MCAT Biology : Other Reactions

Study concepts, example questions & explanations for MCAT Biology

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Example Questions

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Example Question #1 : Other Reactions

Which of these is a dehydration synthesis reaction?

I.  Formation of a disulfide bond between two cysteine residues

II.  Carboxylation of a carbohydrate 

III.  Formation of an amide bond

IV.  Splitting of dipeptides into amino acids

V.  Addition of hydrogen to an unsaturated fatty acid 

Possible Answers:

II

IV

III

V

I

Correct answer:

III

Explanation:

Condensation reactions remove a small molecule—usually water—to bond two reactant molecules. In amide bonding, the carboxylic (–COOH, acid) portion of one amino acid is juxtaposed to the amide (–NH2, basic) end of a second amino acid. A molecule of water is extracted and the amide bond (–CONH) is formed. This is a variant of the classic statement, "Acid plus base yields salt plus water."

Technically, condensation reactions can remove small molecules other than water, but often the terms "condensation" and "dehydration" are used interchangeably in biochemistry (but not in organic chemistry). Incidentally, two cysteine molecules linked by a disulfide bond is renamed cystine (notice spelling alteration).

Example Question #16 : Reaction Types

Drain cleaners a common household staple, used to open clogged drains in bathtubs and sinks. Human hair is a common culprit that clogs pipes, and hair is made predominately of protein. Drain cleaners are effective at breaking down proteins that have accumulated in plumbing. Drain cleaners can be either acidic or basic, and are also effective at breaking down fats that have accumulated with proteins.

A typical reaction—reaction 1—which would be expected for a drain cleaner on contact with human hair, would be as follows in an aqueous solution:

Pic_1

Another reaction that may occur, reaction 2, would take place as follows in an aqueous solution:

Pic_2

An alcohol reacts with the protein reactant in Reaction 2. Which atom in the protein reactant is likely to be the site of a nucleophilic attack?

Possible Answers:

The carbonyl oxygen

The nitrogen

Both the carbonyl carbon and the nitrogen

The carbonyl carbon

The carbonyl oxygen and the nitrogen

Correct answer:

The carbonyl carbon

Explanation:

Carbonyl carbons bond with a strongly polar bond to the carbonyl oxygen. This strongly polar bond gives the carbon a partial positive charge, and thus makes it receptive to nucleophilic attack by other oxygens (e.g., alcohols).

Example Question #1433 : Mcat Biological Sciences

Which of these methods can be used to synthesize a secondary alcohol?

Possible Answers:

Reacting a ketone with lithium aluminum hydride, then adding water

All of these answer choices are correct

Adding a Grignard reagent to an aldehyde, then reacting with acid

Reacting propene with water and acid

Correct answer:

All of these answer choices are correct

Explanation:

All of these methods can successfully synthesize secondary alcohols.

Lithium aluminum hydride and sodium borohydride are strong and weaker reducing agents, respectively. Both are able to reduce ketones to secondary alcohols.

Adding water and acid to an alkene (such as propene) results in Markovnikov addition of a hydroxyl group, also creating a secondary alcohol.

Grignard reagents (organometallic halides) add to the carbonyl carbon of an aldehyde, adding an alkane group and forming an alcohol product.

Example Question #2 : Other Reactions

Which of the following is an example of an anabolic reaction in the body?

Possible Answers:

Condensation reactions

Hydrolysis

The conversion of glycogen to glucose

Decomposition reactions

Correct answer:

Condensation reactions

Explanation:

Anabolic reactions are reactions that construct molecules from smaller primary units. Catabolism is just the opposite, where larger molecules are degraded into simpler subunits. In the body larger macromolecules, such as proteins, are frequently created via condensation reactions. In condensation reactions, water is formed as a byproduct of joining two molecules together.

All other three processes describe a scenarios where a larger molecule is broken down into smaller subunits, known as catabolic processes.

Example Question #3 : Other Reactions

In the human body, glycerol and three fatty acids can act together to form triacyl glycerol in a process known as esterification. The reverse of this process is known as __________.

Possible Answers:

reverse esterification

decarboxylation

saponification

transesterification

Correct answer:

saponification

Explanation:

When an alcohol and carboxylic acid are reacted together they can form an ester, in a process known as esterification. This is what happens with glycerol and fatty acids to form triacyl glycerol. The reverse of this process is an organic chemistry reaction known as saponification, in which an ester and water are reacted to form carboxylic acids and alcohol.

