harvesting stored energy

Harvesting stored energy• Glucose is the model

– catabolism of glucose to produce ATP

C6H12O6 6O2 ATP 6H2O 6CO2+ + +

CO2 + H2O + heatfuel(carbohydrates)

COMBUSTION = making a lot of heat energy by burning fuels in one step

RESPIRATION = making ATP (& some heat)by burning fuels in many small steps

CO2 + H2O + ATP (+ heat)

ATP

glucose

glucose + oxygen energy + water + carbondioxide

resp

iratio

n

O2 O2

+ heat

enzymesATP

2

ATP = adenosine triphosphate-the energy “currency” of cells

ATP stores energy in the bonds between phosphates

3

Energy Currency of Cells

When the bond between phosphates is broken:

ATP ADP + Pi

energy is released

ADP = adenosine diphosphatePi = inorganic phosphateThis reaction is reversible.

ATP

Really high energy bond

ADP + Pi

How do we harvest energy from fuels?• Digest large molecules into smaller ones

– break bonds & move electrons from one molecule to another• as electrons move they “carry energy” with them• that energy is stored in another bond,

released as heat or harvested to make ATP

e-

+ +e-

+ –loses e- gains e- oxidized reduced

oxidation reduction

redox

e-

How do we move electrons in biology?• Moving electrons in living systems

– electrons cannot move alone in cells• electrons move as part of H atom• move H = move electrons

pe

+

H

+H

+ –loses e- gains e- oxidized reduced

oxidation reduction

C6H12O6 6O2 6CO2 6H2O ATP+ + +oxidation

reductionH e-

Moving electrons in respiration• Electron carriers move electrons by

shuttling H atoms around– NAD+ NADH (reduced)– FAD+2 FADH2 (reduced)

+ Hreduction

oxidation

PO–

O–

O

–O

PO–

O–

O

–O

CC

O

NH2

N+

H

adenine

ribose sugar

phosphates

NAD+

nicotinamideVitamin B3niacin

PO–

O–

O

–O

PO–

O–

O

–O

CC

O

NH2

N+

HNADH

carries electrons as a reduced molecule

reducing power!

How efficient!Build once,use many ways

H

8

Steps of Respiration

The complete oxidation of glucose proceeds in stages:

1. glycolysis2. pyruvate oxidation3. Krebs cycle4. electron transport chain & chemiosmosis

9

Glycolysis

glucose pyruvate2x6C 3C

That’s not enoughATP for me!

• Breaking down glucose – “glyco – lysis” (splitting sugar)

– 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

– occurs in cytosol

intermembranespace inner

membrane

outermembrane

matrixcristae

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

• free in matrix & membrane-bound

mitochondrialDNA

What cells would have a lot of mitochondria?

Mitochondria – Function

What does this tell us about the evolution of eukaryotes?Endosymbiosis!

Dividing mitochondriaWho else divides like that?

Advantage of highly folded inner membrane?More surface area for membrane-bound enzymes & permeases

Membrane-bound proteinsEnzymes & permeases

bacteria!

pyruvate acetyl CoA + CO2

Oxidation of pyruvate

NAD3C 2C 1C[2x ]

• Pyruvate enters mitochondrial matrix

– 3 step oxidation process– releases 2 CO2 (count the carbons!)– reduces 2 NAD 2 NADH (moves e-)– produces 2 acetyl CoA

• Acetyl CoA enters Krebs cycle

Wheredoes theCO2 go?Exhale!

14

3. Krebs Cycle-oxidizes the acetyl Co-A-occurs in the matrix of the mitochondria

15

Krebs Cycle

After glycolysis, pyruvate oxidation, and the Krebs cycle, glucose has been oxidized to:

- 6 CO2

- 4 ATP- 10 NADH- 2 FADH2

These electron carriers proceedto the electron transport chain.

• Electron Transport Chain – series of proteins built into

inner mitochondrial membrane– yields ~36 ATP from 1 glucose!– only in presence of O2 (aerobic respiration)

O2Thatsounds morelike it!

NAD+

Q

C

NADH H2O

H+

e–

2H+ + O2

H+H+

e–FADH2

12

NADH dehydrogenase

cytochrome bc complex

cytochrome coxidase complex

FAD

e–

• Electron carriers pass electrons & H+ to ETC– H cleaved off NADH & FADH2– electrons stripped from H atoms H+ (protons)

• electrons passed from one electron carrier to next in mitochondrial membrane (ETC)

• flowing electrons = energy to do work– transport proteins in membrane pump H+ (protons)

across inner membrane to intermembrane space

H+ H+ H+

H+

ADP + Pi

H+ H+

H+

H+ H+

H+H+H+

ATP

Chemiosmosis:

• Set up a H+

gradient• Allow the protons

to flow through ATP synthase

• Synthesizes ATP

ADP + Pi ATP

“proton-motive” force

H+

H+

O2+

Q C

ATP

Pyruvate fromcytoplasm

Electrontransportsystem

ATPsynthase

H2O

CO2

Krebscycle

IntermembranespaceInner

mitochondrialmembrane

1. Electrons are harvested and carried to the transport system.

2. Electrons provide energy

to pump protons across the membrane.

3. Oxygen joins with protons to form water. 2H+

NADH

NADH

Acetyl-CoA

FADH2

ATP4. Protons diffuse back in

down their concentrationgradient, driving the synthesis of ATP.

Mitochondrial matrix

21

H+

H+

O2

H+

e-

e-

e-

e-

ATP

Cellular respiration

2 ATP 2 ATP ~36 ATP+ +

~40 ATP

21

Oxidation Without O2Respiration occurs without O2 via either:

1. anaerobic respiration-methanogens (CO2 CH4)-sulfur bacteria (SO4 H2S)

2. fermentation-ethanol (yeast)-lactic acid (animal cells)

Pyruvate is a branching pointPyruvate

O2O2

mitochondriaKrebs cycleaerobic respiration

fermentationanaerobicrespiration

Fermentation (anaerobic)• Bacteria, yeast

1C3C 2Cpyruvate ethanol + CO2

Animals, some fungipyruvate lactic acid

3C 3C

beer, wine, bread

cheese, anaerobic exercise (no O2)

NADH NAD+

NADH NAD+

back to glycolysis

back to glycolysis

24

Catabolism of Protein & FatIn the absence of carbohydrates, animals

can break down other molecules:

-proteins: amino acids converted to a molecule that enters glycolysis or the Krebs cycle

-fats: fatty acids enter Krebs cycle (produces more energy than glucose)

25