KNOW THIS: - ANSWER The alpha carbon determines whether the amino acid is
Test Bank for Lippincott Illustrated Reviews: in the D or L configuration
Pharmacology 8th Edition by Karen Whalen|
*Many biochemical compounds (including drugs) are only active as either the D or L
isomer.*
KNOW THIS: - ANSWER 1) RNA is susceptible to alkaline hydrolysis, whereas Your patient has a mechanical heart valve and is chronically anemic due to damage
DNA is not. to red blood cells as they pass through this valve. One of the signals that target
damaged red blood cells for removal from the circulation is the presence of
2) Under alkaline conditions, the hydroxyl group can act as a nucleophile and attack phosphatidylserine in the outer leaflet of the red cell membrane. Phosphatidylserine
the phosphodiester linkage between adjacent nucleotides, breaking the linkage and is an integral part of cell membranes and is normally found in the inner leaflet of the
leading to the transient formation of a cyclic nucleotide. red cell membrane. This flip-flop of phosphatidylserine between membrane leaflets
exposes which part of the phosphatidylserine to
3) As this can occur at every phosphodiester linkage in RNA, hydrolysis of the RNA the environment?
will occur due to these reactions. As DNA lacks the 2′-hydroxyl group, this reaction
cannot occur, and (A) The head group
DNA is very stable under alkaline conditions. (B) Fatty acids
(C) Sphingosine
Symptoms of adenosine deaminase deficiency: - ANSWER 1) History of chronic (D) Glycerol
diarrhea and multiple pneumonias (E) Ceramide - ANSWER A.
2) The chest X-ray shows a pneumonia, but also reveals an abnormally small Thus, when a phospholipid fl ip-fl ops across the membrane, the head group will
thymus. always end up facing the aqueous environment.
3) Blood work shows a distinct lack of circulating lymphocytes. A couple has had five children, all of who exhibit short
stature, eyelid droop, and some degree of muscle weakness and hearing loss (some
*Here you have no working B or T cells* severe, some mild). The mother also has such problems, although at a mild level.
The father has no symptoms. The mutation that afflicts the children most likely
* This disorder leads to an accumulation of deoxyadenosine and S- resides in DNA found in which intracellular organelle?
adenosylhomocysteine,
which are toxic to immature lymphocytes in the thymus.* (A) Mitochondria
(B) Peroxisome
4) The most likely inherited enzymatic defect in this child leads to an inability to alter (C) Lysosome
a purine nucleotide at position 6 of the ring structure (where deamination occurs and (D) Endoplasmic reticulum
is replaced with a carbonyl group) (E) Nucleus - ANSWER A.
Inosine and Wobbling - ANSWER Inosine is a wobble base pair former, having the The mother and children are experiencing the effects of a mitochondrial disorder.
ability to base pair with *adenine, uracil, or cytosine*
KNOW THIS: - ANSWER Lactase will split the β-1,4 linkage between *They key here is that all of the kids have the issue and the mother as well but the
galactose and glucose in lactose. father shows no symptoms*
The lactose thus passes unmetabolized to the bacteria inhabiting the gut, and their There are multiple mitochondrial disorders associated with muscular dystrophy:
metabolism of the disaccharide leads to the observed symptoms.
1) Kearns-Sayer syndrome(this case)
Combining two sugars in a dehydration reaction creates a glycosidic bond. 2) Leigh syndrome (non-X-linked)
3) Pearson syndrome
Adding a sugar to the nitrogen of a nitrogenous base also creates an N-glycosidic 4) Mitochondrial DNA depletion syndrome
bond. 5) Mitochondrial encephalomyopathy
, 3) Glucuronic acid is added to the xenobiotic at position 1, using the activated
Membrane formation occurs, in part, due to low lipid solubility in water due to intermediate UDP glucuronate.
primarily which of the following?
Early clinical signs of Creutzfeldt-Jakob disease: - ANSWER 1) Mood changes
(A) Hydrogen bond formation between lipids and water 2) Minor loss of memory
(B) Covalent bond formation between lipids and water 3) Decreased motor skills
(C) A decrease in water entropy
(D) An increase in water entropy Caused by a misfolded prion protein, leading to protein aggregates in the brain.
