Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Chapter 5 Cell Respiration & Metabolism 5-1

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Chapter 5 Outline  Glycolysis  Aerobic Respiration  Fat & Protein Metabolism 5-2

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Metabolism  Is all reactions in body that involve energy transformations  Divided into 2 categories:  Catabolism breaks down molecules & releases energy  Is primary source of energy for making ATP  Anabolism makes larger molecules & requires energy  Source of body’s large energy-storage compounds 5-3

Glycolysis 5-4

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Glycolysis  Is metabolic pathway by which glucose is converted to 2 pyruvates  Does not require oxygen  Overall net equation is:  glucose + 2NAD + 2ADP + 2P i  2 pyruvates + 2NADH + 2 ATP 5-5

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Glycolysis continued  Glycolysis is exergonic - produces net of 2ATPs & 2NADHs  However, glucose must be activated with 2ATPs (phosphorylation) before energy can be obtained  Phosphorylation traps glucose inside cell  Below can see 2ATPs added & 4 are produced for a net gain of 2 ATP Fig

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Glycolysis continued Fig

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Lactic Acid Pathway  To avoid end-product inhibition, NADHs produced in glycolysis need to give Hs away  In absence of O 2, NADH gives its Hs to pyruvate creating lactic acid (anaerobic respiration)  Makes muscles feel fatigued Fig

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Lactic Acid Pathway continued  RCCs don't have mitochondria; use only lactic acid pathway  Occurs in skeletal & heart muscle when oxygen supply falls below critical level  During heavy exercise or vascular blockage 5-9

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Glycogenesis & Glycogenolysis  For osmotic reasons cells can't store many free glucoses  Instead store glucose as glycogen (glycogenesis)  Skeletal muscle & liver store lots of glycogen  Glycogenolysis clips glucose out of glycogen as glucose 6-phosphate  Phosphate groups trap molecules in cells 5-10

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.  Skeletal muscles use trapped glucose-6- phosphate for own energy needs  Only liver has glucose-6- phosphatase that removes phosphate groups  So glucose can be secreted Glycogenesis & Glycogenolysis continued Fig

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Cori Cycle  Some skeletal muscle lactic acid goes to liver  Where it is converted back through pyruvate to glucose & glycogen  Called gluconeogenesis  Also can happen with amino acids & glycerol Fig

Aerobic Respiration 5-13

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Aerobic Respiration  Begins when pyruvate formed by glycolysis enters mitochondria  C0 2 is clipped off pyruvate forming acetyl CoA (coenzyme A is a carrier for acetic acid)  C0 2 goes to lungs  Energy in acetyl CoA is extracted during aerobic respiration in mitochondria Fig

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Krebs Cycle  Begins with acetyl CoA combining with oxaloacetic acid to form citric acid  In a series of reactions citric acid converted back to oxaloacetic acid to complete the pathway Fig

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Krebs Cycle continued  Produces 1 GTP, 3 NADH, & 1 FADH 2  NADH & FADH 2 carry electrons to Electron Transport Chain (ETC) 5-16

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Krebs Cycle continued Fig

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Electron Transport & Oxidative Phosphorylation  The electron transport chain is a linked series of proteins on the cristae of mitochondria  Proteins are FMN, coenzyme Q, & cytochromes Fig

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Electron Transport & Oxidative Phosphorylation continued  NADH & FADH 2 from Krebs carry electrons to ETC  Which are then shuttled in sequence through ETC  NAD & FAD are regenerated to shuttle more electrons from Krebs Cycle to ETC 5-19

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Electron Transport & Oxidative Phosphorylation continued  As each protein in ETC accepts electrons it is reduced  When it gives electrons to next protein it is oxidized  This process is exergonic  Energy is used to phosphorylate ADP to make ATP  Called oxidative phosphorylation Fig

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Chemiosmotic theory  Energy gathered by ETC is used to pump H + s into mitochondria outer chamber  Creating high H + concentration there  As H + s diffuse down concentration & charge gradient thru ATP synthase, & back into inner chamber, their energy drives ATP synthesis (Chemiosmotic theory) Fig

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Function of Oxygen  Electrons added to beginning of ETC are passed along until reach end  Have to be given away or would stop ETC  O 2 accepts these electrons & combines with 4H + s  O e H +  2 H 2 0 Fig

