Cellular respiration

Cellular respiration

The process by which cells harvest the energy stored in foodCellular respiration1SAVING FOR A Rainy DaySuppose you earned extra money by having a part-time job. At first, you might be tempted to spend all of the money, but then you decide to open a bank account.What are the benefits of having a bank account? What do you have to do if you need some of this money? What might your body do when it has more energy than it needs to carry out its activities?What does your body do when it needs energy?

2Feel the BurnDo you like to run, bike, or swim? These all are good ways to exercise. When you exercise, your body uses oxygen to get energy from glucose,a six-carbon sugar.How does your body feel at the start of exercise, such as a long, slow run? How do you feel 1 minute into the run; 10 minutes into the run?What do you think is happening in your cells to cause the changes in how you feel?Think about running as fast as you can for 100 meters. Could you keep up this pace for a much longer distance?

3How do living organisms fuel their actions? Cellular respiration: the big picture

4ATP

AdenineRibose3 Phosphate groups5ATP

ATPEnergyEnergyAdenosine diphosphate (ADP) + Phosphate Adenosine triphosphate (ATP)PartiallychargedbatteryFullychargedbattery6

GlucoseGlycolysis Krebs cycle ElectrontransportFermentation (without oxygen)Alcohol or lactic acidSection 9-1Chemical Pathways7Cellular Respiration: The Big PictureC6H12O6 + 6O2 6CO2 + 6H2O + Energy (ATP)

Glucose + Oxygen Carbon dioxide + Water + Energy (ATP)

8Cellular Respiration: The big picture

99All living organisms extract energy from the chemical bonds of molecules (which can be considered food) through a process called cellular respiration. To generate energy, fuels such as glucose and other carbohydrates, proteins, and fats are broken down in three steps: (1) glycolysis, (2) the Krebs cycle, and (3) the electron transport chain.

Figure 4-34 The steps of cellular respiration: from glucose to usable energy.

GlucoseGlycolysisCytoplasmPyruvic acidElectrons carried in NADHKrebs CycleElectrons carried in NADH and FADH2Electron Transport ChainMitochondrionCellular Respiration: The Big PictureMitochondrionSection 9-110Three-Step ProcessBiggest ATP payoff (90%) occurs during the electron transport chain.

1111Glycolysis (terribly inefficient) occurs in the cytoplasm; the Krebs cycle and the electron transport chain occur in the mitochondria. Acetyl-CoA production is a necessary preparatory step to the Krebs cycle.

Figure 4-34 The steps of cellular respiration: from glucose to usable energy.

Cellular RespirationSection 9-2Glucose(C6H1206)+Oxygen(02)GlycolysisKrebsCycleElectronTransportChainCarbon Dioxide(CO2)+Water(H2O)12Cellular RespirationRequires (1) fuel and (2) oxygen.Potential energy stored in chemical bonds of sugar, protein, and fat molecules.Breaks bonds to release the high-energy electrons captured in ATP.Oxygen is electron magnet.

13Cellular Respiration

14In HumansEat foodDigest itAbsorb nutrient molecules into bloodstreamDeliver nutrient molecules to the cells

At this point, our cells can begin to extract some of the energy stored in the bonds of the food molecules15Aerobic Respiration the video

16Glycolysis is the universal energy-releasing pathwaysplitting (lysis) of sugar (glyco) 1st step all organisms on the planet take in breaking down food moleculesfor many single-celled organisms this one step is sufficient to provide all of the energy they need

17Glycolysis is the universal energy-releasing pathway

18GlycolysisThree of the ten steps yield energyquickly harnessed to make ATPHigh-energy electrons are transferred to NADHNet result:each glucose molecule broken down into two molecules of pyruvateATP molecules producedNADH molecules store high-energy electrons

19GlycolysisGlucose (6C) is broken down into 2 PGAL (Phosphoglyceraldehyde 3 Carbon molecules) Cost: 2 ATP

20Glycolysis2 PGAL (3C) are converted to 2 pyruvates Result: 4 ATP, 2 NADHnet ATP production = 2 ATP

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22How Glycolysis WorksAnimationAnimation

23Glycolysis: The Movie

24The Fate of PyruvateYeast: pyruvic acid is decarboxylated and reduced by NADH to form a molecule of carbon dioxide and one of ethanolaccounts for the bubbles and alcohol in, for examples, beer and champagne (alcoholic fermentation)process is energetically wasteful because so much of the free energy of glucose (~95%) remains in the alcohol (a good fuel!)Red blood cells and active muscles: pyruvic acid is reduced by NADH forming a molecule of lactic acid (lactic acid fermentation)process is energetically wasteful because so much free energy remains in the lactic acid moleculeMitochondria: pyruvic acid is oxidized completely to form CO2 & H2O (cellular respiration)~ 40% of energy in original glucose molecule is trapped in molecules of ATP