(E) Ionic bond formation between lipids and water - ANSWER D.
This patient will probably die within 1 year.
Cage forming decreases water entropy, which is
unfavorable, and this leads to the hydrophobic effect, in which the lipid molecules all There is no current treatment for the disease.
come together such that only one large cage needs to be formed about the lipid
molecules, rather than many small cages about each individual lipid molecule. As the disease progresses, he will probably develop blindness, involuntary
movements, and severe deterioration of mental function.
The lipids do not form covalent or ionic bonds with water, and, as mentioned above,
lipids in water leads to a decrease in water entropy (which is unfavorable), rather KNOW THIS: - ANSWER Bisphosphonates decrease bone resorption by the
than an increase in the entropy of water (which would be a favorable event). osteoclasts, thereby strengthening the bone, even with the defective collagen
molecule.
KNOW THIS: - ANSWER Precipitation of uric acid occurs in "cold" areas of the
body, such as the great toe. You are visited by a 40-year-old female patient complaining of weight loss,
numbness in the hands and feet, fatigue, and difficulty swallowing. Physical exam
A single-stranded DNA molecule contains 20%A, 25%T, notes an enlarged tongue, enlarged liver, a rubbery
30%G, and 25%C. When the complement of this strand feeling around the joints, and bruising around the
is synthesized, the T content of the resulting duplex will eyes. A bone marrow biopsy shows an abnormal
be which one of the following? staining of denatured protein (see below). These
denatured proteins are most likely to be which of the
(A) 20% following?
(B) 22.5%
(C) 25% (A) Antibody light chains
(D) 27.5% (B) Collagen
(E) 30% - ANSWER B. (C) Fibrillin
(D) Albumin
For the entire duplex then, the T content (E) Transaminases - ANSWER A.
is the average of 25% and 20%, or 22.5% for the duplex. The [A] in the duplex will
also be 22.5% (again, since [A] = [T]), and the concentrations of [G] and [C] will each *The patient is exhibiting the symptoms of primary amyloidosis*
be 27.5% for the duplex.
Primary amyloidosis - ANSWER 1) A protein folding disease in which
KNOW THIS: - ANSWER The glycosylation of hemoglobin primarily occurs on the immunoglobulin light chains are improperly processed and cannot be degraded.
N-terminal valine residues of the β chains (which contain a free amino group).
2) These proteins then form fibrils in tissues,
The rate of degradation of nonmodified hemoglobin and HbA1c are the same. which are insoluble. This disrupts the normal function of the tissue, and many tissues
can accumulate these fibrils.
KNOW THIS: - ANSWER 1) In order to make a xenobiotic more soluble, a
hydrophilic group needs to be added 3) The protein deposits in primary amyloidosis are made up of immunoglobulin light
to the xenobiotic. chain proteins.
2) Glucuronic acid (glucose with a carboxylic acid at position 6 instead of an alcohol 4) These light chain proteins are created in the bone marrow by malfunctioning
group) is a hydrophilic molecule. plasma cells.
,Primary amyloidosis - ANSWER 1) A protein folding disease in which
immunoglobulin light chains are improperly processed and cannot be degraded. An 8-month-old infant exhibits jaundice and lethargy.
Physical exam detects splenomegaly. Blood work displays a microcytic anemia with
2) These proteins then form fibrils in tissues, abnormal erythrocytes under all conditions. This defect is
which are insoluble. This disrupts the normal function of the tissue, and many tissues most likely due to a hereditary mutation in which of the
can accumulate these fibrils. following?
3) The protein deposits in primary amyloidosis are made up of immunoglobulin light (A) Hemoglobin
chain proteins. (B) Glucose-6-phosphate dehydrogenase
(C) Iron transport into the erythrocyte
4) These light chain proteins are created in the bone marrow by malfunctioning (D) Spectrin
plasma cells. (E) Methemoglobin reductase - ANSWER D.
Symptoms of Myasthenia Gravis - ANSWER 1) Trouble keeping your eyes open The child is exhibiting the symptoms of hereditary spherocytosis, a defect in spectrin
and swallowing in the erythrocyte membrane.