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. ATP Formation  ATP can be made 2 ways:  Direct (substrate-level) phosphorylation  Where ATP is generated when bonds break  Both ATPs in glycolysis made this way  2 ATPs/glucose in Kreb's made this way  Oxidative phosphorylation in Kreb's  Where ATP generated by ETC  ATPs made this way 5-23

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. ATP Formation continued  3H + s pass thru ATP synthase to generate 1 ATP  This yields ATPs/glucose  However some of these are used to pump ATPs out of mitochondria  So net yield is ATPs/glucose  Really takes 4H + s to generate 1 exported ATP 5-24

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Production of ATP by ETC  2.5 ATP produced for each pair of electrons NADH donates  1.5 ATP produced for each pair of electrons FADH 2 donates  Net of 26 ATP produced in ETC 5-25

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Net Production of ATP  26 ATP produced in ETC  2 from glycolysis  2 from direct phosphorylation in Kreb’s  For total of 30 ATPs for each glucose 5-26

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 5-27

Fat & Protein Metabolism 5-28

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Fats & Proteins as Energy Sources  Fats can be hydrolyzed to glycerol & fatty acids  These can be modified to run thru Kreb's  Proteins can be broken down to amino acids  Which can be deaminated & run thru Kreb's  These pathways can be used to interconvert carbohydrates, fats, & proteins 5-29

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.  When more energy is taken in than consumed, ATP synthesis is inhibited  Glucose converted into glycogen & fat Fig 5.11 Energy Storage 5-30

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Acetyl CoA  Is a common substrate for energy & synthetic pathways Fig

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Fat Synthesis (Lipogenesis)  Acetyl CoAs can be linked together to form fatty acids  Fatty acids + glycerol = Fat (triglycerides)  Occurs mainly in adipose & liver tissues  Fat is major form of energy storage in body  Yields 9 kilocalories/g  Carbs & proteins yield only 4/g 5-32

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Lipolysis  Is breakdown of fat into fatty acids & glycerol  Via hydrolysis by lipase  Acetyl CoAs from free fatty acids serve as major energy source for many tissues 5-33

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.  Beta-oxidation clips acetyl CoAs off fatty acid chains  Which can be run thru Kreb's giving 10ATPs each  Plus  - oxidation itself yields 4 ATPs Acetyl CoA from Fat --Beta-Oxidation 5-34 Fig 5.13

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Brown Fat  Amount of brown fat greatest at time of birth  Major site for thermogenesis in the newborn  Brown fat produces uncoupling protein, causing H + to leak out of inner mitochondrial membrane  Less ATP produced, causes electron transport system to be more active  Heat produced instead of ATP 5-35

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Ketone Bodies  Triglycerides are continually broken down & resynthesized  Ensures blood will contain fatty acids for aerobic respiration  During fasting & diabetes lots of fat is broken down  Causes high levels of ketone bodies  Fat metabolites  Gives breath an acetone smell 5-36

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Amino Acid Metabolism  Nitrogen (N) ingested primarily as protein  Which is used in body as amino acids  Excess is excreted mainly as urea 5-37

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Nitrogen (N) Balance  Nitrogen balance = N ingested minus N excreted  Positive N balance: more N ingested than excreted  Negative N balance: less N ingested than excreted  In healthy adults amount of N excreted = amount ingested  Excess amino acids can be converted into carbos & fat 5-38

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Essential & Non-essential Amino Acids  20 amino acids used to build proteins  12 can be produced by body  8 must come from diet (= essential amino acids) 5-39

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Transamination  New amino acids can be obtained by transamination  Which is addition of -NH 2 to pyruvate or Kreb's cycle ketones to make a new amino acid  Catalyzed by transaminase 5-40

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Transamination continued Fig

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Oxidative Deamination  Is process by which excess amino acids are eliminated  -NH 2 is removed from glutamic acid, forming keto acid & ammonia  Ammonia is converted to urea & excreted  Keto acid goes to Kreb’s or to fat or glucose Fig

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Gluconeogenesis  Occurs when amino acids are converted to Keto acids, then pyruvate, then glucose 5-43

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Uses of Different Energy Sources  Different cells have different preferred energy substrates  Brain uses glucose as its major source of energy 5-44