Biological Energetics - Biochemistry

The G values given in the question relate to the reactions' thermodynamics. A negative G value means that a reaction is thermodynamically spontaneous. A spontaneous reaction can occur without further energy input. This does not tell us anything about the reaction's rate (kinetics). A spontaneous reaction may be slow or it may be fast.

A catalyst lowers the activation energy of a reaction. This could be accomplished through stabilization of the transition state by lowering its energy. A catalyst does not change the free energy difference between products and reactants, so no change in G of the reaction is observed.

This question is asking us to determine what effect a pH change would have on the reaction in which ATP is hydrolyzed into ADP. First, we have to realize that if pH were lowered, that means we are dealing with a more acidic solution. A more acidic solution, in turn, means that we have an increased concentration of . So, in essence, the question is asking what effect an increased concentration will have on the reaction. In the reaction, we can see that is on the product side of the reaction (on the right side). Therefore, if we drive the concentration up, the reaction will be pushed toward the left according to Le Chatelier's principle. Furthermore, it's important to note that changing the concentration of any of the reactants or products will not have an effect on the equilibrium constant, . In fact, it is precisely because the equilibrium constant doesn't change that the reaction will shift to the left, so that the constant will remain just that, constant. Moreover, the only thing that can change an equilibrium constant is the temperature at which the reaction takes place.

Because for the reaction is negative, it is spontaneous and proceeds favorably to the right. Equilibrium does not occur when the concentrations of reactants and products are equal; it occurs when the rates of forward and reverse reactions are equal. At equilibrium thus there is no net change in the concentration of either the reactants or the products.

Insulin is produced by pancreatic beta cells in response to a rise in blood sugar, which occurs after eating a meal rich in carbohydrates (sugars and starches). It causes other cells of the body to take up the blood sugar (primarily glucose) and use it for energy production, and it prompts the liver to store excess glucose as glycogen. Glucagon is produced when blood sugar is too low, and it blocks glycolysis and prompts liver cells to convert stored glycogen back to glucose and release it and also produce glucose through gluconeogenesis. This is always determined by the ratio of the levels of two hormones - if there is far more insulin than glucagon, its physiological effects will dominate. There is never absolutely zero of either hormone unless the individual is diabetic to such a degree that their cells cannot produce insulin.

If two complementary single strands of DNA are put into a solution, they will spontaneously form dsDNA. This process results in a loss of heat from the system - demonstrating that it is an enthalpically favorable process. However, it is entropically unfavorable given the formation of a more ordered structure.

A negative change in Gibbs free energy means that a reaction will take place spontaneously. By using the equation:

We can see that if both entropy and enthalpy are positive, will only be negative when is sufficiently high.

Reaction coupling is the pairing of one unfavorable reaction to another reaction that is favorable. The energetics of the favorable reaction drive the unfavorable one forward.

It is a common misconception that at chemical equilibrium, movement between the product and reactant sides of the equation has stopped. In reality, reactants and products are still converting back and forth to one another, however there is no longer any net movement from one side of the equation to the other. Also, Q=Keq at equilibrium.

All of the answer choices given in this question are true statements, and they are all reasons why endergonic reactions can occur within living things.

Oftentimes, reactions that require a large input of energy are thermodynamically coupled to the hydrolysis of ATP, the energy currency of the cell. As a result, ATP is able to provide the fuel, so to speak, for powering the reaction.

Also, it's important to note that standard free energy changes are much different than the free energy changes that occur under physiological conditions. Standard state assumes that all reactants and all products of a reaction start out at a concentration of , but this concentration is absurdly high for just about any compound found within cells.

Lastly, the products of some endergonic reactions are often used up quite readily. As a result of this, the concentration of product is kept at a low level, which means that the reactions becomes favored toward making more product.

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.

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.

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.

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.

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.

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 .

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.

The stomach: The lower pH will result in the drug being in the neutral form, and this less polar form will be able to pass through the membrane more easily and absorbed into the blood stream.

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 .