Question

1) Under which of the following conditions do you expect to see treadmilling of an actin filament?

The critical concentrations of F-actin are:

(+)-end: 0.12 microM
(-)-end: 0.6 microM

a) The cytosolic concentration of G-actin-ATP is 0.4 microM, but you have added 0.3 microM of the sequestering protein thymosin to your reaction. Thymosin binds to G-actin ATP at a ratio of 1:1.

b) The cytosolic concentration of G-actin-ATP is 0.15 microM and of G-actin ADP is 0.2 microM.

c) The cytosolic concentration of G-actin-ATP is 0.7 microM, but your reaction also contains profilin, an enzyme that converts G-actin-ADP into G-actin-ATP.

d) The cytosolic concentration of G-actin-ATP is 0.4 microM, but you have also added the (-)-end capping protein tropomodulin to your reaction

e) The cytosolic concentration of G-actin-ATP is 0.1 microM

2) In small hypernating animals, the inner mitochondrial membrane of brown adipocytes are enriched in transmembrane proteins of the UCP family. In the mitochondria of these cells, ATP production is low, but oxygen consumption is similar to other cell types. Which of the statements below provides the most likely explanation for the function of the UCP proteins?

a) UCPs block the electron transfer chain

b) UCPs block cytochrome c motility inside the membrane

c) UCPs make the inner mito membrane permeable to protons

d) UCPs block the pyruvate transporter

e) UCPs block ATP synthase

Answer 1

1.Correct answer is:b) The cytosolic concentration of G-actin-ATP is 0.15 microM and of G-actin ADP is 0.2 microM.

Reason:Treadmilling is known to occur only when the cytosolic concentration of G-actin ATP will be hiher than 0.12 microM and that of G-actin ADP will be lower than 0.6 microM.The process of treadmilling occurs at one end, the rate of subunit addition will be equal to the the rate of subunit loss at the other end,while the filament length remaining constant.

2.Correct answer is:c. UCPs make the inner mito membrane permeable to protons

Reason:Uncoupling protein (UCP) that are located in the inner mitochondrial membrane of brown adipocytes function to dissipates energy in form of heat and this is done via transportation of protons from the cytosol into the mitochondrial matrix