Lecture 18 - Electron transport 2

Question 1

Slide 30 - 38

Question 2

Describe the mitochondrial electron transport system

Answer 2

Electrons from NADH enter the electron transport system at complex I, then flow to coenzyme Q, complex III, and complex IV. A total of 10 H+ are concomitantly translocated.

Electron pairs are derived from FADH2 oxidation at complex II (succinatedehydrogenase), from ETF-Q oxidoreductase of the fatty acid oxidation pathway, or from mitochondrial glycerol-3-phosphate dehydrogenase, which is part of the glycerol-3-phosphate shuttle. A total of 6 H+ are concomitantly translocated when electrons are derived fromFADH2.

Question 3

What is Complex I called in the METS and what does it do

Answer 3

NADH-Ubiquinone Oxidoreductase

NADH oxidation coupled to FMN reduction

At least 7 Fe-S centres carrying 1e- at a time

Translocates 4 H+ into intermembrane space

Question 4

How does complex I work in METS

Answer 4

NADH transfers 2 e- to FMN

2e- transferred from carrier to carrier

2e- + 2H+ bind Q, forming QH2

Question 5

What does rotenone do

Answer 5

blocks electron transport in complex I, prevents reduce reactions between 2 Fe-S centres

Question 6

What is FMN

Answer 6

Flavin Mononucleotide

Question 7

What is the job of FMN in OP

Answer 7

FMN accepts one electron

Reduction by one electron forms a semiquinone intermediate

Reduction by a second electron leads to the fully reduced species (FMNH2)

Isoalloxazine ring identical to that of FAD

Question 8

How are the Fe-S clusters composed and what are they coordinated by

Answer 8

2 Fe-2 S clusters or 4 Fe-4 S cluster

coordinated through cysteine residues in the protein subunits

Question 9

How many electrons does each Fe-S cluster transfer to the next

Answer 9

1

Question 10

What is the redox potential in the Fe-S clusters

Answer 10

-0.5V to +0.4V depending on protein microenvironment

Sequence of Fe-S clusters in complex I will have increasing redox potentials

Question 11

What is Coenzyme Q also known as

Answer 11

Ubiquinone/ Ubiquinol

Question 12

What are the key roles of CoQ

Answer 12

Mobile, lipid-soluble e- carrier - transports electrons in membrane from complex I to III

2. Entry point into electron transport system for e- pairs from citric acid cycle, fatty acid oxidation, and glycerol-3-phosphate dehydrogenase
3. Converts 2e- transport system in complexes I and II to 1e- system in complex III, which then passes electrons one at a time to cytochrome c

Question 13

What is complex II also called

Answer 13

Succinate Dehydrogenase

Question 14

What does Complex II do

Answer 14

Direct physical link to CA cycle

Oxidises succinate to fumarate, coupled with FAD-FADH2

Electron pair then used to reduce Q via Fe-S and a haem

Question 15

What is complex III also called

Answer 15

Ubiquinone-Cytochrome C Oxidoreductase

Question 16

How many binding sites does complex III have

Answer 16

2 Q bonding sites - Qp and QN

along with several prosthetic groups which act as electron carriers

Question 17

What does complex III do

Answer 17

Reduces Cyt c while translocating 4H+

Dimeric complex - 2x11 subunits

CoQ uses Q cycle to convert 2e- processes into two 1e- transfers

Question 18

What does a type a haem have

Answer 18

Hydrophobic tail

Question 19

What does a type b haem have

Answer 19

standard

Question 20

What does a type c haem have

Answer 20

Protein link between 2 cysteine residues

Question 21

What is Complex IV also called

Answer 21

Cytochrome c oxidase

Question 22

What does complex IV do

Answer 22

Cyt C oxidation

then electron transfer through one monomer of the homodimer, culminating in O2 reduction to form H2O

Four H+ are involved in the complex IV reactions:

  2 H+ translocated into
  intermembrane space

  2 H+ used to form H2O