CHAPTER 9 CELLULAR RESPIRATION Cellular Respiration breaking down

CHAPTER 9 – CELLULAR RESPIRATION Cellular Respiration → breaking down food to get ATP 1

MITOCHONDRIA POWERHOUSE OF THE CELL!! The mitochondria is the organelle responsible for cellular respiration. The Krebs cycle and also the ETC take place here to produce ATP. It is a double membrane with the inner membrane highly folded (to increase surface area and make the mitochondria more efficient. Intermembran e Space 2

� � � Organic compounds possess potential energy as a result of the arrangement of electrons in the bonds between their atoms. Enzymes catalyze the systematic degradation of organic molecules that are rich in energy. Some of the released energy is used to do work; the rest is dissipated as heat. Fermentation, leads to the breakdown of sugars without the use of oxygen (anaerobic. ) A more efficient catabolic process, aerobic respiration, consumes oxygen as a reactant. Although cellular respiration technically includes both aerobic and anaerobic processes, the term is commonly used to refer only to the aerobic process. 3

CELLULAR RESPIRATION – BACKGROUND INFO � � � Carbohydrates, fats, and proteins can all be used as the fuel, but it is most useful to consider glucose: Equation C 6 H 12 O 6 + 6 O 2 6 CO 2 + 6 H 2 O + energy (ATP + heat) The catabolism of glucose is exergonic, with G = − 686 kcal per mole of glucose. 4

OXIDATION AND REDUCTION Note: Look at the proximity of the electrons; they lose potential energy as they get closer to the electronegative atoms. In Cellular Respiration, Glucose is oxidized and is. Reducing agent = the thing that gets oxidized (glucose!) Oxidizing agent = the thing that gets reduced (oxygen!) Reduction – Gaining an electron; becomes more negative (hint: usually it gains a H+ too to keep it neutral – so look for the one that got a hydrogen added to it) 5

ELECTRONS “FALL” CLOSER TO OXYGEN USING THE ETC AND NADH = nicotinamide adenine dinucleotide (nicotinamide is a nitrogen base that is NOT found in DNA or RNA) � � NADH shuttles electrons from the food to the ETC Glucose → NADH → ETC → Oxygen NAD+ = oxidized form NADH = reduced form (note the H Controlled release of energy in steps via the ELECTRON TRANSPORT CHAIN (ETC)! 6

GENERAL OVERVIEW – CELLULAR RESPIRATION Glycolysis → in cytosol; turns glucose to 2 pyruvate, net gain of 2 ATP and 2 NADH; anaerobic Intermediate Step Pyruvate gets transported into the mitochondria and gets converted into Acetyl-Co. A, thereby losing a Carbon and releasing CO 2 during this step; Acetyl Co. A enters the Krebs (Citric Acid Cycle) → in mitochondrial matrix; 1 glucose powers 2 turns of Krebs, makes little ATP, NADH, and FADH 2 (electron taxis); passes e- to ETC → uses oxidative phosphorylation (concentration gradients and chemiosmosis) to make lots of ATP 7

OXIDATIVE PHOSPHORYLATION VS. SUBSTRATE LEVEL PHOSPHORYLATION Substrate Level Phosphorylation → when the P from one molecule gets attached to ADP to make ATP; it gets directly added on; ATP is made this way in glycolysis and the Krebs Oxidative Phosphorylation → uses a concentration gradient to power chemiosmosis; 90% of the ATP is made this way; very efficient; used in the ETC 8

GLYCOLYSIS Main Goal of Glycolysis is to turn glucose into two pyruvate: - Series of 10 steps Two phases: Energy Investment and Energy Payoff - Produces a net gain of 2 ATP and 2 NADH (e- carriers) - From here it can go to the Krebs cycle (aerobic respiration) or to Fermentation (anaerobic) - Does NOT release any 02 - Occurs in the cytosol Overall: Glucose → 2 Pyruvate; net gain 2 ATP and 2 NADH Glycolysis is ANAEROBIC…. does NOT require 9

GLYCOLYSIS – ENERGY INVESTMENT PHASE In the energy investment phase, 2 ATP are put into the process. Glucose → Glucose – 6 – phosphate → Fructose -6 - phosphate → Fructose- 1, 6 – biphosphate → 10

