How Cells Harvest Energy

Chapter 9

We EAT sunlight energy

trapped in arrangement of atoms

CELLULAR RESPIRATION why do we need oxygen?

energy

Breathing by-product of photosynthesis? • Cellular Energy Harvest

• Cellular Respiration – Glycolysis – Oxidation of Pyruvate – Krebs Cycle – Electron Transport Chain

• Catabolism of Protein and Fat • Fermentation • Evolution of Metabolism

burning fuel in the car

•Organic compounds + O2 -> CO2 + H2O + Energy

HEAT

•Catabolic pathways release energy

Autotrophs self feeders use photosynthesis (usually) to make their own food

produce organic molecules from CO2

ALSO source for all nonautotrophic food! • Heterotrophs (us) consumers of biosphere

– feed on • plants and others • dead organisms (feces, fallen leaves)

– dependent on photoautotrophs for: – food – oxygen

Cellular Respiration • Cells harvest energy • break chemical bonds and shift electrons OXIDATION OF GLUCOSE – GLUCOSE LOSES ELECTRONS (also protons ie hydrogen)

– aerobic respiration - final electron acceptor is oxygen

– anaerobic respiration - final electron acceptor is inorganic molecule (not oxygen)

– fermentation - final electron acceptor is an organic molecule

LIFE IS A LOT OF WORK!

•Carbohydrates, fats, and proteins - all fuel

•traditional - glucose

•C6H12O6 + 6O2 -> 6CO2 + 6H2O + Energy (ATP + heat)

•The catabolism of glucose is exergonic •delta G = 686 Kcal per mole of glucose. •positive or negative? •WASTE PRODUCTS HAVE LESS ENERGY • Remember Chemical reactions - exergonic or endergonic - based on free energy Do these products have more or less energy?

• SPONTANEOUS (less energy, releases heat)

Overall reaction:

glucose + oxygen -> carbon dioxide + water + energy

C6H12O6 + 6O2 6CO2 + 6H2O + energy

how could this be measured in the lab?

ATP

• Adenosine Triphosphate • energy currency – drive movement – drive endergonic reactions • ATP Energy Currency : • adenosine triphosphate

• nucleotide – nitrogenous base (adenine) – sugar (ribose) – three phosphate groups

Figure 8.14a ATP

•phosphate bonds –covalent, but weak - each has negative charge

•repulsion contributes to instability

– Negatives repel – Phosphates are negative

– ATP (three phosphates), ADP (two phosphates)

– Linking them requires overcoming repulsion Requires energy

– ATP from ADP and a third phosphate requires energy (endergonic)

– Releasing phosphate from ATP generates energy (exergonic) • bonds between phosphate groups broken by hydrolysis

– Hydrolysis forms adenosine diphosphate –

– [ATP -> ADP + Pi]

– releases 7.3 Kcal of energy per mole of ATP

– delta G is -13 kcal/mol

Cell membrane •How IT WORKS IN extracellular Enzyme muscle cells Calcium ions –Calcium ions move to enzyme ATP binding Ca++ site Ca++ ATP –ATP splits -ADP and P phosphate ADP Ca++ P Cytosol –energy transfers phosphate intracellualr onto protein Ca++ P – –shape change drives calcium across membrane P

biochemical pathways •ATP: Important Energy Storage Molecule energy stored as phosphate bond in ATP

3rd phosphate group energy released added to ADP when phosphate bond broken using energy from food p p p

ATP energy energy IN OUT

energy hill p p p p p p P + ADP P + ADP which is exergonic? enderogonic? but we only have about .5 - 3 min worth of ATP stored! Home runs and creatine? Creatine donates phosphate group!

creatine – natural amino acid (not protein)

C4H10N3O5P (liver, kidney)

Lots in muscle, cardiovascular tissues

increases phosphocreatine -> ATP

“reservoir” for ATP production 1 g diet; 1 g synthesized

high intensity exercise (baseball)

• transfer of phosphate group from ATP phosphorylation Substrate level phosphorylation – changes shape - work (transport, mechanical, or chemical)

– returns to alternate shape

MUSCLE-RECYCLES 10 MILLION ATP/SEC Also oxidative phosphyloration

• Uses proton gradient to produce ATP

• What are protons? H +

• Our cells do both

redox reactions transfer electron(s) from one reactant to another oxidation-reduction reactions loss of electrons - oxidation (degrades, catabolic – ENERGY OUT)

\addition of electrons – reduction (energy IN, anabolic)

Hydrogen, electrons

NAD is a Cofactor (co enzyme, organic) Na + Cl Na+ Cl- salt - redox reaction *Na is oxidized -the reducing agent *Cl is reduced – the oxidizing agent

(Cl charge is reduced - drops from 0 to -1) electron donor (sodium) - reducing agent electron recipient (cloride) - oxidizing agent need both donor and acceptor

Oxygen - potent oxidizing agent (it is reduced!)

