Releasing Chemical Energy Ø Energy From Carbohydrates Ø Aerobic Respiration/ Stages Ø Fermentation Ø Food as a Source of Energy
How Do Cells Access the Chemical Energy in Carbohydrayes?
Aerobic Respiration Ø Oxygen is required Ø About 36 ATP are produced per glucose molecule Ø Takes place in the mitochondria
Fermentation Ø No oxygen is required Ø 2 ATP per glucose molecule Ø Common in bacteria and in some eukaryotic cells
Aerobic Cellular Respiration Main energy-releasing pathway in nearly all eukaryotes
ENERGY CO 2 H 2 O O 2 sugars ENERGY Cycling of carbon, hydrogen and oxygen through living organisms
Cellular Respiration Takes Place in the Mitochondria of Eukaryotic Cells
Stages of Cellular Respiration
How Is ATP Formed? ATP is made from ADP in two different processes: Ø Substrate level phosphorylation: An enzyme transfers a phosphate group from a substrate to ADP Ø Oxidative phosphorylation: Metabolic pathway that uses energy released by the oxidation of nutrients to produce ATP
First Stage: Glycolysis/ Cytoplasm Glucose (6C) is broken into two molecules of Pyruvate (3C) 2 ATP are required 2 NADH, 4 ATP are produced per glucose ATP produced by substrate-level phosphorylation No oxygen is required
Figure 7-2 p117
The second stage of aerobic respiration occurs after pyruvate molecules diffuse into the mitochondria/ Matrix Includes two sets of reactions: Ø Acetyl CoA formation Ø The Krebs cycle
Acetyl-CoA Formation Ø One carbon splits from pyruvate and diffuses out of the cell as CO 2 Ø NAD + is reduced to NADH Ø Remaining two carbon fragment: acetyl group (-COHCH 3 ) Ø Coenzyme A joins the acetyl group to form acetyl CoA
Citric Acid Cycle/ Kreb s Cycle ➊ A pyruvate molecule is split into a two-carbon acetyl group and CO 2, releasing electrons and a hydrogen ion that are transferred to NAD +, so NADH forms. The acetyl group is transferred to coenzyme A, so acetyl CoA forms, and the CO 2 leaves the cell. coenzyme A pyruvate NADH CO 2 ➋ The citric acid cycle starts as two carbon atoms are transferred from acetyl CoA to oxaloacetate, a fourcarbon molecule. Coenzyme A is regenerated, and citrate, a six-carbon molecule, forms. citrate ➌ Electrons and a hydrogen ion are transferred from an intermediate to NAD +, so NADH forms. Oxidizing the intermediate causes it to lose a carbon atom that leaves the cell in CO 2. NADH CO 2 coenzyme A acetyl CoA CITRIC ACID CYCLE ➑ The product of the final redox reaction is oxaloacetate. oxaloacetate NADH ➐ Electrons and a hydrogen ion are transferred from an intermediate to NAD +, so NADH forms. FADH 2 ➍ A carbon atom is removed from an intermediate, releasing electrons and a hydrogen ion that are transferred to NAD +, so NADH forms. The carbon atom leaves the cell in CO 2. Pyruvate s three carbon atoms have now exited the cell, in CO 2. NADH CO 2 ADP + P i ATP ➏ Electrons and hydrogen atoms are transferred from an intermediate to the coenzyme FAD, which thereby becomes reduced to FADH 2. ➎ One ATP forms by substrate-level phosphorylation.
Citric Acid Cycle/ Kreb s Cycle Ø 2 molecules of acetyl-coa are generated from one glucose Ø Per Acetyl-CoA 2 C removed as CO 2 3 NAD + reduced to NADH, 1 FAD* reduced to FADH 2 1 ATP (substrate level phosphorylation) * Flavin Adenine dinucleotide Ø Total per glucose return: 2 ATP, 6 NADH, 2 FADH 2, 4 CO 2
Third Stage: Oxidative Phosphorylation Process responsible for most ATP production Takes place in the inner membrane of the mitochondria Relies on the electron transport chain and chemiosmosis
Electron Transfer Phosphorylation
Ø The final acceptor of electrons is oxygen Ø Oxygen combines with the electrons and hydrogen ions at the end of the electron transfer chain to form water Ø About 32-34 ATP molecules are formed by oxidative phosphorylation
At what stage(s) is CO 2 released? At what stage(s) is H 2 O produced? At what stage(s) are ATP molecules produced?
Fermentation A way of harvesting energy without oxygen Occurs in the cytoplasm Relies on glycolysis: 2 ATP, 2 NADH Provides an anaerobic way to recycle NADH into NAD + / without which glycolysis would stop
Alcohol Fermentation
Yeast uses alcohol fermentation Making beer, wine and bread
Lactic Acid Fermentation
Some fungi and bacteria (Lactobacillus) use lactic acid fermentation Cheese, yoghurt and buttermilk making
It is not just about Glucose