the removal of Coenzyme A (CoA) to make citrate (6C) a.k.a. citric acid

15. Citrate(6C) is oxidized and a carbon is lost to become CO2 • Result is a compound called • a-ketoglutarate (5C)

16. a–ketoglutarate is oxidized and another carbon is lost to make carbon dioxide, thus leaving succinate (4C)molecule. NAD+ is reduced to NADH

17. This Succinate (4C) molecule goes through a series of reactions in which hydrogens are removed then collected by hydrogen carrying coenzymes such as FADH2 and NADH. One ATP is created from ADP + Pi • The final molecule left at the end of the cycle is called oxaloacetate (4C)

19. In summary, one turn of the krebs cycle yields: • 2 CO2 • 3 NADH + H+ • 1 FADH2 • 1 ATP

21. Krebs Cycle Review • Krebs Cycle will run twice for each glucose molecule entering cellular respiration! • Totals from one Glucose molecule • 4 CO2 • 6 NADH + H+ • 2 FADH2 • 2 ATP

22. Oxidative Phosphorylation • Third and final step of cellular respiration • Electron transport carriers (proteins)are strategically arranged over the inner membrane of the mitochondrian (called the electron transport chain) • Electrons get passed through a series of proteins of increasing electronegativity • The final electron acceptor is oxygen(high electronegativity) which then binds with hydrogen to form water • As these carriers oxidize NADH + H+ and FADH2 (products of the Krebs cycle), energy is released

24. This energy forces hydrogen ions to move across the concentration gradient from the mitochondrial matrix (inner portion) to the space between the two membranes (intermembrane space)

25. Eventually the hydrogen ions flow back into the matrix through protein channels in specialized molecules called ATP Synthase • As the ions flow down the gradient (via the ATP Synthase protein channels) energy is released and ATP is made Oxidative Phophorylation Animation

27. Structure and Function of Mitochondria • The mitochondria is specially designed to promote efficiency of respiration: • Membranes fold in upon themselves to form cristae • Cristae provide a larger surface area for the electron transport chain • The space between the outer and inner membranes provides room for the accumulation of hydrogen ions

28. Photosynthesis8.2

29. Photosynthesis occurs in the chloroplasts of plant leaf cells Chloroplast structure includes Double membrane Grana Look like a stack of coins Membrane is called the “thylakoid membrane” Stroma Fluid surrounding the grana 8.2.1

30. 8.2.1

31. 8.2.2 • Photosynthesis consists of light-dependant and light-independent reactions • Light-dependent reaction (aka photolysis) • Consists of Photosystems I and II • Occurs in the thylakoid membrane of the grana • Thylakoid membrane contains chlorophyll (pigment that absorbs red and blue light and reflects yellow and green)

32. 8.2.7 • this phenomenon can be demonstrated by an absorption spectrum, which shows chlorophyll’s light absorption vs. wavelength of light, or an action spectrum, which shows the effectiveness of different wavelengths of light at driving photosynthesis

33. 8.2.3 • The light-dependent reaction begins with a chlorophyll molecule at the beginning of Photosystem II that has an absorption peak at 680 nm and is referred to as P680 • The P680 cholorophyll molecule absorbs a photon of light • As a result, one of it’s electrons becomes excited and moves to a higher energy state

34. 8.2.3 • This energized electron is transferred along a series of electron acceptors located in the thylakoid membrane (called the electron transport chain) • As the electron is passed from carrier to carrier the energy released is used to pump hydrogen ions from the stroma to the thylakoid space (inside of the thylakoid) • These protons then diffuse back to the stroma down the concentration gradient

35. 8.2.3 • They are able to cross the thylakoid membrane by traveling through protein channels in ATP Synthase, thus producing ATP • This process is called chemiosmosis (8.2.4) • Once the electron leaves the last carrier in Photosystem II it moves on to replace an electron that is lost from the chlorophyll of Photosystem I after it has been excited by a photon of light • The chlorophyll in Photosystem I is called P700 due to the fact that its peak wavelength of light absorption is 700 nm

36. 8.2.3 • Once the electron from P700 is excited it is passed down another electron transport chain until it reaches the carrier ferredoxin • Ferredoxin passes the electron to NADP which, when given two electrons, will bind with H+, forming NADPH • The electron originally lost from P680 in Photosystem II is replaced by the splitting of water and results in the release of oxygen (two water molecules must be split in order for one molecule of O2)

37. 8.2.3 • There are two types of electron transport: Noncyclic and Cyclic • Noncyclic includes both Photosystem I and II • Cyclic only utilizes Photosystem I • The electron excited in P700 replaces itself when ferredoxin passes it back

38. 8.2.3 • Energy from the electron transport chain pumps hydrogen ions across the thylakoid membrane • The ions diffuse back into the stroma via ATP Synthase and ATP is made (chemiosmosis) • Cyclic phosphorylation cannot be used as the basis for photosynthesis as NADPH is required to reduce CO2 to carbohydrate (light-independent reaction)

39. 8.2.3 • scientists do not know for sure why cyclic phosphorylation exists but hypothesize that it may occur when there is not enough NADP present • they also agree that this process was used by ancient bacteria to produce ATP from light energy

41. 8.2.5 • Light-independent Reaction (aka the Calvin Cycle or the C3 cycle) • Occurs in the stroma • Consists of thirteen reactions that are divided up into three phases • CO2 uptake • carbon reduction • RuBP (ribulose biphosphate) regeneration

42. 8.2.5 • during the C02 reuptake phase a single reaction takes place in which carbon dioxide combines with a phosphorylated five-carbon compound called RuBP • the enzyme that catalyzes the reactions is called Rubisco and may be one of the most abundant proteins in the biosphere • the product of this reaction is an unstable six-carbon intermediate which immediately breaks down into two molecules of phosphoglycerate (PGA) with three carbons each (hence the term ‘C3’ cycle)

43. 8.2.5 • The carbon reduction phases consists of two steps in which the energy and reduction power of ATP and NADPH (both produced in the light-dependant reactions) are used to convert the PGA molecules to glyceraldehyde-3-phosphate (G3P) • For every six turns of the cycle (in which 6 carbons have been “fixed” from C02) 12 G3P molecules are created

44. 8.2.5 • 2 of these 12 G3P molecules are released from the cycle and will combine together to form glucose or fructose • The remaining 10 G3P molecules will go through a complex series of 10 reactions called the RuBP regeneration phase: • their atoms are rearranged and then phosphorylated in order to create 6 molecules of RuBP which can help the cycle to start again

45. 8.2.5

46. C4 and CAM plants • fix CO2 at lower rates than C3 plants • live in conditions in which survival depends on opening stomata less and thus taking in less CO2 (i.e. desert plants that don’t want to lose too much water) • The key component of the C4 pathway is an enzyme called PEP carboxylase that has an extremely high affinity for CO2

47. CAM plants live in extremely dry/hot conditions and therefore fix CO2 at night, then store it until the daytime in which light can be absorbed for photosynthesis

48. 8.2.6 • The chloroplast structure is closely related to its function • Has an intricately folded membrane that provides more surface area for light absorption • These foldings form the thylakoids, which, when stacked upon each other, form grana

49. 8.2.6 • The thylakoids provide a small space inside for the accumulation of protons to use in ATP production • The fluid in the chloroplast (stroma) has enzymes that are used in the Calvin cycle (aka Rubisco)

50. 8.2.8 • Limiting factors in photosynthesis • Limiting factors are conditions that are essential for the life of the plant • Can affect how well the plant can photosynthesize and thus how well it survives • Many plants prefer a particular amount of light intensity