1. Section 1 Glycolysis and Fermentation
Chapter 7
Objectives
Identify the two major steps of cellular respiration.
Describe the major events in glycolysis.
Compare lactic acid fermentation with alcoholic fermentation.
Calculate the efficiency of glycolysis.

2. Harvesting Chemical Energy
Section 1 Glycolysis and Fermentation
Chapter 7
Harvesting Chemical Energy
Cellular respiration is the process by which cells break down organic compounds (food) to produce ATP (energy)
Organic compounds are needed to drive processes of cellular respiration just like gasoline is used to create energy to drive the processes for cars
Both autotrophs and heterotrophs use cellular respiration to make CO2 and water from organic compounds and O2.
The products of cellular respiration are the reactants in photosynthesis; conversely, the products of photosynthesis are reactants in cellular respiration.
Cellular respiration can be divided into two stages: first comes glycolysis and then aerobic respiration.

3. Overview of Cellular Respiration
Section 1 Glycolysis and Fermentation
Chapter 7
Overview of Cellular Respiration
Glycolysis is the process of converting organic compounds into three-carbon molecules of pyruvic acid, producing a small amount of ATP and NADH (electron carrier molecule)
Glycolysis is an anaerobic process because it doesn’t require the presence of oxygen
Aerobic Respiration takes place when oxygen is present in the cell’s environment, pyruvic acid is broken down and NADH is used to make a large amount of ATP
The following equation summarizes cellular respiration: C6H12O6 + 6O2 enzymes CO2 + 6H2O + energy (ATP)

4. Photosynthesis-Cellular Respiration Cycle
Section 1 Glycolysis and Fermentation
Chapter 7
Photosynthesis-Cellular Respiration Cycle

5. Section 1 Glycolysis and Fermentation
Chapter 7
Glycolysis
Cellular respiration begins with glycolysis, which takes place in the cytosol of cells.
During glycolysis, one six-carbon glucose molecule is oxidized to form two three-carbon pyruvic acid molecules.
A net yield of two ATP molecules is produced for every molecule of glucose that undergoes glycolysis.

6. Chapter 7 Glycolysis Section 1 Glycolysis and Fermentation
When glycolysis occurs a molecule of glucose is split, two molecules of pyruvic acid are made and some ATP is produced

7. Section 1 Glycolysis and Fermentation
Chapter 7
Fermentation
If oxygen is not present, some cells can convert pyruvic acid into other compounds through additional biochemical pathways that occur in the cytosol. The combination of glycolysis and these additional pathways is fermentation.
Fermentation does not produce ATP, but it does regenerate NAD+, which allows for the continued production of ATP through glycolysis.

8. Cellular Respiration Versus Fermentation
Section 1 Glycolysis and Fermentation
Chapter 7
Cellular Respiration Versus Fermentation

9. Fermentation, continued
Section 1 Glycolysis and Fermentation
Chapter 7
Fermentation, continued
Lactic Acid Fermentation
In lactic acid fermentation, an enzyme converts pyruvic acid into another three-carbon compound, called lactic acid.
When muscles are exercised excessively in the absence of sufficient oxygen, lactic acid is produced...this can cause cramping
When there is not enough oxygen, there will be excess or extra lactic acid present

10. Fermentation, continued
Section 1 Glycolysis and Fermentation
Chapter 7
Fermentation, continued
Alcoholic Fermentation
Some plants and unicellular organisms, such as yeast, use a process called alcoholic fermentation to convert pyruvic acid into ethyl alcohol and CO2.

11. Two Types of Fermentation
Section 1 Glycolysis and Fermentation
Chapter 7
Two Types of Fermentation
Some cells engage in lactic acid fermentation when oxygen is absent. In this process, pyruvic acid is reduced to lactic acid and NADH is oxidized to NAD+
Some cells engage in alcoholic fermentation, converting pyruvic acid into ethyl alcohol. Again, NADH is oxidized to NAD+
Figures 7-4 and 7-6
Pgs

12. Efficiency of Glycolysis
Section 1 Glycolysis and Fermentation
Chapter 7
Efficiency of Glycolysis
The minimum efficiency for glycolysis is about 2 percent
Much of the energy originally contained in glucose is still held in pyruvic acid.
Glycolysis alone or as part of fermentation is not very efficient at transferring energy from glucose to ATP.

