1. What type of interaction would you expect between the R groups of the followi

Question

1. What type of interaction would you expect between the R groups of the following amino acids in a tertiary structure? phenylalanine and isoleucine aspartic acid and histidine asparagine and tyrosine alan a. b. c. d. ine and proline 2. A portion of a polypeptide chain contains the following sequence of amino acids -Leu-Val Cys-Asp -Ser- Which amino acid(s) could form a disulfide crosslink? Which amino acid(s) are likely to be found on the inside of the protein structure? Why? a. b. . Which amino acid(s) are likely to be found on the outside of the protein structure? Why?

Explanation / Answer

Tertiary structure of protein is nothing but a 3 dimensional structure of protein. And then comes amino acids, which are put together in a polypeptide chain, on the ribosome during synthesis of protein.

There are 20 most common amino acids which have been listed and been observed. These sows different interactions among themselves.

solution to (1)

1. Phenylalanine and isoleucine

--> they both are normally buried inside the protein core and show hydrophobic interactions.

2. Aspartic acid and histidine

--> they are often observed in making side chains and thus show charged ion pair or hydrogen bond interactions.

3. Aspargine and tyrosine

--> they show polar interactions and are usually seen as proton acceptor or donor.

4. Alanine and proline

--> they show hydrophobic interactions.

solution to (2)

a) Cysteine amino acid is the only amino acid that is capable to form a disulphide bond and thus can only do so with other Cysteine groups. So in the above polypeptide chain, cysteine and serine could form a disulphide crosslink.

b) leucine and valine are the amino acids which are likely to be found inside the protein structure. This is so because they are hydrophobic and form hydrophobic interactions.

c) aspartic acid is the amino acid which is likely to be found outside the protein structure. This is so because they are charged and form side chains.

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