Hair is comprised largely of keratin, a fibrous protein consisting of two α-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 sequence positions of the first aligned residue in each polypeptide strand.Diagram:- **Human Sequence (5 to 219):** ``` FEQYINNLRRQLDSIVGERGRLDSSELRNMQDLVEDFKNKYEDENKRTTAE ```- **Ovine Sequence (7c to 158):** ``` FEGYIETLRREAECVEADSGRLSSSELNHVQEVLEGYKKYKYEQEVALRATAE ``` This alignment compares specific sequences of human and ovine keratin, focusing on differences in amino acids and their properties.

Amino acids are biomolecules that have an amino group and a carboxyl group linked to the same carbon…

Answered: Hair is comprised largely of keratin, a…

Biochemistry

9th Edition

ISBN:9781319114671

Author:Lubert Stryer, Jeremy M. Berg, John L. Tymoczko, Gregory J. Gatto Jr.

Publisher:Lubert Stryer, Jeremy M. Berg, John L. Tymoczko, Gregory J. Gatto Jr.

Chapter1: Biochemistry: An Evolving Science

Section: Chapter Questions

Problem 1P

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What would you predict about the ratio of hydrophilic to hydro- phobic amino acid residues in a series of monomeric globular proteins that range in size from a molecular weight of 10,000 g/mole to a molecular weight of 100,000 g/mole? Note that the volume of a sphere is 4/3nr³, while the sur- face area of the outside of a sphere is 4пr².
Histidine is an amino acid with three titratable groups: an -NH3+ group (pKa = 9.2), a -COOH group (pKa = 1.8), and an imidazole (amine-like) group (pKa = 6.0). The titration curve for histidine is shown below with four points highlighted. (a) Identify which point on the titration curve corresponds to the pKa for each of the titratable groups, and which point corresponds to the pI. Explain your choices. (b) Calculate the value of pI for histidine
In the molecule of oligomeric protein there are 19 lysine residues. 12 of them may be easily acetylated with anhydrides of dicarbon acids (it react with NH2-groups). The acetylation of extra two residues of lysine will dissociate the protein to the subunits. The rest 5 lysine residues may be modified only after denaturation of the protein. Suggest, how many lysine residues are: a) on a surface of protein globule; b) inside globule: c) in a site which is responsible for the contact within subunits
Consider a protein in which a negatively charged glutamic acid side chain (pKa = 4.2) makes a salt bridge (ion-ion interaction) with a positively charged histidine side chain (pKa = 6.5). Part A Do you predict that this salt bridge will become stronger, become weaker, or be unaffected as pH increases from pH = 7.2 to pH = 7.8? The salt bridge will become stronger. The salt bridge will become weaker. The salt bridge will be unaffected. Submit Part B Previous Answers Correct At pH = 7.2 the glutamic acid (Glu) side chain will carry a charge of ~ -1 (at 3 pH units above the pKa for Glu, the side chain will be almost fully ionized); whereas the histidine (His) side chain will carry a charge of < +0.5 (at pH = pK₂ the charge on His would be +0.5; since pH = 7.2 is above its pKa, it will carry less (+) charge as it becomes more deprotonated). As the pH increase to 7.8, the charge on Glu will remain ~ -1 and the charge on His will decrease; thus, this salt bridge is predicted to become weaker…
Provide the number of polypeptide chains present andthe number of amino acid residues in each chain. for https://www.rcsb.org/structure/6j20 Provide the molecular weight of the protein orprotein complex and the total number of atoms. (All of this information can be found in the PDBpage.) Create a figure (available in the PDB page) that shows the topology of your protein, i.e.the secondary structures adopted by different regions of the protein (alpha helix, beta strand).Make sure to also provide a figure legend that helps interpret the figure and appropriate figurecaption that briefly explains the figure.
Consider the peptides Pro-Gin-Val-Phe-His-Asp-Cys and His-Gln-Pro-Cys-Asp-Phe-Val. How do these two peptides differ? (Select all that apply.) The two peptides have different compositions. The two peptides have different isoelectric points. The two peptides have different titration curves. The two peptides differ in amino acid sequence. [References] If you were to have a mythical amino acid based on glutamic acid, but one in which the hydrogen that is attached to the y-carbon were replaced by another amino group, what would be the predominant form of this amino acid at pH 12 if the pK, value were 10 for the unique amino group? (Select all that apply.) Both of the carboxyl groups are deprotonated. The amino acid-carries a negative 2 charge. The amino acid carries a negative 4 charge. The amino groups are in the form -NH". Both of the amino groups are deprotonated.
What would you predict about the ratio of hydrophilic to hydro- phobic amino acid residues in a series of monomeric globular proteins that range in size from a molecular weight of 10,000 g/mole to a molecular weight of 100,000 g/mole? Note that the volume of a sphere is 4/3nr³, while the sur- face area of the outside of a sphere is 4nr². How would your prediction change if the monomeric proteins were fibrous instead of globular?
Using a copy of a helical wheel (attached to the end) plot the amino acids of the helix on the helical wheel. Is there any evidence of the helix as a whole being amphipathic or having a “sidedness"? Explain yes or no. Are the amino acid side chains in close proximity of one another or staggered to minimize steric hinderance between side chains? Explain the pattern you observe.
At physiological pH (i.e. 7.4), polylysine assumes a random structure in solution. Given that the pKa for the e-amino group of lysine is 10.5, under what conditions would you expect polylysine to form an a-helix? Explain your reasoning. Under what conditions would you expect polyglutamate to form an a-helix, given that the pKa for the side-chain COOH group is 4.3?
There are a total of six different amino acid sequences for a tripeptide containing one molecule each of serine, valine, and glycine. Using three-letter abbreviations for the amino acids, draw the six possible sequences of amino acids.
What is the optimum pH to separate a mixture of lysine, arginine, andcysteine using electrophoresis? Draw the structures of the three amino acidsin the protonation state that would predominate at the pH you have chosen.(as shown) For each amino acid, indicate the net charge at the chosen pH as well as the direction of migration and relative mobility in the electric field.
Draw Glu-His-Trp-Ser-Gly-Leu-Arg-Pro-Gly peptide. What is the net charge of this peptide at pH 3, 8 and 11? What can you say about pI value of this peptide?

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