Respiration Cellular respiration is the process by which cells transfer chemical energy from sugar molecules to ATP molecules. As this happens cells release CO2 and use up O2 Respiration can be AEROBIC or ANAEROBIC

Breathing supplies oxygen to our cells and removes carbon dioxide Breathing supplies oxygen to our cells and removes carbon dioxide Breathing provides for the exchange of O2 and CO2 Between an organism and its environment CO2 O2 Bloodstream Muscle cells carrying out Cellular Respiration Breathing Glucose + O2 CO2 +H2O +ATP Lungs Figure 6.2

. The human body uses energy from ATP for all its activities. ATP powers almost all cellular and body activities .

CELLULAR RESPIRATION Cellular respiration is an energy- releasing process. It produces ATP ATP is the universal energy source Making ATP Plants make ATP during photosynthesis Cells of all organisms make ATP by breaking down carbohydrates, fats, and protein

The energy in an ATP molecule Lies in the bonds between its phosphate groups Phosphate groups ATP Energy P Hydrolysis Adenine Ribose H2O Adenosine diphosphate Adenosine Triphosphate + ADP Figure 5.4A

REDOX REACTIONS The loss of electrons is called oxidation. The addition of electrons is called reduction

Overview of Aerobic Respiration C6H12O6 + 6O2  6CO2 + 6H2O +ATP glucose oxygen carbon water dioxide

When glucose is converted to carbon dioxide It loses hydrogen atoms, which are added to oxygen, producing water C6H12O6 6 O2 6 CO2 6 H2O Loss of hydrogen atoms (oxidation) Gain of hydrogen atoms (reduction) Energy (ATP) Glucose + Figure 6.5A

STAGES OF CELLULAR RESPIRATION Overview: Cellular respiration occurs in three main stages Glycolysis Krebs Cycle or Citric Acid Cycle Electron Transport Chain or Phosphorylation

No oxygen needed. It is universal Stage 1: Glycolysis No oxygen needed. It is universal Occurs in the cytoplasm Breaks down glucose into pyruvate, producing a small amount of ATP (2)

GLYCOLYSIS Where?: In the cytosol of all cells. Both aerobic and anaerobic respiration begin with glycolysis. What happens?: The cell harvests energy by oxidizing glucose to pyruvate. One molecule of glucose (6 carbons) is converted to two pyruvate molecules (3 carbons) through a series of 10 reactions mediated by enzymes. Result: 2 pyruvate molecules (each with a 3 carbon backbone) 2 NADH molecules. Carrier that picks up hydrogens stripped from glucose. 2 ATP molecules. 4 are made but cells use 2 to start glycolysis so net gain is 2

An overview of cellular respiration

Preparatory steps to enter the Krebs cycle The 2 pyruvate molecules enter the mitochondrion and an enzyme strips one carbon from each pyruvate. This two carbon molecule is picked up by Co-enzyme A in preparation for the Krebs cycle. This is acetyl CoA. This is what enters the Krebs cycle: C-C-CoA (oxaloacetate)

The citric acid cycle or Krebs cycle Stage 2 : The citric acid cycle or Krebs cycle Takes place in the mitochondria Completes the breakdown of glucose (catabolism), producing a small amount of ATP (2ATP) Pyruvate is broken down to carbon dioxide More coenzymes are reduced .Supplies the third stage of cellular respiration with electrons (hydrogen carriers such as NADH)

KREBS CYCLE or citric acid cycle This cycle involves a series of 8 steps forming and rearranging. Each time it releases CO2 and NADH carries hydrogen to the last step. 6 CO2 are given off as waste (this is the most oxidized form of Carbon) In total: 6 CO2 6 NADH are produced and 2 FADH and only 2 ATP

An overview of cellular respiration

Oxidative phosphorylation or electron transport chain Stage 3: Oxidative phosphorylation or electron transport chain Occurs in the mitochondria (inner membrane) Uses the energy released by “falling” electrons to pump H+ across a membrane Harnesses the energy of the H+ gradient through chemiosmosis, producing ATP

Chemiosmosis Chemiosmosis is an energy coupling mechanism that uses energy stored on H+ Chemiosmosis is the coupling of the REDUX reactions of the electron transport chain to ATP synthesis

