MCAT Physical : Biochemistry, Organic Chemistry, and Other Concepts

Study concepts, example questions & explanations for MCAT Physical

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Example Questions

Example Question #4 : Other Electrochemical Principles

Listed below are three substances that dissolve in water.

I. Acetic acid

II. Acetone

III. Hydrochloric acid

Which of the following correctly lists the substances in decreasing order of electrical conductivity?

Possible Answers:

Correct answer:

Explanation:

Electrical conductivity is a measure of the ability of a substance to conduct electricity. A substance with a high electrical conductivity will easily conduct electricity, and a substance with low electrical conductivity will not conduct electricity.

In solution, a substance can conduct electricity if it can dissociate into ions. Of the three substances listed, hydrochloric acid is likely to have the highest electrical conductivity. Recall that hydrochloric acid () is a strong acid; therefore, it will completely dissociate into hydrogen and chlorine ions in water.

The substance with the second highest electrical conductivity is acetic acid. Although acetic acid is an acid, it is a weak acid. This means that the acetic acid will not completely dissociate into ions in water. If you have the same concentration of hydrochloric acid and acetic acid, hydrochloric acid will produce more ions in water and will be able to conduct more electricity; therefore, hydrochloric acid has a higher electrical conductivity than acetic acid.

Acetone is soluble in water; however, it does not dissociate into ions and will have the lowest electrical conductivity.

The correct order of electrical conductivity is: .

Example Question #191 : Biochemistry, Organic Chemistry, And Other Concepts

Which of the following amino acids are acidic?

I. Glutamate

II. Proline

III. Glycine

IV. Arginine

Possible Answers:

I only

I, II and IV

I and IV

II and III

Correct answer:

I only

Explanation:

Glutamate (glutamic acid), is the only one of which that contain an acidic functional group (carboxylic acid). Arginine is basic while proline and glycine considered non-polar.

Example Question #192 : Biochemistry, Organic Chemistry, And Other Concepts

What properties of phospholipids make the formation of cell membranes possible?

Possible Answers:

Phospholipids are amphiphatic

Phospholipids are completely polar

Phospholipids are completely non-polar

Phospholipids are inorganic

Correct answer:

Phospholipids are amphiphatic

Explanation:

Phospholipids have two fatty acid tails made of hydrocarbons, which are nonpolar, and a phosphate head, which is polar. Their structure allows phospholipids to group up into a bilayer such that the polar heads face the outside environment while the non-polar fatty tails face inward, protected from the aqueous environment. Phospholipids are not completely polar or non-polar, they are amphiphathic.

Example Question #193 : Biochemistry, Organic Chemistry, And Other Concepts

Cellulose is a polymer that is composed of what monomer?

Possible Answers:

Glycerol

Fructose

Glycogen

Galactose

Glucose

Correct answer:

Glucose

Explanation:

Cellulose is a polysaccharide (a sugar). Glucose is the monosaccharide used to generate the structure of cellulose via  linkages. Cellulose is composed of several hundred glucose molecules bound in this chain. Due to the nature of the beta linkage, humans cannot digest cellulose.

Example Question #194 : Biochemistry, Organic Chemistry, And Other Concepts

Chymotrypsin is a proteolytic enzyme that is released by the pancreas. Using a water molecule, it cleaves the traget polypeptide and creates the new N and C termini for the newly made fragments.

Based on this enzymatic function, what type of enzyme is chymotrypsin?

Possible Answers:

Ligase

Transferase

Lyase

Hydrolase

Correct answer:

Hydrolase

Explanation:

Chymostrypsin creates smaller peptide segments, so it is not a ligase or transferase. Since it employs the use of a water molecule in order to cleave the polymer, it is classified as a hydrolase enzyme. Lyases also shorten polymers, but not with the use of a water molecule.

Example Question #1 : Inhibition And Inhibitors

Chymotrypsin is a proteolytic enzyme that is released by the pancreas. Using a water molecule, it cleaves the traget polypeptide and creates the new N and C termini for the newly made fragments.

Suppose an inhibitor interacts with chymotrypsin. If the inhibitor acts by noncovalently binding to chymotrypsin, and only decreases its maximum catalytic rate, what type of inhibitor is being used?

Possible Answers:

Suicide inhibitor

Mixed inhibitor

Noncompetitive inhibitor

Competitive inhibitor 

Correct answer:

Noncompetitive inhibitor

Explanation:

We are told that the inhibitor binds noncovalently, so suicide inhibitors are not an option. Since the inhibitor only affects the catalytic rate of the enzyme, and not the Michaelis constant, we can say that the inhibitor is following a mechanism such as that of a noncompeitive inhibitor.

Example Question #34 : Phase Changes

A brass disk with an outer diameter of  has a  diameter hole cut through its center. If the disk is initially at  and is then placed into a freezer at , what is the final area of the hole?

The linear expansion coefficient for brass is: 

Possible Answers:

Correct answer:

Explanation:

First, find the original area of the hole, in square meters: 

We will also convert the temperatures to Kelvin.

The linear thermal expansion equation is:

Similarly, the thermal expansion of an area is given by the equation:

We are given the value of the constant, we know the original area, and we have the change in temperature. Using these values, we can solve for the change in area.

Find the final area of the hole by adding the change in area to the original area.

 

Example Question #194 : Biochemistry, Organic Chemistry, And Other Concepts

Which of the following describes a transition from gas to solid?

Possible Answers:

Deposition

Fusion

Crystallization

Vaporization

Sublimation

Correct answer:

Deposition

Explanation:

There are six possible phase changes between the three phases of matter. Deposition describes the change from gas to solid, while sublimation describes the transition from solid to gas. Freezing (crystallization) is the transition from liquid to solid, while fusion (melting) is the transition from solid to liquid. Condensation is the transition from gas to liquid, while vaporization (boiling) is the transition from liquid to gas.

Example Question #33 : Phase Changes

What conditions best favor the gaseous state?

Possible Answers:

High temperature and high pressure

Low temperature and low pressure

High temperature and low pressure

Low temperature and high pressure

Correct answer:

High temperature and low pressure

Explanation:

Low pressure ensures that the molecules are not confined to a more organized state such as liquid or solid, while high temperature means higher kinetic energy, which means that the molecules have more energy to move away from one another and into the gaseous state. Low temperature would mean molecules have less energy to move away from one another, and high pressure will force molecules to be in a more organized state. 

Example Question #1212 : Mcat Physical Sciences

Raining is an example of what type of phase change? 

Possible Answers:

Evaporation

Deposition

Sublimation

Condensation

Correct answer:

Condensation

Explanation:

Raining occurs when water vapors become liquid water in the sky. Deposition is the phase change from gas to solid, sublimation is the phase change form solid to gas, and evaporation is the phase change from liquid to gas.

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