BCHS EXAM 2 PART 2

Carbon monoxide binds to heme ___.

• resulting in the oxidation of the Fe

• to replace carbon dioxide which must be transported out

• with a higher affinity than oxygen

• from the side opposite to oxygen, causing CO poisoning

Answer explanation

Carbon monoxide binds to heme with a higher affinity than oxygen, which prevents oxygen from binding effectively. This is a key factor in CO poisoning, as it disrupts normal oxygen transport in the body.

From the dissociation curves shown below, you can conclude that hemoglobin has a ___ P50 than myoglobin, indicating hemoglobin's affinity to oxygen is ___ than myoglobin.

• higher; lower

• lower; higher

• higher; higher

• lower; lower

Answer explanation

Hemoglobin has a higher P50 than myoglobin, meaning it requires a higher partial pressure of oxygen to achieve 50% saturation. This indicates that hemoglobin's affinity for oxygen is lower than that of myoglobin.

Regarding Bohr Effect, which of the following is NOT true?

• Hb's affinity to O2 drops when pH goes down

• Hb's P50 increases when the blood CO2 partial pressure increases

• the T-R equilibrium shifts toward the T-state when lower pH facilitates ion pairs at the C-ter of hemoglobin subunits

• The Y02 for Hb increases when pH goes down

• Hb + 4 O2 <----> Hb(O2)4 + 2.4 H+

Answer explanation

The statement 'The Y02 for Hb increases when pH goes down' is NOT true. In fact, lower pH decreases Hb's affinity for O2, leading to a higher P50, which means Y02 decreases, not increases.

Which of the following best represents a tertiary protein structure?

• alpha helix

• beta sheet

• myoglobin

• hemoglobin

• collagen

Answer explanation

Myoglobin is a protein that exhibits a tertiary structure, characterized by its three-dimensional folding. In contrast, alpha helices and beta sheets are secondary structures, while hemoglobin and collagen are more complex and involve quaternary structures.

Which of the following polypeptides is predicted to have the highest absorbance at 280nm?

• WYF

• WAH

• LYE

• DRF

• GAC

Answer explanation

WYF has the highest absorbance at 280nm due to the presence of two aromatic amino acids (W and Y), which strongly absorb UV light. In contrast, the other polypeptides contain fewer or no aromatic residues.

A UH student wants to use anion exchange chromatography to capture Protein Zeta (pI=6.8). He should use ______ column and use a pH___ buffer.

• DEAE, 8

• CM, 5

• Q, 7

• SP, 6

Answer explanation

To capture Protein Zeta (pI=6.8), an anion exchange column like DEAE is suitable at pH 8, where the protein is negatively charged. This allows effective binding, making DEAE, 8 the correct choice.

Which of the following amino acids will be the first to elute from a cation-exchange column at pH8?

• His

• Ala

• Arg

• Asp

• Ser

Answer explanation

At pH 8, Asp (aspartic acid) is negatively charged due to its carboxyl group, making it the least retained on a cation-exchange column. His, Ala, Arg, and Ser are either neutral or positively charged, thus eluting later.

A polypeptide ARYCGQKRWILPAGDELMAGCP is digested with chymotrypsin and several fragments are generated. What method will you use to separate these fragments?

• size exclusion chromatography

• Ion exchange chromatography

• either of above method

• none of above method

Answer explanation

Both size exclusion chromatography and ion exchange chromatography can effectively separate polypeptide fragments based on size or charge, respectively. Therefore, either method is suitable for separating the chymotrypsin-digested fragments.

Which of the following is an example of affinity chromatography?

• isolating proteins based on difference in solubility

• isolating proteins based on difference in physical size

• isolating His-tagged protein from a mixture

• ion exchange chromatography

• size exclusion chromatography

Answer explanation

Affinity chromatography specifically isolates proteins based on their binding affinity to a ligand. Isolating His-tagged proteins utilizes this principle, as the His-tag binds to nickel or cobalt ions in the chromatography medium.

In which order will Asp, Arg and Ala be eluted from a carboxymethyl column at pH7?

• Asp, Arg, Ala

• Arg, Ala, Asp

• Ala, Arg, Asp

• Asp, Ala, Arg

Answer explanation

At pH 7, Asp (acidic) will elute first due to its negative charge, followed by Ala (neutral), and finally Arg (basic) with a positive charge. Thus, the correct order is Asp, Ala, Arg.