Cellular Respiration: The Release of Energy in Cells

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Cellular Respiration:

Cellular Respiration:The Release of Energy in CellsCellular RespirationCopyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Cells need energy to carry out activities

Muscles need energy to contract (or to relax)Neurons need energy to transmit impulses

Cells get their energy from breaking down absorbed molecules in a process called:CELLULAR RESPIRATIONHow do Cells Get Energy?Cells obtain energy by breaking the chemical bonds of glucose

Covalent bonds between atoms = stored energy

One glucose molecule yields as many as 38 ATP molecules

What is ATP?Adenosine Tri PhosphateA nucleotideA molecule that serves as an energy carrier Carries energy in useable amountsIs transported to wherever energy is needed to perform reactions in cell High energy bonds between phosphates store chemical energy

How Does ATP Store and Release Energy?

Energy is stored when a third phosphate is attached to ADP adenosine di phosphate, forming ATPEnergy is released when the bond between the last two phosphates is broken, making ADP The ADP can be used to make another ATP

ADPADP + Phosphate ATP stores energy

ATP ADP +Phosphate releases energy

Two ways to Release Chemical Energy from MoleculesSeries of reactions called metabolic pathways

Aerobic RespirationRequires oxygenMakes as many as 38 ATP

Anaerobic RespirationDoes not require oxygenMakes only 2 additional ATP Aerobic RespirationATP production begins in the cytoplasmcontinues in the mitochondria

Aerobic Respiration ReactionGlucose + Oxygen + 38 ADP + inorganic phosphate Yields Carbon Dioxide + Water + 38 ATP Formulas:

C6H12O6 + O2 + 38ADP + 38Pi

CO2 + H2O + 38 ATPReactantsProductsPi = inorganic phosphateOxidation - removal of electrons from a moleculeReduction - addition of electrons to a molecule a hydrogen atom is usually also transferredThe breakdown of glucose is an Oxidation-Reduction reactionOxidation-Reduction Reactions

Coenzymes Carry ElectronsTwo Coenzymes are used to carry electrons from one part of the reaction to another:NAD+ (nicotinamide adenine dinucleotide)FAD+ (flavine adenine dinucleotide)They receive the hydrogen atoms removed from glucose along with the electronsNAD+ becomes NADHFAD+ becomes FADH2

What are the Steps in Aerobic Respiration?There are four main phases:Glycolysis glucose (6 C) splits into two 3-carbon moleculesPreparatory reaction each 3-carbon molecule divides into a 2-carbon molecule and CO2Citric acid cycle (or Krebs cycle) CO2, NADH, FADH2, and ATP produced Electron transport chain + Oxidative Phosphorylationlargest amount of ATP produced

Step 1: GlycolysisOccurs in the cytoplasmGlucose is broken into two three carbon molecules called pyruvateNo oxygen is requiredOccurs in aerobic and anaerobic respirationGlucose (6 C) 2 Pyruvate (3 C)Step 1: Glycolysis

Investment Stage:Two ATP are used to begin the reaction NADH is made from NAD by transfering electrons from glucosePayoff Stage:Four ATP are Produced (NET of 2 ATP)Step 2: Preparatory ReactionsOccurs in the MATRIX of a Mitochondria Pyruvate enters the mitochondria matrix

1. Pyruvate (C3) is oxidized into an acetyl group (C2) and one carbon dioxide (CO2) molecule is released

2. Electrons are picked up by NADNAD+ + H NADH 3. The acetyl group is attached to coenzyme A producing acetyl CoA

Preparatory Reactions

Citric Acid CycleOccurs in mitochondria matrix. Final steps to break down glucose Acetyl CoA attaches to a 4 carbon molecule then is broken downKrebs CycleProducts:2 CO2, 4 NADH, 6 FADH2, and 2 ATPEach NADH is converted to 3 ATPs2 from glycolysis, 2 from preparatory reaction, 6 from Krebs cycle 10 x 3 = 30Each FADH2 is converted to 2 ATPs 2 x 2 = 4 A total of 34 ATPs will be produced in this stepElectron Transport ChainMost of the ATP is created in this stepOccurs on the cristae (inner membrane) of the mitochondria

Intermembrane spaceHow Does the Electron Transport Chain Work?H+ from the matrix is actively transported into the intermembrane space, creating a concentration gradientThe H+ ions are then allowed to diffuse back across the membrane turning an ATP generator

High energy electrons released by NADH or FADH2 are transported from carrier to carrier in the membrane. Each transfer releases enough energy to pump H+ across the membrane. Finally electrons are handed off to O2 - the final electron carrier (this is the aerobic part) The oxygen combines with H+ to make - (ta da!) Water

The concentration gradient of H+ will be used to produce ATPPassive transport (diffusion) activates ATP synthase for ATP synthesis What are the reactants and products of each step?Recap of Reactants and ProductsStageReactantsProductsGlycolysisGlucose, 2 ATP, 4 ADP, NAD +Pyruvate, 4ATP, NADHPreparatory ReactionPyruvate, NAD, CoAAcetyl CoA, CO2, NADHCitric Acid CycleAcetyl CoA, NAD, FAD+, ADPCO2, NADH, FADH2, 2 ATPElectron TransportNADH, FADH2, O2H2O, 34 ATPHow many ATP molecules are produced in each step?

GlycolysisNet 2Preparatory Reactions 0Citric Acid Cycle 2Electron Transport Chain 34Anaerobic RespirationGlycolysis will occur (its anaerobic) in the cytoplasm

Only 2 ATPs generatedPyruvate is broken down by fermentation Fermentation does not generate more ATP

Two main types of fermentation: lactic acid fermentationalcohol fermentationLactic Acid Fermentation:Glucose + 2 ADP Lactic Acid + 2 ATPOccurs:In certain bacteriaHuman muscle cells: when used strenuously, not enough O2 can be supplied cells switch from aerobic to anaerobic to keep working; lactic acid buildup causes fatigue, crampsAnaerobic Respiration Alcoholic fermentation: Glucose + 2 ADP Ethyl alcohol + CO2 + 2 ATPPerformed by yeasts (kind of fungi) in bread making, alcohol brewingAnaerobic respirationAerobic vs. Anaerobic Respiration Aerobic AnaerobicNeeds Does not need 38 2More steps Faster energy CO2 + H2O Lactic acid or alcohol and CO2 OxygenATP ProducedProcessingEnd productsLocationCytoplasm & MitochondriaCytoplasm