2) Slurred speech
3) Weakness in arms and legs This membrane problem leads to an abnormal shape of the red blood cell, such that
the spleen removes them from circulation (hence, the large spleen), leading to an
The underlying etiology of this disorder involves auto-antibodies that are against the anemia due to a reduction of red blood cells in circulation.
acetylcholine receptor
A laboratory worker was working with a potent organophosphorus inhibitor of
Treatment with edrophonium chloride leads to a transient increase in acetylcholine acetylcholinesterase in the lab when a drop of the inhibitor fl ew into his eye. This
levels (through the temporary inactivation of acetylcholinesterase) such that resulted in a pin-point pupil in that eye that was nonreactive and unresponsive to
acetylcholine can bind to receptors (via competition with the antibodies) atropine. He eventually (over a period of weeks) recovered from this incident. The
reason for the long recovery period is which of the following?
A 3-year-old boy is evaluated by the pediatrician as the
child has trouble rising from a sitting position. Examination reveals calf hypertrophy (A) Retraining of the ciliary muscles
and limb-girdle weakness. The inborn error in this patient is due to which of the (B) Regrowth of neurons which were damaged by the
following? inhibitor
(C) Resynthesis of the inhibited enzyme
(A) Defective muscle mitochondria (D) Induction of enzymes which take the place of the
(B) A mutation in the β-chain of hemoglobin inhibited enzyme
(C) A defect in the structure of the hepatocyte membrane (E) Induction of proteases to reactivate the inhibited
(D) A defect in the structure of the sarcolemma enzyme - ANSWER C.
(E) A defect in the transcription of muscle-specific genes - ANSWER D.
Once acetylcholinesterase has been covalently modified by an inhibitor, it cannot be
The boy has Duchenne muscular dystrophy, which is due to mutations in the protein reactivated.
dystrophin,
found in the muscle sarcolemma (plasma membrane). The only way to regain this activity is by new synthesis of acetylcholinesterase,
which would not have the covalent modification found in the inhibited enzyme.
The lack of dystrophin alters the permeability properties of the plasma membrane,
eventually leading to cell death. A patient has midlife onset of the following symptoms:
abnormal, involuntary jerking body movements, an
The disorder is not found in mitochondria, unsteady gait, personality changes, and chewing and
the liver, or in the β-chain of hemoglobin. swallowing difficulty, which has led to a gradual weight
loss. The patient's father had similar symptoms before
This disease also does not alter gene transcription. his death at the age of 45. Cellular analysis indicated
precipitated proteins in the nucleus. This disease has, at
As the muscles weaken, their function is compromised, leading to the complications its origins, which biochemical problem?
of this form of muscular dystrophy.
, (A) An exonic deletion (D) Zero X conceptions
(B) A polyglutamine tract in an exon of the defective (E) Trisomy 21 conceptions - ANSWER B.
gene
(C) A nonsense mutation leading to the production of a A 32-year-old woman exhibited a high fever, malaise,
truncated protein generalized lymphadenopathy, weight loss, and esophageal candidiasis. She had a
(D) A splicing mutation, leading to the insertion of history of drug abuse and needle sharing. Blood analysis indicated a CD4
intronic sequences into the mature protein lymphocyte count of less than 200. Which of the following compounds would be a
(E) Production of an unstable mRNA, leading to reduced protein production - drug of choice for this patient? - ANSWER The woman is suffering from AIDS, and
ANSWER B. one class of drugs used to stop the spread of the virus is the dideoxynucleosides.
*The key here is the personality changes and unsteady gait* The dideoxynucleosides interfere with DNA synthesis after they are activated to the
triphosphate level through purine salvage
The patient is suffering from Huntington pathway enzymes.
disease, which is transmitted in an autosomal
dominant pattern in which a triplet repeat is expanded within the Huntington disease Since these compounds lack a 3′-hydroxyl group, once they are incorporated into a
gene. growing DNA strand, they cannot form a phosphodiester bond with the next
nucleotide, and synthesis stops.
This triplet repeat codes for a polyglutamine tract in the mature protein, which leads
to its eventual failure and disease symptoms. KNOW THIS: - ANSWER Methotrexate, an agent which inhibits dihydrofolate
reductase and blocks the synthesis of thymidine, thereby blocking DNA synthesis. It
Huntington's is not caused by an exonic deletion is used as a treatment for psoriasis and was used, in the past, as a
or a nonsense mutation. chemotherapeutic agent.