CH4 + 2O2 CO2 + 2H2O

*CH4 is oxidized

*O2 is reduced

*oxidation often involves the loss of H

Importance of electrons

*key role in atom’s reactivity

*CR - Transfer of e- through a series of steps releases energy the cell can use

WHY SMALL STEPS? - HEAT cellular respiration – series of redox

• glucose is oxidized, releasing energy (oxidation -loses electrons)

C6H12O6 + 6O2 -> 6CO2 + 6H2O + energy (including heat) • oxygen is reduced (gains electrons)

Hypoxia Shock Sepsis Altitude sickness Blood loss Systemic inflammation

Path of e- in cellular respiration:

food NADH e- transport chain oxygen Oxidation

C6H12O6 + 6O2 6CO2 + 6H2O + energy

Reduction

* happens over a series of steps that involve special molecules called electron transporters

• Electron Carrier Molecules Shuttle Electrons

– Most important electron carrier is NAD+.

COFACTOR NAD+ - oxidizing agent, accepts a hydrogen atom and TWO electrons, becoming NADH

– NADH can carry electrons down energy hill on to another acceptor (also FAD/FADH) – Enzymes coordinate these transfers.

- - - - NAD+ NADH NAD+ empty loaded empty

+ + H proton NAD

+ H oxidized - + - + NAD NAD H - - - + - H reduced + H Electron loss accompanied by protons (hydrogen ion) “dehydrogenation” 4 stages of cellular respiration 1.Glycolysis 2.Pryuvate Oxidation 3.Krebs cycle 4.Electron transport chain *net result of the 4 stages is about 36 ATP per glucose molecule

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

Cytoplasm Glucose

NADH Glycolysis ATP

Pyruvate

NADH Pyruvate CO Intermembrane oxidation 2 space Acetyl- CoA Mitochondrial matrix

NADH CO2 Krebs cycle ATP

FADH2

H2O ATP NAD+ and FAD - e Electron transport chain Inner mitochondrial membrane Mitochondrion •cellular respiration uses oxygen as a reactant to breakdown organic molecules

•Most occurs in “matrix” of mitochondria

•BUT 1st step (glycolysis) occurs in cytoplasm (before mitochondria)

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

OVERVIEW OF GLYCOLYSIS

1 2 3 6-carbon glucose (Starting material) 2 ATP

P P P P

6-carbon sugar diphosphate 6-carbon sugar diphosphate SOME ENERGY OUT!

P P P P

ENERGY IN!!!!!! 3-carbon sugar 3-carbon sugar 3-carbon sugar 3-carbon sugar phosphate phosphate phosphate phosphate NADH NADH

2 ATP 2 ATP

3-carbon 3-carbon pyruvate pyruvate Priming reactions. Priming Cleavage reactions. Then, the Energy-harvesting reactions. reactions. Glycolysis begins with six-carbon molecule with two Finally, in a series of reactions, each the addition of energy. Two high- phosphates is split in two, forming of the two three-carbon sugar energy phosphates from two two three-carbon sugar phosphates is converted to molecules of ATP are added to the pyruvate. In the process, an energy- six-carbon molecule glucose, phosphates. rich hydrogen is harvested as producing a six-carbon molecule NADH, and two ATP molecules are with two phosphates. formed.

glycolysis - steps 1. glucose (6 carbon-sugar) split into two, 3- carbon sugars

2. sugars are oxidized and rearranged to form 2 molecules of pyruvate.

3. Each step catalyzed by specific enzyme

4. steps divided into 2 phases: an energy investment phase and an energy payoff phase. *Most of the energy contained in glucose is still stored in pyruvate, which goes into the Krebs Cycle Glycolysis yields 2 ATP and 2 pyruvates, 2 NADH net yield of glycoloysis

2ATP, 2NADH, 2 pyruvates Can it end here?

