Bio 353 - Ch 15

Front 1

Where does the rest of ATP coming from

Back 1

it comes from the process which involves the transport of electrons along membranes....generates an electrochemical proton gradient which is used for the synthesis of ATP

Front 2

Chemiosmotic coupling

Back 2

The process of ATP synthesis based on the energy of proton gradient which is formed as a result of the electron transport in memebranes

Front 3

Stage 1

Back 3

Electrons transport drives pump that pumps protons across membrane

Front 4

Stage 2

Back 4

Proton gradient is harnessed by ATP synthase to make ATP

Front 5

Peter D. Mitchell

Back 5

Nobel prize in chem in 1978 for his contirbution to the understanding of biological energy transfer through the formation of the chemiosmotic theory

Front 6

Essential requirements for chemiosmotic coupling in mitochondria

Back 6

1. The inner mitochondrial membrane

2. a source of high-energy electrons (NADH molecules)

3. two sets of protein complexes embedded in the membrane
-the first set transfers electrons and pumps protons
-the second set is involved in the synthesis of ATP

4. Protons (H+ are derived from water)

Front 7

The inner mitochondrial membrane contains

Back 7

1. proteins involved in the electron transport

2.the atp synthase

3. transport proteins that allow the passage of metabolites into and out of the membrane

Front 8

The inner membrane is impermeable

Back 8

Because an electrochemical gradient of H+, which drives the ATP synthase, is established across this membrane, it must be impermeable to ions and small charge molecules.

Front 9

Electron transport chain

Back 9

the set of proteins in the inner mitochondrial membrane, together with the small molecules involved in the orderly sequence of electrons transfers

aka - the respiratory chain

Front 10

The inner mitochondrial membrane has a distinct lipid composition

(cardiolipin)

Back 10

Cardiolipin is an usual lipid in the inner membrane...it is a double phospholipid that contains four fatty acids. It constitutes about 20% of the total lipid in the inner mitochondrial membrane. It helps make the membrane especially impermeable to ions.

Front 11

Oxidative phosphorylation

Back 11

The process of ATP synthesis involved in the consumption of molecular oxygen and occurs through the addition of a phosphate group to ADP

Front 12

Electron-transport chain 2
Features:

Back 12

1. Each complex contains metal ions and other chemical groups that form a pathway for the passage of electrons through the complex

2. Each complex not only transfers electrons, but is the site of proton pumping

Front 13

Electron-transport chain 3

Back 13

begins when a hydride ion is removed from NADH and is converted into a proton and tow high energy electrons. This reaction is catalyzed by the NADH dehydrogenase which accepts electrons.

Front 14

Electron transfer

Back 14

is an oxidation reduction reaction which releases energy. The energy of electron transfers can be harnessed to generate a proton gradient across the membrane

Front 15

The active pumping of protons has two major consequences

Back 15

1. it generates a gradient of proton concentration (pH gradient) across the inner mitochondrial membrane with the pH higher in the matrix than the intermembrane space

2. It generates a membrane potential (voltage) across the inner mitochondrial membrane (the inside is negative and the outside is positive as a result of outflow of protons)

As a result of this distribution, protons will tend to move back in the direction of the concentration gradient. because the inner membrane is more negative, this will pull positively charged protons into the cell

Front 16

Net force

Back 16

Called the electrochemical gradient.

driving positively charged protons across the membrane back inside the mitochondria and composed of two forces.

1. one due to the concentration gradient

2. the other due to the voltage across the membrane.

Front 17

In the case of the inner mito membrane, the pH gradient and membrane potential work together to create a strong electrochemical proton gradient

Back 17

the total electrochemical gradient of H+ across the inner mito membrane consists of a large force due to the membrane potential and smaller force due to the H+ concentration gradient (delta pH)

Front 18

delta pH

Back 18

contributes ~ 10% to the total electrochemical gradient....therefore the membrane potential increases the amount of energy stored in the proton gradient.

