What is Glycolysis? Breaking down glucose: glyco lysis (splitting sugar) Most ancient form of energy capture. Starting point for all cellular respiration. Inefficient: generates only 2 ATP for every 1 glucose. Happens in the cytosol. Why does that make evolutionary sense? Evolutionary perspective Life on Earth first evolved without free oxygen (O 2 ) in atmosphere. Energy had to be captured from organic molecules in absence of O 2 Organisms that evolved Glycolysis are ancestors of all modern life All organisms still utilize glycolysis. Overview 10 reactions Convert 6C glucose to two 3C pyruvate Produce 2 ATP & 2 NADH Glycolysis Summary Endergonic Invest some ATP. Exergonic Harvest a little ATP & a little NADH. Overall 1
Glycolysis Reaction Overview 10 Reactions Total 9 Different Enzymes needed. 2015 AP Biology - Cell Respiration Priming reactions. Glycolysis begins with the addition of energy. Two high energy phosphates from two molecules of ATP are added to the six-carbon molecule glucose, producing a sixcarbon molecule with two phosphates. Cleavage reactions Then, the six-carbon molecule with two phosphates is split in two, forming two three-carbon sugar phosphates. Energy-harvesting reactions. Finally, in a series of reactions, each of the two three-carbon sugar phosphates is converted to pyruvate. In the process, an energyrich hydrogen is harvested as NADH, and two ATP molecules are formed. 2
Substrate-level Phosphorylation In the last step of glycolysis, where did the P come from to make ATP? P is transferred from PEP to ADP o kinase enzyme o ADP ATP Is that all there is? Not a lot of energy For 1 billon years+ this is how life on Earth survived Only harvest 3.5% of energy stored in glucose Slow growth, slow reproduction We can t stop there Going to run out of NAD+. How is NADH recycled to NAD+? Without regenerating NAD+, energy production would stop so another molecule must accept H from NADH. 3
The answer? Fermentation. In Bacteria & Yeast. 2015 AP Biology - Cell Respiration o beer, wine, bread o at ~12% ethanol, kills yeast In Animals & some Fungi. o cheese, yogurt o anaerobic exercise (no O2), this is why your legs burn when running. 4
Glycolysis is only the start 2015 AP Biology - Cell Respiration Glycolysis Pyruvate has more energy to yield 3 more C to strip off (to oxidize) If O 2 is available, pyruvate enters mitochondria Enzymes of Krebs cycle complete oxidation of sugar to CO 2 What is the point? TO MAKE ATP!!! Oxidation of pyruvate Pyruvate enters mitochondria o 3 step oxidation process o Releases 1 CO 2 (count the carbons!) o Reduces NAD NADH (stores energy) o Produces acetyl CoA Acetyl CoA enters Krebs cycle o Where does CO 2 go? 1
Pyruvate oxidized to Acetyl CoA Yield = 2C sugar + CO 2 + NADH Krebs cycle Aka Citric Acid Cycle o in mitochondrial matrix o 8 step pathway each catalyzed by specific enzyme step-wise catabolism of 6C citrate molecule Evolved later than glycolysis o Does that make evolutionary sense? bacteria 3.5 billion years ago (glycolysis) free O 2 2.7 billion years ago (photosynthesis) eukaryotes 1.5 billion years ago (aerobic respiration (organelles) 2
So we fully oxidized glucose: C 6 H 12 O 6 CO 2 & ended up with 4 ATP! 3
So why is the Citric Acid Cycle so great? Krebs cycle produces large quantities of electron carriers NADH FADH 2 Stored energy! go to ETC (Electron Transport Chain) Energy accounting of Krebs Cycle Net gain = 2 ATP = 8 NADH + 2 FADH 2 So why the Krebs cycle? If the yield is only 2 ATP, then why? o Value of NADH & FADH 2 Electron carriers Reduced molecules store energy! To be used in the Electron Transport Chain 4
ATP accounting so far Glycolysis 2 ATP Kreb s cycle 2 ATP Life takes a lot of energy to run, need to extract more energy than 4 ATP! There s got to be a better way! There is a better way! Electron Transport Chain o Series of molecules built into inner mitochondrial membrane o Mostly transport proteins o Transport of electrons down ETC linked to ATP synthesis o Yields ~34 ATP from only 1 glucose! o Only in presence of O 2 (aerobic) Mitochondria (Form fits function!) Double membrane o outer membrane o inner membrane highly folded cristae* fluid-filled space between membranes = intermembrane space o matrix central fluid-filled space Electron Transport Chain 2015 AP Biology - Cell Respiration 1
Remember the NADH? 2015 AP Biology - Cell Respiration Glycolysis = 4 NADH Kreb s Cycle = 8 NADH, 2 FADH 2 lectron Transport Chain NADH passes electrons to ETC Electron Transport Chain NADH passes electrons to ETC o H cleaved off NADH & FADH 2 o electrons stripped from H atoms H+ (H ions) o electrons passed from one electron carrier to next in mitochondrial membrane (ETC) o transport proteins in membrane pump H+ across inner membrane to intermembrane space 2
