Mitochondrial Respiratory chain and Oxidative Phosphorylation Flashcards
What is the inner membrane of the mitochondria impermeable to?
- small molecules and ions
- including H+
Overview of the electron transport chain
- complex 1, complex 2, Q , complex III,
complex C (cytochrome C), complex 4 - enter electrons as NADH into complex 1
OR as FADH2 into complex 2 - electrons are shuttled by Q into complex 3
- movement of electrons shifts protons
Complex 1 of the mitochondrial respiratory chain:
- 2 electrons from NADH pass to FMN
- electrons pass one at a time through a
series of Fe-S centers to UBIQUINONE
(coenzyme Q) to form QH2 = exergonic - Fe is positive and attracted to negatively
charged electrons; motion of electrons
causes a conformational change to
complex 1 and releases energy - QH2 diffuses into the lipid bilayer
- Flow of electrons transduced into H+
PUMPING = endergonic
***overall reaction: NADH + H+ + Q -> NAD+
+ QH2
complex 1 = proton pump
Complex 1 of the mitochondrial respiratory chain
- large portion of complex 1 is embedded in
the mitochondrion matrix
Complex 2 of the mitochondrial respiratory chain:
- enzyme succinate dehydrogenase
- also part of the TCA cycle converting
succinate to fumurate - TCA: succinate binds to subunit A and
passes electrons to FAD. FAD reduced to
FADH2 at binding site - FADH2 moves through FE-S centers (Fe
positive etc) - transferred to ubiquinone to form reduced
ubiquinol QH2 - Heme b not part of pathway: prevents
stray electrons forming damaging ROS
(reactive oxygen species) - complex 2 = NOT a proton pump
Complex 2 of the mitochondrial respiratory chain:
- also large portion is present in the
mitochondrial matrix
Ubiquinone (5):
- lipid soluble
- can accept one e- or 2 e- to become
ubiquinol QH2 - freely diffusible within lipid bilayer of inner
mitochondrial membrane - shuttles electrons between other less
mobile electron carriers - central role in coupling electron flow
Ubiquinol serves as an —— —– for electrons into the electron transport chain from pathways other than ——- or —.
- entry point
- complex 1
- complex 2
- can be from G3p or fatty acid metabolism
Complex III of the mitochondrial respiratory chain:
- couples the transfer of 2 e- from ubiquinol
(QH2) to 2 molecules of CYTOCHROME C - in the process, 4 MORE PROTONS (H+) are
transported from the matrix into the
intermembrane space - complex is made of two identical porteins
with 11 subunits - ubiquinone can shuttle between two
binding sites; Qn (matrix side) and Qp
(intermembrane side) transferring protons
and electrons
complex III = proton pump
Cytochrome C of the mitochondrial respiratory chain:
- soluble protein of the intermembrane
space (electron carrier) - can accept one electron (Fe2+ -><- Fe3+)
- once its haeme group has accepted an
electron from complex III it moves to
donate its electron to complex IV
Complex IV of the mitochondrial respiratory chain:
- cytochrome oxidase
- two cytochrome C each donate one
electron to a copper center - OXYGEN now binds to haema and accepts
donate electrons - delivery of two more electrons creates
O22- which combines with 4 H+ from the
matrix to produce water - in the process, 4H+ are pumped across the
from the matrix into the inter membranal
space
complex IV = proton pump
For every 1 NADH molecule how many protons are pumped during the mitochondrial respiratory chain?
