biomedical sub test[kalplan 2001] Discussion is welcome!

zhangheng1020UID: 2130513

kaplan 2001 的 sub biochemistry资料是我的朋友给我的，当时下载的时候，转到.DOC格式上很多的错行和乱码，所以我一个个的贴到这里，一边看，同时整理。
前60道题是独立的，
后面题是前面题目的乱序。时间不够可以只看前面的。


1
A chronic alcoholic develops severe memory loss with marked confabulation. Deficiency of which of the following   vitamins would be most likely to contribute to the neurologic damage underlying these symptoms?
                 A. Folic acid
                 B. Niacin
                 C. Riboflavin
                 D. Thiamine
                 E. Vitamin B12

[ Last edited by zhangheng1020 on 2005-12-2 at 15:22 ]

zhangheng1020UID: 2130513

Explanation:
         The correct answer is D. Wernicke-Korsakoff syndrome refers to the constellation of neurologic symptoms caused by thiamine deficiency. Among these, a severe memory deficit, which the patient may attempt to cover by making up bizarre explanations (confabulation), is prominent. Anatomical damage to the mamillary bodies and periventricular structures has been postulated as the cause. In the U.S., severe thiamine deficiency is seen most commonly in chronic alcoholics. Thiamine deficiency can also damage peripheral nerves ("dry" beriberi) and the heart ("wet" beriberi). Folic acid deficiency (choice A) produces megaloblastic anemia without neurologic symptoms.  Niacin deficiency (choice B) produces pellagra, characterized by depigmenting dermatitis, chronic diarrhea, and  anemia. Riboflavin deficiency (choice C) produces ariboflavinosis, characterized by glossitis, corneal opacities, dermatitis, and erythroid hyperplasia.   Vitamin B12 deficiency (choice E) produces megaloblastic anemia accompanied by degeneration of the posterolateral spinal cord.

[ Last edited by zhangheng1020 on 2005-12-1 at 23:06 ]

zhangheng1020UID: 2130513

A 25-year-old woman with sickle cell anemia complains of steady pain in her right upper quadrant with radiation to the right shoulder, especially after large or fatty meals. Her physician diagnoses gallstones. Of which of the following compounds are these stones most likely composed?
                 A. Calcium bilirubinate
                 B. Calcium oxalate
                 C. Cholesterol
                 D. Cholesterol and calcium bilirubinate
                 E. Cystine

[ Last edited by zhangheng1020 on 2005-12-1 at 23:06 ]

zhangheng1020UID: 2130513

Explanation:
         The correct answer is A. Bilirubin is a degradative product of hemoglobin metabolism. Bilirubin (pigment) stones are specifically associated with excessive bilirubin production in hemolytic anemias, including sickle cell anemia. Bilirubin stones can also be seen in hepatic cirrhosis and liver fluke infestation. Calcium oxalate stones (choice B) and cystine stones (choice E) are found in the kidney, rather than the gallbladder. Pure cholesterol stones (choice C) are less common than mixed gallstones, but have the same risk factors, including obesity and multiple pregnancies
         Mixed stones (choice D) are the common "garden variety" gallstones, found especially in obese, middle aged patients, with a female predominance.

[ Last edited by zhangheng1020 on 2005-12-1 at 23:07 ]

zhangheng1020UID: 2130513

Two sisters are diagnosed with hemolytic anemia. Their older brother was previously diagnosed with the same  disorder. Two other brothers are asymptomatic. The mother and father are second cousins. Deficiency of which of  the following enzymes would be most likely to cause this disorder?
                A. Debranching enzyme
                B. Glucose-6-phosphatase
                C. Glucose-6-phosphate dehydrogenase
                D. Muscle phosphorylase
            E. Pyruvate kinase

[ Last edited by zhangheng1020 on 2005-12-1 at 23:08 ]

zhangheng1020UID: 2130513

Explanation:
         The correct answer is E. In general, you should associate hemolytic anemia with defects in glycolysis or the hexose monophosphate shunt (pentose phosphate pathway). Only two enzymes of those listed in the answer choices specifically involve these pathways and cause hemolytic anemia: pyruvate kinase and glucose-6-phosphate dehydrogenase. Glucose-6-phosphate dehydrogenase (G6PD) deficiency is inherited as an X-linked recessive trait, so females would not be affected. Pyruvate kinase is a glycolytic enzyme; pyruvate kinase deficiency is an autosomal recessive disorder, affecting males and females approximately equally. If this enzyme is deficient, red cells have trouble producing enough ATP to maintain the Na+/K+ pump on the plasma membrane, secondarily causing swelling and lysis.
         Debranching enzyme (choice A) defects produce Cori's disease, one of the glycogen storage diseases.
         Defects in glucose-6-phosphatase (choice B) produce Von Gierke's disease, one of the glycogen storage diseases.
         Glucose-6-phosphatase dehydrogenase (choice C) deficiency produces an X-linked hemolytic anemia.
         Defects in muscle phosphorylase (choice D) produce McArdle's disease, one of the glycogen storage diseases.