25If glycolysis is very inefficient, why do it?Because pyruvate can be metabolized to yield more waterBecause pyruvate can be metabolized to yield more CO2Because pyruvate can be metabolized to absorb more electronsBecause pyruvate can be further metabolized to yield more energy26Answer: 426The mitochondrion27Mitochondria: found in all cells in the human body except RBCs Surrounded by an outer membrane w/transport proteins through lipid bilayerInner membrane impermeable to ions and other small molecules, except where a path is provided by transport proteinsInner membrane has many folds called cristaeMatrix: central area of organelleSite for production of cellular energy using Krebs cycle

The Preparatory Phase to the Krebs Cycle

2828The two pyruvate molecules move into the mitochondria and then undergo three quick modifications that prepare them to be broken down in the Krebs cycle:Modification 1. Each pyruvate molecule passes some of its high-energy electrons to the energy-accepting molecule NAD+, building two molecules of NADH. Modification 2. Next, a carbon atom and two oxygen atoms are removed from each pyruvate molecule and released as carbon dioxide. The CO2 molecules diffuse out of the cell and, eventually, out of the organism. In humans, for example, these CO2 molecules pass into the bloodstream and are transported to the lungs, from which they are eventually exhaled. Modification 3. In the final step in the preparation for the Krebs cycle, a giant compound known as coenzyme A attaches itself to the remains of each pyruvate molecule, producing two molecules called acetyl-CoA. Each acetyl-CoA molecule is now ready to enter the Krebs cycle.

Figure 4-30 Preparations of pyruvate.The Conversion of Pyruvate to Acetyl Co-A for Entry Into the Krebs Cycle29After glycolysis (cytoplasm), pyruvic acid interior of mitochondrionCO2 removed from each 3C pyruvic acid molecule acetic acidacetic acid combines with coenzyme A acetyl coenzyme A (acetyl CoA)Once acetyl CoA is formed, Krebs cycle beginsIn the process, electrons and a hydrogen ion are transferred to NAD to form high-energy NADH

The Conversion of Pyruvate to Acetyl Co-A for Entry Into the Kreb's Cycle2 NADH are generated 2 CO2 are released

30The Krebs Cycle extracts energy from sugar31Acetic acid (from) + oxaloacetate = citrateAcetyl CoA carries acetic acid from one enzyme anotherAcetyl CoA is released by hydrolysis, combine w/another acetic acid, re-enters Krebs cycle

3232There are eight separate steps in the Krebs cycle. Three general outcomes are depicted here.Outcome 1. A new molecule is formed. Acetyl-CoA adds its two-carbon acetyl group to a molecule of the starting material of the Krebs cycle, a four-carbon molecule called oxaloacetate. This process creates a six-carbon molecule. Outcome 2. High-energy electron carriers (NADH) are made and carbon dioxide is exhaled. The six-carbon molecule then gives electrons to NAD+ to make the high-energy electron carrier NADH. The six-carbon molecule releases two carbon atoms along with four oxygen atoms to form two carbon dioxide molecules. This CO2 is carried by the bloodstream to the lungs from which it is exhaled into the atmosphere. Outcome 3. The starting material of the Krebs cycle is re-formed, ATP is generated, and more high-energy electron carriers are formed. After the CO2 is released, the four-carbon molecule that remains from the original pyruvate-oxaloacetate molecule formed in Outcome 1 is modified and rearranged to once again form oxaloacetate, the starting material of the Krebs cycle. In the process of this reorganization, one ATP molecule is generated and more electrons are passed to one familiar high-energy electron carrier, NADH, and a new one, FADH2. The formation of these high-energy electron carriers increases the energy yield of the Krebs cycle. One oxaloacetate is reformed, the cycle is ready to break down the second molecule of acetyl-CoA. Two turns of the cycle are necessary to completely dismantle our original molecule of glucose.

Figure 4-31 Overview of the Krebs cycle.The Krebs Cycle extracts energy from sugar6 NADH2 FADH22 ATP4 CO2 (to atmosphere)

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The Krebs Cycle extracts energy from sugar34

The Krebs Cycle extracts energy from sugar35AnimationKrebs: The Movie36

Review of Cellular Respiration37Review Animation