1. Essential knowledge 2.A.1:
All living systems require constant input of free energy
a. Life requires a highly ordered system.
b. Living systems do not violate the second law of thermodynamics, which states that entropy increases over time.
c. Energy-related pathways in biological systems are sequential and may be entered at multiple points in the pathway.
d. Organisms use free energy to maintain organization, grow and reproduce.
e. Changes in free energy availability can result in changes in population size.
f. Changes in free energy availability can result in disruptions to an ecosystem.

2. Essential knowledge 2.A.2:
Organisms capture and store free energy for use in biological processes.
a. Autotrophs capture free energy from physical sources in the environment
b. Heterotrophs capture free energy present in carbon compounds produced by other organisms.
c. Different energy-capturing processes use different types of electron acceptors.
d. The light-dependent reactions of photosynthesis in eukaryotes involve a series of coordinated reaction pathways that capture free energy present in light to yield ATP and NADPH, which power the production of organic molecules.

3. Essential knowledge 2.A.2:
Organisms capture and store free energy for use in biological processes.
e. Photosynthesis first evolved in prokaryotic organisms; scientific evidence supports that prokaryotic (bacterial) photosynthesis was responsible for the production of an oxygenated atmosphere; prokaryotic photosynthetic pathways were the foundation of eukaryotic photosynthesis.
f. Cellular respiration in eukaryotes involves a series of coordinateenzyme-catalyzed reactions that harvest free energy from simple carbohydrates.
g. The electron transport chain captures free energy from electrons in a series of coupled reactions that establish an electrochemical gradient across membranes.
h. Free energy becomes available for metabolism by the conversion of ATP→ADP, which is coupled to many steps in metabolic pathways.

4. Cellular Respiration
Usually involves breakdown of high energy glucose to low energy carbon dioxide and water (exergonic process)
Energy extracted from glucose molecule:
Released step-wise
Allows ATP to be produced efficiently
Oxidation-reduction enzymes include NAD+ and FAD as coenzymes

5. Oxidation of Organic Fuel Molecules During Cellular Respiration
Glucose is oxidized and oxygen is reduced
(Removes hydrogen)
C6H12O6 + 6O CO2 + 6H2O + Energy
becomes oxidized
becomes reduced
(Adds hydrogen)
*oxygen is more electronegative than carbon, that means transfer of electrons releases energy
to form more stable compounds with less free energy

6. Cells mostly use glucose but also “burn” other organic molecules
Respiration releases the chemical bond energy of glucose, which is stored by the cell in the chemical bonds of ATP

7. Cells typically store ~39-40% of glucose energy in ATP molecules - the rest is lost as heat (aerobic resp)
Anaerobic resp. harvests only ~2% of energy in glucose

8. NAD+ and FAD NAD+ (nicotinamide adenine dinucleotide)
Called a coenzyme of oxidation-reduction it can
Oxidize a metabolite by accepting electrons
Reduce a metabolite by giving up electrons
Each NAD+ molecule used over and over again
FAD (flavin adenine dinucleotide)
Also a coenzyme of oxidation-reduction
Sometimes used instead of NAD+

9. NAD+ (nicotinamide adenine dinucleotide) is a coenzyme that cells make from vitamin niacin
NAD+ is used to shuttle electrons
NAD+ removes 2 H+ and 2 e-, it keeps 1 H+ and 2 e- to become NADH or becomes reduced to become NADre

10. Cellular Respiration: Overview of 4 Phases
1.Glycolysis:
Occurs in cytoplasm
Glucose broken down to two molecules of pyruvate
ATP, NADH is formed
2.Preparatory reaction:
Both pyruvates are oxidized to acetyl CoA
Electron energy is stored in NADH
Two carbons are released as CO2
3.Citric acid or Krebs cycle:
Occurs in mitochondria
Electron energy is stored in NADH and FADH2
ATP is formed

11. 4.Electron transport chain and chemiosmosis:
occurs on inner membrane of mitochondria
Extracts energy from NADH & FADH2
* Both glycolysis and the citric acid cycle are exergonic and make small amounts of ATP (2 +2) by substrate level phosphorylation, the main function of glycolysis and Krebs is to supply last stage with electrons

