Question 1

Synthetic dyes constitute a commercially significant area of organic chemistry. The color producing properties

of these compounds are the result of highly delocalized electron systems giving rise to electronic transitions

whose absorptions occur in the visible region. Most commercially useful dyes can be classified as one of three

types – anthraquinones, azo dyes, or triarylmethyl salts. Examples of each type are illustrated in Figure 1.

Figure 1

In order for a dye to be useful in the fabric industry, it must have sufficient affinity for the polymeric fibers of

which the material is composed; the dye must not only impart a color to the fabric, but must also do so in a

relatively permanent manner (color fastness). Proper design of synthetic polymers requires the placement of

acidic or basic side chains along the polymer backbone such that binding sites are available for dying. Similarly,

dyes must be produced not only with the appropriate color-producing structure, but also with an affinity for the

fabric in question. The structural units of several common synthetic fibers are shown in Figure 2.

Figure 2

Dacron belongs to which of the following general classifications?

Section: Biological Sciences

Options :

A : Polyamide

B : Polyester

C : Polyurethane

D : Polypeptide

Answer: B

Question 2

It is critical for the human body blood to maintain its pH at approximately 7.4. Decreased or increased blood pH

are called acidosis and alkalosis respectively; both are serious metabolic problems that can cause death. The

table below lists the major buffers found in the blood and/or kidneys.

Table 1

Buffer

pKa of a typical conjugate acid:*

Histidine side chains

Organic phosphates

N-terminal amino groups

6.1

6.3

6.8

7.0

8.0

9.2

Reaction 1

How does the titration of a weak monoprotic acid with a strong base differ from the titration of a strong

monoprotic acid with a strong base?

Section: Physical Sciences

Options :

A : The equivalence point will occur at a higher pH.

B :

The equivalence point will occur at a lower pH.

C : The equivalence point will occur at the same pH.

D : Whether the equivalence point is higher or lower depends on the particular monoprotic acids used.

Answer: A

Question 3

Four major blood types exist in the human ABO blood system: types A, B, AB, and O; and there are three

alleles that code for them. The A and B alleles are codominant, and the O allele is recessive. Blood types are

derived from the presence of specific polysaccharide antigens that lie on the outer surface of the red blood cell

membrane. The A allele codes for the production of the A antigen; the B allele codes for the production of the B

antigen; the O allele does not code for any antigen.

While there are many other antigens found on red blood cell membranes, the second most important antigen is

the Rh antigen. Rh is an autosomally dominant trait coded for by 2 alleles. If this antigen is present, an

individual is Rh+; if it is absent, an individual is Rh−. For example, a person with type AB blood with the Rh

antigen is said to be AB+.

These antigens become most important when an individual comes into contact with foreign blood. Because of

the presence of naturally occurring substances that closely mimic the A and B antigens, individuals who do not

have these antigens on their red blood cells will form antibodies against them. This is inconsequential until

situations such as blood transfusion, organ transplant, or pregnancy occur.

Erythroblastosis fetalis is a condition in which the red blood cells of an Rh+ fetus are attached by antibodies

produced by its Rh− mother. Unlike ABO incompatibility, in which there are naturally occurring antibodies to

foreign antigens, the Rh system requires prior sensitization to the Rh antigen before antibodies are produced.

This sensitization usually occurs during the delivery of an Rh+ baby. So while the first baby will not be harmed,

any further Rh+ fetuses are at risk.

The Coombs tests provide a method for determining whether a mother has mounted an immune response

again her baby’s blood. The tests are based on whether or not agglutination occurs when Coombs reagent is

added to a sample. Coombs reagent contains antibodies against the anti-Rh antibodies produced by the

mother. The indirect Coombs test takes the mother’s serum, which contains her antibodies but no red blood

cells, and mixes it with Rh+ red blood cells. Coombs reagent is then added. If agglutination occurs, the test is

positive, and the mother must be producing anti-Rh antibodies. The direct Coombs test mixes the baby’s red

blood cells with Coombs reagent. If agglutination occurs, the test is positive, and the baby’s red blood cells

must have been attacked by its mother’s anti-Rh antibodies.

Based on information in the passage, what does the reaction below represent?

Section: Biological Sciences

Options :

A : Negative direct Coombs test

B : Positive direct Coombs test

C : Positive indirect Coombs test

D : Negative indirect Coombs test

Answer: B

Question 4

Nitric oxide, NO, has recently been found to have widespread physiological effects, acting as a major regulator

in the nervous, cardiovascular, and immune systems. The production of NO in the body is regulated by specific

NOS enzymes which exist in at least three different isoforms – bNOS, eNOS, and macNOS. Each of these

isoforms differ in location and function and serve to mediate different physiological responses to NO. Some

physiological roles of NO have been demonstrated as follows:

I. In the central nervous system, NO production is regulated by bNOS. Calcium ion concentrations of 200-400

nM in the central nervous system activate bNOS to catalyze the formation of NO. NO exerts definite effects on

brain function although its specific roles are not well established. bNOS inhibitors have been found to block the

release of neurotransmitter from presynaptic neurons. Excess levels of NO are also thought to contribute to

neurodegenerative disorders such as Alzheimer’s disease.

