How might a protein kinase select the correct residues
tophosphorylate given the availability of serine and
threonineresidues on the surface of globular proteins?

The flanking residues  facilitate recognition and specificity.

Explanation:

The kinase is able to to specifically phosphorylate serine and threonine due to the recognition of the flanking residues. Altogether, these form a consensus sequence across the substrate.

the relative atomic mass of an element is the mass of one atom of that element, relative to 1/12th of the mass of a  1212c atom. to convert to an absolute mass in kg, it is necessary to multiply by  1.661×10−271.661×10−27.

the relative atomic mass is roughly equal to the number of neutrons, plus the number of protons, in the nucleus of the atom.

for elements with more than one stable isotope (different types of nucleus with different numbers of neutrons but the same number of protons), the quoted mass is usually the average mass, weighted by the relative abundance of the different isotopes.

the answer is 95 degrees