Splicing is normal for the gene, and the mature mRNA is stable. 5-fluorouracil (5FU) is an inhibitor of thymidylate synthase.
KNOW THIS: - ANSWER The triplet repeat expansion leads to no expression of the 5FU blocks thymidine synthesis and stops overall DNA synthesis. It is used for
FMR1 gene, which certain tumors as an anticancer drug.
produces a protein required for brain development.
KNOW THIS: - ANSWER All RNA polymerases lack 3' to 5' exonuclease activity
The syndrome was called fragile X because the X chromosome that carries the and one error usually occurs
repeat expansion is subject to DNA strand break under certain conditions (such as
lack of folic acid), which does not occur with normal X chromosomes. The high mutation rate of the human immunodeficiency virus (HIV) is due in part to a
property of which of the
KNOW THIS: - ANSWER Cytosine spontaneously deaminates to form uracil while following host cell enzymes?
in DNA.
(A) DNA polymerase
When adenine deaminates, the base hypoxanthine is formed (inosine as part of a (B) RNA polymerase
nucleoside). (C) DNA primase
(D) Telomerase
Guanine deamination will lead to xanthine production. (E) DNA ligase - ANSWER B.
A couple sees an obstetrician due to difficulties of the 1) During the life cycle of the HIV, the double-stranded DNA which was produced
woman keeping a pregnancy to term. She has had three miscarriages over the past from the genomic RNA integrates randomly into
6 years, and the couple is searching for an answer. Karyotype analysis of the woman the host chromosome.
gave the result of 45,XX,der(14;21). A likely potential cause of the miscarriages may
be which of the following? 2) Cellular RNA polymerase then transcribes the viral DNA to produce viral RNA,
which is used in the translation of viral proteins, and as the genomic material for new
(A) Imbalance of DNA in polyploid conceptions virions.
(B) Imbalance of DNA in euploid conceptions
(C) Triple X conceptions
Test Bank for Lippincott Illustrated Reviews: in the D or L configuration
Pharmacology 8th Edition by Karen Whalen|
*Many biochemical compounds (including drugs) are only active as either the D or L
isomer.*
KNOW THIS: - ANSWER 1) RNA is susceptible to alkaline hydrolysis, whereas Your patient has a mechanical heart valve and is chronically anemic due to damage
DNA is not. to red blood cells as they pass through this valve. One of the signals that target
damaged red blood cells for removal from the circulation is the presence of
2) Under alkaline conditions, the hydroxyl group can act as a nucleophile and attack phosphatidylserine in the outer leaflet of the red cell membrane. Phosphatidylserine
the phosphodiester linkage between adjacent nucleotides, breaking the linkage and is an integral part of cell membranes and is normally found in the inner leaflet of the
leading to the transient formation of a cyclic nucleotide. red cell membrane. This flip-flop of phosphatidylserine between membrane leaflets
exposes which part of the phosphatidylserine to
3) As this can occur at every phosphodiester linkage in RNA, hydrolysis of the RNA the environment?
will occur due to these reactions. As DNA lacks the 2′-hydroxyl group, this reaction
cannot occur, and (A) The head group
DNA is very stable under alkaline conditions. (B) Fatty acids
(C) Sphingosine
Symptoms of adenosine deaminase deficiency: - ANSWER 1) History of chronic (D) Glycerol
diarrhea and multiple pneumonias (E) Ceramide - ANSWER A.
2) The chest X-ray shows a pneumonia, but also reveals an abnormally small Thus, when a phospholipid fl ip-fl ops across the membrane, the head group will
thymus. always end up facing the aqueous environment.
3) Blood work shows a distinct lack of circulating lymphocytes. A couple has had five children, all of who exhibit short
stature, eyelid droop, and some degree of muscle weakness and hearing loss (some
*Here you have no working B or T cells* severe, some mild). The mother also has such problems, although at a mild level.