13. Efficiency of Glycolysis cont.
Section 1 Glycolysis and Fermentation
Chapter 7
Efficiency of Glycolysis cont.
To figure efficiency of glycolysis use the following equation:
Eff. of glycolysis = Number of ATP molecules X Energy required to make ATP Energy released by oxidation of glucose X 100
Two ATP molecules are produced from every glucose molecule that is broken down by glycolysis – so when figuring this you need to take the energy required to make ATP and multiply it by 2
If the formation of a standard amount of ATP under certain conditions requires 12 kcal of energy and the complete oxidation of glucose yields 686 kcal of energy, how efficient is glycolysis at extracting energy from glucose?

14. Chapter 7 Objectives Section 2 Aerobic Respiration
Relate aerobic respiration to the structure of a mitochondrion.
Summarize the events of the Krebs cycle.
Summarize the events of the electron transport chain and chemiosmosis.
Calculate the efficiency of aerobic respiration.
Contrast the roles of glycolysis and aerobic respiration in cellular respiration.

15. Overview of Aerobic Respiration
Section 2 Aerobic Respiration
Chapter 7
Overview of Aerobic Respiration
In eukaryotic cells, the processes of aerobic respiration occur in the mitochondria. Aerobic respiration only occurs if oxygen is present in the cell.
REMEMBER: Cellular Respiration begins in the cell’s cytoplasm and ends in the mitochondria
The Krebs cycle occurs in the mitochondrial matrix. The electron transport chain (which is associated with chemiosmosis) is located in the inner membrane.

16. The Krebs Cycle Quick Overview
Section 2 Aerobic Respiration
Chapter 7
The Krebs Cycle Quick Overview
The Krebs Cycle is a biochemical pathway that breaks down acetyl CoA, producing CO2, hydrogen atoms, and ATP.
In the mitochondrial matrix, pyruvic acid produced in glycolysis reacts with coenzyme A to form acetyl CoA. Then, acetyl CoA enters the Krebs cycle.
One glucose molecule is completely broken down in two turns of the Krebs cycle. These two then produce four CO2 molecules, two ATP molecules, and hydrogen atoms that are used to make six NADH and two FADH2 molecules.
The bulk of the energy released by the oxidation of glucose still has not been transferred to ATP.

17. Chapter 7 The Krebs Cycle cont. Follow steps in your book, pgs 138-139
Section 2 Aerobic Respiration
Chapter 7
The Krebs Cycle cont.
Follow steps in your book, pgs
In step 1, a two-carbon molecule of acetyl CoA combines with a four-carbon compound, oxaloacetic acid, to produce a six-carbon compound, citric acid
In step 2, citric acid releases a CO2 molecule and a hydrogen atom to form a five-carbon compound. The loss of the hydrogen atom with its electron causes citric acid to become oxidized. NAD+ becomes NADH.
In step 3, the five-carbon compound formed in step 2 also releases a CO2 molecule and a hydrogen atom, forming a four-carbon compound, NAD+ is reduced to NADH, and a molecule of ATP is synthesized from ADP.

18. Chapter 7 The Krebs Cycle cont. Follow steps in your book, pgs 138-139
Section 2 Aerobic Respiration
Chapter 7
The Krebs Cycle cont.
Follow steps in your book, pgs
In step 4, the four-carbon compound formed in step 3 releases a hydrogen atom to form another four-carbon compound. In this step, the hydrogen atom is used to reduce FAD to FADH2
FAD is very similar to NAD+, FAD accepts electrons during redox reactions
In step 5, the four-carbon compound formed in step 4 releases a hydrogen atom to regenerate oxaloacetic acid, which keeps the Krebs cycle operating. The electron in the hydrogen atom reduces NAD+ to NADH.

