Getting Energy to make ATP Section 9.3 Getting Energy to make ATP

Cellular Respiration The process by which mitochondria break down food molecules to produce ATP is called cellular respiration. The process is composed of three stages. Stage 1- glycolysis is anaerobic, does not need oxygen. Stage 2 and 3-the citric acid cycle, and the electron transport chain are aerobic, require oxygen.

Glycolysis Takes place in the cytoplasm of the cell. Breaks down glucose (6C) into 2 pyruvic acid (3C) molecules. 2 ATP used; 4 ATP produced NAD+ accepts e- s to produce NADH The pyruvic acid moves into the mitochondria.

GLYCOLYSIS

The Citric Acid Cycle Also called the Krebs cycle, is a series of chemical reactions similar to the Calvin Cycle. Sir Hans Adolf Krebs-German physician-1953 Nobel prize in physiology or medicine- for working out the details of these reactions.

The Citric Acid Cycle Pyruvic acid (3C) gives off CO2 and combines with Coenzyme A to form Acetyl-CoA (2C). This reaction produces a molecule of NADH and H+.

The Citric Acid Cycle In the Krebs cycle the last molecule produced is needed for the first reaction For each turn of the cycle, one molecule of ATP, and two molecules of carbon dioxide are produced. Because glucose produces 2 Acetyl-CoA, each glucose produces 2 ATP.

The Citric Acid Cycle Each electron carrier, NADH+ and FADH2, pass two energized electrons along to the inner membrane of the mitochondria for the last stage of cellular respiration

The Electron Transport Chain ETC in inner membrane of mitochondria, similar to ETC in thylakoid membrane of chloroplast. NADH and FADH2 deliver energized electrons to the top of the chain. Electrons pass from protein to protein slowly giving off energy. Some of the energy is used to form ATP.

The Electron Transport Chain The last electron acceptor in the ETC is oxygen. H+ ions combine with oxygen to form water This is why oxygen is so important. With out oxygen electrons cannot move along the electron transport chain ATP production would stop.

Fermentation In the absence of oxygen, the Krebs cycle and the ETC will not function. During heavy exercise, muscle cells can be without oxygen for a short time. An anaerobic process called fermentation follows glycolysis. ATP production continues until oxygen is available again.

Fermentation Two types of fermentation Lactic acid fermentation. Under anaerobic conditions the ECT backs up because of the lack of oxygen as the final electron acceptor. NADH and FADH2 cannot release their electrons. With out NAD+ and FAD, the Krebs cycle and glycolysis shut down.

Fermentation FAD cannot be replaced under anaerobic conditions; but, NAD+ can be replaced through lactic acid fermentation. Two molecules of pyruvic acid from glycolysis use NADH to form two molecules of lactic acid. The NAD+ is released to be used in glycolysis allowing the production of two ATP molecules.

Fermentation Lactic acid builds up in muscles cells during strenuous exercise causing muscle fatigue and pain. It is transferred from the muscle cells to the liver and converted back to pyruvic acid.

Fermentation Alcoholic fermentation Yeast cells and some bacteria produce CO2 and ethyl alcohol. The process is used commercially in the wine and beer industry, and the baking industry.

Glycolysis (pyruvic acid) ATP Production Comparison of Fermentation to Cellular Respiration Lactic Acid Alcoholic Cellular Respiration Glucose ↓ Glycolysis (pyruvic acid) Lactic acid + 2ATP Glycolysis (pyruvic acid) Carbon dioxide Ethyl Alcohol ( pyruvic acid) Water 36 ATP

Comparing Photosynthesis to Cellular Respiration The production and breakdown of food molecules are processes with certain similarities. Both use electron carriers and a cycle of chemical reactions to produce ATP Both use ETC to produce ATP and create a concentration gradient of H+ ions. The H+ ion are used to form ATP by chemiosis.

Contrasting Photosynthesis and Cellular Respiration Photosynthesis produces high energy carbohydrates and oxygen. Cellular respiration uses oxygen to break down carbohydrates to form ATP. An end product of cellular respiration is the start of photosynthesis, CO2

Photosynthesis vs Cellular Respiration Food is made or accumulated Food is Broken down Energy from sun is stored as glucose Energy from glucose is released to be used by body Carbon dioxide (CO2) is taken in CO2 is given off as a waste product Oxygen (O2) is given off as waste Oxygen is needed and is taken in Produces glucose Produces CO2 and H2O as waste Can happen only when some light is available Can occur all day and all night Requires Chlorophyll, can only happen in plants Occurs in all living cells - plants and animals

Summary Cellular Respiration uses the products of photosynthesis to make ATP for energy. Its’ reaction is the opposite of photosynthesis: 6 O2 + C6H12O6  ATP (energy) + 6CO2 + 6H2O Respiration has 3 steps: 1) Glycolysis- each glucose results in 2 ATP 2) Citric Acid Cycle (Kreb’s Cycle) = 2 ATP 3) Electron Transport Chain = 32 ATP

Summary In the end, each molecule of glucose can produce 36 ATP through cellular respiration. When there is NOT enough Oxygen: 1) Lactic Acid Fermentation occurs, producing just 2 ATP per glucose molecule, as well as lactic acid that leads to painful muscle fatigue. 2) Alcoholic Fermentation occurs in some bacteria and yeast, producing CO2. We use this to produce alcoholic beverages and breads.