Example Question #4 : Other Reactions

Triacylglycerols are broken down in the body by lipases. In the presence of water, lipase is used to break down the triacylglycerol into a glycerol molecule and three fatty acids. Based on this information, the breakdown of a triacylglycerol is the opposite of which reaction?

Possible Answers:

Saponification

Esterification

Decarboxylation

Hydrolysis

Correct answer:

Esterification

Explanation:

The molecular structure of a triacylglycerol reveals that the three fatty acid tails are attached to the glycerol molecule, resulting in three ester functional groups. Remember that fatty acids have a carboxylic acid functional group at one end, which is created after the cleavage described in the question. Since the ester bonds are broken and carboxylic acids are created following the hydrolysis of a triglyceride, the opposite of esterification has taken place.

The process described (breakdown of an ester into a carboxylic acid) is also known as saponification.

Example Question #5 : Other Reactions

Which of the following is not capable of oxidizing a secondary alcohol to a ketone?

Possible Answers:

Pyridinium chlorochromate (PCC)

, , acetone

Lithium aluminum hydride

All of these answers can oxidize secondary alcohols to ketones

Correct answer:

Lithium aluminum hydride

Explanation:

Lithium aluminum hydride is correct because it is a reducing agent, and is therefore not capable of oxidizing secondary alcohols. Instead, LAH could be used to perform the reverse reaction, reducing a ketone to an alcohol. The other answer choices are oxidizing agents.

Example Question #47 : Organic Chemistry, Biochemistry, And Metabolism

Carbonic anhydrase is a very important enzyme that is utilized by the body. The enzyme catalyzes the following reaction:

A class of drugs that inhibits this enzyme is carbonic anhydrase inhibitors (eg. acetazolamide, brinzolamide, dorzolamide). These drugs are commonly prescribed in patients with glaucoma, hypertension, heart failure, high altitude sickness and for the treatment of basic drugs overdose.   

In patients with hypertension, carbonic anhydrase inhibitors will prevent the reabsorption of sodium chloride  in the proximal tubule of the kidney. When sodium is reabsorbed back into the blood, the molecule creates an electrical force. This electrical force then pulls water along with it into the blood. As more water enters the blood, the blood volume increase. By preventing the reabsorption of sodium, water reabsorption is reduced and the blood pressure decreases. 

When mountain climbing, the atmospheric pressure is lowered as the altitude increases. As a result of less oxygen into the lungs, ventilation increases. From the equation above, hyperventilation will result in more  being expired. Based on Le Chatelier’s principle, the reaction will shift to the left. Since there is more bicarbonate than protons in the body, the blood will become more basic (respiratory alkalosis). To prevent such life threatening result, one would take a carbonic anhydrase inhibitor to prevent the reaction from shifting to the left.  

Carbonic anhydrase inhibitors are useful in patients with a drug overdose that is acidic. The lumen of the collecting tubule is nonpolar. Due to the lumen's characteristic, molecules that are also nonpolar and uncharged are able to cross the membrane and re-enter the circulatory system. Since carbonic anhydrase inhibitors alkalize the urine, acidic molecules stay in a charged state.

A patient overdosed on an unknown drug. Two hours after being admitted into the hospital, acetazolamide was administered. A realtime measurement of the drug's concentration in the patient's blood was taken the moment the patient was admitted every 30 minutes. Which of the following best explains the lab results shown? 

 

Possible Answers:

The unknown drug was acidic

The sample was influenced by the body's metabolic 

The unknown drug was basic

The unknown drug was innate

The unknown drug destroyed the renal system

Correct answer:

The unknown drug was basic

Explanation:

From the data, the concentration of the unknown drug in the blood increased shortly after the patient received the carbonic anhydrase inhibitor. The increase in the blood's concentration of the drug meant that the body is reabsorbing the drug. The only way for the drug to be reabsorbed is if it is able to cross the membrane of the renal's lumen. In order to cross the renal's membrane, the drug must be noncharged and nonpolar. Basic molecules in a basic environment will stay uncharged.  

Example Question #6 : Other Reactions

Carbonic anhydrase is a very important enzyme that is utilized by the body. The enzyme catalyzes the following reaction:

A class of drugs that inhibits this enzyme is carbonic anhydrase inhibitors (eg. acetazolamide, brinzolamide, dorzolamide). These drugs are commonly prescribed in patients with glaucoma, hypertension, heart failure, high altitude sickness and for the treatment of basic drugs overdose.   