GLYCOLYSIS – ENERGY PAYOFF PHASE In the energy payoff phase, 4 ATP are produced (net gain of 2) and 2 NADH are made (to be shipped to the ETC). G 3 P → 1, 3 – biphosphoglycerate → 3 -phosphogylcerate → 2 - phosphoglycerate → Phosphoenolpyruvate → Pyruvate 11

INTERMEDIATE STEP Specific Steps of the Intermediate Step: 1. A carboxyl group is removed from the pyruvate as CO 2. 2. The remaining two-carbon fragment is oxidized to form acetate. An enzyme transfers the pair of electrons to NAD+ to form NADH. 3. Acetate combines with coenzyme A to form acetyl Co. A. This is what enters the krebs cycle. Pyruvate (made in the cytosol via glycolysis) gets transferred into the mitochondria (active transport!). As it comes in, it loses a carbon (goes from 3 C to 2 C) when it produces one molecule of CO 2. This new 2 C molecule is acetyl Co. A. Acetyl Co. A is what goes into the Krebs cycle. Also, 1 molecule of NADH is made per pyruvate (so…. 2 per glucose). So…summary of intermediate is - 1 glucose 2 acetyl Co. A - 2 CO 2 made for each glucose (b/c 2 pyruvate) - 2 NADH made for each glucose 12

KREBS/ CITRIC ACID CYCLE Main Function of the Krebs → to make electron carriers (NADH and FADH 2) to send to the ETC Series of 8 steps; Occurs in the mitochondrial matrix So… 1 glucose produces: 2 ATP 6 NADH 2 FADH 2 (remember: 1 glucose = 2 pyruvates) **Also 2 CO 2 released per turn (so 4 for one glucose) Acetyl Co. A becomes acetate and that enters the Krebs and combines with oxaloacetate form citrate (hence citric acid cycle) 13

Krebs → Makes 1 ATP, 3 NADH, and 1 FADH 2 per turn The acetyl group of acetyl Co. A joins the cycle by combining with the compound oxaloacetate, forming citrate. The next seven steps decompose the citrate back to oxaloacetate. 14

ELECTRON TRANSPORT CHAIN (ETC) Occurs on the inner membrane of the mitochondria (highly folded to increase SA); Energy from NADH and FADH 2 power ATP synthesis The ETC is a series of proteins throughout the membrane; the electrons lose energy every time they get passed down the chain Electron carriers in the chain: Flavoprotein Iron-Sulfur Protein Lipids (Ubiquinone Q) Cytochromes (iron prosthetic group) Electron carriers flip between reduced and oxidized versions as they accept and donate electrons. OXYGEN IS THE FINAL ELECTRON ACCEPTOR!!! → oxygen combines with the electrons and H+ to make WATER 15

Main Goal of the ETC → it’s a stepwise free energy drop from food to oxygen; it creates a proton gradient that powers chemiosmosis to create ATP via oxidative phosphorylation (the ETC makes no ATP directly) Note: NADH drops off its electrons at a higher level than FADH 2 because their electrons carry more energy. The ETC uses energy from the electrons and pumps the protons OUT of the matrix into the intermembrane space; it then diffuses back in via ATP synthase. 16

CHEMIOSMOSIS As electrons flow down the ETC, H+ are pumped FROM THE MATRIX into the INTERMEMBRANE SPACE, and the H+ diffuse BACK INTO the matrix via the ATP SYNTHASE Definition → energy coupling mechanism that uses energy stored in the form of a H+ gradient across a membrane to drive work How it works → as the electrons move down the ETC, the proteins pump H+ OUT of the matrix and then they use ATP Synthase to allow the H+ to diffuse back in. As the H+ diffuse back in, the ATP Synthase proteins make ATP 17

ATP SYNTHASE ATP Synthase is a protein that is powered by the H+ gradient and converts ADP to ATP. It works like a water wheel and forces a conformational change which activates the catalytic sites on ADP to bond with P to form ATP. This is how ATP is produced = CHEMIOSMOSIS 18