20. Electron Transport Chain and Chemiosmosis
Section 2 Aerobic Respiration
Chapter 7
Electron Transport Chain and Chemiosmosis
High-energy electrons in hydrogen atoms from NADH and FADH2 are passed from molecule to molecule in the electron transport chain along the inner mitochondrial membrane.
Electron transport and chemiosmosis take place along the inner mitochondrial membrane and involve five steps
Figure 7-11, Page 140

21. Electron Transport Chain and Chemiosmosis, continued
Section 2 Aerobic Respiration
Chapter 7
Electron Transport Chain and Chemiosmosis, continued
Protons (hydrogen ions, H+) are also given up by NADH and FADH2.
As the electrons move through the electron transport chain, they lose energy. This energy is used to pump protons from the matrix into the space between the inner and outer mitochondrial membranes.
The resulting high concentration of protons creates a concentration gradient of protons and a charge gradient across the inner membrane.

22. Electron Transport Chain and Chemiosmosis, continued
Section 2 Aerobic Respiration
Chapter 7
Electron Transport Chain and Chemiosmosis, continued
As protons move through ATP synthase and down their concentration and electrical gradients, ATP is produced. Oxygen combines with the electrons and protons to form water.

23. Electron Transport Chain and Chemiosmosis,
Section 2 Aerobic Respiration
Chapter 7
Electron Transport Chain and Chemiosmosis,
The Importance of Oxygen
ATP can be synthesized by chemiosmosis only if electrons continue to move along the electron transport chain.
By accepting electrons from the last molecule in the electron transport chain, oxygen allows additional electrons to pass along the chain.
As a result, ATP can continue to be made through chemiosmosis.
With oxygen present, the Krebs cycle and the electron transport chain provide organisms an alternative to glycolysis, produce most of the ATP needed for life, and break down glucose to produce carbon dioxide, water, and ATP.

24. Efficiency of Cellular Respiration
Section 2 Aerobic Respiration
Chapter 7
Efficiency of Cellular Respiration
Cellular respiration can produce up to 38 ATP molecules from the oxidation of a single molecule of glucose. Most eukaryotic cells produce about 36 ATP molecules per molecule of glucose.
Thus, aerobic respiration is nearly 20 times more efficient than glycolysis alone.

25. Efficiency of Cellular Respiration
Section 2 Aerobic Respiration
Chapter 7
Efficiency of Cellular Respiration
To figure efficiency of cellular respiration use the following equation:
Eff. of cellular respiration = Number of ATP molecules X Energy required to make ATP Energy released by oxidation of glucose X 100
Minimum energy to make ATP is 7kcal (if not given to you this is the amount you use)
If a cell generates 32 ATP molecules and uses 686 kcal of energy released by the oxidation of glucose how efficient is cellular respiration?

26. A Summary of Cellular Respiration
Section 2 Aerobic Respiration
Chapter 7
A Summary of Cellular Respiration
Cellular respiration occurs in two stages
Glycolysis – glucose is converted into pyruvic acid, producing a small amount of ATP and NADH, oxygen is not needed
Aerobic respiration – pyruvic acid is converted to CO2 and water in the presence of oxygen, producing a large amount of ATP
In cellular respiration, most energy is transferred during the electron transport chain

27. A Summary of Cellular Respiration cont.
Section 2 Aerobic Respiration
Chapter 7
A Summary of Cellular Respiration cont.
Another Role of Cellular Respiration
Providing cells with ATP is not the only important function of cellular respiration.
Molecules formed at different steps in glycolysis and the Krebs cycle are often used by cells to make compounds that are missing in food.

28. Summary of Cellular Respiration
Section 2 Aerobic Respiration
Chapter 7
Summary of Cellular Respiration
Looking at this diagram we can see the steps of cellular respiration. Look closely at the top dealing with the breakdown of different molecules to create ATP. When living cells break down molecules, energy is stored as ATP, but it also releases some heat.
The book gives the example (pg 143) that an automobile is only about 25 percent efficient at extracting energy from gasoline, most of the 75% that is left is lost as heat.