In patients with hypertension, carbonic anhydrase inhibitors will prevent the reabsorption of sodium chloride  in the proximal tubule of the kidney. When sodium is reabsorbed back into the blood, the molecule creates an electrical force. This electrical force then pulls water along with it into the blood. As more water enters the blood, the blood volume increase. By preventing the reabsorption of sodium, water reabsorption is reduced and the blood pressure decreases. 

When mountain climbing, the atmospheric pressure is lowered as the altitude increases. As a result of less oxygen into the lungs, ventilation increases. From the equation above, hyperventilation will result in more  being expired. Based on Le Chatelier’s principle, the reaction will shift to the left. Since there is more bicarbonate than protons in the body, the blood will become more basic (respiratory alkalosis). To prevent such life threatening result, one would take a carbonic anhydrase inhibitor to prevent the reaction from shifting to the left.  

Carbonic anhydrase inhibitors are useful in patients with a drug overdose that is acidic. The lumen of the collecting tubule is nonpolar. Due to the lumen's characteristic, molecules that are also nonpolar and uncharged are able to cross the membrane and re-enter the circulatory system. Since carbonic anhydrase inhibitors alkalize the urine, acidic molecules stay in a charged state.

Glaucoma involves the pressure within the eye increasing to a dangerously high level due to improper draining of the vitreous humor. Blindness usually follows due to damage to the nerves. How might administering a carbonic anhydrase inhibitor help in patients with glaucoma?

Possible Answers:

Increase intraocular pressure 

Lower the rate of vitreous humor drainage

Prevent the excess production of fluid

Increase acid production

Increase the production of fluid

Correct answer:

Prevent the excess production of fluid

Explanation:

From the equation: 

We can see that carbonic anhydrase functions in both the forward and backward reactions. In the eye, the equation shifts to the left and more water is produced. Water is one of the main substances in vitreous humor. As the production of water increases, pressure increases as well. By blocking the production of water, the pressure is lowered.  

Example Question #7 : Other Reactions

Carbonic anhydrase is a very important enzyme that is utilized by the body. The enzyme catalyzes the following reaction:

A class of drugs that inhibits this enzyme is carbonic anhydrase inhibitors (eg. acetazolamide, brinzolamide, dorzolamide). These drugs are commonly prescribed in patients with glaucoma, hypertension, heart failure, high altitude sickness and for the treatment of basic drugs overdose.   

In patients with hypertension, carbonic anhydrase inhibitors will prevent the reabsorption of sodium chloride  in the proximal tubule of the kidney. When sodium is reabsorbed back into the blood, the molecule creates an electrical force. This electrical force then pulls water along with it into the blood. As more water enters the blood, the blood volume increase. By preventing the reabsorption of sodium, water reabsorption is reduced and the blood pressure decreases. 

When mountain climbing, the atmospheric pressure is lowered as the altitude increases. As a result of less oxygen into the lungs, ventilation increases. From the equation above, hyperventilation will result in more  being expired. Based on Le Chatelier’s principle, the reaction will shift to the left. Since there is more bicarbonate than protons in the body, the blood will become more basic (respiratory alkalosis). To prevent such life threatening result, one would take a carbonic anhydrase inhibitor to prevent the reaction from shifting to the left.  

Carbonic anhydrase inhibitors are useful in patients with a drug overdose that is acidic. The lumen of the collecting tubule is nonpolar. Due to the lumen's characteristic, molecules that are also nonpolar and uncharged are able to cross the membrane and re-enter the circulatory system. Since carbonic anhydrase inhibitors alkalize the urine, acidic molecules stay in a charged state.

When a patient is not ventilating efficiently, the kidneys try to compensate by producing more bicarbonate to buffer the decreasing pH of the blood due to the buildup of . Which of the following will increase the amount of  in the blood?

I. Increase  level in the blood

II. Increase  level in the blood

III. Increase metabolism 

Possible Answers:

I only

I, II, and III

II only

III only

I and III

Correct answer:

I and III

Explanation:

To answer this question, we must understand Le Chatelier’s principle. The reaction favorites the product when there is more of the reactants. The opposite is also true in that when there is a buildup of the products, the reaction will reverse and favorite the reactants. Increasing the metabolism will produce more , which will shift the equation to the right.  

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