Patients suffering from sickle cell anemia have a mutation in the gene that codes for one of the hemoglobin chains, in which a single glutamate is replaced by a valine. Propose an explanation for why this substitution has such a striking effect on protein structure and function with explanation.  Suggest two other amino acids that would be less likely to cause such serious impairment of hemoglobin function if each was substituted for glutamate. Briefly explain your answer.

Most animals cannot use wool for nourishment. An exception is the clothes moth: it can derive nourishment from eating clothing made of natural fibers such as wool (which is rich in a-keratin). The digestive tract of the larvae of clothes moths provides a highly reducing environment. Why is this beneficial to the larvae? The reducing environment will reduce the disulfide linkages, making it easier to digest the proteins. The reducing environment will hydrolyze the peptide bonds. The reducing environment will interfere with the H-bonding between the tropocollagen molecules, making the type of protein found in most natural fibres easier to digest. The reducing environment will help to kill bacterial pathogens. The reducing environment will detoxify the carcinogenic dyes used in the textile industry.

Consider the following situation; Fresh pineapple contains the enzyme bromelain that hydrolyzes peptide bonds in proteins. a. The directions in making a gelatin (protein) dessert say not to add fresh pineapple. However, canned pineapple where pineapple is heated to high temperatures can be added. Why? b. Fresh pineapple is used in a marinade to tenderize tough meat. Why? c. What structural level of a protein does the bromelain enzyme destroy?

Draw the structure of the a-keto acid formed by removal of the amino group during the catabolism of leucine. Note: Reference the Naturally-occurring amino acids table for additional information. Click and drag to start drawing a structure. x

Theoretical and experimental data show that in many cases the ionic and hydrogen-bonding interactions to ΔH for protein folding are close to zero. Provide an explanation for this result.

Consider the phenolic hydroxyl group of a particular Tyr residue in a protein. Suppose the hydroxyl group in the unfolded protein in aqueous solution, where the group is exposed to H2O, has a pKa of 10.0. If that group is found in a hydrophobic environment in the interior of the protein when the protein is folded into its native tertiary structure, would you expect the pKa of the phenolic hydroxyl to be higher or lower in the folded protein interior than in H2O? Explain your reasoning.

Consider protein folding that results when the following components interact:   Where the solution is at a pH of 7, green (thick-dotted line) represents aspartic acid (R group contains a carboxylic acid with pKa = 4), orange (thick-solid line) represents lysine (R group contains an amine with pKa = 10), and blue (thin-solid line) represents hydrophilic groups. Rank the three complexes in order from lowest to highest dissociation constants Kd (low Kd values correspond to good binding constants and low energy, while high Kd values correspond to low binding constants and high energy) as determined by intermolecular charge-charge interactions. For those complexes with charge-charge interactions being equal, look at the possibility for the formation of hydrogen bonds via carboxylic acid dimers (only possible when the carboxylic acid is protonated) which are low energy structures.

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Consider a protein with two surface-exposed histidine residues: HisA is a “typical” histidine residue with a pKa = 6.2 HisB is involved in a stabilizing interaction (His-NH+ ..... -O2C-Glu) with a neighboring glutamic acid residue. For HisB, the Gibbs free energy of deprotonation at pH = 7.0 and T = 293K is ΔG'o = +15 kj mol-1. If you had a solution, at pH = 7.0 and T = 293K, containing this protein: a) What fraction of HisA residues are protonated? b) What fraction of HisB residues are protonated? c) What is the pKa of HisB?

You have a peptide that has the following amino acid sequence: GPMG Draw the structure of the polypeptide's most protonated form, and its charge. Then draw the structures of the increasingly deprotonated forms, along with their charges. Use the information from these structures to calculate the pl (isoelectric point) of the peptide using the pKa values provided in the table below. Write the pl as x.yz, for example, 7.62 or 3.09. Group Terminal a carboxyl group Aspartic acid Glutamic acid Histidine Terminal a-amino group Cysteine Lysine Tyrosine Arginine Acid EM 2-0" + H -N H H N-H H N-H T Base 1 1. تر H -5 H H O™ N-H Typical pK, 3.1 4.1 6.0 8.0 8.3 10.8 10.9 12.5