Homeostasis and the Biological Environment - Biochemistry

The Gibbs free energy becomes less favorable, or more positive, as enthalpy increases and entropy decreases.

The electrons around water are not symmetrically positioned; rather, they are distributed toward the oxygen atom, which is highly electronegative. Hence, water's two hydrogen atoms have a net positive charge. Nonetheless, the total charge on water is neutral, with electropositive and electronegative regions, rendering it polar. This polarity allows water molecules to hydrogen-bond with each other.

The important point here is that biological polymers are basically all condensation polymers. In the case of proteins, polysaccharides (carbohydrates), and nucleic acids (like DNA and RNA), synthesis occurs via a loss of a water molecule. Non-biological molecules can also be formed via condensation, such as nylon, which also often has water as its by-product. Polystyrene is an addition polymer; upon formation, monomers do not lose any molecules. Bonds are only rearranged. Although it may seem counterintuitive, the fact is that in nature, polymers do not typically form this way.

Hydrogen bonding occurs when a hydrogen atom covalently bonded to an fluorine, oxygen, or nitrogen interacts with a lone pair of electrons on another fluorine, oxygen, or nitrogen atom. So first, the two hydrogens in water can form hydrogen bonds, as they are connected to an oxygen atom. Next, the oxygen atom in water has two lone pairs of electrons, and those also can form hydrogen bonds. A single water molecule therefore has the capability of forming four hydrogen bonds.

Because of hydrogen bonding, water has a low high heat of vaporization. In other words, it takes more energy to free up water molecules from a hydrogen-bonded liquid state to a gaseous state.

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.