[ppt]chapter 18 oxidative phosphorylation and … · web viewtitle chapter 18 oxidative...

Binding ADP + Pi

Synthesizing ATP

Releasing ATP

The binding-changemechanism

or rotational catalysis(Paul Boyer, 1980s)

Each subunitwill take three

different conformationsin turn during each

cycle of action.

Binding ADP + Pi

Synthesizing ATP

Releasing ATP

The binding-changeMechanism

or rotational catalysis(Paul Boyer, 1980s)

The three subunits exist

in differentconformations (T, L or O) ateach moment.

T

T

T

L

L

L

O

O

O

The binding-change model was elegantly supported by two recent experimental observations.

X-ray crystallography The three subunits of F1 indeed assume three different conformations

subunit

John Walker, 1994

p299-302.

Fluorescence microscopy

Direct observationof the rotation ofthe subunit

p299-302.

No rotation if ATP is absent or inhibitors of F1-ATPaseis present!

Recorded rotation of the actin filament using a CCD camera

Model of the action of E. coli ATP synthase:the proton gradient drives the rotation of the c ring using two half-channels on the a subunit.

Protonation/deprotonation of an Asp is believed to be essential for rotating the c ring and the subunit.

10-14 protons needed for every

3 ATP synthesized.

Thus ~ 4 protons per ATP synthezied

Asp-COO- Asp-COOH

The rotary motion of the bacterial flagella is energized directly by the proton gradient present across the cytoplasmic membrane.

The proton-motive force is used foractive transport through the inner membrane of the mitochondria.

Heat is generated in Brown fat through the action of thermogenin,an uncoupling protein:to produce heat to maintain body temperature for animals in hibernation, of newly born and adapting to the cold (thermogenesis).

Electrons in NADH generated in cytosol are shuttled into mitochondria to enter the respiratory chain.

cytosol Matrix

The malate-aspartateshuttle system

Readily reversible!

Occurs in liver, kidney and heart

The glycerol-3-phosphateshuttle system

Occurs in skeletal muscle and brain

Irreversible

The pathways leading to ATP synthesis are coordinately regulated.

Interlocking regulation of all these pathways is realized by the relative levels of ATP, NADH, ADP, AMP, Pi, and NAD+. [ATP]/([ADP][Pi]) fluctuates only slightly in most tissues due to a coordinated regulation of all the pathways leading to ATP production.

The rate of the respiration is generally controlled by

the availability of ADP (“acceptor control”)

No ATP consumption,No electron flow!

Pyruvate oxidation

Some respiratory proteinsare encoded by the human

mitochondrial genome

Complexes I, III, and IV and ATP synthase

are assembled by usingsubunits made in both thecytosol and mitochondria.

Photosynthetic organisms generate ATP and NADPH (both are needed for carbon fixation) via photophosphorylation, the first stage of photosynthesis.

Summary （ 2 张 PPT 缺失，以下为老版本的）• ATP is synthesized using the same strategy in oxidative

phosphorylation and photophosphorylation.• Electrons collected in NADH and FADH2 are released

(at different entering points) and transported to O2 via the respiratory chain, which consists of four multiprotein complexes (I, II, III, and IV) and two mobile electron carriers (ubiquinone and cytochrome c).

• A proton gradient across the inner membrane of mitochondria is generated using the electron motive force generated by electron transferring through the respiratory chain.

• The order of the many electron carriers on the respiratory chain have been elucidated via various studies, including measurements of the standard reduction potential, oxidation kinetics of the electron carriers, and effects of various respiratory chain inhibitors.

• Electron transfer to O2 was found to be coupled to ATP synthesis from ADP + Pi in isolated mitochondria.

• The chemiosmotic theory explains the coupling of electron flow and ATP synthesis.

• Isotope exchange experiments revealed that the G`0 for ATP synthesis on purified F1 is close to zero!

• ATP synthase comprises a proton channel (Fo) and a ATPase (F1).

• The binding-change model was proposed to explain the action mechanism of ATP synthase.

• The energy stored in the proton gradient can be used to do other work.

• Electrons in NADH generated in cytosol is shuttled into mitochondria to enter the respiratory chain.

• The pathways leading to ATP synthesis is coordinately regulated.

• Photosynthetic organisms generate ATPs (and NADPH) via photophosphorylation.

• It took a long time for humans to understand the chemical process of photosynthesis.

• The major light absorbing pigments on thylakoid membrane was revealed to be chlorophylls.

• Photons absorbed by many chlorophylls funnel into one reaction center via exciton transfer.

• Two types of photochemical reaction centers have been revealed in bacteria.

• Two photosystems (PSII and PSI) work in tandem to move electrons from H2O to NADP+ in higher plants.

• P680+ in PSII extracts electrons from H2O to form O2 via a Mn-containing oxygen-evolving complex.

• ATP synthesis is driven by the H+ gradient across the thylakoid membrane, with a higher concentration in the thylakoid lumen.

• Cyclic electron flow in PSI produces ATP, but not NADPH and O2

• Compounds other than water are also used as electron donors in photosynthetic bacteria.

• A single protein in halophilic bacteria, bacteriorhodopsin, absorbs light and pumps protons