CHEM 421, lab midterm exam, 3-6-2018
Name (print): _____Rose Starbuck______________________
1. (a). Fill in the blanks.
What are the pKas associated with a typical aliphatic carboxylic acid and aliphatic amine, respectively? What are the pKas associated with the following groups that are found in amino acids: β-carboxyl, γ-carboxyl, α-amino, Ɛ-amino, imidazole, and guanidino? Functional group pKa a typical aliphatic carboxylic acid 4.52 a typical aliphatic amine 5.2 α-carboxyl in amino acid 2.3 γ-carboxyl in amino acid (of glutamic acid) 4.258 α-amino in amino acid 9.5
Ɛ-amino in amino acid (of lysine) 10.28 imidazole in amino acid (of histidine) 5.97 guanidine in amino acid (of arginine) 13.2
(b). How are the pKas for the above functional groups affected when amino acids are incorporated into proteins?
The pKa…show more content… Label the N and C-termini. What is the net charge of this tripeptide at pH 6? (you must fill in the blanks).
α-amino group (pka ~ 9.5) Ɛ-amino group (pka ~ 10.8) α-carboxyl group (pka ~ 2.3) γ-carboxyl group (pka ~ 3.4) Net charge pH 12
4. The definition of colorimetry is the use of a spectrophotometer and the application of Beer’s Law to determine the conc. of unknown sample. Unless the solute has its intrinsic character to absorb light at certain wavelength (such as benzene and its derivatives) which is a non-destructive method, most assays have to rely on the development of color prior to use spectrophotometer. Base on the provided information below please answer questions:
(a). Direct spectrophotometric method is commonly used to monitor the concentration of protein solution at 280 nm, why? What kind of cuvette is used and why?
Because most proteins contain Trp, Tyr, and Phe which absorb at 280 nm.
A glass, quartz with a cover lid, quarta without a cover lid, methacrylate plastic, or polystyrene plastic cuvette is used because they allow > 85% of the incoming light to pass through
