1. Draw the structure of any D-aldoheptose in the open chain form, then
a) Close the pyranose ring to form one fixed anomer in either a chair conformation or Haworth projection and answer the following questions:
Please note: you must use either Haworth projection or chair conformation of your anomer in points b to j !
b) How many asymmetric carbon atoms does the above sugar have ?
c) How many stereoisomers of this sugar can theoretically exist ?
d) Draw the structure of an ANOMER of your initial molecule
e) Draw the structure of an ENANTIOMER of your initial molecule
f) Draw the structure of an EPIMER (other than anomer) of your initial molecule
g) Draw the structure of a DIASTEREOMER (other than anomer or epimer) of your initial molecule
h) Draw the structure of the STRUCTURAL ISOMER of your initial molecule
i) Draw the structure of your initial molecule in the furanose form
j) Draw the structure of a non-reducing disaccharide that may be obtained from linking your ketopyranose and ketofuranose forms.
2. How many different disaccharides can be made from D-glucopyranose and D-fructofuranose? (Remember that disaccharide linkages involve at least one anomeric carbon).
3. Using the data on protonation of nucleotides and phosphoric acid species, explain why the double helix of DNA is disrupted when the pH of solution is lowered from 7.0 to 1.0 (please be specific with respect to each of given nucleotides).
Deoxycytidylate : N-3; pKa = 4.5
Deoxyadenylate : N-1; pKa = 3.8
Deoxyguanylate : N-7; pKa = 2.4.
4. One of the bacterial proteases, subtilisin (Mr 27600), can catalyze hydrolysis of certain amino acid esters and amides. For synthetic substrate N-acetyl-L-tyrosine ethyl ester (Ac-Tyr-OEt), subtilisin exhibits KM and kcat values of 0.15 mol/L and 550 s -1, respectively.
a). What is Vmax for the hydrolysis of Ac-Tyr-OEt when the subtilisin concentration is 0.4 mg/mL?
b). Indole is a competitive inhibitor of subtilisin with K i of 0.05 mol/L. What is the Vmax for Ac-Tyr-OEt hydrolysis by 0.40 mg/mL subtilisin in the presence of 6.25 mmol/L indole?
c). What is the V0 when 0.40 mg/mL subtilisin is incubated with 0.25 mol/L Ac-Tyr-OEt and 1.0 mol/L indole?
d). Subtilisin does have a problem, in that it becomes inactivated by oxidation of a methionine Met-222 positioned close to the active site. It is known that subtilisin’s mutants with cysteine show higher kcat value, while either alanine or serine in a place of Met-222 exhibit enzymatic activity nearly half of this of subtilisin itself. Any other amino acid replacement leads to a significant reduction in activity. Explain in detail the reason(s) for such a loss of activity in oxidized subtilisin and in 17 other mutants, and increase in kcat value for M222C mutant.