12. Glycolysis harvests energy by oxidizing glucose to pyruvate Glycolysis
Means “splitting of sugar”

13. Glucose Breakdown: Glycolysis
Occurs in cytoplasm outside mitochondria
Energy Investment Steps:
Two ATP are used to activate glucose
Glucose splits into two G3P molecules
Energy Harvesting (payoff) Steps:
Two electrons (as hydrogen atoms) are picked up by two NAD+ and converted to NADH
Four ATP produced by substrate-level phosphorylation
Net gain of two ATP
Both G3Ps converted to pyruvates

14. Energy investment phase
2 ATP used

15. Energy payoff phase 4 ATP produced
2 used previously resulting in a net gain of 2 ATP molecules
2 NADH also produced

16. Before the citric acid cycle can begin
Preparatory stage
Before the citric acid cycle can begin
Pyruvate must first be converted to acetyl CoA, which links the cycle to glycolysis

17. Conversion of (2) pyruvate to (2) acetyl CoA
Preparatory stage
Conversion of (2) pyruvate to (2) acetyl CoA
Produces (2) NADH
Releases (2) CO2

18. Glucose Breakdown: The Preparatory Reaction
End product of glycolysis, pyruvate, enters the mitochondrial matrix
Pyruvate converted to 2-carbon acetyl group
Attached to Coenzyme A to form acetyl-CoA
Electron picked up (as hydrogen atom) by NAD+

19. Citric Acid cycle
The citric acid cycle completes the energy-yielding oxidation of organic molecules
The citric acid cycle

20. Acetyl CoA joins with oxaloacetic acid to form citric acid**
For 2 Acetyl CoA (from 1 glucose)
4 CO2 released
2 ATP produced (slpp)
2 FADH2 produced (flavin adenine dinucleotide) another electron carrier molecule, similar to NADH

21. Total for 1 glucose from beginning of glycolysis to end of Krebs cycle :
4 ATP
10 NADH
2 FADH2
6 CO2 released

22. During oxidative phosphorylation, chemiosmosis couples electron transport to ATP synthesis
NADH and FADH2

23. Stepwise Energy Harvest via NAD+ and the Electron Transport Chain
Cellular respiration
Oxidizes glucose in a series of steps

24. Electrons from organic compounds
Are usually first transferred to NAD+, a coenzyme

25. NADH, the reduced form of NAD+, carries electrons to electron carrier molecules, which passes the electrons to the electron transport chain
Electrons travel “down” the electron transport chain, where each electron carrier molecule in the chain is successively “lower” in energy

26. Most of these carrier molecules are proteins which are embedded in the mitochondria membrane
The final and ultimate electron acceptor of electron transport chains is oxygen
Cells use energy released in small amounts by redox rxns to produce ATP

27. The electron transport chain
Passes electrons in a series of steps instead of in one explosive reaction

28. Both glycolysis and the citric acid cycle
Can generate ATP by substrate-level phosphorylation

29. The Pathway of Electron Transport
In the electron transport chain
Electrons from NADH and FADH2 lose energy in several steps
NADH and FADH2 capture electrons and transport them to “top” of ETC
ETC uses “downhill” flow of electrons from NADH and FADH2 to pump H+ ions across membrane
Each molecule of ETC will have successively lower energy levels
Enzymes of ETC and ATP synthase are built into the inner membrane of mitochondria

30. At the end of the chain
Electrons are passed to oxygen, forming water

31. Chemiosmosis: The Energy-Coupling Mechanism
ATP synthase
Is the enzyme that actually makes ATP

32. At certain steps along the electron transport chain
Electron transfer causes protein complexes to pump H+ from the mitochondrial matrix to the intermembrane space

33. The resulting H+ gradient
Stores energy
Drives chemiosmosis in ATP synthase

34. Chemiosmosis
Is an energy-coupling mechanism that uses energy in the form of a H+ gradient across a membrane to drive cellular work

35. Electron Transport Chain and Chemiosmosis
H+ ions pumped across inner membrane (into intermembrane space) create an electrostatic gradient
Because inner membrane pumps positive ions across membrane, inner surface becomes more negatively charged
Increase of H+ ions creates osmotic concentration gradient

36. Combined effects of osmotic concentration gradient, and electrostatic gradient create a powerful chemiosmotic gradient
Because of strong chemiosmotic gradient, H+ ions move strongly back across membrane into matrix through special protein channel called ATP synthase

37. NADH starts at the “top” of the electron transport chain, it’s electrons pass through three H+ ion pump/protein complexes
FADH2 starts lower on the ETC, and its electrons only pass through two H+ ion pump/protein complexes