Electron transport chain NADH passes electrons to an electron transport chain As electrons “fall” from carrier to carrier and finally to O2 Energy is released in small quantities H2O NAD+ NADH ATP H+ Controlled release of energy for synthesis of ATP Electron transport chain 2 O2 2e + 1 Figure 6.5C

ELECTRON TRANSPORT CHAIN Electron transport systems are embedded (protein molecules) in inner mitochondrial membranes (cristae) NADH and FADH2 give up electrons that they picked up in earlier stages to electron transport system Electrons are transported through the system The final electron acceptor is oxygen. The hydrogen combines with the oxygen to form water

Electron transport chain Intermembrane space Inner mitochondrial membrane Mitochondrial matrix Protein complex Electron flow Electron carrier NADH NAD+ FADH2 FAD H2O ATP ADP ATP synthase H+ + P O2 Electron Transport Chain Chemiosmosis . OXIDATIVE PHOSPHORYLATION + 2 1 2 Figure 6.10

HOW MUCH TOTAL ATP(ENERGY) WAS PRODUCED? Glycolysis 2 ATP formed by substrate-level phosphorylation Krebs cycle and preparatory reactions Electron transport phosphorylation 32-34 ATP formed 2+2+34=38 Most ATP production occurs by oxidative phosphorylation or electron transport chain

Electron transport phosphorylation requires the presence of oxygen WHY OXYGEN? Electron transport phosphorylation requires the presence of oxygen Oxygen withdraws spent electrons from the electron transport system, then combines with H+ to form water

Web site tutorials to check: http://www.sp.uconn.edu/~terry/Common/respiration.html http://www2.nl.edu/jste/electron_transport_system.htm http://www.wisc-online.com/objects/MBY2604/MBY2604.swf

An overview of cellular respiration

An overview of cellular respiration

Animation: Cell Respiration Overview

How efficient is cellular respiration? Only about 40% efficient. In other words, a call can harvest about 40% of the energy stored in glucose. Most energy is released as heat

Evolution of cellular respiration When life originated, atmosphere had little oxygen Earliest organisms used anaerobic pathways Later, photosynthesis increased atmospheric oxygen Cells arose that used oxygen as final acceptor in electron transport (without oxygen to act as the final hydrogen acceptor the cells will die)

Fermentation Fermentation allows some cells to produce ATP without oxygen. This is Anaerobic respiration

Produce less ATP( 2) than aerobic pathways ANAEROBIC RESPIRATION Fermentation is an anaerobic alternative to cellular respiration Do not use oxygen Produce less ATP( 2) than aerobic pathways Two types. One produces alcohol and the other lactic acid as waste products Fermentation pathways Anaerobic electron transport

Fermentation Begin with glycolysis Under anaerobic conditions, many kinds of cells can use glycolysis alone to produce small amounts of ATP Begin with glycolysis Do not break glucose down completely to carbon dioxide and water Yield only the 2 ATP from glycolysis Steps that follow glycolysis serve only to regenerate NAD+

Carry out alcoholic fermentation Saccharomyces cerevisiae Yeast Single-celled fungi Carry out alcoholic fermentation Saccharomyces cerevisiae Baker’s yeast Carbon dioxide makes bread dough rise Saccharomyces ellipsoideus Used to make beer and wine

Our muscle cells… In the absence of oxygen our muscles can carry out fermentation, but the pyruvate from glycolysis is turned into lactic acid instead of alcohol

In alcohol fermentation NADH is oxidized to NAD+ while converting pyruvate to CO2 and ethanol NAD+ NADH 2 GLYCOLYSIS 2 ADP + 2 P ATP Glucose 2 Pyruvate released CO2 2 Ethanol Figure 6.13B Figure 6.13C

More details…

Two stages of glycolysis Energy-requiring steps ATP energy activates glucose and its six-carbon derivatives Energy-releasing steps The products of the first part are split into three-carbon pyruvate molecules ATP and NADH form

Glycolysis harvests chemical energy by oxidizing glucose to pyruvate In glycolysis, ATP is used to prime a glucose molecule Which is split into two molecules of pyruvate NAD+ NADH H+ Glucose 2 Pyruvate ATP 2 P 2 ADP + Figure 6.7A

