1. Cellular Respiration

2. Key Concepts we will cover today...  Respiration is the release of energy by combining oxygen with digested food (glucose).  Carbon dioxide and water are also produced as byproducts. They are the waste products of respiration.  Cellular respiration has two stages. First glucose is broken down to pyruvate during glycolysis, making some ATP.  The second stage involving the Krebs cycle is a series of reactions that produce energy-storing molecules during anaerobic respiration.  During aerobic respiration, large amounts of ATP are made in an electron transport chain.  When oxygen is not present, fermentation follows glycolysis, regenerating NAD+ needed for glycolysis to continue

3. Cellular Energy  Most of the foods we eat contain energy stored in proteins, carbohydrates, and fats.  Before our cells can use this energy it must be transferred to ATP within the cells.  Cells transfer the energy in organic compounds to ATP through a process called cellular respiration. Process cellular respiration

4. Cellular Energy Oxygen in the air you breath makes the production of ATP more efficient. Some ATP is made without this oxygen however. 1. Metabolic processes that require oxygen are called aerobic processes. 2. Metabolic processes that require NO oxygen are called anaerobic processes.

5. Cellular Energy: Respiration  The energy-producing process in living things is called respiration.  Respiration is the release of energy by combining oxygen with digested food (glucose).  Carbon dioxide and water are also produced as byproducts. They are the waste products of respiration.  A simple formula to show respiration looks like this: Glucose + oxygen  carbon dioxide (waste) + water (waste) + energy

6. Stages of Cellular Respiration  Cellular respiration is the process cells use to extract the energy in organic compounds, particularly glucose.  Cellular respiration occurs in three major stages Stage 1: glucose is converted to pyruvate producing a small amount of ATP and NADH Stage 2: Aerobic respiration occurs: this is when oxygen is present, pyruvate and NADH make more ATP. Stage 3: In an electron transfer chain, continuing reactions create a large amount of ATP from the materials from stage 2.

7. Stage 1: Breakdown of Glucose  The primary fuel for cellular respiration is glucose which is formed when carbohydrates such as starch and sucrose are broken down.  In the First stage of cellular respiration, glucose is broken down in the cytoplasm during a process called glycolysis.  Glycolysis is an enzyme-assisted anaerobic process that breaks down one six carbon molecule of glucose to two three-carbon pyruvate ions 1

8. Stage 1: Breakdown of Glucose: Glycolysis Glycolysis can be summarized in 4 steps Step 1: in a series of three reactions, phosphate groups from two ATP molecules are transferred to a glucose molecule

9. Stage 1: Breakdown of Glucose: Glycolysis Glycolysis can be summarized in 4 steps Step 2: In two reactions, the resulting six-carbon molecule is broken down to two three-carbon compounds, each with a phosphate group

10. Stage 1: Breakdown of Glucose: Glycolysis Glycolysis can be summarized in 4 steps Step 3: Two NADH molecules are produced, and one more phosphate group is transferred to each three-carbon compound.

11. Stage 1: Breakdown of Glucose: Glycolysis Glycolysis can be summarized in 4 steps Step 4: In a series of 4 reactions, each three carbon compound is converted to a three-carbon pyruvate, producing 4 ATP molecules in the process

12. Stage 1: Breakdown of Glucose: Glycolysis Summary : In this 4 step process: 1. Glycolysis uses two ATP molecules 2. but produces four ATP molecules in return. 3. Thus, we gain two ATP molecules for a gain ratio of 2 to 1.  Glycolysis is followed by another set of reactions that uses the energy temporarily stored in NADH to make more ATP.

13. Stage 2: Production of ATP  When oxygen is present, pyruvate produced during glycolysis enters a mitochondrion and is converted to a two-carbon compound.  This reaction produces one carbon dioxide molecule, one NADH molecule, and one two- carbon acetyl group  The acetyl group is attached to a molecule called coenzyme A forming a compound called acetyl-CoA.

14. Stage 2: Production of ATP  Acetyl-CoA enters a series of enzyme-assisted reactions called the Krebs Cycle.  The Krebs Cycle has several steps we will be breaking down.

15. Stage 2: Production of ATP Step 1: Acetyl-CoA combines with a 4 carbon compound, forming a six carbon compound and releasing “ coenzyme A”

16. Stage 2: Production of ATP Step 2:  Carbon Dioxide (CO 2 ) is released from the six- carbon compound, forming a five-carbon compound.  Electrons are transferred to NAD+, making a molecule of NADH.

17. Stage 2: Production of ATP Step 3:  Carbon dioxide is released from the five-carbon compound, resulting in a four-carbon compound.  A molecule of ATP is made, and a molecule of NADH is produced.

