Negative feedback provides the body with a method for shutting down a reaction once sufficient product has been created. Parathyroid hormone (PTH) is responsible for increasing blood calcium levels, but once the level is sufficient, the parathyroid glands detect the sufficient calcium level and no longer produce PTH. PTH works in coordination with calcitonin to maintain this balance via its negative feedback loop.

Positive feedback, in contrast, involves the exponential increase of a reaction upon detection. Very few examples of positive feedback exist in the body, though oxytocin follows this model during childbirth.

Competitive inhibitors block substrates by binding noncovalently to the active site on enzymes. This prevents the substrate from entering the active site.

Noncompetitive inhibitors, in contrast, will act on regions outside of the active site to prevent binding. Uncompetitive inhibition is a specialized form of noncomptitive inhibition in which the inhibitor binds to the enzyme complex after the substrate has entered the active site. Irreversible inhibitors form covalent bonds, and fall outside the common inhibitor classifications.

Noncompetitive inhibitors of enzymes function by binding to a site other than the active site on the enzyme, known as an allosteric site. This causes the enzyme to go through a conformational shift and inhibits binding of the substrate.

Competitive inhibitors bind to the enzyme active site to prevent substrate action. Uncompetitive inhibitors are a sub-category of noncompetitive inhibitors, and bind to an allosteric site only after the substrate has entered the active site, thus preventing the substrate from leaving.

Competitive inhibitors bind to the active site of the enzyme, blocking substrate entry. Increasing the concentration of the substrate helps overcome this type of inhibition by increasing the proportion of substrate to inhibitor in solution. By increasing substrate, the active site is more likely to bind substrate than inhibitor.

Noncompetitive inhibitors and uncompetitive inhibitors are types of allosteric inhibitors, meaning that they bind the enzyme in a site other than the active site. Increasing substrate concentration cannot overcome these types of inhibition because the inhibitor and enzyme are not in direct competition for binding sites.

Enzymes are catalysts that speed up the rate at which a reaction occurs. Competitive inhibitors bind to the active site, affecting the Michaelis constant, but not the maximum reaction rate. Competitive inhibitors can be overcome by adding more substrate to displace the inhibitor. Non-competitive inhibitors bind to an allosteric site, affecting the maximum reaction rate, but not the Michaelis constant. No amount of additional substrate can overcome the inhibitor's effect.

In uncompetitive inhibition, the inhibitor binds to the enzyme-substrate complex. The substrate is required to bind the active site, affecting the Michaelis constant, and is then held in place by the inhibitor, affecting the maximum reaction rate. Uncompetitive inhibitors are, thus, as special class of inhibitor that will affect both values.

This question is referring specifically to the different modes of enzyme inhibition. The given fact that increasing substrate concentration does not restore enzyme function indicates that the inhibitor is binding to the enzyme at an allosteric site (eliminating competitive inhibition). The given fact that inhibitor-specific antibodies restored enzyme function indicates that the inhibition is reversible.

Uncompetitive inhibition is a specific type of noncompetitive inhibition in which the inhibitior binds to the enzyme-substrate complex. We are unable to conclude that this is the case based on the given information alone.

Because ClaI and PsiI both have 100% efficiency in buffer 4, that is the most ideal choice. A combination of buffers is never a valid option, as diluting the buffers fundamentally changes the composition of the reaction and the efficiency of the enzyme. In the absence of two enzymes that can function with 100% efficiency, it is best to find a combination with the greatest possible efficiency or to complete the digest sequentially in the appropriate buffers.

For this problem, we need to know what phosphodiesterases do. Phosphodiesterases catalyze the breakdown of phosphodiester bonds via hydrolysis. Cyclic GMP contains an internal phosphodiester bond. Therefore its breakdown would result in the formation of GMP. The hydrolysis of cGMP should not yield GMP and a phosphate, since cyclic GMP only has one phosphate group. 

The DNA double helix is a structure of double stranded nucleic acids, and is held together by base pairing of these nucleic acids perpendicular to the helical axis. The 5’ carbons and 3’ carbons between the pentoses are involved in phosphodiester bonds, while the 1’ carbons are involved in N-glycosidic bonds with the bases. Not all hydroxyl groups are involved in bonding, however, as there is a free 3’ carbon hydroxyl group on the extreme 3’ end of linked nucleoside monophosphate monomers. Both strands are sequentially unique as base pairing occurs between a purine and pyrimidine only. Finally, the strands are antiparallel, meaning they run in opposition to one another. Thus, the correct answer is that the nitrogenous bases are perpendicular to the axis.

Intra-strand bonds are the covalent bonds between sugars and phosphates in the sugar-phosphate backbone. The other choices are incorrect, as inter-strand bonds in nucleic acids are hydrogen bonds between nitrogenous bases. Additionally, Okazaki fragments are found on the lagging strand of DNA during replication, because DNA on both the leading and lagging strands must be synthesized by DNA polymerase in the 5' to 3' direction.