INTRODUCTION TO CELLULAR RESPIRATION

 Energy is necessary for life processes (growth, transport, manufacture, movement, reproduction, etc.)  Energy that supports life on Earth is captured from sun and used for plant, algae, protist, and bacterial photosynthesis  Photosynthesis produces ___________ and __________.  Other organisms use the O 2 and energy in sugar and release CO 2 and H 2 O  Together, these two processes are responsible for the majority of life on Earth

Sunlight energy ECOSYSTEM Photosynthesis in chloroplasts Glucose Cellular respiration in mitochondria H2OH2O CO 2 O2O2  (for cellular work) ATP Heat energy

 Breathing and cellular respiration are closely related – Breathing is necessary for exchange of CO 2 produced during cellular respiration for atmospheric O 2 – Cellular respiration uses O 2 and produces CO 2

Breathing Cellular Respiration Muscle cells carrying out CO 2 + H 2 O + ATP Lungs Bloodstream CO 2 O2O2 O2O2 Glucose + O 2

C 6 H 12 O 6 + 6O2O2 Glucose Oxygen 6 CO 2 Carbon dioxide + 6 H2OH2O Water + ATPs Energy Cellular respiration is an exergonic process that transfers energy from the bonds in glucose to ATP Cellular respiration produces 38 ATP/glucose molecule Other foods (organic molecules) can be used as a source of energy as well

 When the carbon-hydrogen bonds of glucose are broken, electrons are ultimately transferred to oxygen  Oxygen has a strong tendency to attract electrons, thus pulling electrons towards it  Cellular respiration is the controlled breakdown of organic molecules  Energy is released in small amounts that can be captured by a biological system and stored in ATP

ATP NAD + NADH H+H+ H+H+ 2e – Electron transport chain Controlled release of energy for synthesis of ATP + O2O2 H2OH2O 1212

 The cellular respiration equation explained: – Glucose loses its hydrogen (and electrons) atoms and is ultimately converted to CO 2 – At the same time, O 2 gains hydrogen atoms (and electrons) and is converted to H 2 O – Loss of electrons is called oxidation – Gain of electrons is called reduction – The reducing agent = The molecule carrying the hydrogens (e-) (NADH, FADH2) – The oxidizing agent= The molecule that receives the hydrogens (e-) (NAD+, FAD)

C 6 H 12 O O 2 Glucose Loss of hydrogen atoms (oxidation) 6 CO H 2 O + Energy Gain of hydrogen atoms (reduction) (ATP)

 The average adult human needs about 2,200 kcal of energy per day – A kilocalorie (kcal) is the quantity of heat required to raise the temperature of 1 kilogram (kg) of water by 1 o C – This energy is used for body maintenance and for voluntary activities

 Enzymes are necessary to oxidize glucose and other foods – The enzyme that removes hydrogen from an organic molecule is called dehydrogenase – Dehydrogenase requires a coenzyme called NAD + (nicotinamide adenine dinucleotide) to shuttle electrons

2 H e – Oxidation Dehydrogenase Reduction NAD H NADH + H+H+ (carries 2 electrons)

 There are other electron “carrier” molecules that function like NAD + – They “carry” electrons from glucose to a series of proteins found along the cristae of the mitochondrion – The protein complexes along the cristae are collectively are called the electron transport chain (ETC) Copyright © 2009 Pearson Education, Inc.

STAGES OF CELLULAR RESPIRATION AND FERMENTATION

 Stage 1: Glycolysis – Occurs in the cytoplasm – A single molecule of glucose is enzymatically cut in half through a series of steps to produce two molecules of pyruvate – Two molecules of NAD + are reduced to two molecules of NADH – Two molecules of ATP are produced by substrate-level phosphorylation

 ADP ATP Substrate Enzyme Product Enzyme P P P  In substrate-level phosphorylation, an enzyme transfers a phosphate group from a substrate molecule to ADP, forming ATP

ENERGY INVESTMENT PHASE Glucose Glucose-6-phosphate Fructose-6-phosphate Step ADP ATP P ADP ATP P P P Fructose-1,6-bisphosphate Steps – A fuel molecule is energized, using ATP. 13

Steps – A fuel molecule is energized, using ATP. ENERGY INVESTMENT PHASE Glucose Glucose-6-phosphate Fructose-6-phosphate Step ADP ATP P ADP ATP P P P Fructose-1,6-bisphosphate Glyceraldehyde-3- phosphate (G3P) Step A six-carbon intermediate splits Into two three-carbon intermediates. P P 4 4

P P P P NAD + P P ENERGY PAYOFF PHASE 1,3-Bisphosphoglycerate NADH  H + ADP ATP 3-Phosphoglycerate 2-Phosphoglycerate P P P P P P H2OH2O H2OH2O ADP ATP Phosphoenolpyruvate (PEP) Pyruvate Step A redox reaction generates NADH. Steps – ATP and pyruvate are produced Glyceraldehyde-3-phosphate (G3P) P P NAD + NADH  H

 The pyruvate formed in glycolysis is transported to the mitochondria, and prepared for entry into the citric acid cycle. Preparation occurs in 3 steps: – 1. The removal of a carboxyl group that forms CO 2 – 2. Oxidization of the two-carbon compound remaining – 3. Coenzyme A binds to the two-carbon fragment forming acetyl coenzyme A

Coenzyme A Pyruvate Acetyl coenzyme A CoA NAD + NADH  H + CO

 Stage 2: The citric acid cycle (Kreb’s Cycle) – Occurs in the mitochondrial matrix – Breaks down pyruvate into CO 2 and supplies the third stage with electrons (via NADH, FADH 2 ) – The acetyl group associates with a 4-C molecule (oxaloacetate) forming a 6-C molecule (citrate) – The 6-C molecule then passes through a series of redox reactions that regenerate the 4-Cmolecule

C ITRIC A CID C YCLE NAD + NADH 3 H + CO 2  CoA Acetyl CoA P ADP + ATP FADH 2 FAD

C ITRIC A CID C YCLE CoA 2 carbons enter cycle Acetyl CoA CoA 1 Oxaloacetate 1 Step Acetyl CoA stokes the furnace.