PREPARATORY PHASE (energy investment) In the first phase of glycolysis ATP is used to energize a glucose molecule, which is then split in two  Steps      –   A fuel molecule is energized, using ATP. 1 3 Glucose PREPARATORY PHASE (energy investment) ATP Step 1 ADP P Glucose-6-phosphate 2 P Fructose-6-phosphate ATP 3 ADP P P Fructose-1,6-diphosphate  Step      A six-carbon intermediate splits into two three-carbon intermediates. 4 4 Figure 6.7C

In the second phase of glycolysis ATP, NADH, and pyruvate are formed P P Glyceraldehyde-3-phosphate (G3P)  Step     A redox reaction generates NADH. 5 6 9 NAD  5 NAD  ENERGY PAYOFF PHASE NADH P 6 NADH P 6 +H +H P P P P 1,3 -Diphosphoglycerate  Steps     –      ATP and pyruvate are produced. 6 9 ADP ADP 6 7 7 ATP ATP P P 3 -Phosphoglycerate 7 P P 8 8 2-Phosphoglycerate 8 H2O H2O P P Phosphoenolpyruvate (PEP) ADP 9 ADP 9 9 ATP ATP Pyruvate

Net Energy Yield from Glycolysis Energy requiring steps: 2 ATP invested Energy releasing steps: 2 NADH formed 4 ATP formed Glycolysis net yield is 2 ATP and 2 NADH

Preparatory reactions before the Krebs cycle Pyruvate is oxidized into two-carbon acetyl units and carbon dioxide NAD+ is reduced pyruvate + coenzyme A + NAD+ acetyl-CoA + NADH + CO2 One of the carbons from pyruvate is released in CO2 Two carbons are attached to coenzyme A and continue on to the Krebs cycle

Acetyl CoA (acetyl coenzyme A) Pyruvate is gets ready for the citric acid cycle Prior to the citric acid cycle Enzymes process pyruvate, releasing CO2 and producing NADH and acetyl CoA CO2 Pyruvate NAD+ NADH + H+ CoA Acetyl CoA (acetyl coenzyme A) Coenzyme A Figure 6.8 2 1 3

Krebs cycle Products: Coenzyme A 2 CO2 3 NADH FADH2 ATP The acetyl units are oxidized to carbon dioxide NAD+ and FAD are reduced Products: Coenzyme A 2 CO2 3 NADH FADH2 ATP

The citric acid cycle (Krebs)completes the oxidation of organic fuel (glucose), generating many NADH and FADH2 molecules In the citric acid cycle The two-carbon acetyl part of acetyl CoA is oxidized CoA CO2 NAD+ NADH FAD FADH2 ATP P CITRIC ACID CYCLE ADP + 3 + 3 H+ Acetyl CoA 2 Figure 6.9A

Krebs Cycle or Citric Acid Cycle

For each turn of the Krebs cycle Two CO2 molecules are released (All of the carbon molecules in pyruvate end up in carbon dioxide) Three NADH and one FADH2 (Coenzymes are reduced, they pick up electrons and hydrogen) One molecule of ATP is formed for each turn so the net yield of ATP for the Krebs or Citric Acid cycle is 2 ATP molecules.

What happened to co-enzymes (NAD and FAD) during the first two stages? Co-enzymes were reduced (gained electrons) Glycolysis 2 NADH Preparatory reactions 2 NADH Krebs cycle 2 FADH2 + 6 NADH Total 2 FADH2 + 10 NADH

Most ATP production occurs by oxidative phosphorylation or electron transport chain Electrons from NADH and FADH2 Travel down the electron transport chain to oxygen, which picks up H+ to form water Energy released by the redox reactions Is used to pump H+ into the space between the mitochondrial membranes

ELECTRON TRANSPORT CHAIN OR PHOSPHORYLATION Takes place in the mitochondria Coenzymes deliver electrons to electron transport systems Electron transport sets up H+ ion gradients Flow of H+ down gradients powers ATP formation The net yield from oxidative phosphorilation is 32 to 34 ATP molecules

Making ATP : Chemiosmotic model

In chemiosmosis, the H+ diffuses back through the inner membrane through ATP synthase complexes Driving the synthesis of ATP Intermembrane space Inner mitochondrial membrane Mitochondrial matrix Protein complex Electron flow Electron carrier NADH NAD+ FADH2 FAD H2O ATP ADP ATP synthase H+ + P O2 Electron Transport Chain Chemiosmosis . OXIDATIVE PHOSPHORYLATION + 2 1 2 Figure 6.10

