VI. Reaction Coupling and ATP [cont.]

Transcription

1 VI. Reaction Coupling and [cont.] The cycle hosphorylation Strongly Endergonic Hydrolysis Strongly Exergonic Energy from exergonic reactions AD+ Energy for endergonic reactions Background: VII. Metabolism Metabolism of a cell = Sum of all chemical reactions in cell Chemical reactions linked in metabolic pathways Cells couple exergonic and endergonic reactions Cells regulate chemical rxns through enzymes

2 Cells regulate enzyme activity (to regulate reactions) 1. Regulate synthesis synthesize enzyme only when product needed 2. Regulate active state synthesize in inactive state activate when needed 3. Noncompetitive Inhibition (Allosteric) molecule binds to other site changes active site shape 4. Competitive inhibition molecule binds to active site prevents substrate binding Cells regulate enzyme activity (to regulate reactions) Feedback inhibition - Works on complex, pathway reactions - Final product feeds back and inhibits early enzyme in pathway

3 I. Cellular Energy Harvest: an Overview Energy to Drive Metabolism: Autotrophs use inorganic sources of energy hotoautotrophs harvest sunlight convert radiant energy into chemical energy. Heterotrophs use organic sources of energy live off the energy produced by autotrophs. extract energy from food catabolism Overview: Energy Harvest

4 Overview: How is Glucose metabolized? The reaction (if glucose is used to full potential) Loss of hydrogen atoms (oxidation) C 6 H 12 O 6 + 6O 2 --> 6CO 2 + 6H 2 O + & Heat Gain of hydrogen atoms (reduction) Cellular respiration oxidizes food molecules! Overview: How is Glucose metabolized? Step #1 Glycolysis: In cytoplasm Glucose 2 pyruvate (Yields a little Energy) Aerobic conditions: #2 Cellular respiration: In mitochondria Lots of CO 2 + H 2 O Anaerobic conditions: #2 Anaerobic respiration or #2 Fermentation In cytoplasm To Lactate or Ethanol 2, No high energy e -

5 Releasing Energy from Glucose! Harvesting energy: cells break chemical bonds shift electrons from molecule to molecule.! Where do the electrons go? Aerobic respiration final electron acceptor is Oxygen Anaerobic respiration final electron acceptor is not oxygen, but is an inorganic molecule (e.g. CO 2, SO 4 ) Fermentation final electron acceptor is an organic molecule II. Stages of Aerobic Cellular Respiration Overview Cytoplasm Glucose Glycolysis A. Glycolysis B. oxidation C. Krebs (Citric Acid) Cycle D. Electron Transport Chain oxidation CO 2 Intermembrane space Acetyl- CoA Mitochondrial matrix Krebs cycle CO 2 FADH 2 Mitochondrion e - H 2 O Electron transport chain NAD + and FAD Inner mitochondrial membrane

6 A. Glycolysis: carbon glucose (Starting material) 2 6-carbon sugar diphosphate 6-carbon sugar diphosphate 3-carbon sugar phosphate 3-carbon sugar phosphate 3-carbon sugar 3-carbon sugar phosphate phosphate riming reactions- Energy investment. Cleavage reactions carbon pyruvate 3-carbon pyruvate Energy-harvesting reactions. Transferring Energy: Reduction of NAD + Oxidation: Dehydrogenase removes electrons from substrate Reduction: Electrons in Hydrogen Transferred to NAD + H O H Oxidation Dehydrogenase O + 2H (Enzyme) NAD + + 2H 2H + + 2e! Reduction + H + (carries 2 electrons) Copyright 2005 earson Education, Inc. ublishing as Benjamin Cummings

7 Substrate-Level hosphorylation High energy phosphate bond is transferred enzymatically to AD A. Glycolysis: Summary! Catabolic pathway with 3 major events: 1. riming (Energy Investment) 2. Cleavage (6-C to 2X 3-C) 3. Energy Harvesting Substrate-level phosphorylation! Nets two molecules 2 used generated Net Gain/Glucose = 2 + 2! Universal: All living organisms! Anaerobic process (no O 2 required)

8 What do cells do with and? Depends on whether conditions are Aerobic or Anaerobic Under Aerobic (with O 2 ) Cellular Respiration Use and to generate lots more II. Stages of Aerobic Cellular Respiration Overview Cytoplasm Glucose Glycolysis A. Glycolysis B. oxidation C. Krebs (Citric Acid) Cycle D. Electron Transport Chain oxidation CO 2 Intermembrane space Acetyl- CoA Mitochondrial matrix Krebs cycle CO 2 FADH 2 Mitochondrion e - H 2 O Electron transport chain NAD + and FAD Inner mitochondrial membrane

