Chymotrypsin, trypsin, and elastase are digestive enzymes called serine proteases. the serine proteases differ in substrate specificity: chymotrypsin cleaves peptide bonds after aromatic or bulky hydrophobic side chains; trypsin requires basic amino acid residues; and elastase cleaves bonds following small uncharged side chains. a chart of amino acids can be found here. the specificity pockets (substrate-binding sites) of each of the serine proteases are drawn below.

This graph gives information on changes in sea ice extent in the arctic ocean over a 30-year span. the overall trend shows in the ice extent. to address the trend, scientists need to ask themselves, one direct consequence of the trend is that

Tin has ten stable isotopes. the heaviest, 124sn, makes up 5.80% of naturally occuring tin atoms. how many atoms of 124sn are present in 82.0 g of naturally occurring tin? what is the total mass of the 124sn atoms in this sample?

)benzene and toluene form nearly ideal solutions. consider an equimolar solution of benzene and toluene. at 20 °c the vapour pressures of pure benzene and toluene are 9.9 kpa and 2.9 kpa, respectively. the solution is boiled by reducing the external pressure below the vapour pressure. calculate (i) the pressure when boiling begins, (ii) the composition of each component in the vapour, and (iii) the vapour pressure when only a few drops of liquid remain. assume that the rate of vaporization is low enough for the temperature to remain constant at 20 °c.