Copyright © The McGraw-Hill Companies, Inc. Permission equired for reproduction or display. With oxygen Without oxygen Pyruvate

+ H20 NAD CO2

NADH O2 NADH Acetaldehyde

NADH Acetyl-CoA NAD+

+ Lactate NAD

Krebs cycle Ethanol

• alcohol fermentation- pyruvate converted yeast to ethanol in 2 steps. in absence of oxygen (bread and wine)

dump electrons from NADH onto acetaldehyde

(converted from pyruvic acid by spewing off CO2))

reducing it to ethanol, and regenerating NAD+. • lactic acid fermentation in animals in absence of oxygen (muscle fatigue), pyruvate accepts electrons from NADH and regenerates NAD+, but is converted into lactic acid (muscle burn)

• Muscle cells switch from AR to fermentation to generate ATP when O2 is scarce.

• waste product, lactate -muscle fatigue, but ultimately converted back to pyruvate in the liver

• used to make cheese and yogurt

4 stages of cellular respiration 1.Glycolysis 2.Pryuvate Oxidation 3.Krebs cycle 4.Electron transport chain

*Pryuvate is “Fork in the road”

pyruvate must be converted to Acetyl CoA

Bridge between glycolysis and Krebs Cycle pyruvate enters mitochondria using transport protein in mitochondrial membrane, converted to Acetyl CoA (cofactor) - also releases NADH • Transition between Glycolysis and Krebs Cycle

–In the presence of oxygen, each of the two pyruvic acids travels into the mitochondria.

– Combine with coenzyme A to make acetyl CoA, one NADH, and CO2

–Next - Krebs cycle inner compartment of mitochondria

Mitochondria

• outer and inner phospholipid bilayer membrane

• outer is smooth, inner membrane is folded crista (s) cristae(p)

-matrix –SOLUTION - high concentration of enzymes

REMEMBER mitochondrion?

•For LAST stage -enzyme ATP synthase embedded in inner membrane channel through which protons cross membrane Protons move down concentration gradient

.ATP synthesis - rotary motor

.driven by a gradient of protons 4 stages of cellular respiration 1.Glycolysis 2.Pryuvate Oxidation 3.Krebs cycle 4.Electron transport chain

*Pryuvate is “Fork in the road”

4 stages of cellular respiration

3rd step - Krebs Cycle

*occurs in mitochondrial matrix

*gives off 2 CO2/turn (each) *Yields 1 ATP, 3 NADH, & 1 FADH2 (each)

glycolysis mitochondrion

pyruvic acid

cytosol NAD+

coenzyme A NADH to electron transport chain

CoA acetyl coenzyme A CO2

inner Krebs compartment cycle SUMMARY OF THE KREBS CYCLE 6 NADH GLYCOLYSIS

2 FADH2

CoA Krebs CO acetyl coenzyme A cycle 2 2 ATP

electron transport chain

note 1st product oxaloacetic acid 1. citric acid citric acid NAD+ NADH NADH NAD+ cycle 2. 6. CO2

α-ketoglutaric acid note CO2 malic acid 3. + CO2 FADH2 FAD NAD+ NADH 5. ADP

succinic acid 4. α-ketoglutaric acid derivative

ATP

Krebs Cycle *8 reactions, 8 enzymes in the matrix *3 NADHs made for every Acetyl CoA molecule

*1FADH2 for every Acetyl CoA *1ATP for every Acetyl CoA •cycle (aka citric acid cycle)

• Importance of Krebs Cycle

– Acetyl CoA broken down into CO2

– Only 1 ATP made for each acetyl CoA that enters (total 2 ATP per glucose)

– But, most electrons have been “captured” onto 6 NADH and 2 FADH2 (per glucose) for last stage (electron transport chain) 4 stages of cellular respiration 1.Glycolysis 2.Pryuvate Oxidation 3.Krebs cycle 4.Electron transport chain

*Pryuvate is “Fork in the road”

4 stages of cellular respiration finally - Payoff Electron transport chain *in inner mitochondria membrane

*yields CO2 and water *AND Yields about 38 ATP!!

