Question

1) You have 100 ml of a solution of ATP. You take 25 ?l, and dilute it to a final volume of 1ml. The absorbance of the diluted solution at 259 nm is 0.550.

a) What is the ATP concentration in the original, undiluted solution?

**The molar extinction coefficient for ATP at 259 nm is 15,600 l mol-1cm-1.

b. How many mg of ATP are there in total in the original, undiluted solution?

**The formula weight of ATP is 551.14 g/mole.

2) Fill in the blanks, with one of these 5 amino acids

Lysine/Cysteine/ Valine/ Tryptophan/Aspartate

a) If you dissolve (blank) in water, the resulting pH would be about 8.5

b) if you dissolve (blank) in water, the resulting pH would be about 4

c) (blank) residues would most likely be buried in the core of a folded protein structure

d) Collagen does not absorb strongly at 280 nm. This is because its sequence does not contain many (blank) residues.

e) (blank) can form disulfide bridges in proteins

3) You mix 100 ml of 0.1 M acetic acid with 100 ml of 0.1 M sodium acetate. The pKa of acetic acid is 4.76.

a) What is the pH of this mixture?

b) You then add 10 ml of 25 mM HCl. What will the new pH be?

c) What would the resulting pH be if you just added 10 ml of 25mM HCl to 200 ml of distilled water?

Answer 1

1.

A = e*c* L

where A = absorbance = 0.550 , e = 15600 , L = 1cm

c = concentration =?

0.550 = 15600 x c x 1

C= 0.550/15600

c = 3.53*10^-5 M

Dilution fold = 1ml/25 ul = 1000/25 = 40 fold

So, the concentration of ATP in original solution = Diluted solution* 40 fold

=3.53*10^-5 M * 40

=1.412 * 10^-3 M

a. ATP concentration in original undiluted solution = 3.53*10^-5 M ( ans)

b.mg of ATP are there in total in the original, undiluted solution can be found out as below:

= (1.412 * 10^-3 M / 1L ) *1L/1000ml *100ml*551.14

=0.078g

=78 mg (ans)

2.

a) If you dissolve Lysine in water, the resulting pH would be about 8.5

b) if you dissolve Aspartate in water, the resulting pH would be about 4

c)Tryptophan residues would most likely be buried in the core of a folded protein structure

d) Collagen does not absorb strongly at 280 nm. This is because its sequence does not contain many valine residues.

e)Cysteine can form disulfide bridges in proteins