Front 19

H+ electrochemical gradient is also called

Back 19

the proton-motive force

Front 20

The electrochemical gradient across the inner mito membrane

Back 20

drives ATP synthesis

Front 21

ATP synthase

Back 21

enzyme creates a hydrophilic pathway across the inner mito membrane that allows protons to flow down their electrochemical gradient. As these ions flow through the ATP synthase, they are used to drive the energetically unfavorable reaction of ATP synthesis from ADP and inorganic phosphate

Front 22

ATP synthase 2

Back 22

is composedof many protein subunits...

is capable of producing more than 100 molecules of ATP per second...about 3 protons need to pass through the synthase to make each molecule of ATP

Front 23

What is the source of protons for the pH gradient

Back 23

water is a reservoir of H+...diffuses readliy from the cytosol inside the mito matrix.

The protons in water are highly mobile and rapidly dissociate from one water molecule in order to associate with another...thus is a reservoir for donating and accepting protons.

Protons are readily moved by the transfer of eletrons

Front 24

The redox potential is a measure of electron affinities

Back 24

The tendency of the oxidation-reduction reaction to proceed spontaneously depends on the free energy for the electron transfer, which in turn depends on the relative affinities of the two molecules for electrons.

Front 25

Electron donor

Back 25

the molecule which loses its electrons

Front 26

Electron acceptor

Back 26

the molecule which takes electrons

Front 27

redox pair

Back 27

the electron donor and acceptor molecules form...example NADH and NAD+

Front 28

Redox potential (mV)

Back 28

A measure of the tendency of a given system to acquire electrons and thereby be reduced.

As defined, electrons will move spontaneously from a redox

pair as NADH/NAD+

with a low
redox

potential (a low affinity for electrons) to a redox
pair as O2
/H2
O with a high redox
potential (a high affinity for electrons).

Front 29

Redox potential increases

Back 29

along the mitochondrial electron-transport chain....

Those pairs of compounds that the the most negative redox potentials have the weakest affinity for electrons and therefore the strongest tendency to donate electrons. Those pairs that have the most positive redox potentials have the strongest affinity for electrons and therefore the strongest tendency to accept electrons.

Front 30

How exactly electrons travel in the electron transport chain and how protons are pumped

Back 30

Within each of the three respiratory enzyme complexes, the electrons move mainly between metal atoms that are tightly bound to the proteins.

1. the cytochromes contain a bound heme group whose iron atom changes from the Fe3+ oxidation state to the Fe2+ oxidation state

2. Iron sulfur centers in NASH dehydrogenase complex and cytochrome b-c1

3. Copper atoms - in cytochrome oxidase complex

Front 31

Ubiquinon

Back 31

is a mobile electron carrier that ferries electrons from NADH dehydrogenase to the b-c1 complex inside the membrane. It is the only molecule within the electron transport chain which is not a protein and does not use metals to carry electrons

-a small hydrophobic molecule that dissolves in the lipid bilayer

Front 32

cytochrome c (100aa)

Back 32

second mobile carrier..carries electrons using metals. This protein is held loosely on the outer face of the inner mito membrane by ionic interactions.

-it shuttles electrons between the cytochrome b-c1 complex and the cytochrome oxidase complex.

Front 33

Cytochrome oxidase

Back 33

catalyzes oxygen reduction...this reaction uses ~ 90% of oxygen we breathe

1. cytochrome oxidase holds O2 betwen Fe and Cu in the heme a3 center very tightly until O2 collected all four electrons to produce 2 molecules of water. It is very important to hold O2 very tightly because when O2 receives one electron it is converted into O2 - whcih is called superoxide radical. This radical is extremely active and can oxidize nearby DNA and proteins

2. Electrons actually jump between the metal atoms - electron tunneling

3. metal atoms are buried inside the protein to prevent the escape of electrons through tunneling reactions

4. cyanide an azide bind to cytochrome oxidase to stop electron transport

Front 34

Chemical uncoupling agent

Back 34

H+ carriers that can insert into the mito inner membrane...they render the membrane permeable to protons, allowing H+ to flow into the mtio without passing through ATP synthase. This short circuit effectively uncouples electron transport from ATP sythesis and ATP can no longer be made.

Front 35

Natural uncouplers

Back 35

brown fat cells...most of the energy from oxidation is dissipated as heat rather than converted into ATP....

serve as heating pads...helping to revive hibernating animals and to protect sensitive areas of newborn human babies from cold.