1. Cellular Respiration Chapter 9
9-1 Chemical Pathways

2. Chemical Energy and Food
PHOTOSYNTHESIS
___________ + _________ + ___________ →_______________ + __________
6 CO2
6 H2O
C6H12O6
6O2
CELLULAR RESPIRATION
C6H12O6
6 CO2
_____________ + _________ →________ + __________ + __________
6O2
6 H2O
The two equations are exact opposites!
Discovery School - The Mitochondria (2:44)

3. Comparing Photosynthesis & Cellular Respiration:
Which type(s) of organisms carry out photosynthesis?
Autotroph Heterotroph
Which type(s) of organisms carry out cellular respiration?

6. Overview of Cellular Respiration
Cellular respiration is the process that releases energy from food in the presence of oxygen.
If oxygen is available, organisms can obtain energy from food by a process called cellular respiration.
The summary of cellular respiration is presented below.
6 O2 + C6H12O6  6 CO2 + 6 H2O + Energy (ATP)

7. Structure of the Mitochondria:

9. Chemical Energy and Food
Cellular respiration happens slowly and in many steps.
If all the energy was release in one step… Most would be lost as light and heat!
Cellular respiration breaks down glucose molecules and banks their energy in ATP

10. Chemical Energy and Food
Amount of heat it takes to raise 1 gram of water 1oC = calorie
Amount of heat it takes to raise 1 kilogram of water 1oC = Calorie
Unit for measuring energy in food = Calorie
1 Calorie = 1 kilocalorie = 1,000 calories

11. Comparing Photosynthesis & Cellular Respiration
Function
Location
Reactants
Products
Produces food (chemical energy) for the plant
(glucose C6H12O6)
Produces chemical energy (ATP) for the cell
Chloroplast
Mitochondria
Water (H2O),
Carbon dioxide (CO2)
and sunlight
Oxygen (O2) and
Glucose (C6H12O6)
Water (H2O),
Carbon dioxide (CO2)
and energy (ATP)
Oxygen (O2) and
Glucose (C6H12O6)
Energy Consumption - Virtual Cell Animation (4:41)

12. Compare Photosynthesis to Cellular Respiration
Light Energy
CO2
H2O
Chloroplast
LIGHT
REACTIONS
(in thylakoids)
CALVIN
CYCLE
(in stroma)
NADP+
ADP + P
ATP
NADPH O2
Sugar (C6H12O6)
Electrons
Compare Photosynthesis to Cellular Respiration
How Cells Obtain Energy (14 min)
NADH
FADH2
GLYCOLYSIS
Glucose
Pyruvate
CITRIC ACID CYCLE
OXIDATIVE PHOSPHORYLATION (Electron Transport and Chemiosmosis)
Substrate-level phosphorylation
Oxidative phosphorylation
Mitochondrion
and
High-energy electrons carried by NADH
ATP
CO2
Cytoplasm

13. An Overview of Cellular Respiration:

14. Stages of Cellular Respiration
The three main stages of cellular respiration are
Glycolysis
Krebs cycle
Electron transport chain.

15. Oxygen and Energy
Glycolysis is an ANAEROBIC processes. It does not directly require oxygen, nor does it rely on an oxygen-requiring process to run.
Glycolysis is still considered part of cellular respiration.
Glycolysis takes place in the cytoplasm of a cell.

16. Oxygen and Energy
Pathways of cellular respiration that require oxygen are called aerobic.
The Krebs cycle and electron transport chain are both aerobic processes.
Both processes take place inside the mitochondria.

