CHEM 160 - 2ND EXAM - TOPIC 2: ELECTRON TRANSPORT SYSTEM AND OXIDATIVE PHOSPHORYLATION

Oxidative dietary "fuel"

Most cellular energy derives from _______

fuel + O2 → energy

fuel + O2 → ____________

Oxidation

Transfer of electrons to acceptor

Oxygen

• Last acceptor in ETS

• Aerobic accepter

1. substrate-level phosphorylation

2. oxidative phosphorylation (ETS)

What are the 2 ways to make ATP?

1. Glycolysis: 2 ATP

2. Kreb's cycle: 2 ATP

What is ATP accounting of each cycle?

1. Glycolysis: ?

2. Kreb's cycle: ?

ETS (Electron transport system)

Series of molecules in mitochondrion (inner membrane)

32 ATP from 1 glucose

ETS yields to how many ATP molecules?

Aerobic

is ETC aerobic or anaerobic?

1. Double membrane

2. outer membrane

3. inner membrane
   - highly folded cristae
   - fluid-filled space between membranes = intermembrane space

4. matrix

Parts of Mitochondria

inner membrane

• highly folded cristae

• fluid-filled space between membranes = intermembrane space

matrix

It is the central fluid-filled space and form

4

How many complexes or parts in ETS?

1. COMPLEX I – NADH dehydrogenase

2. COMPLEX II – Succinate dehydrogenase

3. COMPLEX III – Cytochrome bc1 complex

4. COMPLEX IV – Cyctochrome c oxidase and Ubiquinone

What are the different parts of ETS?

NADH dehydrogenase

What is COMPLEX I

Succinate dehydrogenase

What is COMPLEX II

Cytochrome bc1 complex

What is COMPLEX III

Cyctochrome c oxidase

COMPLEX IV

Ubiquinone

Mobile part of ETS that traverses the inner mitochondrion membrane

• Complex I

• NADH dehydrogenase

What complex accepts e- from NADH?

• Complex II

• Succinate dehydrogenase

What complex accepts e- from FADH2?

I > III > IV

Path of e- from NADH

II > III > IV

Path of e- from FADH

Ubiquinone, CoQ

This carries e- from:
I => III

or
II => III

Cyt C

Carries e- from III → IV

Occurs at: Cplx I

NADH reacts with FMN resulting in NAD+ and FMNH2

What is the Step 1?

Occurs at: Cplx I

FMNH2 reacts with 2 Fe(III)SP resulting in 2 Fe(II)SP and FMN

FMN → Step 1

2 Fe(II)SP → 3

What is the Step 2?

Occurs at: Inner membrane space

Transfer of e- to CoQ

2 Fe(III)SP transfers e- and H+ to CoQ, yielding:
2 Fe(II)SP => Step 1
CoQH2 => Step 4

OR

FADH2 transfers electron and 2H to CoQ, yielding:
FAD
CoQH2 → Step 4

Step 3

Occurs at: Cplx III boundary
Coenzyme/e- carrier: 2 cyt b

CoQH2 transfers e- to 2 Fe3+

Yields:
CoQ → Step 3
2 Fe2+ → Step 5

Step 4

Occurs at: Cplx III
Coenzyme/e- carrier: 2 cyt c1

2Fe2+ transfers e- to 2 Fe3+

Yields:
2 Fe3+ → Step 4
2 Fe2+ → Step 6

Step 5

Occurs at: Cplx III boundary
Coenzyme/e- carrier: 2 cyt c

2Fe2+ transfers e- to 2 Fe3+

Yields:
2 Fe3+ → Step 5
2 Fe2+ → Step 7

Step 6

Occurs at: Cplx IV boundary
Coenzyme/e- carrier: 2 cyt a

2Fe2+ transfers e- to 2 Fe3+

Yields:
2 Fe3+ → Step 6
2 Fe2+ → Step 8

Step 7

Occurs at: Cplx IV
Coenzyme/e- carrier: 2 cyt aa3

2Fe2+ transfers e- to 2 Fe3+

Yields:
2 Fe3+ → Step 7

And:
2 Fe2+ → 1/2 O2 (Last e- acceptor)

Yielding:
2 Fe3+ (Step 8)
H2O (end)

Step 9

1/2 O2

Last electron acceptor at IV

Prevents bulk release of energy that can result in high T

Why is the ETS divided into steps?

Chemiosmotic Theory

What drives ATP synthesis?

Peter Mitchell

Who proposed the Chemiosmotic Theory?

1. Electrical potential

2. pH gradient

2 requirements of ATP synthesis according to Peter Mitchell:

ATP synthase

• enzyme in inner membrane of mitochondria

• ADP + Pi => ATP

ATP synthase

It is the only channel permeable to H+

• Chemiosmosis couples ETC to _________________

• Build up of H+ gradient just so H+ could flow through ATP synthase enzyme to build ATP

ATP synthesis

1. Open - ADP and inorganic phosphate attach

2. Loose - Start to react

3. Tight - ATP production

4. Open - ATP is released and new ADP and Pi attach
   (Repeat)

Conformations of ATP Synthase

C6H12O6 + 6O2 => 6CO2 + 6H2O + ~36 ATP

Summary of cellular respiration

Food

Where did the glucose come from?

Inhaled

Where did the O2 come from?

1. ETC backs up

2. ATP production ceases

3. cells run out of energy

4. and you die!

So what happens if O2 unavailable?

Kreb cycle

Where did the CO2 come from?

ETS

Where did the H2O come from?

Majority from ETS

Where did the ATP come from?

We need O2 in ETS

Why do we breathe?

• Most mitochondrial reactions are said to be tightly coupled.
  

• That is there is no electron flow without phosphorylation and no phosphorylation without electron flow.
  

• For example, in the absence of ADP or O2 electron flow stops, reduced substrate is not consumed and no ATP is made.

ETS Control (3)

Punches hole at inner mitochondrial membrane, decreases H+ gradient => no ATP production

2,4 Dinitrophenol (DNP)
Valinomycin
Thermogenin

Defn and 3 examples of uncouplers

Valinomycin

Releases K+ to the matrix, makes matrix more positive and decreases electric gradient

Blocking

Directly blocks the flow of H+ through the Fo, directly inihibiting OP

Antibiotic oligomycin

Example of blocker

Antibiotic oligomycin

It blocks the flow of H+ through the Fo , directly inhibiting OP.

Redox Inhibitors

stops transfer of electrons

rotenone, amytal

Redox Inhibitors

block e- from NADH to CoQ

antimycin A

blocks cyt b => cyt c1

HCN, CO

block at cyt aa3 => O2

Brown adipose (fat) cells

Contain natural uncouplers to warm animals - cold adaptation and hibernation.

Thermogenin

natural uncouplers

Energy from redox reactions at ETS is released as heat
No ATP production since it is not needed

How uncouplers can be used to warm body