The father has no symptoms. The mutation that afflicts the children most likely
* This disorder leads to an accumulation of deoxyadenosine and S- resides in DNA found in which intracellular organelle?
adenosylhomocysteine,
which are toxic to immature lymphocytes in the thymus.* (A) Mitochondria
(B) Peroxisome
4) The most likely inherited enzymatic defect in this child leads to an inability to alter (C) Lysosome
a purine nucleotide at position 6 of the ring structure (where deamination occurs and (D) Endoplasmic reticulum
is replaced with a carbonyl group) (E) Nucleus - ANSWER A.
Inosine and Wobbling - ANSWER Inosine is a wobble base pair former, having the The mother and children are experiencing the effects of a mitochondrial disorder.
ability to base pair with *adenine, uracil, or cytosine*
KNOW THIS: - ANSWER Lactase will split the β-1,4 linkage between *They key here is that all of the kids have the issue and the mother as well but the
galactose and glucose in lactose. father shows no symptoms*
The lactose thus passes unmetabolized to the bacteria inhabiting the gut, and their There are multiple mitochondrial disorders associated with muscular dystrophy:
metabolism of the disaccharide leads to the observed symptoms.
1) Kearns-Sayer syndrome(this case)
Combining two sugars in a dehydration reaction creates a glycosidic bond. 2) Leigh syndrome (non-X-linked)
3) Pearson syndrome
Adding a sugar to the nitrogen of a nitrogenous base also creates an N-glycosidic 4) Mitochondrial DNA depletion syndrome
bond. 5) Mitochondrial encephalomyopathy
, 3) Glucuronic acid is added to the xenobiotic at position 1, using the activated
Membrane formation occurs, in part, due to low lipid solubility in water due to intermediate UDP glucuronate.
primarily which of the following?
Early clinical signs of Creutzfeldt-Jakob disease: - ANSWER 1) Mood changes
(A) Hydrogen bond formation between lipids and water 2) Minor loss of memory
(B) Covalent bond formation between lipids and water 3) Decreased motor skills
(C) A decrease in water entropy
(D) An increase in water entropy Caused by a misfolded prion protein, leading to protein aggregates in the brain.
(E) Ionic bond formation between lipids and water - ANSWER D.
This patient will probably die within 1 year.
Cage forming decreases water entropy, which is
unfavorable, and this leads to the hydrophobic effect, in which the lipid molecules all There is no current treatment for the disease.
come together such that only one large cage needs to be formed about the lipid
molecules, rather than many small cages about each individual lipid molecule. As the disease progresses, he will probably develop blindness, involuntary
movements, and severe deterioration of mental function.
The lipids do not form covalent or ionic bonds with water, and, as mentioned above,
lipids in water leads to a decrease in water entropy (which is unfavorable), rather KNOW THIS: - ANSWER Bisphosphonates decrease bone resorption by the
than an increase in the entropy of water (which would be a favorable event). osteoclasts, thereby strengthening the bone, even with the defective collagen
molecule.
KNOW THIS: - ANSWER Precipitation of uric acid occurs in "cold" areas of the
body, such as the great toe. You are visited by a 40-year-old female patient complaining of weight loss,
numbness in the hands and feet, fatigue, and difficulty swallowing. Physical exam
A single-stranded DNA molecule contains 20%A, 25%T, notes an enlarged tongue, enlarged liver, a rubbery
30%G, and 25%C. When the complement of this strand feeling around the joints, and bruising around the
is synthesized, the T content of the resulting duplex will eyes. A bone marrow biopsy shows an abnormal
be which one of the following? staining of denatured protein (see below). These
denatured proteins are most likely to be which of the
(A) 20% following?
(B) 22.5%
(C) 25% (A) Antibody light chains
(D) 27.5% (B) Collagen
(E) 30% - ANSWER B. (C) Fibrillin
(D) Albumin
For the entire duplex then, the T content (E) Transaminases - ANSWER A.
is the average of 25% and 20%, or 22.5% for the duplex. The [A] in the duplex will
also be 22.5% (again, since [A] = [T]), and the concentrations of [G] and [C] will each *The patient is exhibiting the symptoms of primary amyloidosis*
be 27.5% for the duplex.
