Cellular Respiration Chapter 08

Cellular Respiration 2OutlineGlycolysis Transition Reaction Citric Acid Cycle Electron Transport System Fermentation Metabolic Pool  Catabolism  Anabolism

Cellular Respiration 3 Essential Knowledge 2.A.1: All living systems require constant input of free energy. c. Energy-related pathways in biological systems are sequential and may be entered at multiple points in the pathway. Krebs cycle Krebs cycle Glycolysis Glycolysis Fermentation Fermentation

Cellular Respiration 4 Essential Knowledge 2.A.2: Organisms capture and store free energy for use in biological processes. c. Different energy-capturing processes use different types of electron acceptors. Oxygen in cellular respiration Oxygen in cellular respiration

Cellular Respiration 5 A cellular process that requires oxygen and gives off carbon dioxide Usually involves breakdown of glucose to carbon dioxide and water  Energy extracted from glucose molecule: ­ Released step-wise ­Allows ATP to be produced efficiently  Oxidation-reduction enzymes include NAD + and FAD as coenzymes

6 Glucose Breakdown: Summary Reaction

Cellular Respiration 7 NAD + and FAD NAD + (nicotinamide adenine dinucleotide)  Called a coenzyme of oxidation-reduction it can ­Oxidize a metabolite by accepting electrons ­Reduce a metabolite by giving up electrons  Each NAD + molecule used over and over again FAD (flavin adenine dinucleotide)  Also a coenzyme of oxidation-reduction  Sometimes used instead of NAD +  Accepts two electrons and two hydrogen ions (H + ) to become FADH 2

8 NAD + Cycle

9 Glucose Breakdown: Overview of 4 Phases

Cellular Respiration 10 Glucose Breakdown: Glycolysis Occurs in cytoplasm outside mitochondria Energy Investment Steps:  Two ATP are used to activate glucose  Glucose splits into two G3P molecules Energy Harvesting Steps:  Two electrons (as hydrogen atoms) are picked up by two NAD +  Four ATP produced by substrate-level phosphorylation  Net gain of two ATP  Both G3Ps converted to pyruvates

11 Glycolysis

12 Glycolysis

Cellular Respiration 13 Glucose Breakdown: The Preparatory (Prep) Reaction End product of glycolysis, pyruvate, enters the mitochondrial matrix Pyruvate converted to 2-carbon acetyl group  Attached to Coenzyme A to form acetyl-CoA  Electron picked up (as hydrogen atom) by NAD +  CO 2 released, and transported out of mitochondria into the cytoplasm

14 Mitochondrion: Structure & Function

Cellular Respiration 15 Glucose Breakdown: The Citric Acid Cycle A.K.A. Krebs cycle Occurs in matrix of mitochondria Both acetyl (C 2 ) groups received from the preparatory reaction:  Join with an enzyme CoA molecule to make acetyl- CoA  Acetyl (C 2 ) group transferred to oxaloacetate (C 2 ) to make citrate (C 6 )  Each acetyl oxidized to two CO 2 molecules  Remaining 4 carbons from oxaloacetate converted back to oxaloacetate (thus “cyclic”) NADH, FADH 2 capture energy rich electrons ATP formed by substrate-level phosphorylation

16 The Citric Acid Cycle

Cellular Respiration 17 Electron Transport Chain Location:  Eukaryotes: cristae of the mitochondria  Aerobic Prokaryotes: plasma membrane Series of carrier molecules:  Pass energy rich electrons along  Complex arrays of protein and cytochromes ­Cytochromes are respiratory molecules ­Complex carbon rings with metal atoms in center Receives electrons from NADH & FADH 2 Produce ATP by oxidative phosphorylation

Cellular Respiration 18 Electron Transport Chain The fate of the hydrogens:  Hydrogens from NADH deliver enough energy to make 3 ATPs  Those from FADH 2 have only enough for 2 ATPs  “Spent” hydrogens combine with oxygen Recycling of coenzymes increases efficiency  Once NADH delivers hydrogens, it returns (as NAD + ) to pick up more hydrogens  However, hydrogens must be combined with oxygen to make water  If O 2 not present, NADH cannot release H  No longer recycled back to NAD +

19 Electron Transport Chain

20 Organization of Cristae

Cellular Respiration 21 Glucose Catabolism: Overall Energy Yield Net yield per glucose:  From glycolysis – 2 ATP  From citric acid cycle – 2 ATP  From electron transport chain – 32 ATP Energy content:  Reactant (glucose) 686 kcal  Energy yield (36 ATP) 263 kcal  Efficiency 39%; balance is waste heat

22 Overall Energy Yielded per Glucose Molecule

Cellular Respiration 23 Fermentation (1) When oxygen limited:  Spent hydrogens have no acceptor  NADH can’t recycle back to NAD +  Glycolysis stops because NAD + required Fermentation:  “Anaerobic” pathway  Can provide rapid burst of ATP  Provides NAD + for glycolysis  NADH combines with pyruvate to yield NAD +

Cellular Respiration 24 Fermentation (2) Pyruvate reduced by NADH to:  Lactate ­Animals & some bacteria ­Cheese & yogurt; sauerkraut  Ethanol & carbon dioxide ­Yeasts ­Bread and alcoholic beverages Allows glycolysis to proceed faster than O 2 can be obtained  Anaerobic exercise  Lactic acid accumulates  Causes cramping and oxygen debt When O 2 restored, lactate broken down to acetyl-CoA and metabolized

25 Products of Fermentation Efficiency

Cellular Respiration 26 Metabolic Pool: Catabolism (1) Foods:  Sources of energy rich molecules  Carbohydrates, fats, and proteins Catabolism (breakdown side of metabolism) Breakdown products enter into respiratory pathways as intermediates  Carbohydrates ­Converted into glucose ­Processed as above

27 The Metabolic Pool Concept

Cellular Respiration 28 Metabolic Pool: Catabolism (2) Breakdown products enter into respiratory pathways as intermediates (cont.)  Proteins ­Broken into amino acids (AAs) ­Some AAs used to make other proteins ­Excess AAs deaminated (NH 2 removed) in liver  Results in poisonous ammonia (NH 3 )  Quickly converted to urea ­Different R-groups from AAs processed differently ­Fragments enter respiratory pathways at many different points

Cellular Respiration 29 Metabolic Pool: Anabolism (1) All metabolic reactions part of metabolic pool Intermediates from respiratory pathways can be used for anabolism Anabolism (build-up side of metabolism):  Carbs: ­Start with acetyl-CoA ­Basically reverses glycolysis (but different pathway)  Fats ­G3P converted to glycerol ­Acetyls connected in pairs to form fatty acids ­Note – dietary carbohydrate RARELY converted to fat in humans!

Cellular Respiration 30 Metabolic Pool: Anabolism (2) Anabolism (cont.):  Proteins: ­Made up of combinations of 20 different amino acids ­Some amino acids (11) can be synthesized from respiratory intermediates  organic acids in citric acid cycle can make amino acids  Add NH 2 – transamination ­However, other amino acids (9) cannot be synthesized by humans  Essential amino acids  Must be present in diet or die

Cellular Respiration Ending Slide Chapter 08