Ox Phos regulation

Question 1

Describe the transfer of electrons in oxidative phosphorylation including any equations that are involved

What is the relationship between delta G and delta E?

Answer 1

Electrons flow from the molecules with the lower standard redox potential to the ones with the highest standard redox potential (deltaE)

Delta E and G are INVERSELY related

deltaG= -nF(deltaE)

Question 2

Describe the importance of the proton gradient

Answer 2

It powers the synthesis of ATP

Electrons are transferred through the respiratory chain and leads to the pumping of H+ from the matrix to the inner mitochondrial space; this results in the inner matrix having a high pH (lower H+) and the inter membrane space has a low pH (high H+)

Question 3

Describe the chemiosmotic hypothesis (3 postulates)

Answer 3

Proposed by Peter Mitchell

1. ETC translocates protons across the inner mitochondrial membrane as the electrons flow down the chain from one complex to the next (from high standard redox potential to low)
2. ATP synthase uses the proton motive force (pdf) to drive the phosphorylation of ADP
3. The inner mitochondrial membrane is impermeable to H+ and O- (because you want this difference in protons: If it is NOT impemable then ATP synthesis cannot occur)

Question 4

What are the two factors that constitute a proton motive force?

Answer 4

1. pH gradient (chemiosomotic hypothesis)

2. Membrane potential

Question 5

Describe the ATP synthase structure

Answer 5

Also known as complex V

Ball and a stick model: The F0 subunit is the stick and is embedded in the inner mitochondrial membrane and has the proton channel within it. The F1 subunit is the ball portion of the synthase which protrudes into the matrix and contains catalytic activity

F1 has 5 subunits that make up a hexametric ring: Alpha and Beta units from dimers and the gamma subunit breaks the symmetry of the hexamer. HAS the catalytic domains (B subunits)

Question 6

Describe the F1 subunit in detail

Answer 6

There are 3 alpha, 3 beta (catalytically active) and a gamma, delta, and epsilon subunits

The alpha and beta arrange themselves in a hexametric ring with each unit having the ability to bind nucleotide, but the beta units are the only ones that are catalytically active

Gamma subunit is a long helical coil that extends into the alpha and beta hexamer

Question 7

Describe how ATP synthase molecules interact with each other

Answer 7

They form dimers, which are called oligomers. These help to stabilize the individual molecules to rotational forces that are required for catalysis

Maintains the curvature of the inner membrane

The cristae allow the proton gradient to be in close proximity with the ATP synthase (like culdesacs: the neighbors are closer than they would be if it were 4-5 houses along one straight street)

Question 8

Describe the relationship between ATP and proton motive force (pmf)

Answer 8

ATP is able to be made without the pmf being present however the pmf is required in order for the ATP to be released from the synthetase

Question 9

What are the 3 actions of the Beta subunits (catalytic domains)

Answer 9

1. ADP and Pi binding
2. ATP synthesis
3. ATP release

Question 10

Describe the path of a proton through the membrane in the ATP synthetase

Answer 10

A proton that is in the rich H+ environment on the cytoplasmic side of the inner mitochondrial membrane will enter the complex and bind to a glutamate amino acid. The synthetase will spin and then the proton will eventually make its way to the other side of the membrane and bind to a glutamic acid closest to the proton poor side (low H+) and then is released into the matrix of the mitochondria

This movement of protons powers the rotation of the c ring

Question 11

Describe the ATP translocase

Answer 11

ATP and ADP cannot travel freely over the inner mitochondrial membrane so it needs a carrier

The translocase family is on the outer and inner mitochondrial membranes and works with the carriers

It couples the movement of ADP and ATP; ADP will enter the matrix and ATP will leave, so that the cycles continue to occur (ATP inhibits the cycles that are happening inside the matrix)

(COMPLEX VI)

Question 12

What are the two ways in which reduced NADH is able to cross the mitochondrial membrane?

Answer 12

1. Malate aspartate shut

2. Glycerophosphate shuttle

Question 13

Describe the malate-aspartate shuttle

Answer 13

Operates in the heart, liver, and kidneys

Electrons are transferred from NADH in the cytoplasm to oxaloacetate which can form into malate and cross the membrane

Then the malate that is inside the matrix is able to be taken back to oxaloacetate and NADH is a byproduct which is then able to be taken to complex 1

Question 14

Describe the glycerophosphate shuttle

Answer 14

Operates in the brain and skeletal muscle

Electrons from the NADH are added to dihydroxyacetone phosphate to make glycerol and phosphate

An electron pair goes and binds to the FAD (prosthetic group on Complex II) and then is transferred into FADH2 which is then able to regenerate dihydroxyacetone phosphate

Question 15

Describe uncoupling and heat generation

Answer 15

some organisms are able to uncouple the oxidative phosphorylation which is able to produce heat that is required for say, times of hibernation

The uncoupling protein (UCP) is able to transfer the electrons and “short circuit” the proton battery and instead of releasing ATP from the transfer of electrons, it releases heat

Therefore, instead of the energy that is created by the proton motive force being used for the rotation of the ATP synthase, it is used solely to generate heat

Question 16

Describe the adipose tissue that is commonly seen in animals that are able to uncouple oxidative phosphorylation and ATP synthesis

Answer 16

Brown adipose tissue. It gets its color from the cytochromes and the hemoglobin

It is V rich in mitochondria