Primary amyloidosis - ANSWER 1) A protein folding disease in which
KNOW THIS: - ANSWER The glycosylation of hemoglobin primarily occurs on the immunoglobulin light chains are improperly processed and cannot be degraded.
N-terminal valine residues of the β chains (which contain a free amino group).
2) These proteins then form fibrils in tissues,
The rate of degradation of nonmodified hemoglobin and HbA1c are the same. which are insoluble. This disrupts the normal function of the tissue, and many tissues
can accumulate these fibrils.
KNOW THIS: - ANSWER 1) In order to make a xenobiotic more soluble, a
hydrophilic group needs to be added 3) The protein deposits in primary amyloidosis are made up of immunoglobulin light
to the xenobiotic. chain proteins.
2) Glucuronic acid (glucose with a carboxylic acid at position 6 instead of an alcohol 4) These light chain proteins are created in the bone marrow by malfunctioning
group) is a hydrophilic molecule. plasma cells.
,Primary amyloidosis - ANSWER 1) A protein folding disease in which
immunoglobulin light chains are improperly processed and cannot be degraded. An 8-month-old infant exhibits jaundice and lethargy.
Physical exam detects splenomegaly. Blood work displays a microcytic anemia with
2) These proteins then form fibrils in tissues, abnormal erythrocytes under all conditions. This defect is
which are insoluble. This disrupts the normal function of the tissue, and many tissues most likely due to a hereditary mutation in which of the
can accumulate these fibrils. following?
3) The protein deposits in primary amyloidosis are made up of immunoglobulin light (A) Hemoglobin
chain proteins. (B) Glucose-6-phosphate dehydrogenase
(C) Iron transport into the erythrocyte
4) These light chain proteins are created in the bone marrow by malfunctioning (D) Spectrin
plasma cells. (E) Methemoglobin reductase - ANSWER D.
Symptoms of Myasthenia Gravis - ANSWER 1) Trouble keeping your eyes open The child is exhibiting the symptoms of hereditary spherocytosis, a defect in spectrin
and swallowing in the erythrocyte membrane.
2) Slurred speech
3) Weakness in arms and legs This membrane problem leads to an abnormal shape of the red blood cell, such that
the spleen removes them from circulation (hence, the large spleen), leading to an
The underlying etiology of this disorder involves auto-antibodies that are against the anemia due to a reduction of red blood cells in circulation.
acetylcholine receptor
A laboratory worker was working with a potent organophosphorus inhibitor of
Treatment with edrophonium chloride leads to a transient increase in acetylcholine acetylcholinesterase in the lab when a drop of the inhibitor fl ew into his eye. This
levels (through the temporary inactivation of acetylcholinesterase) such that resulted in a pin-point pupil in that eye that was nonreactive and unresponsive to
acetylcholine can bind to receptors (via competition with the antibodies) atropine. He eventually (over a period of weeks) recovered from this incident. The
reason for the long recovery period is which of the following?
A 3-year-old boy is evaluated by the pediatrician as the
child has trouble rising from a sitting position. Examination reveals calf hypertrophy (A) Retraining of the ciliary muscles
and limb-girdle weakness. The inborn error in this patient is due to which of the (B) Regrowth of neurons which were damaged by the
following? inhibitor
(C) Resynthesis of the inhibited enzyme
(A) Defective muscle mitochondria (D) Induction of enzymes which take the place of the
(B) A mutation in the β-chain of hemoglobin inhibited enzyme
(C) A defect in the structure of the hepatocyte membrane (E) Induction of proteases to reactivate the inhibited
(D) A defect in the structure of the sarcolemma enzyme - ANSWER C.
(E) A defect in the transcription of muscle-specific genes - ANSWER D.
Once acetylcholinesterase has been covalently modified by an inhibitor, it cannot be
The boy has Duchenne muscular dystrophy, which is due to mutations in the protein reactivated.
dystrophin,
found in the muscle sarcolemma (plasma membrane). The only way to regain this activity is by new synthesis of acetylcholinesterase,
which would not have the covalent modification found in the inhibited enzyme.
