In chickens, comb shape is determined by alleles at two loci (R, r and P, p). A walnut comb is produced when at least one dominant allele R is present at one locus and at least one dominant allele P is present at a second locus (genotype R_ P_). A rose comb is produced when at least one dominant allele is present at the first locus and two recessive alleles are present at the second locus (genotype R_pp). A pea comb is produced when two recessive alleles are present at the first locus and at least one dominant allele is present at the second (genotype rrP_). If two recessive alleles are present at the first and at the second locus (rrpp), a single comb is produced. Which of the following cross would produce ½ walnut and ½ pea comb ?

#Question id: 177

#Unit 1. Molecules and their Interaction Relevant to Biology

The titration curve of alanine shows the ionization of two functional groups with pKa values of 2.34 and 9.69, corresponding to the ionization of the carboxyl and the protonated amino groups, respectively. The titration of di-, tri-, and larger oligopeptides of alanine also shows the ionization of only two functional groups, although the experimental pKa values are different. The trend in pKa values is summarized in the table. Which of the following is a reason for this shift in pK values

#Question id: 178

#Unit 1. Molecules and their Interaction Relevant to Biology

Given the pKa values of different acidic sites in cysteine, the principal ionic form which will never exist at any pH

#Question id: 179

#Unit 1. Molecules and their Interaction Relevant to Biology

The average molecular weight of the 20 standard amino acids is 138, but biochemists use 110 when estimating the number of amino acids in a protein of known molecular weight.  Why?

#Question id: 180

#Unit 1. Molecules and their Interaction Relevant to Biology

Which of the following statements about aromatic amino acids is correct?

#Question id: 181

#Unit 1. Molecules and their Interaction Relevant to Biology

Titration of valine by a strong base, for example NaOH, reveals two pK’s. The titration reaction occurring at pK2 (pK2 = 9.62) is:

#Question id: 182

#Unit 1. Molecules and their Interaction Relevant to Biology

Which amino acid is least likely to participate in acid-base catalysis?