II. In the blood vessels, NO is produced by eNOS which is activated by Ca2+ concentrations of 200-400 nM. NO

acts as the major endogenous vasodilator in blood vessels. It diffuses into smooth muscle cells and leads to

muscle relaxation by stimulating cGMP formation through activation of guanylyl cyclase. In addition, NO

regulates the vascular system by inhibiting platelet aggregation and adhesion.

III. The role of NO in the immune system is regulated by macNOS through a pathway that is not Ca2+

dependent. Rather, exposure to cytokines, including interleukin-1 and interferon- γ, leads to synthesis of large

amounts of NO by activation of macNOS in response to inflammatory stimuli. The NO produced plays a

definitive role in the mediation of the activities of macrophages and neutrophils. NO also acts to inhibit the

mechanism of viral replication.

A “knock out” mouse with a mutant bNOS protein was generated by recombination techniques. The mutant

protein was identical to the wild-type protein except for the identity of amino acid 675; the mutated bNOS has

Tryptophan instead of Cysteine at position 675. Which of the following is responsible for the mutant protein?

Section: Biological Sciences

Options :

A :

Frame shift mutation

B :

Single base-pair deletion

C : Point mutation

D : Nonsense mutation

Answer: C

Question 5

Due to ever-increasing paranoia about the transmission of hepatitis and AIDS via blood transfusions and the

frequent difficulty of procuring matching blood donors for patients, researchers have been working at a feverish

pace to produce disease-free and easy-to-use blood substitutes. The difficulty most synthetic blood researches

have had is in formulating a substance that combines qualities of sterility, high capacity for carrying oxygen to

body tissues, and versatility within the human body. Three major substitute technologies have been developed

to date; each has certain advantages and shortcomings.

“Red blood,” the first of the blood substitute technologies, is derived from hemoglobin which has been recycled

from old, dead, or worn-out red blood cells and modified so that it can carry oxygen outside the red blood cell.

Hemoglobin, a complex protein, is the blood’s natural oxygen carrier and is attractive to scientists for use in

synthetic blood because of its oxygen-carrying capacity. However, hemoglobin can sometimes constitute a twofold threat to humans when it is extracted from the red blood cell and introduced to the body in its naked form.

First, hemoglobin molecules are rarely sterile and often remain contaminated by viruses to which they were

exposed in the cell. Second, naked hemoglobin is extremely dangerous to the kidneys, causing blood flow at

these organs to shut down and leading, ultimately, to renal failure. Additional problems arise from the fact that

hemoglobin is adapted to operate optimally within the intricate environment of the red blood cell. Stripped of the

protection of the cell, the hemoglobin molecule tends to suffer breakdown within several hours. Although

modification has produced more durable hemoglobin molecules which do not cause renal failure, undesired

side effects continue to plague patients and hinder the development of hemoglobin-based blood substitutes.

Another synthetic blood alternative, “white blood”, is dependent on laboratory synthesized chemicals called

perfluorocarbons (PFCs). Unlike blood, PFCs are clear oil like liquids, yet they are capable of absorbing

quantities of oxygen up to 50% of their volume, enough of an oxygen carrying potential for oxygen-dependent

organisms to survive submerged in the liquid for hours by “breathing” it. Although PFCs imitate real blood by

effectively absorbing oxygen, scientists are primarily interested in them as constituents of blood substitutes

because they are inherently safer to use than hemoglobin-based substitutes. PFCs do not interact with any

chemicals in the body and can be manufactured in near-perfect sterility. The primary pitfall of PFCs is in their

tendency to form globules in plasma that can block circulation. Dissolving PFCs in solution can mitigate

globulation; however, this procedure also seriously curtails the PFCs’ oxygen capacity.

The final and perhaps most ambitious attempt to form a blood substitute involves the synthesis of a modified

version of human hemoglobin by genetically-altered bacteria. Fortunately, this synthetic hemoglobin seems to

closely mimic the qualities of sterility, and durability outside the cellular environment, and the oxygen-carrying

efficiency of blood. Furthermore, researchers have found that if modified hemoglobin genes are added to

bacterial DNA, the bacteria will produce the desired product in copious quantities. This procedure is extremely

challenging, however, because it requires the isolation of the human gene for the production of hemoglobin,

and the modification of the gene to express a molecule that works without support from a living cell.

While all the above technologies have serious drawbacks and difficulties, work to perfect an ideal blood

substitute continues. Scientists hope that in the near future safe synthetic blood transfusions may ease blood

shortages and resolve the unavailability of various blood types.

It can be inferred from the passage that the difficulty of producing an ideal blood substitute is compounded by

all of the following EXCEPT:

Section: Verbal Reasoning

Options :

A :

there is no known way to isolate the DNA responsible for hemoglobin.

B : naked hemoglobin tends to break down in the bloodstream.

C :

non-globulating PFCs have significantly abbreviated oxygen-carrying capacities.

D :

the use of PFCs may lead to blood clotting.

Answer: A

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