17. Overview of Cellular Respiration
Occurs in three main stages:
Stage 1: Glycolysis
Occurs in the cytoplasm
Breaks down glucose into pyruvate, producing a small amount of ATP
Stage 2: The Citric Acid Cycle (Krebs cycle)
Takes place in the mitochondria
Completes breakdown of glucose, produces a small amount of ATP
Provides third stage of cell respiration with electrons
Stage 1
Stage 2
Stage 3

18. Overview of Cellular Respiration
Stage 3: Oxidative phosphorylation (ETC)
Occurs in the mitochondria
Uses the energy released by “falling” electrons to pump H+ across a membrane
Harnesses the energy of the H+ gradient through chemiosmosis, producing ATP
Stage 3

19. Understanding Oxidation and Reduction
Oxidation is the loss of electrons; electrons are removed from hydrogen atoms contained in glucose.
Reduction is the gain of electrons; oxygen atoms accept hydrogen and electrons forming water H2O.
Hydrogen is a source of electrons.
Remember:
OIL RIG (Oxidation Is Loss, Reduction Is Gain)
LEO the lion goes GER (Lose Electrons – Oxidation) (Gain Electrons – Reduce)
In cellular respiration, glucose is oxidized and oxygen is reduced.

20. Electron Carriers (enzymes) Involved
NAD+ (Nicotinamide adenine dinucleotide)
Accepts H+ to become NADH
FAD (Flavin adenine dinucleotide)
Accepts 2H+ to become FADH2

21. Overview of Cellular Respiration
NADH
FADH2
GLYCOLYSIS
Glucose
Pyruvate
CITRIC ACID CYCLE
OXIDATIVE PHOSPHORYLATION (Electron Transport and Chemiosmosis)
Substrate-level phosphorylation
Oxidative phosphorylation
Mitochondrion
and
High-energy electrons carried by NADH
ATP
CO2
Cytoplasm
Stage 1
Stage 3
Stage 2
Krebs

22. 9.2 Glycolysis ATP (Glykos = sweet, Lysis = split apart)
The first step in cellular respiration = Glycolysis
Happens in the CYTOPLASM outside the mitochondria
Does not require oxygen, BUT it needs some energy to get it started.
What molecule is going to supply the energy?
ATP
Glycolysis Overview - Virtual Cell Animation (3:00)

23. Put in 2 ATP and get back 4 ATP
Glycolysis
________ ↓
___________ → → _____________
____________________ + _______________
GLUCOSE
2 PYRUVIC ACID
ATP ATP ATP ATP
NADH NADH
Put in 2 ATP and get back 4 ATP
Net gain of 2 ATP and 2 NADH

24. Glycolysis Reactions - Virtual Cell Animation (5:00)
Produces pyruvic acid (pyruvate = 3-carbon compound)
Cell needs to invest some energy to get a higher return (2 ATP gained)
Occurs quickly, in milliseconds to respond to increased energy demand
Glycolysis Reactions - Virtual Cell Animation (5:00)

25. The Advantages of Glycolysis
Glycolysis produces ATP very fast, which is an advantage when the energy demands of the cell suddenly increase.
Glycolysis does not require oxygen, so it can quickly supply energy to cells when oxygen is unavailable.

26. How Efficient is Glycolysis?
Complete oxidation of glucose releases 686 kcal
Production of a standard amount of ATP from ADP absorbs 12 kcal
2 ATP are produced from every glucose molecule broken down by glycolysis
Energy required to make ATP
Efficiency of ==
Glycolysis Energy released by oxidation of glucose
Efficiency of glycolysis = 3.5%

27. 9-2 The Krebs Cycle and Electron Transport

28. Mitochondria Structure
Has a double membrane, with an intermembrane space between the two layers.
Cristae are folds of the inner membrane
The matrix is the innermost compartment, which is filled with a gel-like fluid.
Krebs Cycle occurs in the matrix of the mitochondria.