9 B. Oxidation C. Kreb s Cycles (Citric Acid Cycle) Mitochondrion

10 II. Stages of Aerobic Cellular Respiration Overview Cytoplasm Glucose Glycolysis A. Glycolysis B. oxidation C. Krebs (Citric Acid) Cycle D. Electron Transport Chain oxidation CO 2 Intermembrane space Acetyl- CoA Mitochondrial matrix Krebs cycle CO 2 FADH 2 Mitochondrion e - H 2 O Electron transport chain NAD + and FAD Inner mitochondrial membrane Electron Transport Chain: Generalized Scheme 1. and FADH 2 pass electrons to an electron transport chain 2. Energy is released as electrons fall and lose energy 3. Energy is harvested as NAD + + H + 2e! * Controlled release of energy for synthesis! Electron Transport Chain H + 2e! O 2 H 2 O

11 Intermembrane space. rotein complex H + H + H + H + H + H + H + H + H + Electron carrier synthase Inner mitochondrial membrane Mitochondrial matrix FADH 2 NAD + FAD H + H + H + H + H 2 O AD + H + H + O 2 H + Electron Transport Chain synthase + OXIDATIVE HOSHORYLATION = One Type of Chemiosmosis O 2 is the final electron acceptor in the electron transport chain; it is reduced to H 2 0 Synthase, Chemiosmosis & Synthesis CHEMIOSMOSIS: The passage of high-energy electrons along the electron transport chain, which is coupled to the pumping of protons through synthase, driving the production of Synthase

12 II. Stages of Aerobic Cellular Respiration Overview Cytoplasm Glucose Glycolysis A. Glycolysis B. oxidation C. Krebs (Citric Acid) Cycle D. Electron Transport Chain oxidation CO 2 Intermembrane space Acetyl- CoA Mitochondrial matrix Krebs cycle CO 2 FADH 2 Mitochondrion e - H 2 O Electron transport chain NAD + and FAD Inner mitochondrial membrane Aerobic Respiration Efficiency 2 Glucose Glycolysis Acetyl-CoA Krebs cycle FADH2 4 Total net yield = 36

13 Contrasting Energy Yields From 1 molecule of glucose: Aerobic respiration Glycolysis (2 ) Oxidation (none) Citric Acid cycle (2 ) Respiratory chain (32 ) ~ 36 total Fermentation Glycolysis (2 ) Fermentation (none) A. Fermentation Stage 1: Glycolysis carbon glucose (Starting material) 2 6-carbon sugar diphosphate 6-carbon sugar diphosphate 3-carbon sugar phosphate 3-carbon sugar phosphate 3-carbon sugar 3-carbon sugar phosphate phosphate riming reactions. Cleavage reactions carbon pyruvate 3-carbon pyruvate Energy-harvesting reactions.

14 A. Fermentation Stage 2: Recycling Alcohol fermentation In cytoplasm Glucose H G H C OH 2 AD L CH 3 Y 2 NAD+ 2 Ethanol 2 C O L 2 Y O H S C O C O I CO 2 C O S CH 3 2 Acetaldehyde CH 3 2 Yeast cells (single celled fungi) Lactic acid fermentation In cytoplasm O 2 AD 2 C O C O CH 3 Glucose G L Y C O L Y S I S 2 2 NAD+ 2 O C O H C OH CH 3 2 Lactate Most animal cells, lactate removed from cells by blood B. Anaerobic respiration! Archaebacteria Only Methanogens Live in anaerobic environments (no oxygen) Use CO 2 gas as final electron acceptor; convert to methane gas (CH 4 ) Found in swamps, sewage treatment plants, digestive tracts of animals Break down cellulose for herbivores (cows) roduce marsh gas or intestinal gas (methane) Sulfur Bacteria Live in anaerobic environments (no oxygen) Use inorganic sulfates (SO 4 ) as final electron acceptor; convert to hydrogen sulfide (H 2 S) Found in sulfur springs Red Sulfur Bacteria

15 Summary: Respiration without oxygen 1. Glycolysis produces a net of 2 2. Fermentation - recycles to NAD +» Lactic acid fermentation» CO 2 and Ethanol fermentation» NO Oxidation, NO Kreb s Cycle, NO electron transport! 3. Anaerobic Respiration! Methanogens Final electron acceptor: CO 2, convert to CH 4! Sulfate-reducing Bacteria Final electron acceptor: SO 4, convert to to H 2 S IV. Catabolism of Macromolecules

16 How is cellular E carried between coupled rxns? Example: Using glucose E to build a protein