10 protons pumped across the inner mitochondrial membrane
complex 1 = 4
complex 3 = 4
complex 4 = 2
Reduction potentials drive the transfer of electrons along the electron transport chain:
- redox potential becomes more positive
- downhill attraction (exergonic)
Synthesis of ATP:
Inner mitochondrial membrane is generally impermeable to ions, but 3 specifc systems in the membrane:
1) Transport ADP and Pi into the matrix
(substrates for substrate level
phosphorlyation
2) synthesise ATP
3) transport ATP into the cytosol
Chemiosmotic model of ATP synthesis:
- utilises electrical and chemical potential
energy: PROTON MOTIVE FORCE - caused by difference in H+ conc acrosss
inner membrane provided by proton
pumping of the ETC - proton motive forces drive synthesis of
ATP using ATP synthase
ATPase Structure: F0:
- functional domain
- oligomycin sensitive proton channel
ATPase Structure: F1:
- functional domain
- projects into the matrix of the mitochondria
F1 domain of ATPase: subunits:
- nine subunits: alpha x3, beta x3, gamma,
delta, epsilon - Beta and alpha are arranged alternatively
- gamma = rod in middle
- delta on the side
Beta (x3) subunits of F1 domain of ATPase:
have catalytic sites for ATP synthesis
Binding-Change model for ATP syntehsis:
- 3 beta subunits take it in turns to catalyse
ATP synthesis - any given beta subunit starts in a
conformation for binding ADP and Pi (B-
ADP conformation) - the beta subunit changes conformation so
the active site now binds the ATP product
tightly (B-ATP conformation) - the beta subunit changes conformation
again to give the active site a very low
affinity for ATP (B-empty conformation) so
ATP is released
Rotational Catalysis: Binding-Change model for ATP synthesis:
- the PROTON MOTIVE FORCE causes
rotation of the shaft (gamma subunit) - the shaft rotates 120 degrees and touches
each ab subunit in turn - *** causes a change in the conformation
of beta subunit, altering its ADP/ATP
binding properties - the F1 subunits interact with each other: if
one subunit takes on the B-empty
conformation, its neighbour must adop B-
ADP and the other B-ATP
During the mitochondrial respiratory chain how much ATP is made?
- each NADH will pump 10H+ into the
mitochondrial intermembrane space - each succinate via FADH2 will pump 6H+
into the intermembrane space- 4 are used to fully make 1 ATP!!!!
- 3H+ used in ATP synthesis
- 1H+ used in Pi, ATP, ADP transport
ATP yield from complete oxidation of 1 glucose molecule:
total 30 or 32
Malate-Aspartate Shuttle
Oxaloacetate turned into malate using malate dehydorgenase and producing NAD+
Malate alpha ketoglutarate transporter takes malate from intermembrane space into the matrix
Malate dehydrogenase then converted by malate dehydrogenase into oxaloacetate and produces NADH
Aspartate aminotransferase changes oxoaoacetate in the matrix into aspartate which travels through the glutamate-aspartate transporter
aspartate in the intermembrane space and is converted to oxaloacetate using aspartate aminotransferase
***purpose = moving NADH produced during glycolysis into the matrix for use by complexes during oxidative phosphorylation
insert slide
Glycerol-3-Phosphate shuttle:
- MAKES LESS ATP BECAUSE LESS PROTONS
PUMPED AS COMPLEX 2 IS NOT A PROTON
PUMP
Uncoupling Reagants
- normally e- flow and phosphorylation are
tightly coupled - uncouplers dissipate the pH gradient by
transporting H+ back into the matrix so
**bypassing ATP synthase - thus an uncoupler (eg DNP) severs the link
between e- flow and ATP synthesis, with
energy released as heat
Uncoupling and Brown Fat: thermogenesis:
- brown adipose fat: specialised for heat
generation - high numbers of mitochondria can cause
brown appearance - mitochondria contain thermogenin UCP1
receptor provides an alternative route for
protons to re-enter the matrix cauisng
energy conserved by proton pumping to be
dissipated as heat - ***important in new borns
Brown adipose tissue location
- between shoulder blades
- surrounding kidneys
- neck
- along the spinal cord
Exogenous uncoupling agent: 2,40dinitrophenol:
- soluble weak acid
- carries H+ across membrane
- dissipating the proton gradient
- uncouples electron transport from
oxidative phosphorylation which raises the
metabolic rate - toxicity arises from liver damage,
respiratory acidosis and hyperthermia
How can NADH from glycolysis be transported into the mitochondrial matrix for use during oxidative phosphorylation?
1) Malate-Aspartate
2) Glyceraldehyde 3-phosphate shuttle