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Intermembrane H+ space H+ H+ H+ + H+ H+ H H+

Rotor

Rod

Catalytic head ADP + Pi

ATP H+ Mitochondrial matrix chemiosmosis • Coupling (linking)

• A) the movement of protons (Hydrogen minus its electron)

• across a membrane (mitochondria)

• B) to the synthesis of ATP outer inner membrane membrane

H + + H + H + H + H electron transport chain

Krebs H + cycle + H + H

H+ e-

O2

outer H2O compartment

inner compartment

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Intermembrane space H+ H+ Inner H+ H+ H+ mitochondrial membrane

ADP + Pi NAD+

NADH ATP Proton pump H+

Mitochondrial matrix ATP synthase

• Electron Transport Chain

• NADH and FADH2 drop off electrons onto molecules in inner membrane. – Movement of electrons powers the movement of H+ ions against concentration gradient. – pumps H+ from matrix into intermembrane space. – now H+ move down gradient back into matrix – energy is used to transfer phosphate onto ADP to make ATP. – Greatest amount made in this stage (28- 30 ATP /glucose)

+ – end of the chain O2 + 2 electrons + 2 H = H2O

– why we must breathe Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Intermembrane space H+ H+ Inner H+ H+ H+ mitochondrial membrane

ADP + Pi NAD+

NADH ATP Proton pump H+

Mitochondrial matrix ATP synthase

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

Pyruvate from Intermembrane Inner + H space cytoplasm mitochondrial H+ membrane Electron transport system Q C

NADH e- 2. Electrons H+ 1. Electrons are harvested provide energy to pump - Acetyl-CoA and carried to the e transport system. protons across the membrane. NADH e- H2O Krebs e- 3. Oxygen joins FADH 1 O cycle 2 with protons to 2 2 + O2 form water. 2H+

CO2 H+

2 ATP H+ 32 ATP 4. Protons diffuse back in down their concentration ATP Mitochondrial gradient, driving the synthase matrix synthesis of ATP.

electrochemical gradient 1) H+ ions pumped out of matrix during the ETC

2) H+ flows through ATP synthase

3) shape change allows ADP to be phosphorylated how do mitochondria use energy released? Chemiosmosis - coupling energy released in the ETC to synthesis of ATP

ATP production ATP generation in ETC oxidative phosphorylation occurs as result of redox reactions

REMEMBER? • transfer of phosphate group from ATP phosphorylation

Substrate level phosphorylation transfer of phosphate group from ATP phosphorylation

Substrate level phosphorylation uses enzymes

oxidative phosphorylation Uses proton gradient to produce ATP

GLYCOLYSIS mitochondrion KREBS CYCLE

inner ELECTRON TRANSPORT membrane CHAIN 32 inner compartment ATP O H O 2 2 outer compartment

outer compartment ATP SYNTHESIS H+ H+ H+ H+ H+ + + + + + inner + H H H H+ H H+ H H+ H H+ H+ membrane H+ H+ H+ H+ H+ H+ H+ H+ + + + H H H + H H+ H+ H+ H+ H+ NADH H+ ATP NAD+ synthesis + 2 H + 1/2 O2 ADP + P inner compartment H2O ATP ELECTRON TRANSPORT CHAIN

Duration of maximal exercise

Seconds Minutes 10 30 60 2 4 10 30 60 120

Percent 90 80 70 50 35 15 5 2 1 anaerobic

Percent 10 20 30 50 65 85 95 98 99 aerobic

ATP Generation during Exercise –What is greatest source of energy—aerobic or anaerobic –HOW fast would we go without mitrochondria? Feedback mechanisms control cellular respiration • Metabolic control of cellular respiration - supply and demand

– If ATP levels drop, catabolism speeds up to produce more ATP

– based on regulating activity of enzymes at strategic points in the catabolic pathway

example: third step of glycolysis

• catalyzed by phosphofructokinase (PKF)

• Allosteric regulation of phosphofructokinase sets the pace of respiration

Allosteric?

remote site Without oxygen

• Fermentation

• ALSO carbon dioxide (Archaea) • ALSO sulfur (bacteria)

• Carbohydrates, fats, and proteins all catabolized through the same pathways!!!! a gram of fat will generate twice as much ATP as a gram of carbohydrate

How did we get here? Evolution • Break down carbon (store in ATP) • Glycolysis (series 2 billion years old) • Photosynthesis - no oxygen • Photosynthesis - forming oxygen • Nitrogen “fixation” before oxygen • Aerobic respiration which is faster enzyme activity lab

Or NEXT TIME

cellular respiration lab?

•Recall cellular respiration

•C6H12O6 + 6O2 -----> 6CO2 + 6H2O + Energy •compare to photosynthesis :

6CO2 + 6H2O + light energy -----> C6H12O6 + 6O2