Oxidative phosphorylayion (ETC)

Question 1

What do reduction potentials measure?

Answer 1

Affinity for electron acceptor and donors in Volts.
Free energy exchange in REDOX reactions is proportional to the ability of reactants to donate or accept electrons -delta G is represented by the redox potential

Question 2

What is a central feature of metabolism?

Answer 2

Transfer of inorganic phosphate groups

Question 3

What is responsible for the work done?

Answer 3

The flow of electrons in oxidation and reduction

Question 4

What are the 4 ways electrons can be transferred in REDOX reactions

Answer 4

1. Directly as electrons
2. As H atoms (one H atom contains one proton and one electron)
3. Transfer of a hydride ion (H-) (in reaction 6 of glycolysis to NAD+- oxidation and phosphorylation)
4. Direct combination with oxygen

Question 5

What does a highly negative redox potential indicate?

Answer 5

High electron transfer potential- ability to donate electrons will be stronger by NADH

Question 6

What are the small activation energies overcome by in stepwise oxidation of sugar?

Answer 6

Body temperature

Question 7

What does a highly positive redox potential indicate?

Answer 7

Oxygen will be a good electron acceptor

Question 8

How many carriers are in the ETC?

Answer 8

5

Question 9

What are the metabolic carriers?

Answer 9

NAD+ and FAD

Question 10

What are the ETC carrier components?

Answer 10

Ubiquinone, Cytochromes and Fe-S proteins

Question 11

Where does ubiquinone (Q complex) move in the membrane?

Answer 11

It can move freely in the hydrophobic part of the membrane. It transfers the electrons from complext I and II to complex III (in reduced form of QH2)

Question 12

What is Q called?

Answer 12

Ubiquinone

Question 13

What is QH2 called?

Answer 13

Ubiquinol

Question 14

What is a cytochrome?

Answer 14

Heme containing proteins

Question 15

What are the mobile carriers in ETC?

Answer 15

QH2 and cytochrome C

Question 16

What does complex I do?

Answer 16

NADH dehydrogenase; catalyses electron transfer from NADH to ubiquinone Q to form ubiquinol (QH2) where it transfers electrons to complex III

Question 17

What does complex II do?

Answer 17

Succinate dehydrogenase; Contains CA intermediate succinate and cataylses electron transfer from succinate (formation of FADH as in CAC) to QH2 ubiquinone (which transfers electrons to complex III)

Question 18

What does complex III do?

Answer 18

Ubiquinone: cytochrome c oxidoreductase

• contains cytochromes and Fe-S centres
• receives electrons from ubiquinol (QH2) and reoxidises to ubiquinone, Q. (very complex)
• 4 H pumped across (2 from matrix, 2 from QH2)

Question 19

What does complex IV do?

Answer 19

Cytochrome oxidase; catalyses e- transfer to O2
- contains cyt a,a3 and 2 Cu ions 
- Involves 2 e- centres to reduce O2
O2+ 4H+ 4e-  --> 2H2O 
- 2 H+pumped across 

• transfers electrons DIRECTLY to oxygen

Question 20

How is a proton gradient formed?

Answer 20

From the transfer of electrons down electron transport chain

Question 21

What is the proton gradient affected by?

Answer 21

The pH gradient (matrix pH= 8 and outside pH=7)

- Voltage gradient (matrix is electronegative compared to outside space)

Question 22

To try and make the membrane more neutral, what happens?

Answer 22

A proton motive force occurs where the protons flow in from intermembrane space to matrix. (PMF)

Question 23

When E0 is sufficiently large, what occurs in ETC?

Answer 23

PROTONS are pumped across the inner mitochondrial membrane to INTERMEMBRANE SPACE

Question 24

Which strucutre controls flow of protons back into the matrix?

Answer 24

ATP synthase

Question 25

How is ATP actually snythesised in ETC?

Answer 25

From the ADP and Pi using the energy obtained from the protomotive force (PMF) - ATP synthase being an enzyme links enzymatic reactions with electron transport

Question 26

What is chemiosmotic theory?

Answer 26

Energy derived from electron transfer reactions is temporarily stored as transmembrane differnce in charge and pH which subsequently drives the formation of ATP in oxidative phosphorylation

Question 27

What maintains the proton gradient?

Answer 27

the complexes in the ETC pumping protons into intermembrane space

Question 28

What would happen if the ATP synthase stopped turning?

Answer 28

Cell would die because no electric potential left to generate energy

Question 29

Which side of the inner membrane has a highly positive charge of protons; intermembranal space or matrix?

Answer 29

The intermembranal space. Protons are pumped in ETC from matrix TO INTERMEMBRANAL SPACE to maintain the concnetration gradient.

Question 30

What does oxidative phosphorylation mean?

Answer 30

That the transfer of electrons causes oxygen to be reduced to H2O as well as phosphorylation of ADP to ATP. (Synthesis of ATP and transfer of e-s are COUPLED)

Question 31

What is the F0 component of ATP snythase?

Answer 31

The channel part; protons enter from the intermembrane space (proton conc high)

Question 32

What is the F1 component of ATP synthase?

Answer 32

Movement of electrons causes conformational change which activates enzymatic activity (rotates once H atom bind to it) - Also converts ADP to ATP

Question 33

What is oxidative phosphorylation regulated by?

Answer 33

Level of ADP in the system

Question 34

What needs to occur to maintain coupling?

Answer 34

The mitochondiral membrane (inner must remain intact)

Question 35

What is an artificial situation to break the inner mitochondrial membrane and what is the effect?

Answer 35

When you harvest mitochondria in lab can cause mechanical damage (inner membrane). Membrane becomes leaky- can't maintain and generate PMF so cant synthesise ATP (no more proton gradient) - electron transfer occurs but no phosphorylation (processes have been uncoupled)

Question 36

What are chemicals that can cause uncoupling?

Answer 36

2,4-dinitrophenol (DNP) can bind protons in intermembranal space and diffuse through through innner mitochondiral membrane back into matrix (destroys proton gradient so no PMF) - oxygen consumption occuring but no ATP synthesis hence uncpoupling

Question 37

What do venturicidin and oligomycin do?

Answer 37

Inhibit ATP synthase complex (block F0 channel and prevent movement of protons back into mitochondrial matrix)-uncoupled processes -no ATP synthesis - inhibit electron transport and ATP synthesis only in coupled mitochondira

Question 38

What is a natural uncoupler?

Answer 38

Brown (due to mitochondria) fat in babies. Mitochondria have uncoupling protein called thermogenin (because babies need to keep warm rather than produce energy) - transfer electrons like usual but energy produced for synthesising ATP is instead used to generate heat. (does't move through ATP synthase) - Hibernating animals

Question 39

Which complex does cyanide (CN-) inhibit?

Answer 39

It inhibits at complex IV -prevents transfer of electrons to oxygen

Question 40

What do the inhibitor inhibit?

Answer 40

BOTH the electron transport AND the ATP synthesis

Question 41

What does an increase in ADP activate?

Answer 41

ATP synthase,electron transfer, and oxygen consumption (regulation is respiratory control)