1. Cellular Respiration
Topic 3.7 and 3.8

2. Assessment Statements: Core
3.7.1 Define cell respiration State that, in cell respiration, glucose in the cytoplasm is broken down by glycolysis into pyruvate, with a small yield of ATP Explain that, during anaerobic cell respiration, pyruvate can be converted in the cytoplasm into lactate, or ethanol and carbon dioxide, with no further yield of ATP Explain that, during aerobic cell respiration, pyruvate can be broken down in the mitochondrion into carbon dioxide and water with a large yield of ATP.

3. Assessment Statements: Higher Level

4. Energy metabolism and REDOX reactions
REDOX (oxidation-reduction) reactions play a key role in energy flow through organisms
This is because the electrons flowing from one molecule to another are carrying energy with them
Metabolism is the sum of all of the chemical reactions in an organism: catabolic (breakdown) and anabolic (synthetic)
Respiration is a catabolic pathway
Photosynthesis is an anabolic pathway
The two processes are closely linked in plants

5. REDOX reactions OIL RIG LEO says GER OXIDATION REDUCTION
Loss of electrons
Gain of electrons
Gain of oxygen
Loss of oxygen
Loss of hydrogen
Gain of hydrogen
Results in C-O bonds
Results in C-H bonds
Results in a compound with lower potential energy
Results in a compound with higher potential energy
OIL RIG
LEO says GER

6. Definition of cellular respiration
Controlled release of energy from organic compounds to produce ATP
Cells break down organic compounds by SLOW oxidation
Chemical energy is stored in covalent bonds
By releasing energy in a controlled way, it can be trapped in the ‘useful’ form of ATP

7. REDOX reactions in respiration
Cells tap energy from electrons transferred from organic fuels to oxygen
Glucose gives up energy as it is oxidized: it transfers its electrons (and energy) to water
The protons follow the electrons to produce water
Loss of hydrogen atoms
Energy
Gain of hydrogen atoms

8. Where Does Cellular Respiration Take Place?
glycolysis occurs in the cytoplasm
Krebs Cycle & ETC Take place in the mitochondria

10. Cellular Respiration: Standard level
How does the process of cellular respiration yield ATP (chemical energy) from food?
What do you already know about cellular respiration?
What organelle in the cell is the “powerhouse” that makes energy for the cell?

11. What is ATP? Energy ‘currency’ used by all cells
Adenosine triphosphate
Organic molecule containing high-energy phosphate bonds

12. Chemical Structure of ATP
Adenine Base
3 Phosphates
Ribose Sugar

13. How Do We Get Energy From ATP?
By breaking the high- energy bonds between the last two phosphates in ATP ATP hydrolase (ATP’ase) catalyses the breakdown of ATP into ADP + Pi

14. Each day, you hydrolyse 1025 ATP molecules
ATP-ase
ATP Synthetase

15. HYDROLYSIS (Adding H2O)

16. How is ATP re-made?
Substrate-level phosphorylation (using enzymes: in the cytoplasm of the cell and the matrix of the mitochondrion)
Chemiosmosis (in the mitochondria, using ATP synthase)

17. Substrate level phosphorylation and chemiosmosis
GLYCOLYSIS
ELECTRON TRANSPORT CHAIN AND CHEMIOSMOSIS
KREBS CYCLE
Glucose
Pyruvic acid
Substrate Level Phos. Substrate Level Phos. Oxidative Phos.

18. REDOX reactions in respiration
Cells tap energy from electrons transferred from organic fuels to oxygen
Glucose gives up energy as it is oxidized: it transfers its electrons (and energy) to water
The protons follow the electrons to produce water
Loss of hydrogen atoms
Energy
Gain of hydrogen atoms

19. Hydrogen carriers such as NAD+ shuttle electrons in redox reactions
Enzymes remove electrons from glucose molecules and transfer them to a coenzyme
OXIDATION
Dehydrogenase and NAD+
REDUCTION

20. Redox reactions release energy when electrons “fall” from a hydrogen carrier to oxygen
NADH delivers electrons to a series of electron carriers in an electron transport chain
As electrons move from carrier to carrier, their energy is released in small quantities
Energy released and now available for making ATP
ELECTRON CARRIERS of the electron transport chain
Electron flow

21. Two mechanisms generate ATP
ATP can be made by transferring phosphate groups from organic molecules to ADP
This process is called substrate-level phosphorylation
Occurs in cytoplasm and in matrix of the mitochondrion

22. Two mechanisms generate ATP
1. Cells use the energy released by “falling” electrons to pump H+ ions across a membrane
The energy of the gradient is harnessed to make ATP by the process of chemiosmosis
also known as oxidative phosphorylation
High H+ concentration
ATP synthase uses gradient energy to make ATP
Membrane
Electron transport chain
ATP synthase
Energy from
Low H+ concentration
Figure 6.7A

23. Definition of cellular respiration
Controlled release of energy from organic compounds to produce ATP
Cells break down organic compounds by SLOW oxidation
Chemical energy is stored in covalent bonds
By releasing energy in a controlled way, it can be trapped in the ‘useful’ form of ATP