18. Stage 2: Production of ATP Step 4:  The existing four-carbon compound is then converted to a new four- carbon compound.  Electrons are transferred to an electron acceptor called FAD, making a molecule of FADH2.  FADH2 is another type of electron carrier.

19. Stage 2: Production of ATP  After the Krebs Cycle, NADH and FADH2 now contain much of the energy that was previously stored in glucose and pyruvate.  When the Krebs Cycle is completed, the four-carbon compound that began the cycle has been recycled, and acetyl-CoA can enter the cycle again.

20. Electron Transfer Chain  In aerobic respiration, electrons donated by NADH and FADH 2 pass through an electron transport chain.  Step 1: The electron transfer chain pumps hydrogen ions out of the inner compartment

21. Electron Transfer Chain  Step 2: At the end of the chain, electrons and hydrogen ions combine with oxygen, forming water (H 2 O).

22. Electron Transfer Chain  Step 3: ATP is produced as hydrogen ions diffuse into the inner compartment through a channel protein.

23. Electron Transfer Chain  Hydrogen ions diffuse back into the inner compartment through a carrier protein that adds a phosphate group to ADP, making ATP.  At the end of the electron chain, hydrogen ions and spent electrons combine with oxygen molecules (O 2 ) forming water molecules (H 2 0)

24. Respiration in the Absence of Oxygen  What happens when there is not enough oxygen for aerobic respiration to occur?  When oxygen is not present, NAD+ is recycled in another way  Under anaerobic conditions, electrons carried by NADH are transferred to pyruvate produced during glycolysis.  This process recycles NAD+ needed to continue making ATP through glycolysis.  This recycling of NAD+ using an organic hydrogen acceptor is called fermentation.

25. Respiration in the Absence of Oxygen  Two important types of fermentation are lactic acid fermentation and alcoholic fermentation.  Lactic acid fermentation by some prokaryotes and fungi is used in the production of foods such as yogurt and some cheeses.

26. Lactic Acid Fermentation  Lactate is the ion of an organic acid called lactic acid. For example, during exercise, pyruvate in muscles is converted to lactate when muscles must operate without enough oxygen.  Fermentation enables glycolysis to continue producing ATP in muscles as long as the glucose supply lasts. Blood removes excess lactate from muscles.  Lactate can build up in muscle cells if it is not removed quickly enough, sometimes causing muscle soreness.

27. Alcoholic Fermentation  Alcoholic fermentation is a two- step process.  First, pyruvate is converted to a two-carbon compound, releasing carbon dioxide.  Second, electrons are transferred from a molecule of NADH to the two-carbon compound, producing ethanol.

28. Alcoholic Fermentation  Alcoholic fermentation by yeast, a fungus, has been used in the preparation of many foods and beverages.  Wine and beer contain ethanol made during alcoholic fermentation by yeast.  Carbon dioxide released by the yeast causes the rising of bread dough and the carbonation of some alcoholic beverages, such as beer.  Ethanol is actually toxic to yeast. At a concentration of about 12%, ethanol kills yeast.  Thus, naturally fermented wine contains about 12% ethanol.

29. Production of ATP: Summary  The total amount of ATP that a cell is able to harvest from each glucose molecule that enters glycolysis depends on the presence or absence of oxygen.  Cells use energy most efficiently when oxygen is present.  In the first stage of cellular respiration, glucose is broken down to pyruvate during glycolysis. Glycolysis is an anaerobic process (no oxygen required), and it results in a gain of two ATP molecules.  In the second stage of cellular respiration, the pyruvate passes through either aerobic respiration (requires oxygen) or fermentation. When oxygen is not present, fermentation occurs instead.

30. Production of ATP: Summary  Most of a cell’s ATP is made during aerobic respiration. (requiring oxygen)  For each molecule of glucose that is broken down, as many as two ATP molecules are made directly during the Krebs cycle,  and up to 34 ATP molecules are produced later by the electron transport chain.

31. Key Concepts: Review...  Cellular respiration has two stages. First glucose is broken down to pyruvate during glycolysis, making some ATP.  The Krebs cycle is a series of reactions that produce energy- storing molecules during anaerobic respiration  During aerobic respiration, large amounts of ATP are made in an electron transport chain.  When oxygen is not present, fermentation follows glycolysis, regenerating NAD+ needed for glycolysis to continue

32. Computer Lab Activities  Go to the following Web-based activities and watch and complete both activities including the quiz at the end of the second site  video 1 cellular respiration video 1 cellular respiration  Aerobic respiration UK version Aerobic respiration UK version  Aerobic Respiration Aerobic Respiration