Since some amino acids, such as Glu and His, can be viewed as weak acids or bases, the ratio of their protonated form to their deprotonated form is dependent on pH. Furthermore, you can use this knowledge to predict whether a given amino acid will exist predominantly in its protonated or deprotonated form at a given pH. To do this, it is easier to think about the pK, of the amino acid functional group. Recall from general chemistry that the pK, is equal to -log(K). Using the K, value for the Glu side chain, which is 5.62 x 10-5, calculate the pK, for the Glu side chain. pKa =

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Mass is the amount of matter in an object.  weight is the measurement of the pull of gravity on an object.  say for example, you travel to the moon which has a different gravitational field compared to the gravitational field of earth. (gravitational fields: earth = 1, moon = 0.165)  now when you are on the moon, the pull of gravity on you is different than on the earth. and as weight is the measurement of the pull of gravity on an object, that means yes, your weight can and will change on the moon.  however, on the moon, on earth or even on jupiter, the amount of mass inside of you remains the same. meaning your physical mass remains constant.  in conclusion it is possible for your weight to change as your mass remains constant.