26. Breakdown of one glucose results in 36 to 38 ATP molecules
Cellular Respiration
Breakdown of one glucose results in 36 to 38 ATP molecules
Metabolic Pathway that breaks down carbohydrates
Process is exergonic as high-energy glucose is broken into CO2 and H2O
Process is also catabolic because glucose breaks into smaller molecules

27. Equations for aerobic respiration
All of these are fine!....

28. Equation for Cellular Respiration
C6H12O O2
YIELDS
6CO2 + 6H20 + e ATP + heat

29. Stages of Cellular Respiration
Glycolysis ALWAYS OCCURS
Anaerobic pathways if no oxygen available (Lactic acid and Ethanol fermentation)
Aerobic pathways if oxygen available (Link reaction, Krebs cycle, electron transport chain)

31. Where Does Cellular Respiration Take Place?
glycolysis occurs in the cytoplasm
Krebs Cycle & ETC Take place in the mitochondria

33. Glycolysis: Always the initial stage of respiration
Location: cytoplasm
Substrate: glucose
Requires input of 2 ATP
Products: pyruvate, (NADH), 4 ATP Glycolysis is an anaerobic process: no oxygen required
the movie...

34. Glycolysis

35. Summary of glycolysis Occurs in the cytoplasm of the cell
Two ATP molecules are used to start the process (‘energy investment phase’)
A total of 4 ATP’s are produced (net gain of 2 ATP)
2 molecules of NADH are produced
Involves substrate level phosphorylation, lysis, oxidation and ATP formation
Controlled by enzymes: when ATP levels in the cell are high, feedback inhibition will block the first enzyme in the pathway
Produces 2 pyruvate molecules at the end

36. If no oxygen is available, glycolysis (anaerobic) is followed by fermentation (anaerobic)

37. Why fermentation?
In the absence of oxygen, glycolysis soon stops unless there is an alternative acceptor for the electrons produced from the glycolytic pathway

38. Fermentation
1. Alcoholic fermentation Pyruvate is converted into ethanol plus carbon dioxide and NAD+
Lactate fermentation
Pyruvate is converted into lactate and NAD+

39. Alcoholic fermentation in yeast

40. Alcoholic fermentation in yeast
Pyruvate is produced from glycolysis
3-carbon pyruvate is converted to 2-carbon ethanol and carbon dioxide
Generation of carbon dioxide helps bread products to rise
Yeast is used to produce ethanol

41. Lactate fermentation in mammals
Lactate is a 3-carbon molecule
NAD+ is regenerated to allow glycolysis to continue

42. Aerobic respiration: Higher level
8.1.4: Explain aerobic respiration: the Link reaction, the Krebs cycle, the role of NADH and H+, the electron transport chain and the role of oxygen 8.1.5: Explain oxidative phosphorylation in terms of chemiosmosis

43. Aerobic respiration
Takes place in the mitochondria of eukaryotic cells
Substrate: pyruvate
Produces LOTS of ATP (28 – 38 ATP): 90% of total ATP from respiration
Also produces carbon dioxide, water and heat
Oxygen is the final electron acceptor

44. Aerobic respiration 2 pyruvate molecules enter the mitochondrion
Pyruvate loses a CO2 molecule and becomes acetyl CoA
Krebs cycle produces 2 ATP, 4 CO2, 6 NADH and 3 FADH2
Electron transport chain produces 34 ATP and water
Aerobic respiration completely oxidises glucose
Anaerobic respiration does not completely oxidise glucose – ethanol, lactate and carbon dioxide are by-products

45. Get to know your mitochondrial structure!

47. Stages of aerobic respiration
The ‘link’ reaction
The Krebs cycle
The electron transport chain
Chemiosmosis and oxidative phosphorylation

48. The Link Reaction After glycolysis, when there is ample oxygen…
Steps 2 in aerobic respiration (step 1 is glycolysis in the cytoplasm)
After glycolysis, when there is ample oxygen…
2 pyruvate molecules from glycolysis move into the matrix of the mitochondrion for the Link reaction and the Krebs cycle

49. Matrix – Link Reaction 2
Krebs Cycle 2

50. The Link reaction
The link reaction converts pyruvate (3C) into acetyl Coenzyme A (2C), producing carbon dioxide and NADH in the process

51. The Krebs Cycle (Citric Acid/TCA cycle)
Krebs: The walk-through...
Krebs: the movie…
The 2C acetyl Coenzyme A enters the Krebs cycle
It joins oxaloacetate (4C) to form citrate (6C).
Two carbon atoms are then lost as carbon dioxide and the cycle repeats.
Hydrogen is released during this cycle to reduce the coenzymes NAD+ and FAD to 3 NADH and 1 FADH2 for each cycle
ATP is also released

52. Krebs cycle turns TWICE for each molecule of glucose
Each molecule of glucose produces
2 pyruvates in glycolysis
Leading to 2 acetyl CoA molecules in the link reaction

