Lecture 13
ATP synthase structure
F1Fointeractions
∗ δ tightly linked to an α, and to 2 b subunits
∗ γ loosely associated with α/β ring, tightly associated with c ring
∗ β subunits⇨ catalytic
∗ α subunit has two half-channels
∗ ε tightly associated with γ and some c subunits
∗ c, γ, ε subunits rotate in unison
∗ Rotation driven by discharge of proton gradient
∗ Proton enters a half channel, associates with c
∗ After nearly one rotation, leaves via another a half channel Binding change mechanism
∗ Rotation of γ driven by rotation of c subunit ringof F caused by H translocation
o
∗ Rotating γ induces cycle of conformational changesin β subunits
∗ Nucleotide binding site of 1 β subunit cycles through 3 conformational states:
∗ O: very poor ATP binding, poor binding for ADP + Pi
∗ L: binds ADP + Pi more strongly
∗ T: very tight binding of ADP + Pi ↔ATP
∗ O → L → T → O cycle: ADP + Pi → ATP
Proton translocation and c ring rotation
Once a proton enters the
cytoplasmic half-channel,
the c subunit moves away
from the a subunit into
the membrane, driving
the rotation of the c
subunits until the proton
comes into contact with
the matrix half-channel
and is released into the
matrix. ATP/ADP translocase (antiporter)
∗ As the γ subunit rotates, β subunit changes
conformation.
∗ Exchanges cytosolic ATP for mitochondrial ATP
∗ Involves conformational changes driven by
membrane potential
∗ Phosphate transported into mitochondria via
-
antiport with OH, combines with translocated
proton
∗ One translocated protein allocated to ATP/ADP
and Pi transport processes
+
Regenerating cytosolic NAD
Anti-porting aspartate for
Glutamate.
Malate dehydrogenase helps
regenerate cytosolic NAD+ that
was used in glycolysis.
Oxaloacetate itself does not
move across the mitochondrial
inner membrane.
Involves two transporters:
- Aspartate/Glutamate
- Malate/α-Ketoglutarate How many ATP for each NADH oxidized?
- +
∗ Transfer of electrons from 1 NADH (2 e) to O →2transfer of 10 H from matrix to IMS
∗ 10 c subunits in ATP synthase
+
∗ 1 full rotation of c ring: translocation of 10 H from IMS to matrix
∗ 3 ATP synthesized for each full rotation of c ring
∗ 1 ATP per 3.3 (3) protons translocated
∗ 1 proton translocated from IMS to matrix for each ADP/ATP pair translocated
+
∗ Net synthesis/transport of 1 ATP requires translocation of 4 H
∗ 2.5 ATP synthesized and transported per NADH oxidized
∗ Note the difference between synthesized and transported!
Respiratory control
Oxygen consumption over time in a
suspension of mitochondria provided with
fuel to oxidize.
Note that the rate of O2 consumption
shoots up (steeper slope) when ADP is
added.
The discharge or the proton gradient is
coupled to the synthesis of ATP. Inhibitors Uncouplers
Acidic aromatic compounds such as 2, 4
dinitrophenol can uncouple oxidation and
phosphorylationthey carry protons
across inner membrane (discharge proton
gradient)
Release of energy:
C 6 12+ 6 O6→ 6 H O + 62CO 2 2 Lecture 14
The ultimate source of biological energy is sunlight
Photosynthetic organisms capture light energy and use it to:
∗ transfer the H atoms from water to acceptor molecules
∗ form molecular oxygen
∗ synthesize ATP from ADP and phosphate
∗ transfer H atoms from acceptor to carbons derived from CO to fo2m glucose (carbon fixation)
Net: 6 H O + 6 CO → C H O + 6 O
2 2 6 12 6 2
Photosynthesis: overview
∗ CO 2 H 02→ (CH O) 2 O . E2dergonic, driven by absorption of light
+ +
∗ Light reactions: 2 H 2O + 2 NADP + 3 ADP + 3 Pi → O + 22H + 2 NADPH + 3 ATP
+ +
∗ Dark reactions: CO +22 H + 2 NADPH + 3 ATP → CH O + H O2+ 2 N2DP + 3ADP + 3 Pi (Calvin
cycle) Light absorption and energy transformation in photosynthesis
Light absorbed by pigments in the thylakoid membrane. Photosynthesis “action spectrum” corresponds
to absorbance spectrum of three pigments
Chlorophyll has a
prophirin ring, another
ring, and a long
hydrophobic side
chain. It is overall a
very hydrophobic
molecule.
Highlighted electrons
get excited when light
is absorbed.
How does the absorption of light drive an (otherwise) energetically unfavourable redox reaction ?
Because of the configuration of donor/acceptor
molecules in a photosystem, excited electrons
can get transferred to an acceptor molecule
instead of returning to the ground state. Photoinduced charge separations occur in photosystem reaction centers
When the chlorophyll has a strong positive
charge it becomes a strong oxidizing agent
and can grab electrons.
Light harvesting complexes
Light energy can be transferred from one
compound to the next through resonance energy
transfer (No net gain or loss, excitation energy is
simply transferred from molecule to molecule).
Energy gets funneled to a special pair of
chlorophylls in the photosynthetic reaction center. Resonance energy transfer
Two cooperating photosystems, photosynthetic electron transport and photophosphorylation
Two photosystems cooperate to generate NADPH, proton gradient
∗ Photosystem II charge separation: H O → ½ O , Q → QH
2 2 2
∗ Transfer of electrons from QH t2 plastocyanin (Pc) catalyzed by cytochrome b/fcomplex: QH + 2
2Pcox Q + Pc red
+
∗ Photosystem I charge separation: 2 PC red→ 2 PC ,oxADP → NADPH
∗ = Linear electron flow → acidification of lumen
∗ Proton movement from lumen back to stroma mediatedby chloroplast ATP synt
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