Show your works or explains to receive points. Please be direct with your explai

Question

Show your works or explains to receive points. Please be direct with your explaination, dont include unrelated info. preferred short answer.

1. Calculate Isoelectric Point for Tyrosine. Given that the pka of alpha carboxyl and amino groups are 2.2 and 9.1 respectively. The pka of the side chain is 10.1  

2. Amino acids can act as buffers. glycine has a carboxyl pka of 2.3 and amino  pka of 9.6.

Calculate the PH range that glycine could function as a buffer?

3.Chymotrypsin cleaves after aromatic residues. Write the products that would result from chymotrypsin cleavage of the following unlikely peptide;

ADEFGHIKLMNPQRSTVWY

4. Why water clustered about non polar molecules contribute to hydrophobic interaction ?

Explanation / Answer

1. pI of tyrosine = pKa1(carboxyl) + pKa2(amino) / 2 = 2.2+9.1 /2 = 5.65

2. AMino acids function as buffers in a range that is +1 or -1 around its pI value.

Now pI value of Glycine = 2.3+9.6 /2 = 5.95

Thus buffering range for glycine = 4.95 - 6.95

3. As chymotrypsin cleaves after aromatic residues we shall thus get the following fragment sequences:

ADEF, GHIKLMNPQRSTVW, Y

Chymotrypsin can also cleave after the residue L and M, but at very slow and almost negligible rates.

4. When the water molecules form a cage around individual non-polar molecules then this would mean that as many such 'water cages' will need to be formed as the number of non-polar molecules. Thus, this would result in a large size of such cages and a large accumulation of water molecules, which would actually be a highly energetically unfavourable process.

Thus to avoid this, the water cages fuse together by bringing all the non-polar molecules together into a single cage. Such a clustering of all non-polar molecules within the single water cage prevents the interaction of the non-polar molecules with water and thus contributes to the hydrophobic interactions.

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