You have purified the receptor for a hormone by affinity chromatography. During gel filtration chromatography under native conditions the receptor elutes between pyruvate decarboxylase (250 kDa) and glutamine synthetase (620 kDa). During SDS-PAGE, in the absence of reducing agents, the receptor migrates as a single band of approximately 230 kDa. When SDS-PAGE is carried out in the presence of 2-mercaptoethanol the receptor migrates as two bands of approximately 95 and 135 kDa. Explain this result.

the hormone receptor is a heterotetramer composed of two subunits with 95 kDa and two subunits with 135 kDa

Explanation:

In this case, the heterotetramer is composed of two heterodimers, each composed of two subunits that held together by disulfide bonds. These heterodimers bind together through hydrophobic interactions in order to form a tetramer. The Sodium Dodecyl Sulfate (SDS) is a denaturing detergent that dissociates both heterodimers by interfering with hydrophobic interactions that hold heterodimers together. It is for that reason that only a single band of 230 kDa is observed (135 kDa + 95 kDa = 230 kDa). Moreover, 2-Mercaptoethanol breaks disulfide bonds, thereby separating the two subunits in the heterodimer. In consequence, after the use of this chemical compound (2-Mercaptoethanol), two different bands with 135 kDa and 95 kDa can be observed.

"a.) well–developed vascular system."

cells use diffusion to get substances in and out of themselves. that diffusion will occur across the cell membrane or the outer covering of the cell. because we are talking about the surface of the cell, surface area and volume are  important factors here. as a cell increases in size, its surface area and volume increase as well.  we call that the surface area to volume ratio (sa: vol).  but the catch is that  volume increases at a greater rate than surface  area. in other words, as a cell gets bigger, the sa: vol gets smaller. so a really small cell like bacteria is mostly cell membrane (surface) with very little contents (volume). a really big cell like an egg, is mostly insides with a super thin membrane. so what ends up happening is that the cell cannot efficiently diffuse all of the stuff it needs in/out to survive. therefore cell size is limited to about 100mm. so how do we make organisms bigger than 100mm? cells divide! by dividing and becoming multicellular, organisms are able to grow!   check out the diagrams i attached to see the effect of sa: vol. i hope this ! good luck!