ATP Making energy! The point is to make ATP!

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

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

ATP Living economy Fueling the body’s economy eat high energy organic molecules food = carbohydrates, lipids, proteins, nucleic acids break them down catabolism = digest 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 high energy bonds Adenosine Triphosphate modified nucleotide nucleotide = adenine + ribose + P i  AMP AMP + P i  ADP ADP + P i  ATP adding phosphates is endergonic

How does ATP store energy? P O–O– O–O– O –O–O P O–O– O–O– O –O–O P O–O– O–O– O –O–O P O–O– O–O– O –O–O P O–O– O–O– O –O–O P O–O– O–O– O –O–O P O–O– O–O– O –O–O P O–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 AMP ADPATP

How does ATP transfer energy? P O–O– O–O– O –O–O P O–O– O–O– O –O–O P O–O– O–O– O –O–O 7.3 energy + P O–O– O–O– O –O–O ATP  ADP releases energy ∆G = -7.3 kcal/mole can fuel other reactions Phosphorylation released P i can transfer to other molecules destabilizing the other molecules enzyme that phosphorylates = kinase ADPATP

An example of Phosphorylation… Building polymers from monomers need to destabilize the monomers phosphorylate! C H OH H HOHO C C H O H C + H2OH2O kcal/mol C H OH C H P + ATP + ADP H HOHO C + C H O H CC H P + PiPi “kinase” enzyme -7.3 kcal/mol -3.1 kcal/mol enzyme H OH C H HOHO C

Another example of Phosphorylation… The first steps of cellular respiration beginning the breakdown of glucose to make ATP glucose C-C-C-C-C-C fructose-1,6bP P-C-C-C-C-C-C-P DHAP P-C-C-C G3P C-C-C-P hexokinase phosphofructokinase C H P C P C ATP 2 ADP 2

ATP / ADP cycle Can’t store ATP  too reactive  transfers P i too easily  only short term energy storage  carbohydrates & fats are long term energy storage ATP ADP P kcal/mole A working muscle recycles over 10 million ATPs per second respiration

Cells spend a lot of time making ATP! The point is to make ATP!

H+H+ catalytic head rod rotor H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ ATP synthase ATP But… How is the proton (H + ) gradient formed? ADP P + Enzyme channel in mitochondrial membrane permeable to H + H + flow down concentration gradient flow like water over water wheel flowing H+ cause change in shape of ATP synthase enzyme powers bonding of P i to ADP ADP + P i  ATP

That’s the rest of my story! Any Questions?

Cellular Respiration STAGE 1: Glycolysis

Glycolysis Breaking down glucose “glyco – lysis” (splitting sugar) most ancient form of energy capture starting point for all cellular respiration inefficient generate only 2 ATP for every 1 glucose in cytosol why does that make evolutionary sense? glucose      pyruvate 2x2x 6C3C

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

glucose C-C-C-C-C-C fructose-6P P-C-C-C-C-C-C-P DHAP P-C-C-C PGAL C-C-C-P pyruvate C-C-C 2 ATP 2 ADP 2 NAD + 2 NADH 4 ADP 4 ATP Overview 10 reactions convert 6C glucose to two 3C pyruvate produce 2 ATP & 2 NADH activation energy

Glycolysis summary endergonic invest some ATP exergonic harvest a little more ATP & a little NADH

1st half of glycolysis (5 reactions) Glucose “priming” get glucose ready to split phosphorylate glucose rearrangement split destabilized glucose PGAL

2nd half of glycolysis (5 reactions) Oxidation G3P donates H NAD  NADH ATP generation G3P  pyruvate donates P ADP  ATP

OVERVIEW OF GLYCOLYSIS 123 (Starting material) 6-carbon sugar diphosphate 6-carbon glucose 2 PP 6-carbon sugar diphosphate PP 3-carbon sugar phosphate PPPP Priming reactions. 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 six-carbon molecule with two phosphates. 3-carbon pyruvate 2 NADH ATP 2 NADH ATP 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 energy-rich hydrogen is harvested as NADH, and two ATP molecules are formed. 3-carbon sugar phosphate 3-carbon sugar phosphate 3-carbon sugar phosphate 3-carbon pyruvate

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  kinase enzyme  ADP  ATP

Energy accounting of glycolysis Net gain = 2 ATP some energy investment (2 ATP) small energy return (4 ATP) 1 6C sugar  2 3C sugars 2 ATP2 ADP 4 ADP4 ATP glucose      pyruvate 2x2x 6C3C

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 another molecule must accept H from NADH glucose + 2ADP + 2P i + 2 NAD +  2 pyruvate + 2ATP + 2NADH  Glycolysis NADH

How is NADH recycled to NAD + ? Another molecule must accept H from NADH aerobic respiration ethanol fermentation lactic acid fermentation aerobic respiration NADH

Anaerobic ethanol fermentation Bacteria, yeast 1C 3C2C pyruvate  ethanol + CO 2  Animals, some fungi pyruvate  lactic acid 3C  beer, wine, bread  at ~12% ethanol, kills yeast  cheese, yogurt, anaerobic exercise (no O 2 ) NADHNAD + NADHNAD +

Pyruvate is a branching point Pyruvate O2O2 O2O2 Kreb’s cycle mitochondria fermentation

The Point is to Make ATP! ATP What’s the point?