29. The Krebs Cycle Carbon dioxide is lost to the atmosphere as waste
ATP can be used directly to supply energy for the cell
High energy electron carriers move into the ELECTRON TRANSPORT CHAIN

30. Citric Acid Cycle An Overview (3:17)
The Krebs Cycle
During the Krebs cycle, the 2nd stage of cellular respiration, pyruvic acid produced in glycolysis is broken down into carbon dioxide in a series of energy-extracting reactions.
The Krebs Cycle is also known as the Citric Acid Cycle because citric acid is the first compound formed in this series of reactions.
Citric Acid Cycle An Overview (3:17)

31. The Citric Acid Cycle The Reactions (4:13)
The Krebs Cycle
Pyruvic acid enters the mitochondria matrix
Pyruvic acid is converted into an intermediate 2 carbon molecule called Acetyl-CoA before entering the Krebs Cycle.
The Krebs cycle breaks down carbon compounds into carbon dioxide (waste), ATP, NADH, and FADH2
The Citric Acid Cycle The Reactions (4:13)

32. The Krebs Cycle
Pyruvic acid from glycolysis enters the matrix, the innermost compartment of the mitochondrion.

33. Kreb’s Cycle Pyruvic acid from glycolysis enters the matrix
NAD+ accepts 2 high- energy electrons to form NADH.
One molecule of CO2 is also produced.
The remaining 2 carbon atoms react to form acetyl- CoA.
Diagram by Riedell

34. The Citric Acid Cycle The Reactions (4:13)
The Krebs Cycle
Acetyl-CoA combines with a 4-carbon molecule (oxaloacetic acid) to produce citric acid.
The Citric Acid Cycle The Reactions (4:13)
Diagram by Riedell

35. The Citric Acid Cycle The Reactions (4:13)
The Krebs Cycle
Citric acid is broken down into a 5-carbon compound and then a 4-carbon compound.
Two molecules of CO2 are released.
The 4-carbon compound can then start the cycle again by combining with acetyl-CoA.
The Citric Acid Cycle The Reactions (4:13)

36. KREBS CYCLE
KREBS CYCLE PRODUCES
____ 3 1 1 4
Krebs Cycle Animation

37. The Krebs Cycle
Energy released by the breaking and rearranging of carbon bonds is captured in the forms of ATP, NADH, and FADH2.
For each turn of the cycle, 1 ADP molecule is converted into ATP.
ATP can directly power the cell’s activities.
NADH and FADH2 are used in the electron transport chain to generate ATP.

38. Energy Extraction
Remember! Each molecule of glucose results in 2 molecules of pyruvic acid, which enter the Krebs cycle. So each molecule of glucose results in 2 complete “turns” of the Krebs cycle.
Therefore, for each glucose molecule, 6 CO2 molecules, 2 ATP molecules, 8 NADH molecules, and 2 FADH2 molecules are produced.

39. Summary Sheet Causes 2 turns of the Krebs Cycle 8 NADH (4 per Turn)
Glycolysis of 1 glucose = 2 Pyruvic acid molecules= 2 molecules of acetyl CoA
Causes 2 turns of the Krebs Cycle
8 NADH (4 per Turn)
2 FADH2 (1 per Turn)
2 ATP (+ 2ATP from glycolysis)= 4 ATP thus far
6 CO2 molecules (3 per turn)

40. Summary Sheet Continued
The bulk of energy released by the oxidation of glucose still has not been transferred to ATP.
Requires NADH and FADH2
10 NADH: from Glycolysis
2 from pyruvic acid to acetyl CoA
6 from Krebs Cycle
2 FADH2
THESE MOLECULES DRIVE THE NEXT STAGE OF AEROBIC RESPIRATION!!!

41. Electron Transport Chain
Enzymes (protein complexes) for the electron transport chain are located on the inner mitochondrial membrane.
Several complexes are called cytochromes.
Electron Transport Chain (3:48)

42. Electron Transport Chain
Electrons from NADH and FADH2 travel down the electron transport chain, between protein complexes, to oxygen (final electron acceptor), which picks up H+ to form water
Energy released by the redox reactions is used to pump H+ into the space between the mitochondrial membranes (inter membrane).
H2O
NAD+
NADH
ATP H+
Controlled release of energy for synthesis of ATP
Electron transport chain 2 O2
2e + 1
Electron Transport Chain (2:00)

