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Example Questions
Example Question #611 : Biochemistry
Why is polymerization of nucleoside triphosphates thermodynamically favorable?
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.
During the polymerization, pyrophosphate is released and hydrolyzed driving the reaction forward.
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?
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
It is more stable in the absence of oxygen
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?
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?
Amide
Phosphoester
Phosphoanhydride
Glycosidic
Phosphoanhydride
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
I, II, III, and IV
I and II
II, III, and IV
III and IV
III only
III and IV
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?
Membrane surface area
Diffusion constant
Concentration gradient
All of these affect diffusion flux
Membrane thickness
All of these affect diffusion flux
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?
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?
Activation energy
Temperature
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?
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
Will be spontaneous at high temperatures
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?
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
The RBC will fill with water and burst
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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