53. Fill in your table! Substance Oxidised/Reduced/Neither Reason NAD+
NADH
FADH2
FAD

54. How did you do? Substance Oxidised/Reduced/Neither Reason NAD+ NADH
FADH2
FAD
oxidised
reduced
neither
+ve due to lost electron
gained H from organic molecule
no loss/gain of H/electrons

55. Production PER glucose molecule
Glycolysis: 2 ATP, 2 NADH, 2 pyruvate
Link: 2 NADH, CO2
Krebs : 2 ATP, 6 NADH, 2 FADH2, 2 CO2
Overall: 4 ATP, 10 NADH, 2 FADH2

56. and finally….
The electron transport chain, chemiosmosis and oxidative phosphorylation

57. The movie…

58. Chemiosmosis in the mitochondrion
Protein complex
Intermembrane space
Electron carrier
Inner mitochondrial membrane
Electron flow
Mitochondrial matrix
ELECTRON TRANSPORT CHAIN
ATP SYNTHASE

59. Poisons interrupt critical events in cellular respiration
Rotenone
Cyanide, carbon monoxide
Oligomycin
ELECTRON TRANSPORT CHAIN
ATP SYNTHASE

60. Chemiosmosis powers most ATP production
The electrons from NADH and FADH2 travel down the electron transport chain to oxygen
Energy released by the electrons is used to pump H+ (protons) into the space between the mitochondrial membranes
In chemiosmosis, the H+ ions diffuse back through the inner membrane through ATP synthase, which capture the energy to make ATP

61. Questions…
What is the role and the position of oxygen in the electron transport chain?
What is the benefit of having cristae in the mitochondria?

62. ELECTRON TRANSPORT CHAIN
Chemiosmosis/ ETC occurs on the inner membrane of the mitochondria
Protein complex
Intermembrane space
Electron carrier
Inner mitochondrial membrane
Electron flow
Mitochondrial matrix
ELECTRON TRANSPORT CHAIN
ATP SYNTHASE
Figure 6.12

63. Final checks and balances
Process
ATP used
ATP produced
Net ATP gain
Glycolysis
Krebs cycle
Electron Transport Chain/ Chemiosmosis
Total

64. Final checks and balances
Process
ATP used
ATP produced
Net ATP gain
Glycolysis 2 4
Krebs cycle
Electron Transport Chain/ Chemiosmosis 32
Total 38 36

65. Review of mitochondrial structure and function
Outer mitochondrial membrane
Matrix
Cristae
Inner mitochondrial membrane
Space between inner and outer membranes

66. Review of mitochondrial structure and function
Outer mitochondrial membrane
Separates contents of mitochondrion from rest of cell
Matrix
Like cytoplasm: enzymes for the Link reaction and the Krebs cycle
Cristae
Increases surface area for oxidative photophosphorylation
Inner mitochondrial membrane
Carriers for electron transport chain and ATP synthase and
Space between inner and outer membranes
Reservoir for protons (H+ ions) to create concentration gradient

67. ELECTRON TRANSPORT CHAIN AND CHEMIOSMOSIS
For each glucose molecule that enters cellular respiration, respiration produces up to 38 ATP molecules
Cytoplasmic fluid
Mitochondrion
Electron shuttle across membranes
KREBS CYCLE
GLYCOLYSIS
2 Acetyl CoA
2 Pyruvic acid
KREBS CYCLE
ELECTRON TRANSPORT CHAIN AND CHEMIOSMOSIS
Glucose
by substrate-level phosphorylation
used for shuttling electrons from NADH made in glycolysis
by substrate-level phosphorylation
by chemiosmotic phosphorylation
Maximum per glucose:

68. Some practice questions on respiration…
1. How do cells capture the energy released by cell respiration? A. They store it in molecules of carbon dioxide. B. They produce glucose. C. The energy is released as pyruvate. D. They produce ATP. (Total 1 mark)

69. Some practice questions on respiration…
2. Which process produces the most ATP per molecule of glucose? A. Anaerobic respiration in a yeast cell B. Aerobic respiration in a bacterial cell C. Glycolysis in a human liver cell D. The formation of lactic acid in a human muscle cell (Total 1 mark)

70. Some practice questions on respiration…
3. Which of the following is the best definition of cell respiration? A. A process needed to use energy, in the form of ATP, to produce organic compounds B. A process used to provide oxygen to the atmosphere C. A controlled release of energy, in the form of ATP, from organic compounds in cells D. A controlled release of energy in the production of food from organic compounds (Total 1 mark)

71. Some practice questions on respiration…
4. Which of the following processes produces CO2? I. Glycolysis II. Alcohol (ethanol) fermentation III. Lactic acid production A. I only B. II only C. I and II only D. I, II and III (Total 1 mark)

72. Some practice questions on respiration…
4. Which of the following processes produces CO2? I. Glycolysis II. Alcohol (ethanol) fermentation III. Lactic acid production A. I only B. II only C. I and II only D. I, II and III (Total 1 mark)

73. Some practice questions on respiration…
4. State a word equation for anaerobic cell respiration in humans. (1 mark)