Lactose permease, a protein of E. coli, is composed of a singlepolypeptide that is 417 amino acids in length. By convention, theamino acids within a polypeptide are numbered from the aminoterminalend to the carboxyl-terminal end. Are the following questionsabout lactose permease true or false?A. Because the sixty-fourth amino acid is glycine and the sixty- eighth amino acid is aspartic acid, the codon for glycine,64, is closer to the 3′ end of the mRNA than the codon for aspartic acid, 68.B. The mRNA that encodes lactose permease must be greater than1241 nucleotides in length.

A normal polypeptide and a mutant of the polypeptide were hydrolyzed by an endopeptidase under the same conditions. The normal and mutantpolypeptide differ by one amino acid. The fingerprints of the peptides obtained from the two polypeptides are shown below. What kind of amino acid substitution occurred as a result of the mutation? (That is, is the substituted amino acid more or less polar than the original amino acid? Is its pI lower or higher?) (Hint: Photocopy the fingerprints, cut them out, and overlay them.)

In the folded protein, His108 forms a salt bridge with Asp44. The pKa of the imidazole functional group in the side chain of histidine is 6.0. The pKa of the carboxylic acid functional group in the side chain of aspartate is 4.1. How do you think the pKa of the side chain of His108 will change in the folded protein? a. The pKa will be > 6.0. b. The pKa will be < 6.0. c. The pKa will not change. Use chemical reasoning to justify your answer.

Consider a short peptide that forms an alpha-helix within a larger protein structure. Suppose that one glutamate residue at some specific position in the helix were mutated to a leucine residue. The mutation could either make the helix more stable, or less stable. i) Describe two situations in which a Glu-to-Leu mutation could make the helix more stable. ii) Describe two situations in which the Glu-to-Leu mutation could make the helix less stable. Explain briefly the basis for the stabilizing and destabilizing effect in all cases.

Ornithine is an amino acid that is not used in the synthesis of proteins, but is an important intermediate in several metabloic pathways including the urea cycle and the synthesis of polyamines. It has a perfectly ordinary terminal amino group and terminal carboxyl group like any other amino acid and a side chain with a single ionizable side group with a pKa of 10.3. If ornithine is placed in solution at pH 7.0, it has a net charge of +1. What would the net charge on this amino acid be if the pH of the solution was raised to pH 12.0? Please explain your reasoning.

Hair is comprised largely of keratin, a fibrous protein consisting of two a-helices wrapped around each other in a left-handed coiled-coil. The diagram below compares a partial alignment of the amino acid sequences of a form of human keratin and of ovine keratin. For each pair of dissimilar aligned amino acids, (i) indicate if a side chain is associated with a discrete charge by writing or (at pH 7) adjacent to the letter; and (ii) indicate whether each amino acid is polar (p) or apolar (a) in the case of aligned, electrostatically-neutral, side chains. In the diagram, 219 and 158 designate se-quence positions of the first aligned residue in each polypeptide strand. human II 5 219 ovine II 7c 158 FEQYINNLRRQLDSIVGERGRLDSELRNMQDLVEDFKNKYEDEINKRTTAE FEGYIETLRREAECVEADSGRLSSELNHVQEVLEGYKKKYEQEVALRATAE

Jacqueline isolated an interesting new protein from the broth of a yeast culture. After purification of the protein, she requested an amino acid analysis and found that the protein contained 0.57% tryptophan by weight (tryptophan Mr-204). Calculate the minimum molecular weight of the protein (i.e., assuming there is only one tryptophan residue per protein molecule).

The neighboring amino acid that TYR 368 interacts with is ILE 160. What are the properties of the amino acid ILE 160?

Fluorescent proteins like the green fluorescent protein (GFP) found in jellyfish are a class of colorful proteins that shine a particular color when exposed to ultraviolet light. These proteins, despite exhibiting a wide range of diverse colors, have nearly identical secondary structure across organisms and phenotypes. Each GFP-like protein has a few alpha-helices as well as a characteristic beta-barrel composed of 11 beta-sheets that shields the inside of the protein from solvent (i.e., water). The GFP- like protein shown below is a green fluorescent protein from the great star coral Montastraea cavernosa and contains two alpha-helices in its structure (labeled A and B and colored cyan). A B 1. Helix A contains 6 amino acids, including a phenylalanine and an aspartic acid. Which position (1 or 2, colored in red) would you more likely expect aspartic acid to be located? [Select] 2. If you were to compare helix A to helix B, would you expect the ratio of polar:non-polar residues to be…

There is another melanocyte-stimulating hormone called β-melanotropin.Cleavage of β-melanotropin with trypsin produces the following peptidesplus free aspartic acid.                                        WGSPPK DSGPYK MEHFRIf you assume maximum sequence similarity between α-melanotropin andβ-melanotropin, then what must the sequence of the latter be?