43. Electron Transport Chain OXIDATIVE PHOSPHORYLATION
Chemiosmosis
In chemiosmosis, the H+ diffuses back through the inner membrane through ATP synthase complexes.
Drives the synthesis of ATP!
Intermembrane space
Inner mitochondrial membrane
Mitochondrial matrix
Protein complex
Electron flow
Electron carrier
NADH
NAD+
FADH2
FAD
H2O
ATP
ADP
ATP synthase H+ + P O2
Electron Transport Chain
Chemiosmosis .
OXIDATIVE PHOSPHORYLATION
+ 2 1 2

44. © Pearson Education

45. Electron Transport Chain

46. Electron Transport Chain
The Role of Oxygen
High energy e- from NADH and FADH2 are passed along a series of molecules
As they pass e- lose some energy to pump protons from the matrix
This builds up a concentration gradient between the inner and outer mitochondrial membrane (intermembrane)
The gradient drives the synthesis of ATP by chemiosmosis
The last molecule in the E.T.C needs to unload the e- it accepts, or ATP synthesis would stop
O2 serves as the final electron acceptor
Also accepts the protons that were part of the H atoms
The combination of protons, electrons, and oxygen produces water
O2 + 4 e- + 4 H+  2 H2O

47. Site of the Electron Transport Chain

48. ATP Synthase

49. Overview of Cellular Respiration

50. Cellular Respiration - Glycolysis, Krebs Cycle, ETC (6:00)
Energy Yield
Each NADH in the
E.T.C. = 3 ATP
Each FADH2 in the
E.T.C.= 2 ATP
Cellular Respiration - Glycolysis, Krebs Cycle, ETC (6:00)

51. Energy Yield This represents about 36% of the total energy of glucose.
In most eukaryotes, the NADH made in the cytoplasm during glycolysis cannot diffuse through the inner membrane of the mitochondria.
It must be transported via active transport.
Consumes 2 ATP:
38 ATP – 2 ATP = 36 ATP
In the presence of oxygen, the complete breakdown of glucose through cellular respiration results in the production of 36 ATP molecules.
This represents about 36% of the total energy of glucose.
The remaining 64% is released as heat.

52. Fermentation When pyruvic acid moves to the next step,
if there is no oxygen = anaerobic
if there is oxygen = aerobic

54. Fermentation
Fermentation – process by which cells release energy in the absence of oxygen
Two types of fermentation:
Alcoholic Fermentation
Lactic Acid Fermentation

55. Alcoholic Fermentation
Occurs in yeast cells:
Yeast is added to bread– CO2 produced in fermentation make air spaces in bread and therefore bread rises.
Alcohol evaporates during cooking
Alcohol is toxic to cells. If too much fermentation occurs, alcohol will kill yeast cells.
Happens when:
Yeast make beer
Bacteria make wine
How Stuff Works - Bread (2:35)
How Stuff Works - Whiskey (2:32)

56. Lactic Acid Fermentation
Happens in muscles during exercise when body can’t get oxygen to tissues fast enough.
Lactic acid builds up in muscles causing soreness.
Bacteria use lactic acid fermentation to make: yogurt, cheese, sour cream, pickles, sauerkraut

59. The Totals Cellular Respiration (aerobic: with oxygen)
1 glucose → 36 ATP
Fermentation (anaerobic: without oxygen)
1 glucose → 2 ATP

60. Respiration Questions
List the reactants and products of respiration
List the three steps (stages) involved in respiration
Name two electron carriers involved
What step produces the most ATP

61. Respiration Questions
In your group:
See if you can write the chemical equation for respiration (inputs and outputs)
What is the organelle in cells that is “releasing” energy during respiration?
What primary molecule is energy being “released” from?
How is the sun indirectly involved in respiration?

62. Fermentation Questions
List two types of fermentation
List the reactants for both types of fermentation
List the products for fermentation used to brew beer
List the products for fermentation used to make yogurt
What important molecule cycles back from fermentation to keep glycolysis going?
What process starts fermentation?