Molecule 3g03 Test 3

Enzymes often employ coenzymes to assist with catalysis because proteins alone have limited abilities to catalyze oxidation-reduction reactions. Coenzymes are small organic molecules that work together with enzymes to facilitate and enhance their catalytic activity. They can act as carriers of specific functional groups or electrons, allowing enzymes to perform a wider range of chemical reactions. By binding to the active site of an enzyme, coenzymes can participate in the reaction and help to lower the activation energy, making the reaction more efficient.

Invariant residues are the correct answer because they refer to the amino acid residues that remain the same in all members of a protein family. These residues play a crucial role in maintaining the structure and function of the proteins and cannot be substituted by other amino acids. Therefore, they are essential for the proper functioning of the proteins in the family.

BPG binds to deoxyhemoglobin, which is the form of hemoglobin that does not have oxygen bound to it. By binding to deoxyhemoglobin, BPG stabilizes its conformation. This stabilization reduces hemoglobin's oxygen-binding affinity, meaning that it makes it less likely for oxygen to bind to hemoglobin. Therefore, the correct answer is "reduces."

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When the oxygen concentration is equal to the dissociation constant, the binding of O2 to the heme group of myoglobin is at its maximum. This means that half of the available binding sites on the myoglobin molecule are occupied by oxygen molecules.

The imidazole side chain of histidine can function as either a general acid catalyst or a general base catalyst because in the physiological pH range, the nitrogen in the ring can be easily protonated/deprotonated. This means that the imidazole group can readily donate or accept a proton, allowing it to act as both an acid and a base catalyst depending on the reaction conditions. This versatility makes histidine an important residue in enzyme catalysis, as it can participate in a wide range of chemical reactions.

Tubulin is a protein that forms microtubules, which are crucial for cell structure and movement. The tubulin dimer refers to two tubulin proteins that come together to form a functional unit. These dimers have binding sites that can bind guanosine triphosphate (GTP) and guanosine diphosphate (GDP). GTP is typically bound to tubulin when it is incorporated into the growing end of a microtubule, providing energy for polymerization. As the microtubule grows, GTP is hydrolyzed to GDP. Therefore, the correct answer is GTP and GDP.

To make a phosphate buffer at pH 12.38, you need to add a base to the phosphoric acid to increase the pH. The pK values of phosphoric acid indicate that at pH 12.38, the majority of the acid will be in its conjugate base form. Therefore, you need to add a base such as KOH to neutralize the acid and create the buffer. The correct answer of 25 millimoles of KOH ensures that there is enough base to react with the acid and achieve the desired pH of 12.38. Adding a lower amount of KOH would result in a lower pH, while adding a higher amount would result in a higher pH.

The isoelectric point (pI) of a peptide or protein is the pH at which it carries no net electrical charge. It can be calculated by averaging the pKa values of its ionizable groups. Each amino acid in the sequence has a specific pKa value for its side chain. In this case, Ala, His, Asp, Arg, Val, and Gln all have ionizable groups with different pKa values. By calculating the average pKa values and determining the pH at which the net charge is zero, the isoelectric point is found to be 7.95.

The decreased affinity of fetal hemoglobin for BPG is advantageous because it biases the hemoglobin towards the R state. The R state is the relaxed state of hemoglobin, which has a higher affinity for oxygen. This means that with decreased BPG binding, more oxygen can bind to the heme residues of fetal hemoglobin, allowing for efficient oxygen transport to the developing fetus.

The statement "Hydrogen bonds between the -OH groups of Hyp residues stabilize the helix" does not apply to collagen.

All of the statements mentioned in the answer are correct. The nucleophilicity of a side chain is inversely related to its acidity, meaning that the less acidic a group is, the more nucleophilic it is. Additionally, a more basic group is more likely to react with an electrophilic group, and a more electron-rich group is also more likely to react with an electrophilic group. Therefore, the correct answer is that all of the rest of the statements are correct.

The rate enhancement caused by the enzyme can be calculated by taking the ratio of the rate with the enzyme to the rate without the enzyme. In this case, the rate with the enzyme is 8.2 x 10^4.sec-1 and the rate without the enzyme is 4.1 x 10^-7.sec-1. Dividing these two values gives a rate enhancement of approximately 2.0 x 10^11. This means that the enzyme increases the rate of the reaction by a factor of 2.0 x 10^11.

