Determine the subunit composition of a protein from the following information: a. Molecular mass by gel filtration: 200 kD
b. Molecular mass by SDS-PAGE: 100 kD
c. Molecular mass by SDS-PAGE with 2-mercaptoethanol: 40 kD and 60 kD

Explanation:

The protein comprises of two 60-kD polypeptides and two 40-kD polypeptides. Each one of the 40-kD chains has a disulfide-bond which is directly bonded to a 60-kD chain.

The 100-kD units attach noncovalently to produce a protein with a molecular mass of 200 kD. The interaction among the different subunits in the protein is not affected by the Gel filtration chromatography.

Hence, the protein seems to be 200 kD in size. When SDS-PAGE takes place samples are being subjected to heat and therefore undergoing denaturation conditions. The aftermath effect of this causes disorganization in the 100 kD units.

However, the reducing agent (BME) main task is the reduction of disulfide bonds in a protein.

It implies that BME is responsible for the reduction between the R1-S-S-R2 bond between 40 kD and 60 kD to R1-SH and R2-SH, resulting in seperate proteins.

vanderwaal's forces of attraction are the electrostatic intermolecular forces that exist in a molecule due to the temporary or permanent dipoles that are developed in a molecule. in , the major intermolecular forces are dipole-dipole interactions as the molecule is polar (bent structure). so the vanderwaal's forces of interaction in between molecules are the permanent dipole-dipole interactions that develop due to the dipole that exists in between the polar h - s bond. the positively charged hydrogen atom is attracted towards the negative end of the dipole that is sulfur of the adjacent molecule. therefore, these forces of attraction are relatively stronger than that of london dispersion forces that exist in non polar molecules.

we can conclude that the melting point of table salt is above room temperature (it's actually 801 deg c). the melting point of mercury must be below room temperature (- 39 deg c).