1. Obtaining Energy from Food
Cellular Respiration
Obtaining Energy from Food

2. Role of ATP in linking anabolic and catabolic reactions

3. Energy can be transported by Electron carriers NADH & FADH2.

4. Four Stages of Cellular Respiration
Glycolysis: Enzymes break a 6-carbon molecule of glucose into two 3-carbon molecules of pyruvate. Some ATP is synthesized by substrate-level phosphorylation.
substrate-level phosphorylation: an enzyme-catalyzed reaction that transfers a phosphate group from a substrate to ADP.
Pyruvate Oxidation: Enzymes convert the 3-carbon pyruvate into a 2-carbon acetyl group.
Citric Acid Cycle: which enters the citric acid cycle and is completely oxidized to carbon dioxide. Some ATP is synthesized during the citric acid cycle.
Electron Transfer Chain: High-energy electrons are delivered to oxygen by a sequence of electron carriers in the electron transfer system
Free energy released by electron flow generates an H+ gradient by chemiosmosis.
ATP synthase uses the H+ gradient as the energy source to make ATP.

5. Road Map

6. Glycolysis Occurs in the cytosol Is anaerobic (does not use oxygen)
No CO2 released
Requires 2 ATP activation energy
4 ATP are produced (net gain = 2ATP)
2 (electron) NADH are formed
2 pyruvate produced

7. Glycolysis

8. 10 Steps in Glycolysis
Figure 8.7: Reactions of glycolysis, which occur in the cytosol.
Because two molecules of G3P are produced in reaction 5, all the reactions from 6 to 10 are doubled (not shown). The names of the enzymes that catalyze each reaction are in rust.

9. Pyruvate Oxidation and the Citric Acid Cycle
Active transport moves pyruvate into the mitochondrial matrix where pyruvate oxidation and the citric acid cycle take place
Oxidation of pyruvate generates CO2, acetyl-coenzyme A (acetyl-CoA), and NADH
The acetyl group of acetyl-CoA enters the citric acid cycle

10. Reactions of Pyruvate Oxidation

11. Mitochondria Structure found inside all eukaryotes
Contains a membrane within a membrane
Site of Citric Acid Cycle (inner matrix) and oxidative phosphorylation (inner membrane)
The eight reactions of the citric acid cycle (tricarboxylic acid cycle or Krebs cycle) oxidize acetyl groups completely to CO2 , generate 3 NADH and 1 FADH2, and synthesize 1 ATP by substrate-level phosphorylation.

12. Citric Acid Cycle (Krebs Cycle)
Oxaloacetate (4C) 1 8
Citrate (6C)
Citrate synthase
Malate dehydrogenase
Malate (4C) 2
Aconitase
Fumarase
Isocitrate (6C) 7
Citric Acid Cycle (Krebs Cycle)
Fumarate (4C)
Isocitrate dehydrogenase 3
Succinate dehydrogenase
α -Ketoglutarate dehydrogenase
Succinyl–CoA synthetase 6
Succinate (4C)
α -Ketoglutarate (5C) 5 4
Succinyl–CoA (4C)

13. Citric Acid Cycle

14. Inside the Mitochondria
Pyruvic acid is converted to Acetyl CoA
1 CO2 released
Electrons transferred to NADH
Acetyl CoA enters Citric Acid Cycle
2 CO2 molecules are released (from each Acetyl CoA)
1 ATP molecule is generated
Electrons transferred to 3 NADH and 1 FADH2

15. Electron Transport Chain
NADH and FADH2 carry electrons to Electron Transport Chain.
E.T.C. moves protons into space between inner and outer membrane
Build up of protons causes high ion gradient.
Oxygen picks up electrons and forms water

16. High to Low Free Energy

17. ATP synthase Complex III Complex I Complex IV
Cytosol
Outer mitochondrial membrane
Intermembrane compartment
ATP synthase
Stator
Basal unit
Inner mitochondrial membrane
Complex III
Stalk
Complex I
Complex IV
Head-piece
Complex II
Mitochondrial matrix
Oxidative phosphorylation

18. Making ATP Protons packed between inner and outer membranes
Protons move into inner matrix through protein channels (ATP synthase)
The H+ gradient powers ATP synthesis by ATP synthase by chemiosmosis
ATP synthase binds ADP with Pi

19. Total Energy - summary Where Steps ATP NADH FADH2 Cytosol
1. Glycolysis
2 (net gain) 2 -
Mitochondria
2. Pyruvate Oxidation
3. Krebs Cycle
2 (1 in each cycle)
6 (3 in each cycle)
Total 4
10 = 30 (10x3)
2 = 4 ( 2X2)
Oxidative Phosphorylation
Substrate level phosphorylation
The total number of ATP produced from one Glucose molecule is 38. In some cases, NADH are produced in the cytosol during glycolysis, resulting in 2 ATP per NADH rather than 3. So the total ATP in those cases would be 34 instead of 38
Note: about 3 ATP per NADH and 2 ATP per FADH2 molecules are produced

20. Anaerobic Respiration (no oxygen)
Without Oxygen the E.T.C. cannot function
Citric Acid Cycle shuts down
Pyruvate is still produced from glycolysis
So what do we do with pyruvic acid?

