# calculation.. help - (Dec/01/2006 )

Can anyone help me on this question..thanx

A baby hamster kidney (BHK) cell has a surface area of 3,400 μm2. Assume that the endocytic
clathrin-coated pits account for 2% of this area and that the surface area of a single coated pit is the same of that of a 100 nm diameter clathrin-coated vesicle that will be formed from it. If the cell
surface has 100, 000 transferrin receptors and 70% are localised within coated pits, work out the
following:

I) How many coated pits are there on a BHK cell? How can clathrin-coated pits and vesicles
be identified using electron microscopy on chemically fixed BHK cells?

II) How many transferrin receptors are there in each coated pit? Comment on the content of
soluble and membrane-bound proteins associated with each coated pits and vesicles.

3) What is the relative concentration of transferrin receptors in coated pits compared to the rest
of the cell surface? How does this value define the concept of receptor-mediated endocytosis?

4) If each transferrin receptor binds 2 transferrin molecules and all the receptors re saturated
when the extracellular transferrin concentration reaches 10 nM, how many transferrin molecules
will enter in the fluid phase (i.e. not bound to receptors) at this concentration?

5) What concentration of transferrin would be required to ensure that as many transferrin
molecules enter the fluid phase of a coated vesicle as are bound to the receptors?

6) If the coated pits have a lifetime of 1 minute, how long does it take for a BHK cell to
endocytose the entire surface? What does this mean in terms of the residence lifetime of plasma
membrane lipids and proteins and how are such factors degraded or recycled?

7) If a transferrin receptor has a cross-sectional area of 50 Angstroms X 100 Angstroms (5 x 10
nm), how many receptors could be accomodated in a 100 nm clathrin-coated vesicle assuming that
only 50% of the surface area can be occupied by proteins? Is this value realistic and can this occur
in vivo ?

-microman_101-

well basically i see your topic so please don't re Pm it to me
what do you think answers may be?

-fred_33-