Cellular Respiration Oxidation of Pyruvate Krebs Cycle

Glycolysis is only the start 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 2x2x 6C3C glucose      pyruvate 3C1C pyruvate       CO 2

Cellular respiration

The Point is to Make ATP! ATP What’s the point?

Oxidation of pyruvate Pyruvate enters mitochondria 3 step oxidation process releases 1 CO 2 (count the carbons!) reduces NAD  NADH (stores energy) produces acetyl CoA Acetyl CoA enters Krebs cycle where does CO 2 go? NADNADH 3C2C 1C pyruvate    acetyl CoA + CO 2 [ 2x ]

Pyruvate oxidized to Acetyl CoA Yield = 2C sugar + CO 2 + NADH reduction oxidation

Krebs cycle aka Citric Acid Cycle in mitochondrial matrix 8 step pathway each catalyzed by specific enzyme step-wise catabolism of 6C citrate molecule Evolved later than glycolysis 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) 1937 | 1953 Hans Krebs

4C6C4C 2C6C5C4C CO 2 citrate acetyl CoA Count the carbons! 3C pyruvate x2x2 oxidation of sugars This happens twice for each glucose molecule

4C6C4C 2C6C5C4C CO 2 citrate acetyl CoA Count the electron carriers! x2x2 3C pyruvate reduction of electron carriers NADH FADH 2 NADH ATP This happens twice for each glucose molecule

So we fully oxidized glucose C 6 H 12 O 6  CO 2 & ended up with 4 ATP! Whassup?

 Krebs cycle produces large quantities of electron carriers  NADH  FADH 2  stored energy!  go to ETC NADH & FADH 2

Energy accounting of Krebs cycle Net gain=2 ATP =8 NADH + 2 FADH 2 4 NAD + 1 FAD4 NADH + 1 FADH 2 1 ADP1 ATP 3x3x pyruvate          CO 2 ][ 2x 3C 1C

So why the Krebs cycle? If the yield is only 2 ATP, then why? value of NADH & FADH 2 electron carriers reduced molecules store energy! to be used in the Electron Transport Chain

Cellular Respiration Electron Transport Chain

Cellular respiration

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 series of molecules built into inner mitochondrial membrane mostly transport proteins transport of electrons down ETC linked to ATP synthesis yields ~34 ATP from 1 glucose! only in presence of O 2 (aerobic)

Mitochondria Double membrane outer membrane inner membrane highly folded cristae* fluid-filled space between membranes = intermembrane space matrix central fluid-filled space * form fits function!

Electron Transport Chain

PGAL Glycolysis Kreb’s cycle 4 NADH 8 NADH 2 FADH 2 Remember the NADH?

Electron Transport Chain NADH passes electrons to ETC H cleaved off NADH & FADH 2 electrons stripped from H atoms  H + (H ions) electrons passed from one electron carrier to next in mitochondrial membrane (ETC) transport proteins in membrane pump H + across inner membrane to intermembrane space

But what “pulls” the electrons down the ETC?

Electrons flow downhill Electrons move in steps from carrier to carrier downhill to O 2 each carrier more electronegative controlled oxidation controlled release of energy

Why the build up H + ? ATP synthase enzyme in inner membrane of mitochondria ADP + P i  ATP only channel permeable to H + H + flow down concentration gradient = provides energy for ATP synthesis molecular power generator! flow like water over water wheel flowing H+ cause change in shape of ATP synthase enzyme powers bonding of P i to ADP “proton-motive” force

Chemiosmosis couples ETC to ATP synthesis build up of H+ gradient just so H+ could flow through ATP synthase enzyme to build ATP ATP synthesis

Peter Mitchell Proposed chemiosmotic hypothesis revolutionary idea at the time 1961 | proton motive force

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? C 6 H 12 O 6 6O 2 6CO 2 6H 2 O ~36 ATP  +++

Taking it beyond… What is the final electron acceptor in electron transport chain? O2O2  So what happens if O 2 unavailable?  ETC backs up  ATP production ceases  cells run out of energy  and you die!

The Point is to Make ATP! ATP What’s the point?

Any Questions??