38. 2 H+ ions passing back across ATP synthase produces 1 ATP molecule
Since NADH transports across 6 H+ ions, it generates enough energy to produce ~ 3ATP/NADH

39. Glycolysis + Krebs produce :
10 NADH X ~ 3ATP = ATP (COPP)
2 FADH2 X ~2ATP = 4 ATP (COPP)
32-34 ATP
+ 2 ATP – glycolysis (SLPP)
+ 2 ATP – Krebs (SLPP)
36-38 ATP

40. An Accounting of ATP Production by Cellular Respiration
During respiration, most energy flows in this sequence
Glucose to NADH to electron transport chain to proton-gradient to ATP

41. About 39% of the energy in a glucose molecule
Is transferred to ATP during cellular respiration, making approximately ATP

42. A Comparison of Chemiosmosis in Chloroplasts and Mitochondria
Generate ATP by the same basic mechanism: chemiosmosis

43. Oxidative phosphorylation - oxidation of compounds provides energy to phosphorylate ATP - results in net loss of energy by organism (ETC of respiration)
Photophosphorylation (PPP) - light provides energy for phosphorylation - organism increase in energy (ETC of photosynthesis)

44. The spatial organization of chemiosmosis
Differs in chloroplasts and mitochondria

45. In both organelles ATP synthase
Redox reactions of electron transport chains generate a H+ gradient across a membrane
ATP synthase

46. In the absence of oxygen
Fermentation enables some cells to produce ATP without the use of oxygen
Cellular respiration
Relies on oxygen to produce ATP
In the absence of oxygen

47. Glycolysis
Can produce ATP with or without oxygen, in aerobic or anaerobic conditions
Couples with fermentation to produce ATP

48. Fermentation consists of
Types of Fermentation
Fermentation consists of
Glycolysis plus reactions that regenerate NAD+, which can be reused by glycolysis

49. In alcohol fermentation
Pyruvate is converted to ethanol in two steps, one of which releases CO2

50. During lactic acid fermentation
Pyruvate is reduced directly to NADH to form lactate (lactic acid) as a waste product
Lactic acid causes muscle ache during exercise
Used to make cheese and yogurt

51. Fermentation and Cellular Respiration Compared
Both fermentation and cellular respiration
Use glycolysis to oxidize glucose and other organic fuels to pyruvate

52. Cellular respiration Produces more ATP = 36-38 compared to 2
18-19X more efficient

53. Pyruvate is a key juncture in catabolism

54. The Evolutionary Significance of Glycolysis
Probably evolved in ancient prokaryotes before there was oxygen in the atmosphere

55. Glycolysis and the citric acid cycle connect to many other metabolic pathways

56. The Versatility of Catabolism
Catabolic pathways
Funnel electrons from many kinds of organic molecules into cellular respiration

57. Biosynthesis (Anabolic Pathways)
The body
Uses small molecules to build other substances
These small molecules
May come directly from food or through glycolysis or the citric acid cycle

58. Metabolic Pool: Catabolism (1)
Foods:
Sources of energy rich molecules
Carbohydrates, fats, and proteins
Catabolism (breakdown side of metabolism)
Breakdown products enter into respiratory pathways as intermediates
Carbohydrates
Processed as above

59. Metabolic Pool: Catabolism (2)
Breakdown products enter into respiratory pathways as intermediates (cont.)
Proteins
Broken into amino acids (AAs)
Some AAs used to make other proteins
Excess AAs deaminated (NH2 removed) in liver
Results in poisonous ammonia (NH3)
Quickly converted to urea
Different R-groups from AAs processed differently

60. Metabolic Pool: Anabolism (1)
All metabolic reactions part of metabolic pool
Intermediates from respiratory pathways can be used for anabolism
Anabolism (build-up side of metabolism):
Carbs:
Start with acetyl-CoA
Basically reverses glycolysis (but different pathway)
Fats
G3P converted to glycerol
Acetyls connected in pairs to form fatty acids

61. Metabolic Pool: Anabolism (2)
Anabolism (cont.):
Proteins:
Made up of combinations of 20 different amino acids
Some amino acids (11) can be synthesized from respiratory intermediates
organic acids in citric acid cycle can make amino acids
Add NH2 – transamination
However, other amino acids (9) cannot be synthesized by humans
Essential amino acids