Cellular Respiration: Electron Transport Chain Ch. 9

Ms. Springstroh AP Biology Adapted from Ms. Gaynor Day and Mr. Grant

AP Biology ATP What’s the point?

The point is to make

ATP

!

2006-2007

ATP accounting so far…

  

Glycolysis



Kreb’s cycle 2 ATP



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! AP Biology A working muscle recycles over 10 million ATPs per second

Stage #3: Oxidative Phosphorylation

( Electron Transport Chain (ETC) + Chemiosmosis)



Chemiosmosis is a process which



connects the processes of electron transport and ATP synthesis NADH and FADH 2



Drop off e ’s at ETC, which powers ATP synthesis using oxidative phosphorylation **OCUURS IN CRISTAE (folds of inner membrane)

Mitochondria

 Double membrane  outer membrane  inner membrane  highly folded cristae  enzymes & transport proteins  intermembrane space  fluid-filled space between membranes

Oooooh! Form fits function!



What is “ oxidative phosphorylation ”?

Recall…



Take H + /e ’s away, molecule = “oxidized”



Give H + /e ’s, molecule = “reduced”

 

Give phosphate



molecule = “phosphorylated” So… oxidative phosphorylation = process that couples removal of H + ’s/ e-’s from one molecule (NADH or FADH 2 ) & giving phosphate molecules to another molecule (ADP)

Difference between oxidative phosphorylation & substrate-level phosphorylation

 Oxidative phosphorylation : generates ATP when electrons are taken from NADH or FADH 2 (which become oxidized) and go down the

electron transport chain

. This causes P i (inorganic phosphate) to join with ADP to form ATP.

 Substrate-level phosphorylation: generates ATP when an enzyme takes a phosphate from a substrate molecule and gives it directly to ADP.

The Pathway of Electron Transport



In the ETC…



e ’s fall from glucose to oxygen not directly, rather in a series of steps. As the e ’s fall from step to step, energy is released in manageable amounts.

**NEEDS O

2

TO PROCEED (unlike glycolysis)

ETC Characteristics

  

Occurs in cristae, which increase surface area of inner mitochondrial membrane



allows more ATP to be produced ETC takes e ’s from NADH/FADH 2 to O 2 and gives them O 2 “pulls” e-’s “down” ETC due to electronegativity (high affinity for e ’s)

What happens at the end of the ETC chain?



Electrons are passed to oxygen, forming water



O

2

= final e- acceptor

How ETC generates ATP



ETC does NOT make ATP directly but provides the stage for chemiosmosis occur to



The energy from “falling” e-’s (exergonic) in the ETC is used to pump H+’s from mitochondrial matrix to intermembrane space



Results in a H+ (proton) gradient inside mitochondria



Inside (matrix) = low [H+]



Outside (intermembrane space) = high [H+]

Glycolysis Oxidative phosphorylation.

electron transport and chemiosmosis http://highered.mcgraw hill.com/olcweb/cgi/pluginpop.cgi?it=swf::53 5::535::/sites/dl/free/0072437316/120071/bi o11.swf::Electron%20Transport%20System %20and%20ATP%20Synthesis Inner Mitochondrial membrane ATP ATP ATP H + H +  Chemiosmosis and the electron transport H +

Protein complex

Cyt

c

chain

Intermembrane of electron space carriers

Q

IV Inner mitochondrial membrane Mitochondrial matrix Figure 9.15

I III NADH + II FADH 2 FAD + NAD + 2 H + + 1 / 2 O 2 H 2 O ATP synthase

ADP + P i ATP

(Carrying electrons from, food)

H +

Electron transport chain

Electron transport and pumping of protons (H + ), which create an H + gradient across the membrane

Chemiosmosis

ATP synthesis powered by the flow Of H + back across the membrane

Oxidative phosphorylation

Chemiosmosis

 A mechanism which uses energy stored in the H+ gradient across any membrane to drive cellular work   Cellular work in this case = synthesis of ATP

Utilizes ATP synthase

 the enzyme that actually makes ATP from ADP and P i

Chemiosmosis: The Energy Coupling Mechanism INTERMEMBRANE SPACE H + H + H + H + H + H + H + ATP Synthase Figure 9.14

ADP + P i MITOCHONDRIAL MATRIX ATP H +

MITOCHONDRION CYTOSOL Electron shuttles span membrane

2 NADH

2 NADH or 2 FADH 2 2 NADH 6 NADH 2 FADH 2

 There are three main processes in this

Glycolysis Oxidative

Glucose 2 Pyruvate 2 Acetyl CoA

Citric acid cycle phosphorylation: electron transport and chemiosmosis + 2 ATP by substrate-level phosphorylation + 2 ATP by substrate-level phosphorylation + about 32 or 34 ATP by oxidative phosphorylation Maximum per glucose: Figure 9.16

About 36 or 38 ATP

 We will cover the following two slides when we learn about photosynthesis, but you can preview them now if you want. You’ll probably understand most of them!

A Comparison of Chemiosmosis in Chloroplasts and Mitochondria



Chloroplasts and mitochondria



Generate ATP by the SAME basic mechanism: chemiosmosis



But use different sources of energy to accomplish this



http://student.ccbcmd.edu/~gkaiser/biotutorials/cellresp/atp ase_flash.html



The spatial organization of chemiosmosis differs in chloroplasts and mitochondria



In both organelles



electron transport chains generate a H + gradient across a membrane



ATP synthase



Uses this proton motive force to make ATP