Biochemistry : Biochemistry

Study concepts, example questions & explanations for Biochemistry

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Example Questions

Example Question #611 : Biochemistry

Why is polymerization of nucleoside triphosphates thermodynamically favorable?

Possible Answers:

During the polymerization, pyrophosphate is released and hydrolyzed driving the reaction forward.

During the polymerization, ATP is released from the nucleoside when the base is attached which, because it is creating energy, is favorable.

The polymerization is coupled to ATP hydrolysis.

The polymerization of nucleoside triphosphates is not thermodynamically favorable, but it is kinetically favorable.

During the polymerization, one phosphate group is released and this drives the reaction forward.

Correct answer:

During the polymerization, pyrophosphate is released and hydrolyzed driving the reaction forward.

Explanation:

A nucleoside triphosphate - as its name suggests - is a DNA base with three phosphate groups. During polymerization, these base groups will be continuously connected to each other in order to form a DNA strand. This is thermodynamically favorable because during the polymerization, two of the three phosphate groups on the nucleoside triphosphate will detach as a pyrophosphate. This will then be hydrolyzed which is extremely thermodynamically favorable. And so, the polymerization itself is considered to be thermodynamically favorable.

Example Question #612 : Biochemistry

Which of the following is false about the hemoglobin R state? 

Possible Answers:

It is more stable in the absence of oxygen

It is more stable in the presence of oxygen

It has a higher affinity for oxygen

It is triggered by oxygen binding

The heme group is planar

Correct answer:

It is more stable in the absence of oxygen

Explanation:

The R (relaxed) state hemoglobin is triggered by hemoglobin binding to oxygen. The heme group in R state hemoglobin is perfectly planar. By nature, R state hemoglobin is stabilized in the presence of oxygen, not in the absence of oxygen. 

Example Question #611 : Biochemistry

Suppose that the enthalpy change for a given biochemical reaction is zero. What is the change in standard free energy for this reaction?

Possible Answers:

Correct answer:

Explanation:

To answer this question, it's important to know how the standard free energy change of a reaction is related to other various parameters of the reaction.

The standard free energy change of a reaction can be presented in different expressions.

For the purposes of this question, the bottom expression is the one we need. If we set the change in standard enthalpy term equal to zero, we can solve for our answer.

Example Question #613 : Biochemistry

The high energy found in a molecule of adenosine triphosphate (ATP) is stored mostly in which type of bond?

Possible Answers:

Amide

Phosphoester

Phosphoanhydride

Glycosidic

Correct answer:

Phosphoanhydride

Explanation:

Phosphoanhydride bonds contain lots of stored energy, with a  of . This energy, when released during ATP hydrolysis, can then be used for various anabolic pathways.

Example Question #614 : Biochemistry

Which of the following types of transport require ATP to function?

I. Diffusion

II. Facilitated diffusion

III. Primary active transport

IV. Secondary active transport

Possible Answers:

I, II, III, and IV

I and II

II, III, and IV

III and IV

III only

Correct answer:

III and IV

Explanation:

Diffusion and facilitated diffusion are methods by which molecules can pass through membranes without the use of ATP. Even though facilitated diffusion does require a channel to function, movement is still controlled by differences in concentration gradients. Primary active transport uses ATP directly to drive molecules against their concentration gradients, and secondary active transport uses the pre-established electrochemical gradient from primary transport to create movement for other molecules - so it still does require ATP to function even though it is indirect.

Example Question #63 : Homeostasis And The Biological Environment

Fick's law of diffusion states that which of the following affect diffusion flux?

Possible Answers:

Membrane surface area

Diffusion constant

Concentration gradient

All of these affect diffusion flux

Membrane thickness

Correct answer:

All of these affect diffusion flux

Explanation:

Fick's law describes the factors that influence diffusion of molecules through a membrane. All of the variables listed as answer choices, if changed, can influence the level of diffusion that can occur through the membrane.

Example Question #64 : Homeostasis And The Biological Environment

What are the Nernst potentials for sodium and potassium, respectively?

Possible Answers:

Correct answer:

Explanation:

The correct Nernst potential for sodium is  and the correct Nernst potential for potassium is . The resting membrane potential for the cell membrane as a whole is about 

Example Question #616 : Biochemistry

When trying to predict the direction of a chemical reaction, which of the following acts as the best indicator?

Possible Answers:

Activation energy

Temperature

Correct answer:

Explanation:

For this question, we're asked to identify the correct measure that allows us to predict the direction of a chemical reaction. Let's take a look at each answer choice.

The change in enthalpy of a reaction, , represents the amount of heat energy absorbed by or given off in a chemical reaction. Generally, chemical reactions that give off heat tend to go in the forward reaction. However, by itself, enthalpy cannot predict the direction of a chemical reaction.

The change in entropy of a reaction, , represents the change in disorder of a chemical reaction. Generally, chemical reactions that become more disordered as they progress tend to be driven in the forward direction. However, this alone is not enough to predict the direction of a chemical reaction.

The temperature at which a reaction occurs is another important factor to take into account when deciding the direction in which a chemical reaction will take. Reactions tend to be driven forward when they give off heat in low temperature environments. Also, reactions tend to be driven forward when they absorb heat in high temperature environments. But, by itself, temperature is not sufficient to predict the direction of a chemical reaction.

The activation energy of a reaction represents the amount of energy that must be put into a reaction in order for the reactants to reach the high-energy transition state. However, activation energy only affects the rate of a reaction and not its direction. Reactions that have higher activation energies will necessarily have a harder time reaching the transition state, which is necessary in order for the reaction to progress. But activation energy does not affect the change in energy of the reactants and products themselves. In other words, activation energy is not concerned with the thermodynamics of a reaction, but rather with the kinetics. Thus, activation energy will not allow us to predict the direction of a chemical reaction.

Finally, let's take a look at the change in Gibb's free energy, . This measurement takes into account several other variables, including , and temperature. In doing so, the  term allows us to accurately predict the direction of a chemical reaction, since it takes these other important factors into account. When the value of  is negative, this indicates a reaction that will be driven in the forward direction, because the reactants are losing free energy as they are converted into products. Conversely, a positive  indicates a reaction that is driven in the reverse direction. Put into the form of an equation,  takes the following form.

Example Question #226 : Fundamental Macromolecules And Concepts

If a chemical reaction has a positive change in enthalpy and a positive change in entropy, then which of the following is true?

Possible Answers:

Will be spontaneous at high temperatures

Will be spontaneous at low temperatures

Will be spontaneous exactly 50% of the time

Will never be spontaneous

Will always be spontaneous

Correct answer:

Will be spontaneous at high temperatures

Explanation:

When  is negative, the reaction will occur spontaneously. So, if the change in enthalpy  and the change in entropy  are both positive,  will only be negative when temperature is high enough to make  greater than .

Example Question #64 : Homeostasis And The Biological Environment

If a red blood cell (RBC) is placed into a hypotonic solution, which of the following is most likely to occur?

Possible Answers:

The RBC will shrivel up and lyse

The RBC will remain unchanged

The cell will use its mitochondria to counteract the change in tonicity

Osmotic pressure in the cell will increase

The RBC will fill with water and burst

Correct answer:

The RBC will fill with water and burst

Explanation:

If the RBC is placed into a hypotonic solution, water will rush into the cell because there is a higher osmotic pressure in the cell than outside of it. The osmotic pressure in the cell will actually decrease as water flows in from the outside. Red blood cells do not have mitochondria.

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