ATP. The point is to make ATP!

Transcription

1 ATP The point is to make ATP!

2 The energy needs of life Organisms are endergonic systems. What do we need energy for? synthesis building biomolecules reproduction movement active transport temperature regulation

3 Where do we get the energy from? Work of life is done by energy coupling. Use exergonic (catabolic) reactions to fuel endergonic (anabolic) reactions. digestion + + energy synthesis + + energy

4 Living economy Fueling the body s economy eat high energy organic molecules food = carbohydrates, lipids, proteins, nucleic acids break them down digestion = catabolism capture released energy in a form the cell can use Need an energy currency a way to pass energy around need a short term energy storage molecule ATP

5 How does ATP store energy? AMP ADP ATP O O O O O O P O P O PO O P O P O O O O O O Each negative PO 4 more difficult to add a lot of stored energy in each bond most energy stored in 3rd P i 3rd P i is hardest group to keep bonded to molecule Bonding of negative P i groups is unstable spring-loaded P i groups pop off easily & release energy Instability of its P bonds makes ATP an excellent energy donor

6 Oxidation & reduction (redox) Oxidation Reduction removing H adding H loss of electrons gain of electrons releases energy stores energy exergonic endergonic oxidation C 6 H 12 O 6 + 6O 2 6CO 2 + 6H 2 O + ATP reduction

7 Cellular respiration

8 Glycolysis Breaking down glucose glyco lysis (splitting sugar) glucose pyruvate 6C 2x 3C In the cytosol? Why does that make evolutionary sense? occurs in cytosol ancient pathway which harvests energy where energy transfer first evolved transfer energy from organic molecules to ATP still is starting point for ALL cellular respiration but it s inefficient generate only 2 ATP for every 1 glucose

9 Evolutionary perspective Prokaryotes first cells (had no organelles) Anaerobic atmosphere Enzymes of glycolysis are well-conserved Life on Earth first evolved without free oxygen (O 2 ) in the atmosphere. Energy had to be captured from organic molecules in absence of O 2. Prokaryotes that evolved glycolysis are ancestors of all modern life. ALL cells still utilize glycolysis.

10 Glycolysis summary ENERGY INVESTMENT endergonic invest some ATP -2 ATP ENERGY PAYOFF G3P C-C-C-P 4 ATP exergonic harvest a little ATP & a little NADH like $$ in the bank NET YIELD net yield 2 ATP 2 NADH

11 Substrate-level Phosphorylation In the last steps of glycolysis, where did the P come from to make ATP? P is transferred from PEP to ADP kinase enzyme ADP ATP the sugar substrate (PEP) ATP H 2 O 9 enolase Phosphoenolpyruvate (PEP) ADP ATP Pyruvate 10 pyruvate kinase Phosphoenolpyruvate (PEP) Pyruvate H 2 O ADP ATP O - C O C O CH 2 O - C O C O CH 3 P I get it! The P i came directly from the substrate!

12 Fermentation (anaerobic) Bacteria, yeast pyruvate ethanol + CO 2 3C NADH NAD + beer, wine, bread dead-end process 2C Animals, some fungi pyruvate lactic acid 3C NADH NAD + 3C cheese, anaerobic exercise (no O 2 ) 1C back to glycolysis back to glycolysis reversible process; lactic acid pyruvate in liver

13 Pyruvate (product of glycolysis) is a branching point Pyruvate O 2 O 2 fermentation (anaerobic respiration) mitochondria Krebs cycle (aerobic respiration)

14 Pyruvate oxidized to Acetyl CoA NAD + reduction Pyruvate C-C-C CO 2 Coenzyme A oxidation Acetyl CoA C-C Yield = 2C sugar + NADH + CO 2 2 x [ ]

15 Krebs cycle aka Citric Acid Cycle Occurs in mitochondrial matrix Evolved later than glycolysis does that make evolutionary sense? bacteria 3.5 billion years ago (glycolysis) free O billion years ago (photosynthesis) eukaryotes 1.5 billion years ago (aerobic respiration = organelles mitochondria) Hans Krebs

16 Count the carbons! pyruvate 3C 4C 2C acetyl CoA 6C citrate This happens twice for each glucose molecule 4C 4C oxidation of sugars x2 6C 5C CO 2 4C 4C CO 2

17 Count the electron carriers! pyruvate NADH 3C 2C 4C 6C acetyl CoA citrate CO 2 NADH This happens twice for each glucose molecule 4C 4C reduction of electron carriers x2 6C 5C CO 2 NADH FADH 2 4C ATP 4C CO 2 NADH

18 Electron Carriers = Hydrogen Carriers Krebs cycle produces large quantities of electron carriers NADH FADH 2 go to Electron Transport Chain! ADP + P i ATP H + H + H + H + H + H + H + H + H +

19 Value of Krebs cycle? If the yield is only 2 ATP then how was the Krebs cycle an adaptation? value of NADH & FADH 2 electron carriers & H carriers reduced molecules move electrons reduced molecules move H + ions to be used in the Electron Transport Chain like $$ in the bank

20 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! I need a lot more ATP! A working muscle recycles over 10 million ATPs per second!

21 There is a better way! Electron Transport Chain series of proteins built into inner mitochondrial membrane along cristae transport proteins & enzymes transport of electrons down ETC linked to pumping of H + to create H + gradient yields ~36 ATP from 1 glucose! only in presence of O 2 (aerobic respiration) That sounds more like it! O 2

22 Mitochondria Structure Double membrane energy harvesting organelle smooth outer membrane highly folded inner membrane cristae intermembrane space fluid-filled space between membranes matrix inner fluid-filled space DNA, ribosomes enzymes outer intermembrane space inner membrane membrane cristae matrix What cells would have AP a lot Biology of mitochondria? mitochondrial DNA

23 But what pulls the electrons down the ETC? O 2 H 2 O electrons flow downhill to O 2 oxidative phosphorylation

24 Electrons flow downhill Electrons move in steps from carrier to carrier downhill to oxygen each carrier more electronegative controlled oxidation controlled release of energy

25 Chemiosmosis The diffusion of ions across a membrane build up of proton gradient so H + could flow through ATP synthase enzyme to build ATP Chemiosmosis links the Electron Transport Chain to ATP synthesis So that s the point!

26 Cellular respiration 2 ATP 2 ATP ~36 ATP + +

27 Summary of cellular respiration C 6 H 12 O 6 + 6O 2 6CO 2 + 6H 2 O + ~40 ATP Where did the glucose come from? Where did the O 2 come from? What is it used for? Where did the CO 2 come from? Where did the CO 2 go? 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?

28 Taking it beyond What is the final electron acceptor in Electron Transport Chain? O 2 NADH So what happens if O 2 unavailable? ETC backs up nothing to pull electrons down chain NADH & FADH 2 can t unload H ATP production ceases cells run out of energy and you die! H + Q NADH dehydrogenase H + e C e FADH 2 FAD 1 NAD + 2 cytochrome bc complex H + e 2H + + O 2 H 2 O cytochrome c oxidase complex

29 Credits Adapted, with permission, from the fabulous work of Kim B. Foglia, ExploreBiology.com.