Certain poisons interrupt critical events in cellular respiration Certain poisons interrupt critical events in cellular respiration Various poisons Block the movement of electrons Block the flow of H+ through ATP synthase Allow H+ to leak through the membrane H+ O2 H2O P ATP NADH NAD+ FADH2 FAD Rotenone Cyanide, carbon monoxide Oligomycin DNP ATP Synthase + 2 ADP Electron Transport Chain Chemiosmosis 1 Figure 6.11

OXIDATIVE PHOSPHORYLATION (Electron Transport and Chemiosmosis) Review: Each molecule of glucose yields many molecules of ATP Oxidative phosphorylation, using electron transport and chemiosmosis Produces up to 38 ATP molecules for each glucose molecule that enters cellular respiration Electron shuttle across membrane Mitochondrion Cytoplasm 2 NADH 2 NADH (or 2 FADH2) 2 NADH 6 NADH 2 FADH2 GLYCOLYSIS OXIDATIVE PHOSPHORYLATION (Electron Transport and Chemiosmosis) Glucose 2 2 Acetyl CoA CITRIC ACID CYCLE Pyruvate + 2 ATP + 2 ATP + about 34 ATP by substrate-level phosphorylation by substrate-level phosphorylation by oxidative phosphorylation About 38 ATP Maximum per glucose: Figure 6.12

Anaerobic Electron Transport Carried out by certain bacteria Electron transport system is in bacterial plasma membrane Final electron acceptor is compound from environment (such as nitrate), NOT oxygen ATP yield is almost as good as from aerobic respiration

INTERCONNECTIONS BETWEEN MOLECULAR BREAKDOWN AND SYNTHESIS Cells use many kinds of organic molecules as fuel for cellular respiration

OXIDATIVE PHOSPHORYLATION (Electron Transport and Chemiosmosis) Carbohydrates, fats, and proteins can all fuel cellular respiration When they are converted to molecules that enter glycolysis or the citric acid cycle OXIDATIVE PHOSPHORYLATION (Electron Transport and Chemiosmosis) Food, such as peanuts Carbohydrates Fats Proteins Sugars Glycerol Fatty acids Amino acids Amino groups Glucose G3P Pyruvate Acetyl CoA CITRIC ACID CYCLE ATP GLYCOLYSIS Figure 6.14

How is energy obtained from proteins? Proteins are broken down to amino acids Amino acids are broken apart Amino group is removed, ammonia forms, is converted to urea and excreted Carbon backbones can enter the Krebs cycle

How do we get energy from fats? Most stored fats are triglycerides Triglycerides are broken down to glycerol and fatty acids Glycerol is converted to PGAL, an intermediate of glycolysis Fatty acids are broken down and converted to acetyl-CoA, which enters Krebs cycle

Carbohydrates Fats Amino acids Sugars Glycerol Fatty acids Glycolysis LE 9-19 Proteins Carbohydrates Fats Amino acids Sugars Glycerol Fatty acids Glycolysis Glucose Glyceraldehyde-3- P NH3 Pyruvate Acetyl CoA Citric acid cycle Oxidative phosphorylation

Food molecules provide raw materials for biosynthesis Cells use some food molecules and intermediates from glycolysis and the citric acid cycle as raw materials This process of biosynthesis Consumes ATP ATP needed to drive biosynthesis ATP CITRIC ACID CYCLE GLUCOSE SYNTHESIS Acetyl CoA Pyruvate G3P Glucose Amino groups Amino acids Fatty acids Glycerol Sugars Carbohydrates Fats Proteins Cells, tissues, organisms Figure 6.15

The fuel for respiration ultimately comes from photosynthesis All organisms Can harvest energy from organic molecules Plants, but not animals Can also make these molecules from inorganic sources by the process of photosynthesis Figure 6.16

Electrons “fall” from organic molecules to oxygen during cellular respiration In cellular respiration, glucose and other fuels are oxidized, releasing energy. In the summary equation of cellular respiration: C6H12O6 + 6O2  6CO2 + 6H2O+ ATP Glucose is oxidized (loses electrons), oxygen is reduced ( gains electrons) Cellular respiration does not oxidize glucose in a single step that transfers all the hydrogen in the fuel to oxygen at one time. glucose is broken down gradually in a series of steps, each catalyzed by a specific enzyme