L16 - Oxidative Phosphorylation

Question 1

Examples of Oxidative reactions:

Answer 1

1. Add O2 to a molecule
2. Removing an electron
3. Removing a pair of hydrogen atom

Question 2

ETC (definition, location, tissues, function and info about components):

Answer 2

Definition:
A process for the transfer of H atoms to oxygen

Location:
Mitochondria

Tissues:
Most tissues and cell types (not red blood cell)

Functions:
‘Energy trapping’ - direct phosphorylation of ADP to produce ATP

Components:
Protein complexes embedded in IMM from
ETC for oxidative phosphorylation.
Transfers hydrogen to oxygen forming water. 
Reoxidise NADH to NAD+ for later use. 

Summary:
Stepwise transfer of H atoms to O2
NADH + O2 + H+ = H2O + NAD+
Energetically favourable as it is done in a series of reactions.
Electrons are taken with hydrogen when H transferred.

Question 3

Components of ETC (H pair acceptor and Electron acceptors):

Answer 3

H pair acceptors:

1. Flavin cofactors
2. Coenzyme Q - CoQ

Electron acceptors:
1. Iron sulphur proteins
2. Cytochrome proteins (have haem group so
have Fe on them).

Question 4

Chemical nature of electron (redox) carriers in IMM:

Answer 4

Each cofactor given redox potential - Eo’

Describes ability of the carrier to donate it’s electron to another electron acceptor molecule

Electron move from negative Eo’ to positive Eo’

O2/H2 –> Cytochrome A –> Cytochrome C

–> Cytochrome B –> CoQ –> FAD –> NAD

From more positive Eo’ to negative Eo’.
NAD/NADH being most negative.

Pathway energetically favourable as negative free energy change.

Question 5

Arrangement of carriers in ETC: THE PATHWAY of ETC included

Answer 5

NADH + H+ = NADH
Transfer electron to Flavin mononucleotide (FMN)

FMN–> CoQ–> Cyt B–> Cyt C–>Cyt A–>O2

I. Out III. Out IV. Out

0.5O2 + 2H+ = H2O

I - Complex 1 (NADH Dehydrogenase complex)

III - Complex 3 (Cytochrome C reductase
complex)

IV - Complex 4 (Cytochrome C oxidase
complex)

Out - in IMM and next to complexes but not in
complex.

H+ transfer causes potential difference of membrane as H+ cause it to be more positive in IMS than matrix (which is negative) as H+ move into IMS. Creates a proton gradient.
Also creates electrochemical gradient due to increase of pH in IMS as H+ concentration increases in IMS).

Electron transfer causes H+ to be pumped out via the complexes to the IMS.

Question 6

ATP Synthesis:

Answer 6

Transport of hydrogen ions into IMS causes proton motive force and would try to pump H+ back into matrix. So uses ATP synthase to do this. Proton motive force provides energy to drive synthesis of ATP.

ADP + Pi –> ATP

ATP produced by transport of H+ back into matrix (making use of proton motive force caused by proton gradient). ATP synthesis by this process is OXIDATIVE PHOSPHORYLATION

Fo part of ATP synthase is in IMM.
F1 part of ATP synthase is in matrix.
ATP synthase is also known as Complex V (5).

ADP and Pi forced together even though reaction energetically unfavourable. Enzyme can catalyse reaction when ADP and Pi in close proximity.

Question 7

How rate of electron transport is controlled by levels of ATP and ADP:

Answer 7

Increase ADP conc, increases rate of O2 uptake - increases rate of ETC.
Low ATP so speeds up ETC and oxidative phosphorylation to make more.

Increases ATP conc, decreases rate of O2 uptake - decreases rate of ETC.
High ATP so more ATP is not required so ETC and oxidative phosphorylation slowed down to reduce ATP synthesis.

Low ADP:ATP
ETC inhibited as oxidation and phosphorylation are tightly coupled - RESPIRATORY CONTROL.
ATP production switched off when high ATP.

Question 8

Info on allosteric inhibitors and activators:

Answer 8

In glycolysis, reactions 1,3,10 are inhibited when high [ATP] as ATP acts as allosteric inhibitor.

ATP - allosteric inhibitor
ADP - allosteric activator

So increase ATP conc stops glycolysis.

Low energy signals are allosteric activator.
Such as NAD and ADP.
High energy signals are allosteric inhibitors.
Such as NADH and ATP.

(Final energy form)
NAD –> NADH
AMP –> ADP –> ATP

Question 9

Inhibitors of oxidative phosphorylation:

Answer 9

1. CN-
   Inhibit Fe containing elements
2. Rotenone
   Inhibit CoQ
3. CO
   Inhibit Fe containing elements and locks onto
   cytochrome in ETC.

They were originally used to work out arrangement of electron carriers in chain.

Question 10

Uncouplers of oxidative phosphorylation:

Answer 10

1. Dinitrophenol (DNP)
2. Thermogenin protein in brown adipose
   tissue
   Natural uncouplers. Brown adipose tissue
   are used by babies to regulate body temp.
   The tissues use ETC for heat production.

Interrupt ETC and embeds in membrane.
Provides easy route back for H+ that bypass ATP synthase.
H+ doesn’t go through ATP synthase.
No ATP produced and ETC continues.
Energy lost has heat causing you to warm up a lot.