C ITRIC A CID C YCLE CoA 2 carbons enter cycle Acetyl CoA CoA 1 Oxaloacetate 1 Step Acetyl CoA stokes the furnace. 2 3 NAD + NADH CO 2 Citrate ADP + + H + P Alpha-ketoglutarate leaves cycle ATP NAD + NADH CO 2 + H + leaves cycle Steps – NADH, ATP, and CO 2 are generated during redox reactions. 23

C ITRIC A CID C YCLE CoA 2 carbons enter cycle Acetyl CoA CoA 1 Oxaloacetate 1 Step Acetyl CoA stokes the furnace. 2 3 NADH CO 2 Citrate ADP  P Alpha-ketoglutarate leaves cycle ATP NADH CO 2 leaves cycle Steps – NADH, ATP, and CO 2 are generated during redox reactions NAD + NADH Malate + H + 4 FADH 2 FAD Succinate Steps – Redox reactions generate FADH 2 and NADH. 45 NAD + + H + NAD + + H +

 Stage 3: Oxidative phosphorylation – Occurs on the cristae of mitochondrion – Electrons are supplied by NADH & FADH 2, then shuttled through the ETC – As e- are transported from protein to protein, H + are concentrated in the intermembrane space – The potential energy of this proton gradient is used to make ATP by a process called chemiosmosis – The concentration gradient drives H + through ATP synthases producing ATP – The ETC + chemiosmosis = oxidative phosphorylation

ATP H+H+ Intermembrane space O2O2 H2OH2O 1212 Inner mitochondrial membrane H+H+ NAD + H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ Mitochondrial matrix Electron flow Electron carrier Protein complex of electron carriers NADH FADH 2 FAD ATP synthase P ADP + Chemiosmosis + 2 O XIDATIVE P HOSPHORYLATION Electron Transport Chain

Mitochondrion CO 2 NADH ATP High-energy electrons carried by NADH NADH C ITRIC A CID C YCLE G LYCOLYSIS Pyruvate Glucose and FADH 2 Substrate-level phosphorylation Substrate-level phosphorylation O XIDATIVE P HOSPHORYLATION (Electron Transport and Chemiosmosis) Oxidative phosphorylation ATP Cytoplasm Inner mitochondrial membrane

Cytoplasm Glucose FADH 2 Mitochondrion Maximum per glucose: O XIDATIVE P HOSPHORYLATION (Electron Transport and Chemiosmosis) C ITRIC A CID C YCLE Electron shuttle across membrane 2 NADH (or 2 FADH 2 ) 2 Acetyl CoA G LYCOLYSIS 2 Pyruvate About 38 ATP  about 34 ATP by substrate-level phosphorylation by oxidative phosphorylation  2 ATP by substrate-level phosphorylation  2 ATP

 Fermentation is an anaerobic (without oxygen) energy-generating process – It involves glycolysis, and the regeneration of the reducing agent NAD + – NADH is oxidized to NAD + when pyruvate is reduced to lactate – Pyruvate serves as an “electron sink,” a place to dispose of the electrons generated by oxidation reactions in glycolysis – Your muscle cells and certain bacteria can oxidize NADH through lactic acid fermentation Copyright © 2009 Pearson Education, Inc.

Glucose NADH NAD NADH 2 NAD ADP P ATP 2 2 Pyruvate 2 Lactate GLYCOLYSIS Lactic acid fermentation  2

 The baking and winemaking industry have used alcohol fermentation for thousands of years – Happens in yeast cells (single-celled fungi) – They convert pyruvate to CO 2 and ethanol while oxidizing NADH back to NAD +

2 ADP P ATP 2 GLYCOLYSIS NADH NAD NADH 2 NAD Pyruvate 2 Ethanol Alcohol fermentation Glucose CO 2 2 released  2

INTERCONNECTIONS BETWEEN MOLECULAR BREAKDOWN AND SYNTHESIS

 Although glucose is considered to be the primary source of sugar for respiration and fermentation, there are actually three sources of molecules for generation of ATP – Carbohydrates (disaccharides) – Proteins (after conversion to amino acids) – Fats

Food, such as peanuts ProteinsFatsCarbohydrates Glucose O XIDATIVE P HOSPHORYLATION (Electron Transport and Chemiosmosis) CITRIC ACID CYCLE Acetyl CoA GLYCOLYSIS Pyruvate Amino acids Glycerol Sugars Fatty acids Amino groups G3P ATP

Cells, tissues, organisms Proteins Fats Carbohydrates Glucose ATP needed to drive biosynthesis CITRIC ACID CYCLE Acetyl CoA GLUCOSE SYNTHESIS Pyruvate Amino acids Glycerol Sugars Fatty acids Amino groups G3P ATP

Cytoplasm Glucose Oxidative phosphorylation (Electron Transport and Chemiosmosis) Citric acid cycle Glycolysis Pyruvate CO 2 ATP CO 2 ATP NADH and FADH 2 Mitochondrion NADH ATP

(a) glucose and organic fuels has three stages produce some generates Cellular respiration uses H + diffuse through ATP synthase by process called chemiosmosis energy for cellular work uses (b) (d) (c) (f) (e) oxidizes C 6 H 12 O 6 to pull electrons down to uses pumps H + to create H + gradient produces many