How Cells Harvest Chemical Energy

Transcription

1 Chapter 6 How Cells Harvest Chemical Energy INTRODUCTION TO CELLULAR RESIRATION hotosynthesis and cellular respiration provide energy for life Cellular respiration makes and consumes O During the oxidation of glucose to CO and H O Birgit Woelker, hd hotosynthesis uses solar energy to produce glucose and O from CO and H O ECOSYSTEM Sunlight energy Breathing supplies oxygen to our cells and removes carbon dioxide CO hotosynthesis in chloroplasts Breathing provides for the exchange of O and CO Between an organism and its environment +! +! H O O O CO Breathing Cellular respiration in mitochondria Cellular respiration makes and consumes O during the oxidation of glucose to CO and H O (for cellular work) CO Lungs Bloodstream O Muscle cells carrying out Cellular Respiratin Heat energy + O CO + H O +

2 Cellular respiration banks energy in molecules Cellular respiration breaks down glucose molecules The human body uses energy from for all its activities powers almost all cellular and body activities And banks their energy in C 6 H O O 6 CO + 6 H O + s Oxygen gas Carbon dioxide Water Energy Figure 6.3 Table 6.4 Cells tap energy from electrons falling from organic fuels to oxygen Electrons lose potential energy passes electrons to an electron transport chain As electrons fall from carrier to carrier and finally to O Energy is released in small quantities During their transfer from organic compounds to oxygen Energy released and available for making! O H O

3 When glucose is converted to carbon dioxide It loses hydrogen atoms, which are added to oxygen, producing water Dehydrogenase removes electrons (in hydrogen atoms) from fuel molecules (oxidation) And transfers them to (reduction) Loss of hydrogen atoms (oxidation) Oxidation H O H O + H Dehydrogenase C 6 H O O 6 CO + 6 H O + Energy Gain of hydrogen atoms (reduction) () + H Reduction NAD!! + e! (carries electrons) Figure 6.5A Figure 6.5B Cellular respiration occurs in three main stages yruvate High-energy electrons carried by CITRIC ACID CYCLE FADH and OXIDATIVE HOSHORYLATION (Electron Transport and Chemiosmosis) Stage : Glycolysis Occurs in the cytoplasm Breaks down glucose into pyruvate, producing a small amount of Cytoplasm Mitochondrion Substrate-level CO CO Substrate-level Oxidative

4 Stage : The citric acid cycle Takes place in the mitochondria Completes the breakdown of glucose, producing a small amount of Supplies the third stage of cellular respiration with electrons Stage 3: Oxidative Occurs in the mitochondria Uses the energy released by falling electrons to pump across a membrane Harnesses the energy of the gradient through chemiosmosis, producing Glycolysis harvests chemical energy by oxidizing glucose to pyruvate In glycolysis, is used to prime a glucose molecule Which is split into two molecules of pyruvate Glycolysis produces by substrate-level In which a phosphate group is transferred from an organic molecule to AD Enzyme + Adenosine Figure 6.7A AD + yruvate Figure 6.7B Organic molecule (substrate) AD

5 In the first phase of glycolysis is used to energize a glucose molecule, which is then split in two Steps 3 A fuel molecule is energized, using. AD Step -6-phosphate REARATORY HASE (energy investment) In the second phase of glycolysis,, and pyruvate are formed Step 5 A redox reaction generates. 6 9 Steps and pyruvate 6 9 are produced. AD ,3 -Diphosphoglycerate 6 AD Glyceraldehyde-3-phosphate (G3) ENERGY AYOFF HASE 3 -hosphoglycerate Fructose-6-phosphate 8 8 -hosphoglycerate Step 4 A six-carbon intermediate splits into two three-carbon intermediates. AD 3 4 Fructose-,6-diphosphate H O AD 8 8 H O hosphoenolpyruvate 9 AD (E) Figure 6.7C Figure 6.7C yruvate yruvate is chemically groomed for the citric acid cycle rior to the citric acid cycle Enzymes process pyruvate, releasing CO and producing and acetyl The citric acid cycle completes the oxidation of organic fuel, generating many and FADH molecules In the citric acid cycle The two-carbon acetyl part of acetyl is oxidized Acetyl NAD! yruvate 3 Acetyl (acetyl coenzyme A) FADH CITRIC ACID CYCLE CO 3 Figure 6.8 CO Coenzyme A Figure 6.9A FAD AD + 3 +! 3

6 and Steps and For each turn of the cycle Two CO molecules are released The energy yield is one, three, and one FADH Most production occurs by oxidative Electrons from and FADH Oxaloacetate Acetyl carbons enter cycle Citrate Travel down the electron transport chain to oxygen, which picks up to form water NAD! CITRIC ACID CYCLE CO leaves cycle Energy released by the redox reactions Malate FADH FAD AD +! NAD! Alpha-ketoglutarate CO leaves cycle Is used to pump into the space between the mitochondrial membranes Succinate NAD! Step Steps Figure 6.9B Acetyl stokes the furnace.,, and CO are generated during redox reactions. Redox reactions generate FADH and. In chemiosmosis, the diffuses back through the inner membrane through synthase complexes. Intermembrane space Driving the synthesis of rotein complex Electron carrier synthase Certain poisons interrupt critical events in cellular respiration Various poisons Block the movement of electrons Block the flow of through synthase Allow to leak through the membrane Rotenone Cyanide, carbon monoxide Oligomycin Inner mitochondrial membrane Q + Cyt c H+ Synthase Electron flow FADH FAD O + DN Mitochondrial matrix H O AD + FADH FAD O +! Electron Transport Chain Chemiosmosis Figure 6. H O AD +! OXIDATIVE HOSHORYLATION Electron Transport Chain Chemiosmosis Figure 6.0

7 Each molecule of glucose yields ~38 molecules of Fermentation is an anaerobic alternative to cellular respiration Electron shuttle across membrane Mitochondrion Under anaerobic conditions, many kinds of cells Cytoplasm yruvate Acetyl (or FADH ) CITRIC ACID CYCLE 6 FADH OXIDATIVE HOSHORYLATION (Electron Transport and Chemiosmosis) Can use glycolysis alone to produce small amounts of about 34 by substrate-level by substrate-level by oxidative Maximum per glucose: About 38 In lactic acid fermentation is oxidized to as pyruvate is reduced to lactate In alcohol fermentation is oxidized to while converting pyruvate to CO and ethanol AD + yruvate Lactate AD + CO released yruvate Ethanol

8 INTERCONNECTIONS BETWEEN MOLECULAR BREAKDOWN AND SYNTHESIS Cells use many kinds of organic molecules as fuel for cellular respiration Cells use many kinds of organic molecules as fuel for cellular respiration Food, such as peanuts Carbohydrates, fats, and proteins can be converted to molecules that enter glycolysis or the citric acid cycle Carbohydrates Fats roteins Sugars Glycerol Fatty acids Amino acids G3 yruvate Acetyl CITRIC ACID CYCLE Amino groups OXIDATIVE HOSHORYLATION (Electron Transport and Chemiosmosis) Food molecules provide raw materials for biosynthesis needed to drive biosynthesis Cells use some food molecules and intermediates from glycolysis and the citric acid cycle as raw materials This process of biosynthesis consumes Amino groups CITRIC ACID CYCLE Amino acids roteins GLUCOSE SYNTHESIS Acetyl yruvate G3 Fatty Glycerol acids Fats Cells, tissues, organisms Sugars Carbohydrates The fuel for respiration ultimately comes from photosynthesis All organisms Can harvest energy from organic molecules lants, but not animals Can also make these molecules from inorganic sources by the process of photosynthesis