21. Fermentation
When oxygen is absent or limited, electrons carried by the 2 NADH produced by glycolysis may be used in fermentation
fermentation
Electrons carried by NADH are transferred to an organic acceptor molecule (converts NADH to NAD+)
Glycolysis continues to supply ATP by substrate-level phosphorylation
Lactate fermentation
Converts pyruvate into lactate
Occurs in some bacteria, plant tissues, skeletal muscle
Used to make buttermilk, yogurt, dill pickles
Alcoholic fermentation
Converts pyruvate into ethyl alcohol and CO2
Occurs in some plant tissues, invertebrates, protists, bacteria, and single-celled fungi such as yeasts
Used to make bread and alcoholic beverages

22. A. Lactate fermentation
Glucose
Glycolysis
Pyruvate
Lactate

23. B. Alcoholic fermentation
Glucose
Glycolysis
Pyruvate
Acetaldehyde
Ethyl alcohol

24. The Versatility of Cellular Respiration

25. Lipid Metabolism Lipid molecules contain carbon, hydrogen, and oxygen
In different proportions than carbohydrates
Triglycerides are the most abundant lipid in the body
Lipid Catabolism (also called lipolysis)
Breaks lipids down into pieces that can be
Converted to pyruvic acid
Channeled directly into TCA cycle
Hydrolysis splits triglyceride into component parts
One molecule of glycerol
Three fatty acid molecules

26. Lipid Metabolism Lipid Catabolism
Enzymes in cytosol convert glycerol to pyruvic acid
Pyruvic acid enters TCA cycle
Different enzymes convert fatty acids to acetyl-CoA (beta-oxidation)

27. Lipid Metabolism Beta-Oxidation A series of reactions
Breaks fatty acid molecules into 2-carbon fragments
Occurs inside mitochondria
Each step
Generates molecules of acetyl-CoA and NADH
Leaves a shorter carbon chain bound to coenzyme A

28. Lipid Metabolism

29. Lipid Metabolism Lipids and Energy Production
For each 2-carbon fragment removed from fatty acid, cell gains:
12 ATP from acetyl-CoA in TCA cycle
5 ATP from NADH
Cell can gain 144 ATP molecules from breakdown of one 18-carbon fatty acid molecule
Fatty acid breakdown yields about 1.5 times the energy of glucose breakdown

30. Lipid Metabolism Free Fatty Acids (FFAs) Are lipids
Can diffuse easily across plasma membranes
In blood, are generally bound to albumin (most abundant plasma protein)
Sources of FFAs in blood
Fatty acids not used in synthesis of triglycerides diffuse out of intestinal epithelium into blood
Fatty acids diffuse out of lipid stores (in liver and adipose tissue) when triglycerides are broken down

31. Protein Metabolism Amino Acid Catabolism
Removal of amino group by transamination or deamination

32. Protein Metabolism Transamination Attaches amino group of amino acid
To keto acid
Converts keto acid into amino acid
That leaves mitochondrion and enters cytosol
Available for protein synthesis

33. Protein Metabolism Deamination
Prepares amino acid for breakdown in TCA cycle
Removes amino group and hydrogen atom
Reaction generates ammonium ion

34. Protein Metabolism Ammonium Ions
Are highly toxic, even in low concentrations
Liver cells (primary sites of deamination) have enzymes that use ammonium ions to synthesize urea (water-soluble compound excreted in urine)

35. Protein Metabolism

36. Protein Metabolism Proteins and ATP Production
When glucose and lipid reserves are inadequate, liver cells
Break down internal proteins
Absorb additional amino acids from blood
Amino acids are deaminated
Carbon chains broken down to provide ATP

37. Protein Metabolism Three Factors Against Protein Catabolism
Proteins are more difficult to break apart than complex carbohydrates or lipids
A byproduct, ammonium ion, is toxic to cells
Proteins form the most important structural and functional components of cells