In coiled coils, hydrophobic residues are typically found at the first and fourth positions of the seven-residue repeats. The first and fourth side chains are buried within the coiled coil structure, while the remaining side chains are exposed to the solvent. Therefore, the more likely sequence to appear in a coiled coil would be one that has hydrophobic residues at the first and fourth positions, and polar or charged residues at the remaining positions. Among the given sequences, "Ile-Gln-Glu-Val-Glu-Arg-Asp" fits this pattern, making it the more likely sequence to appear in a coiled coil.

The correct answer is "Hemoglobin in the venous blood is bluish in colour." Venous blood is blood that has been oxygenated by the tissues and is returning to the heart to be pumped to the lungs for reoxygenation. When hemoglobin is deoxygenated, it has a bluish color, which is why venous blood appears bluish.

The specificity pocket in trypsin refers to a hole on the enzyme surface at the active site that accommodates the residues on the N-terminal side of the scissile peptide bond. This means that the pocket is specifically designed to bind and interact with the amino acids located on the N-terminal side of the peptide bond that will be cleaved by trypsin. The scissile bond refers to the peptide bond that will be cleaved by the enzyme.

Hemoglobin in the blood passing through highly active muscle has less oxygen affinity because increased metabolic activity in the muscle leads to a decrease in pH and an increase in carbon dioxide levels. This acidic and high carbon dioxide environment causes a decrease in oxygen affinity of hemoglobin, facilitating the release of oxygen to the muscle tissues where it is needed.

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Fibrinogen is not likely to be a serine protease zymogen because it is a soluble protein that plays a crucial role in blood clotting by converting to fibrin during the coagulation process. Serine protease zymogens are inactive forms of enzymes that require activation to become active proteases. Factors XI, IX, and X are all examples of serine protease zymogens involved in the coagulation cascade.

Adding 0.025 moles of NaOH to the solution of acetic acid will create an acetate buffer at pH 4.76. The pK value of acetic acid is 4.76, which means that at this pH, the concentration of acetic acid and acetate ions will be equal. By adding NaOH, it will react with acetic acid to form sodium acetate and water. This reaction will increase the concentration of acetate ions, while the concentration of acetic acid will decrease. This shift in concentrations will create a buffer solution with a pH close to the pK value.

The isoelectric point of a molecule is the pH at which it carries no net electrical charge. In the case of His-Tyr, the isoelectric point is 7.68. This means that at a pH of 7.68, the His-Tyr molecule will have an equal number of positive and negative charges, resulting in a neutral overall charge. At pH values below 7.68, the molecule will carry a net positive charge, while at pH values above 7.68, it will carry a net negative charge.

The given statement is incorrect because when the pH decreases, lamprey hemoglobins do not form monomers. It has been mentioned in the passage that the deoxygenated form of lamprey hemoglobin is favored when the pH decreases, but it does not specify that it forms monomers. The passage only states that the tetramers dissociate into monomers when the hemoglobin becomes oxygenated. Therefore, the statement that lamprey hemoglobins form monomers when the pH decreases is incorrect.

The correct answer is Glu 35 has a pK of 5.9 and Asp52 has a pK of 4.5. This is because the question states that one of the residues has a pK of 4.5 and the other has a pK of 5.9. Therefore, Glu 35 must have a pK of 5.9 and Asp52 must have a pK of 4.5.

The correct answer is MGSIGAASME-(50 a.a.)-FFGRCVSP. This is the correct answer because it matches the partial amino acid sequence of the encoded protein given the nucleotide sequence provided. The amino acid sequence is MGSIGAASME, followed by a 50 amino acid gap, and then FFGRCVSP.

The isoelectric point of an amino acid is the pH at which the molecule has no net charge. At a pH below the isoelectric point, the amino acid will have a net positive charge due to the presence of excess protons. At a pH above the isoelectric point, the amino acid will have a net negative charge due to the loss of protons. Therefore, in this case, the isoelectric point of Tyr is 5.7, which means that at a pH of 5.7, Tyr will have no net charge.