Chapter 15 lecture 4

2006-2007

Cellular RespirationStage 4:

Electron Transport Chain

Cellular respiration

2006-2007

What’s thepoint?

The pointis to make

ATP!

ATP

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!

A working muscle recycles over 10 million ATPs per second

There’s got to be a better way!

I need a lotmore ATP!

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 O2 (aerobic respiration)

O2That

sounds morelike it!

Mitochondria Double membrane

outer membrane inner membrane

highly folded cristae enzymes & transport

proteins intermembrane space

fluid-filled space between membranes

Oooooh!Form fits function!

Electron Transport Chain

Intermembrane space

Mitochondrial matrix

Q

C

NADH dehydrogenase

cytochromebc complex

cytochrome coxidase complex

Innermitochondrialmembrane

G3PGlycolysis Krebs cycle

8 NADH2 FADH2

Remember the Electron Carriers?

2 NADH

Time tobreak open

the piggybank!

glucose

Electron Transport Chain

intermembranespace

mitochondrialmatrix

innermitochondrialmembrane

NAD+

Q

C

NADH H2O

H+

e–

2H+ + O2

H+H+

e–

FADH2

12

NADH dehydrogenase

cytochromebc complex

cytochrome coxidase complex

FAD

e–

H

H e- + H+

NADH NAD+ + H

H

pe

Building proton gradient!

What powers the proton (H+) pumps?…

H+

H+H+

H+

H+ H+

H+H+H+

ATP

NAD+

Q

C

NADH H2O

H+

e–

2H+ + O2

H+H+

e–FADH2

12

NADH dehydrogenase

cytochrome bc complex

cytochrome coxidase complex

FAD

e–

Stripping H from Electron Carriers 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

ADP+ Pi

TA-DA!!Moving electrons

do the work!

H+ H+ H+

But what “pulls” the electrons down the ETC?

electronsflow downhill

to O2 oxidative phosphorylation

O2

H2O

Electrons flow downhill Electrons move in steps from

carrier to carrier downhill to oxygen each carrier more electronegative controlled oxidation controlled release of energy

make ATPinstead of

fire!

H+

ADP + Pi

H+H+

H+

H+ H+

H+H+H+We did it!

ATP

Set up a H+

gradient Allow the protons

to flow through ATP synthase

Synthesizes ATP

ADP + Pi ATP

Are wethere yet?

“proton-motive” force

The diffusion of ions across a membrane build up of proton gradient just so H+ could flow

through ATP synthase enzyme to build ATP

Chemiosmosis

Chemiosmosis links the Electron Transport Chain to ATP synthesis

Chemiosmosis links the Electron Transport Chain to ATP synthesis

So that’sthe point!

Peter Mitchell Proposed chemiosmotic hypothesis

revolutionary idea at the time

1961 | 1978

1920-1992

proton motive force

H+

H+

O2+

Q C

ATP

Pyruvate fromcytoplasm

Electrontransportsystem

ATPsynthase

H2O

CO2

Krebscycle

Intermembranespace

Innermitochondrialmembrane

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

ATP

4. Protons diffuse back indown 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

Summary of cellular respiration

Where did the glucose come from? Where did the O2 come from? Where did the CO2 come from? Where did the CO2 go? Where did the H2O come from? Where did the ATP come from? What else is produced that is not listed

in this equation? Why do we breathe?

C6H12O6 6O2 6CO2 6H2O ~40 ATP+ + +

ETC backs up nothing to pull electrons down chain NADH & FADH2 can’t unload H

ATP production ceases cells run out of energy and you die!

Taking it beyond… What is the final electron acceptor in

Electron Transport Chain?

O2

So what happens if O2 unavailable?

NAD+

Q

C

NADH H2O

H+

e–

2H+ + O2

H+H+

e–FADH2

12

NADH dehydrogenase

cytochrome bc complex

cytochrome coxidase complex

FAD

e–

2006-2007

What’s thepoint?

The pointis to make

ATP!

ATP

Respiratory substrates Glucose – primary substrate Lipids & amino acids also can be used Energy values of substrates

Carbohydrates - 15.8 kJ/g Lipids - 39.4 kJ/g Protiens - 17.0 kJ/g

So then why don’t we use fats for energy, they have the greatest value?

THE RESPIRATORY QUOTIENT Animal cells obtain energy in the form

of ATP by oxidizing food molecules through the process of respiration.

Respiration in animal cells depends on oxygen.

Electrons from the chemical bonds of the fuel source combine with oxygen and hydrogen ions to form water and carbon dioxide.

Questions How can we quantify metabolism? How does the energy source affect the

volume of O2 consumed and volume of CO2 produced?

How do they differ among animals and how are they affected by environmental conditions?

THE RESPIRATORY QUOTIENT One ratio that is particularly useful for

understanding animal metabolism is the respiratory quotient.

The respiratory quotient (RQ) measures the ratio of the volume of carbon

dioxide (Vc) produced by an organism

to the volume of oxygen consumed (Vo).

RQ = Vc/Vo This quotient is useful because the

volumes of CO2 and O2 produced depends on which fuel source is being metabolized. Measuring RQ is a convenient way to gain information about the source of energy an animal is using. We can then compare the metabolism of animals under different environmental conditions by simply comparing RQ.

RQ Carbohydrates, such as glucose, are an

important source of fuel. The general formula for a carbohydrate is CnH2nOn. For example, if we take n = 6 we have the formula for glucose, C6H12O6.

We can describe the metabolic reaction of a carbohydrate by the following equation:

CnH2nOn + nO2 --> nCO2 + nH2O

RQ n=6

CnH2nOn + nO2 --> nCO2 + nH2O

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

Now compare the number of molecules of O2 to the molecules of CO2. We have a ratio of 1 to 1, since there are 6 O2 and 6 CO2 molecules.

RQ = Vc/Vo = 6/6 = 1

RQ In humans, the use of fats as a fuel

source is quantitatively more important than glucose. The general formula for a saturated fat is (CH2O)3(CH2)3n(CO2H)3 . For example, if we take n = 17 we have the formula for the fat glycerol tristearate.

C3n+6H6n+9O9 + (4.5n + 3.75)O2 --> (3n + 6)CO2 + (3n + 4.5)H2O

RQ C57H111O9 + 80.25 O2 57 CO2 + 55.5 H2O

RQ = Vc/Vo = 57/80.25 = 0.7 the metabolism of fat consumes a great

deal more oxygen RQ for proteins = 0.9

RQ The respiratory quotient for some

animals can change depending on their activity. At rest, a Desert Locust has an RQ of about 1.0. During flight, however, the RQ decreases to about 0.7. How would you interpret this?