Final e- acceptor after they go down the ETC is OXYGEN (from the atmosphere) …it combines with e- and H+ to make WATER -NADH and FADH 2 drop off e- to the ETC -As the e- get passed down the chain, they lose energy; that energy is used to pump H+ OUT of the matrix into the intermembrane space -This creates a concentration gradient -The protons then diffuse back INTO the matrix via the ATP synthase (chemiosmosis); this creates ATP (oxidative phosphorylation) -Makes a TON of ATP!!! 19

CELLULAR RESPIRATION OVERVIEW ATP Summary → Substrate Level Phosphorylation – 4 ATP (2 from Glycolysis and 2 from Krebs); Oxidative Phosphorylation – 34 ATP (from ETC) Efficiency of Respiration → 34% efficient (66% of energy is lost as heat) 20

CELLULAR RESPIRATION VS. FERMENTATION Oxygen Present → Aerobic Respiration (efficient!) Oxygen NOT Present → Fermentation (not efficient) 21

FERMENTATION � If there is no oxygen present (anaerobic) the pyruvate (from glycolysis) goes to fermentation � The main goal of fermentation is to make NAD+ to put back into glycolysis; it makes NO ATP on its own (it just keeps glycolysis going so that it can make 2 ATP at a time) � Occurs in cytosol � 2 types of fermentation: alcohol and lactic acid 22

ALCOHOLIC FERMENTATION - Pyruvate is turned into ethanol - CO 2 is released (bubbles!) - Done by yeast for brewing, baking, winemaking 3 C Pyruvate → 2 C Ethanol Remember: Goal is to produce NAD+ to send back to glycolysis so it can keep going and produce more ATP 23

LACTIC ACID FERMENTATION - Pyruvate is turned into Lactate (or lactic acid) - Lactate is eventually carried away by the blood to the liver where it gets converted back into pyruvate - The waste product, lactate, was previously thought to cause muscle fatigue and pain, but recent research suggests instead that it may be increased levels of potassium ions (K+) - No CO 2 is released 3 C Pyruvate → 3 C Remember: Goal is to produce NAD+ to send back to glycolysis so it can keep going and produce more ATP 24

LACTIC ACID VS. ALCOHOL FERMENTATION Both start with pyruvate from glycolysis Alcohol makes ethanol and gives off CO 2 Lactic acid makes Lactic acid and does NOT give off CO 2 Both create NAD+ to be sent back to glycolysis Neither make any ATP on their own 25

FERMENTATION - OVERVIEW Obligate Aerobes → needs oxygen; can do respiration only Obligate Anaerobes → will not survive in the presence of oxygen; fermentation only Respiration is 19 times more efficient than fermentation (38 ATP vs. 2 ATP) Facultative Anaerobes → can live with or without oxygen (if given the choice they will use the oxygen to do respiration because it is so much more efficient); can do cellular respiration or fermentation; ex. Human muscle cells 26

The role of glycolysis in both fermentation and respiration has an evolutionary basis � � Ancient prokaryotes likely used glycolysis to make ATP long before oxygen was present in Earth’s atmosphere. The evidence suggests that this pathway evolved very early in the history of life on Earth. 27

WHAT KINDS OF FOOD CAN GO INTO GLYCOLYSIS? A VARIETY OF MOLECULES CAN BE USED TO MAKE ATP Carbohydrates → get broken down into their monomers and then those monomers get converted to glucose; glucose is then turned into pyruvate during glycolysis Proteins → are broken down to their individual amino acids and then the amino groups are removed (called deamination – this nitrogen waste is then excreted as urea or ammonia); the remaining carbon skeletons are then put into glycolysis and the krebs cycle Fats → glycerol is converted into glyceraldehyde phosphate (G 3 P) which is an intermediate of glycolysis; the FA chains are broken down into 2 C components that enter the Krebs as acetyl Co. A (called beta oxidation) 28

FEEDBACK MECHANISMS OF RESPIRATION Phosphofructokinase (PFK) sets the pace for respiration - It is STIMULATED by AMP and ADP - It is INHIBITED by ATP and by citrate (first product of Krebs) This ensures that we are only making as much ATP as we need and not extra that is just getting wasted. PFK is regulated allosterically by the above molecules. 29

CELLULAR RESPIRATION ANIMATION � 6 minutes https: //www. youtube. com/watch? v=Gb 2 Ez. F_Xq. A 30