The lack of dystrophin alters the permeability properties of the plasma membrane,
eventually leading to cell death. A patient has midlife onset of the following symptoms:
abnormal, involuntary jerking body movements, an
The disorder is not found in mitochondria, unsteady gait, personality changes, and chewing and
the liver, or in the β-chain of hemoglobin. swallowing difficulty, which has led to a gradual weight
loss. The patient's father had similar symptoms before
This disease also does not alter gene transcription. his death at the age of 45. Cellular analysis indicated
precipitated proteins in the nucleus. This disease has, at
As the muscles weaken, their function is compromised, leading to the complications its origins, which biochemical problem?
of this form of muscular dystrophy.
, (A) An exonic deletion (D) Zero X conceptions
(B) A polyglutamine tract in an exon of the defective (E) Trisomy 21 conceptions - ANSWER B.
gene
(C) A nonsense mutation leading to the production of a A 32-year-old woman exhibited a high fever, malaise,
truncated protein generalized lymphadenopathy, weight loss, and esophageal candidiasis. She had a
(D) A splicing mutation, leading to the insertion of history of drug abuse and needle sharing. Blood analysis indicated a CD4
intronic sequences into the mature protein lymphocyte count of less than 200. Which of the following compounds would be a
(E) Production of an unstable mRNA, leading to reduced protein production - drug of choice for this patient? - ANSWER The woman is suffering from AIDS, and
ANSWER B. one class of drugs used to stop the spread of the virus is the dideoxynucleosides.
*The key here is the personality changes and unsteady gait* The dideoxynucleosides interfere with DNA synthesis after they are activated to the
triphosphate level through purine salvage
The patient is suffering from Huntington pathway enzymes.
disease, which is transmitted in an autosomal
dominant pattern in which a triplet repeat is expanded within the Huntington disease Since these compounds lack a 3′-hydroxyl group, once they are incorporated into a
gene. growing DNA strand, they cannot form a phosphodiester bond with the next
nucleotide, and synthesis stops.
This triplet repeat codes for a polyglutamine tract in the mature protein, which leads
to its eventual failure and disease symptoms. KNOW THIS: - ANSWER Methotrexate, an agent which inhibits dihydrofolate
reductase and blocks the synthesis of thymidine, thereby blocking DNA synthesis. It
Huntington's is not caused by an exonic deletion is used as a treatment for psoriasis and was used, in the past, as a
or a nonsense mutation. chemotherapeutic agent.
Splicing is normal for the gene, and the mature mRNA is stable. 5-fluorouracil (5FU) is an inhibitor of thymidylate synthase.
KNOW THIS: - ANSWER The triplet repeat expansion leads to no expression of the 5FU blocks thymidine synthesis and stops overall DNA synthesis. It is used for
FMR1 gene, which certain tumors as an anticancer drug.
produces a protein required for brain development.
KNOW THIS: - ANSWER All RNA polymerases lack 3' to 5' exonuclease activity
The syndrome was called fragile X because the X chromosome that carries the and one error usually occurs
repeat expansion is subject to DNA strand break under certain conditions (such as
lack of folic acid), which does not occur with normal X chromosomes. The high mutation rate of the human immunodeficiency virus (HIV) is due in part to a
property of which of the
KNOW THIS: - ANSWER Cytosine spontaneously deaminates to form uracil while following host cell enzymes?
in DNA.
(A) DNA polymerase
When adenine deaminates, the base hypoxanthine is formed (inosine as part of a (B) RNA polymerase
nucleoside). (C) DNA primase
(D) Telomerase
Guanine deamination will lead to xanthine production. (E) DNA ligase - ANSWER B.
A couple sees an obstetrician due to difficulties of the 1) During the life cycle of the HIV, the double-stranded DNA which was produced
woman keeping a pregnancy to term. She has had three miscarriages over the past from the genomic RNA integrates randomly into
6 years, and the couple is searching for an answer. Karyotype analysis of the woman the host chromosome.
gave the result of 45,XX,der(14;21). A likely potential cause of the miscarriages may
be which of the following? 2) Cellular RNA polymerase then transcribes the viral DNA to produce viral RNA,
which is used in the translation of viral proteins, and as the genomic material for new
(A) Imbalance of DNA in polyploid conceptions virions.
(B) Imbalance of DNA in euploid conceptions
(C) Triple X conceptions