But what pulls the electrons down the ETC? 2015 AP Biology - Cell Respiration Electrons flow downhill Electrons move in steps from carrier to carrier downhill to O2 o each carrier more electronegative o controlled oxidation o controlled release of energy 3
Why the build up H+? ATP synthase o enzyme in inner membrane of mitochondria ADP + Pi ATP only channel permeable to H+ H+ flow down concentration gradient provides energy for ATP synthesis o molecular power generator! o flow like water over water wheel o flowing H+ cause change in o shape of ATP synthase enzyme ATP Synthesis Chemiosmosis couples ETC to ATP synthesis build up of H+ gradient just so H+ could flow through ATP synthase enzyme to build ATP 4
Cellular respiration Summary of cellular respiration Where did the glucose come from? Where did the O 2 come from? Where did the CO 2 come from? Where did the H 2 O come from? Where did the ATP come from? What else is produced that is not listed in this equation? Why do we breathe? Taking it beyond What is the final electron acceptor in electron transport chain? O 2 So what happens if O 2 unavailable? o ETC backs up o ATP production ceases o Cells run out of energy and you die! 5
Beyond glucose: Other carbohydrates Glycolysis accepts a wide range of carbohydrates fuels o Polysaccharides glucose (hydrolysis) ex. starch, glycogen o Other 6C sugars glucose (modified) ex. galactose, fructose Beyond glucose: Proteins Proteins amino acids (Hydrolysis) 2015 AP Biology - Cell Respiration Fats glycerol & fatty acids (Hydrolysis) o Glycerol (3C) PGAL glycolysis o Fatty acids 2C acetyl groups acetyl coa Krebs cycle Carbohydrates vs. Fats Fat generates 2x ATP vs. carbohydrate o More C in gram of fat o More O in gram of carbohydrate so it s already partly oxidized. 1
Respond to cell s needs Key points of control o Phosphofructokinase Allosteric regulation of enzyme can t turn back step before splitting glucose AMP & ADP stimulate ATP inhibits citrate inhibits Why is this regulation important? Balancing act: Availability of raw materials vs. Energy demands vs. Synthesis. 2
ATP Accounting (From Glucose to ATP) Glycolysis Glucose + 2 ATP = 2 Pyruvate 4 ATP 2 NADH Oxidation of Pyruvate 2 Pyruvate = 2 Acetyl CoA 2 CO2 2 NADH Kreb s Cycle 2 Acetyl CoA = 4 CO2 2 ATP 2 FADH2 6 NADH ETC 10 NADH + 2 FADH2 = ~34 ATP (~3 ATP per NADH & ~2 ATP per FADH2) This yields approximately 38 Total ATP from 1 glucose molecule. But why does the NADH from Glycolysis make less ATP per molecule than the NADH from the Kreb s Cycle during the ETC?
2014 According to the chemiosmotic model proposed by Peter Mitchell in 1961, an electrochemical gradient is linked to the synthesis of ATP in mitochondria. Construct an explanation of the chemiosmotic model by doing each of the following. (a) Make a claim about the role of the inner mitochondrial membrane in ATP synthesis. (b) Present ONE piece of evidence that supports the role you proposed in part (a). (c) Provide reasoning to explain how the evidence you presented in part (b) supports the claim you made in part (a).
1990 The College Board Advanced Placement Examination BIOLOGY SECTION II Time 1 hour and 30 minutes Answer all questions. Number your answer as the question is numbered below. Answers must be in the essay form. Outline form is NOT acceptable. Labeled diagrams may be used to supplement discussion, but in no case will a diagram alone suffice. It is important that you read each question completely before you begin to write. 1. The results below are measurements of cumulative oxygen consumption by germinating and dry seeds. Gas volume measurements were corrected for changes in temperature and pressure. Cumulative Oxygen Consumed (ml) Time (minutes) 0 10 20 30 40 22 C Germinating Seeds 0.0 8.8 16.0 23.7 32.0 Dry Seeds 0.0 0.2 0.1 0.0 0.1 10 C Germinating Seeds 0.0 2.9 6.2 9.4 12.5 Dry Seeds 0.0 0.0 0.2 0.1 0.2 a. Using the graph paper provided, plot the results for the germinating seeds at 22 C and at 10 C. b. Calculate the rate of oxygen consumption for the germinating seeds at 22 C, using the time interval between 10 and 20 minutes. c. Account for the differences in oxygen consumption observed between: (1) germinating seeds at 22 C and at 10 C; (2) germinating seeds and dry seeds. a. Describe the essential features of an experimental apparatus that could be used to measure oxygen consumption by a small organism. Explain why each of these features is necessary. Copyright 1970 to 2004 by College Entrance Examination Board, Princeton, NJ. All rights reserved. For face to face teaching purposes, classroom teachers are permitted to reproduce the questions. Web or Mass distribution prohibited. GO ON TO THE NEXT PAGE