Cellular Respiration

Cellular Respiration Objectives: Summarize how glucose is broken down in the first stage of cellular respiration. Describe how ATP is made in the second stage of cellular respiration. Identify the role of fermentation in the second stage of cellular respiration. Evaluate the importance of oxygen in aerobic respiration.

How Cells Harvest Chemical Energy Introduction to Cell Metabolism Glycolysis Aerobic Cell Respiration Anaerobic Cell Respiration

Breathing and Cell Respiration are related CO2 Lungs Muscle cells carrying out CO2 Bloodstream O2 CELLULAR RESPIRATION Sugar + O2  ATP + CO2 + H2O

Cellular Respiration uses oxygen and glucose to produce Carbon dioxide, water, and ATP. Glucose Oxygen gas Carbon dioxide Water Energy

How efficient is cell respiration? Energy released from glucose banked in ATP Energy released from glucose (as heat and light) Gasoline energy converted to movement 100% About 40% 25% Burning glucose in an experiment “Burning” glucose in cellular respiration Burning gasoline in an auto engine

Reduction and Oxidation OILRIG Oxidation is losing electrons Reduction is gaining electrons Loss of hydrogen atoms Energy Glucose Gain of hydrogen atoms Glucose gives off energy and is oxidized

Reduction and Oxidation OILRIG Gain or loss of electrons is often in the form of hydrogen. The hydrogen is then passed to a coenzyme such as NAD+

Reduction and Oxidation What are some common co-enzymes? NAD+ and FAD NAD+ + 2 H  NADH + H+ FAD + 2 H  FADH2 Remember that H = 2 electrons and 2H+

Reduction and Oxidation These co-enzymes are very important for cell respiration because they transfer high-energy electrons to electron transport systems (ETS).

Reduction and Oxidation As the electrons move from carrier to carrier, energy is released in small quantities. Electron transport system (ETS)

Generation of ATP There are two ways to generate ATP Chemiosmosis Substrate-Level Phosphorylation

Generation of ATP Chemiosmosis Cells use the energy released by “falling” electrons in the ETS to pump H+ ions across a membrane Uses the enzyme ATP synthase.

Generation of ATP Chemiosmosis

Generation of ATP Substrate Level Phosphorylation Enzyme ATP can also be made by transferring phosphate groups from organic molecules to ADP Adenosine substrate Adenosine product Figure 6.7B

Glycolysis General Outline No Oxygen Anaerobic Oxygen Aerobic Glucose Glycolysis No Oxygen Anaerobic Oxygen Aerobic Pyruvic Acid Transition Reaction Fermentation Krebs Cycle ETS 36 ATP

Glycolysis Where? The cytosol What? Breaks down glucose to pyruvic acid

Glycolysis Energy In: 2 ATP Energy Out: 4 ATP NET 2 ATP Steps – A fuel molecule is energized, using ATP. Glucose 1 3 Step Glycolysis 1 Glucose-6-phosphate 2 Fructose-6-phosphate Energy In: 2 ATP 3 Fructose-1,6-diphosphate Step A six-carbon intermediate splits into two three-carbon intermediates. 4 4 Glyceraldehyde-3-phosphate (G3P) 5 Step A redox reaction generates NADH. 5 1,3-Diphosphoglyceric acid (2 molecules) 6 Steps – ATP and pyruvic acid are produced. 3-Phosphoglyceric acid (2 molecules) Energy Out: 4 ATP 6 9 7 2-Phosphoglyceric acid (2 molecules) 8 2-Phosphoglyceric acid (2 molecules) NET 2 ATP 9 Pyruvic acid (2 molecules per glucose molecule)

General Outline of Aerobic Respiration Glycolysis Transition Reaction Krebs Cycle Electron Transport System

Transition Reaction Each pyruvic acid molecule is broken down to form CO2 and a two-carbon acetyl group, which enters the Krebs cycle Pyruvic Acid Acetyl CoA

General Outline of Aerobic Respiration Glycolysis Transition Reaction Krebs Cycle Electron Transport System

Krebs Cycle Where? In the Mitochondria What? Uses Acetyl Co-A to generate ATP, NADH, FADH2, and CO2.

Krebs Cycle

Krebs Cycle

General Outline of Aerobic Respiration Glycolysis Krebs Cycle Electron Transport System

ELECTRON TRANSPORT CHAIN Electron Transport System Protein complex Intermembrane space Electron carrier Inner mitochondrial membrane Electron flow Mitochondrial matrix ELECTRON TRANSPORT CHAIN ATP SYNTHASE Figure 6.12

Electron Transport System

Electron Transport System For each glucose molecule that enters cellular respiration, chemiosmosis produces up to 38 ATP molecules

Overview of Aerobic Respiration

Fermentation Requires NADH generated by glycolysis. Where do you suppose these reactions take place? Yeast produce carbon dioxide and ethanol Muscle cells produce lactic acid Only a few ATP are produced per glucose

Fermentation

Fermentation in the Absence of Oxygen Fermentation When oxygen is not present, fermentation follows glycolysis, regenerating NAD+ needed for glycolysis to continue. Lactic Acid Fermentation In lactic acid fermentation, pyruvate is converted to lactate.

Each molecule of glucose can generate 36-38 molecules of ATP in aerobic respiration but only 2 ATP molecules in respiration without oxygen (through glycolysis and fermentation).