Which of the following is not an example of positive feedback?

A student observes an enzymatic chemical reaction that normally takes place in human blood. She performs an experiment to see how certain conditions affect the reaction with the enzyme fully saturated with substrate. What should she do to speed the reaction up?

Drain cleaners a common household staple, used to open clogged drains in bathtubs and sinks. Human hair is a common culprit that clogs pipes, and hair is made predominately of protein. Drain cleaners are effective at breaking down proteins that have accumulated in plumbing. Drain cleaners can be either acidic or basic, and are also effective at breaking down fats that have accumulated with proteins.

A typical reaction—reaction 1—which would be expected for a drain cleaner on contact with human hair, would be as follows in an aqueous solution:

Another reaction that may occur, reaction 2, would take place as follows in an aqueous solution:

Protein that forms the hair discussed in the preceeding passage is considered strucutral protein. Functional proteins, such as enzymes, are the other major class. Which of the following is expected in an enzymatic biological reaction?

I. Faster rate than non-enzymatic reaction

II. Enzymatic coupling to hydrolysis reactions

III. More product generation relative to amount of reactant than non-enzymatic reaction

Sildenafil (commonly called Viagra) is a common drug used to treat erectile dysfunction and pulmonary arterial hypertension. Sildenafil's effect comes from its ability to cause vasodilation in smooth muscle cells. For this problem, we're only going to consider its effects on erections in males.

Erectile dysfunction is a common medical problem in older men. Its most significant effect is the prevention of erections. Erections occur when there is an increase in blood flow via enlargement of an artery (vasodilation). Understanding the mechanism by which vasodilations occur is important in order to treat erectile dysfunction.

Erections occur when nitric oxide is released from an area in the penis and binds to guanylate cyclase in other cells of the penis, which creates cyclic guanosine monophosphate (cGMP) from GTP. cGMP causes a relaxation of the arterial wall in order to increase blood flow to the region, thereby causing an erection. cGMP is broken down over time by cGMP-specific phosphodiesterase type 5 (PDE5) into GTP, which reverses the effect and causes vasoconstriction on the arterial wall. Combatting this effect is the major method by which Viagra functions.

Which of the following reactions would you expect PDE5 to catalyze?

Among the most important pH buffer systems in humans is the bicarbonate buffer, which keeps the blood at a remarkably precise 7.42 pH. The bicarbonate buffer system uses a series of important compounds and enzymes to make the system function. Figure 1 depicts the key reactions that take place.

The activity of this buffer system is mainly controlled by the renal and respiratory systems. The renal system excretes bicarbonate in the urine, while the respiratory system “blows off” carbon dioxide as needed. By balancing these two systems as needed, blood pH is maintained in such a narrow range.

Carbonic anhydrase is an organic enzyme. Which of the following is true of carbonic anhydrase? Assume no CO2 or bicarbonate is lost in the reaction.

I. It lowers the activation energy for the conversion of carbon dioxide to carbonic acid

II. It shifts the equilibrium toward carbon dioxide in experimental conditions

III. It modifies chemical species at its allosteric site

Which statement is true about noncompetitive inhibitors?

Scientists use a process called Flourescent In-Situ Hybridization, or FISH, to study genetic disorders in humans. FISH is a technique that uses spectrographic analysis to determine the presence or absence, as well as the relative abundance, of genetic material in human cells.

To use FISH, scientists apply fluorescently-labeled bits of DNA of a known color, called probes, to samples of test DNA. These probes anneal to the sample DNA, and scientists can read the colors that result using laboratory equipment. One common use of FISH is to determine the presence of extra DNA in conditions of aneuploidy, a state in which a human cell has an abnormal number of chromosomes. Chromosomes are collections of DNA, the totality of which makes up a cell’s genome. Another typical use is in the study of cancer cells, where scientists use FISH labels to ascertain if genes have moved inappropriately in a cell’s genome.

Using red fluorescent tags, scientists label probe DNA for a gene known to be expressed more heavily in cancer cells than normal cells. They then label a probe for an immediately adjacent DNA sequence with a green fluorescent tag. Both probes are then added to three dishes, shown below. In dish 1 human bladder cells are incubated with the probes, in dish 2 human epithelial cells are incubated, and in dish 3 known non-cancerous cells are used. The relative luminescence observed in regions of interest in all dishes is shown below.

Cancer cells often invade by breaking through the collagen of a basement membrane of epithelial tissue. Considering the composition of basement membranes, which of the following compounds is most likely to be used by cancer cells for this purpose?

Fetal hemoglobin has a higher binding affinity for oxygen than does adult hemoglobin.

In comparison to the adult oxyhemoglobin dissociation curve, the fetal oxyhemoglobin dissociation curve will __________.

Which of the following changes could lead to loss of enzymatic function?

A supercoiled helix is described by which level of peptide structure?