[ Last edited by zhangheng1020 on 2005-12-1 at 23:08 ]

zhangheng1020UID: 2130513

4
Which of the following amino acids would most likely be found on the surface of a protein molecule?
                 A. Alanine
                 B. Arginine
                 C. Isoleucine
                 D. Leucine
                 E. Phenylalanine
                 F. Tryptophan

zhangheng1020UID: 2130513

Explanation:
         The correct answer is B. This question requires two logical steps: first, you need to appreciate that the  hydrophilic amino acids are more likely to appear on the surface of a protein molecule, while hydrophobic amino acids are most likely be found in its interior. Next, you need to figure out which of the amino acids listed is hydrophilic. If you recall that arginine is a basic amino acid that is positively charged at physiologic pH, you should be able to answer this question right away.
         All of the other choices have neutral side chains and are uncharged at physiologic pH. They would most likely be found in the hydrophobic core of the protein structure. Alanine (choice A), isoleucine (choice C), and leucine (choice D) all have aliphatic side chains; phenylalanine (choice E) and tryptophan (choice F) have aromatic side chains.

zhangheng1020UID: 2130513

5
A Southeast Asian immigrant child is noted to be severely retarded. Physical examination reveals a pot-bellied, pale child with a puffy face. The child's tongue is enlarged. Dietary deficiency of which of the following substances can produce this pattern?
                 A. Calcium
                 B. Iodine
                 C. Iron
                 D. Magnesium
                 E. Selenium

zhangheng1020UID: 2130513

Explanation:
         The correct answer is B. The disease is cretinism, characterized by a profound lack of thyroid hormone in a developing child, leading to mental retardation and the physical findings described in the question stem. Cretinism can be due to dietary deficiency of iodine (now rare in this country because of iodized salt), to developmental failure of thyroid formation, or to a defect in thyroxine synthesis.
         Calcium deficiency (choice A) in children can cause osteoporosis or osteopenia.
         Iron deficiency (choice C) can cause a hypochromic, microcytic anemia.
         Magnesium deficiency (choice D) is uncommon, but can cause decreased reflexes, and blunts the parathyroid response to hypocalcemia.
         Selenium deficiency (choice E) is rare, but may cause a reversible form of cardiomyopathy.

zhangheng1020UID: 2130513

To which of the following diseases is pyruvate kinase deficiency most similar clinically?
                A. α-thalassemia
                B. β-thalassemia
                C. Glucose-6-phosphate dehydrogenase deficiency
                D. Hereditary spherocytosis
                E. Iron deficiency anemia

zhangheng1020UID: 2130513

Explanation:
         The correct answer is C. Both pyruvate kinase deficiency and glucose-6-phosphate dehydrogenase deficiency are red cell enzyme deficiencies characterized clinically by long "normal" periods interspersed with episodes of hemolytic anemia triggered by infections and oxidant drug injury (antimalarial drugs, sulfonamides, nitrofurans). In both of these conditions, the cell morphology between hemolytic episodes is usually normal or close to normal.
         The α(choice A) and β(choice B) thalassemias, in their major forms, are characterized by persistent severe anemia. In the trait forms, they are charactertized by mild anemia.
         Hereditary spherocytosis (choice D) is characterized by intermittent hemolysis, but, unlike pyruvate kinase deficiency and glucose-6-phosphate dehydrogenase deficiency, oxidant drugs are not a specific trigger for hemolysis.
         Iron deficiency anemia (choice E) is characterized by chronic anemia with hypochromic, microcytic erythrocytes.

zhangheng1020UID: 2130513

A baby that was apparently normal at birth begins to show a delay in motor development by 3 months of age. At one year of age, the child begins to develop spasticity and writhing movements. At age three, compulsive biting of fingers and lips and head-banging appear. At puberty, the child develops arthritis, and death from renal failure occurs at age 25. This patient's condition is due to an enzyme deficiency in which of the following biochemical pathways?
                A. Ganglioside metabolism
                B. Monosaccharide metabolism
                C. Purine metabolism
                D. Pyrimidine metabolism
                E. Tyrosine metabolism

zhangheng1020UID: 2130513

Explanation:
         The correct answer is C. The patient has a classical case of Lesch-Nyhan syndrome, an X-linked disorder due to severe deficiency of the purine salvage enzyme hypoxanthine-guanine phosphoribosyl transferase (HPRT). This defect is associated with excessive de novo purine synthesis, hyperuricemia, and the clinical signs and symptoms described in the question stem. The biochemical basis of the often-striking self-mutilatory behavior (which may require restraints and even tooth extraction) has never been established. Treatment with allopurinon inhibits xanthine oxidase and reduces gouty arthritis, urate stone formation, and urate nephropathy. It does not, however, modify the neurologic/psychiatric presentation.

zhangheng1020UID: 2130513

An obese individual is brought to the emergency room by a concerned friend. The patient has been on a self-imposed "starvation diet" for four months, and has lost 60 pounds while consuming only water and vitamin pills. If extensive blood studies were performed, which of the following would be expected to be elevated?
                 A. Acetoacetic acid
                 B. Alanine
                 C. Bicarbonate
                 D. Chylomicrons
                 E. Glucose