a)If you have 14 amino acids in a polypeptide chain, how many peptide bonds are

Question

a)If you have 14 amino acids in a polypeptide chain, how many peptide bonds are there in the polypeptide chain?

b) T/F R groups affect peptide bond formation.

c)What is unique about the peptide bond and how does this characteristic affect the length of the bond?

d)What are the 3 Greek torsion angles and between what atoms are they located?

e)What is the dominant peptide bond conformation and why is this so? What amino acid exhibits the other conformation?

e)If you have 10 different amino acids and want to make a polypeptide chain of 6 amino acids, how many theoretical combinations of amino acids could you make?

f)If the molecular weight of a protein is 2000 Da, how many amino acids are in the protein?

Explanation / Answer

a) 13 peptide bonds, each amino acid will form a peptide bond with the adjacent one except the last one.
b) False. R groups are not involved in the condensation reaction that forms a peptide bond, since the bond forms from the carboxy and amino group.
c) The peptide bond has a unique partial double bond character. The electronegative oxygen can accept electrons from the nitrogen. Because of this, C-N bond length (1.33 Å) in a peptide is shorter than the normal C-N bond (1.45 Å).
d) For the three repeating bonds in a peptide backbone the dihedral angles are defined as:                      Phi - to describe rotation about the N-C(a) bond and involves the C(O)-N-C(a)-C(O) bonds
Psi- to describe rotation about the C(a)-C(O) bond and involves the N-C(a)-C(O)-N bonds
Omega- to describe rotation about the C(O)-N bond and involves the C(a)-C(O)-N-C(a) bonds
e) Almost all peptide bonds in proteins are in trans configuration, because of the steric hindrance (steric clashes) between the functional groups attached to the Ca atoms. Proline demonstrates a cis conformation due to the cyclic nature of the R group in Proline.
f) 10P6=151,200 (we use a permutation and not a combination because order DOES matter)
g) 1 amino acid is about 110 Da, therefore n=2000/110=18.18. So we have 18 amino acids.

 

P.S Cramster would not let me enter greek alphabet, so I had to write them in words.

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