biomedical sub test[kalplan 2001] Discussion is welcome!

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 allopurinol  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

zhangheng1020UID：2130513

Explanation:
The  correct  answer is A.  Long-term starvation  induces many biochemical  changes. Much of the body's energy  requirements  are normally supplied  by serum  glucose, but in  starvation are supplied by both glucose  and lipid-derived  ketone bodies,  including  acetoacetic acid  and beta-hydroxybutyric  acid. Glucose  cannot  be synthesized from  lipids, and is  instead made from amino  acids such as alanine in the process of gluconeogenesis.
Serum alanine (choice B) drops dramatically in starvation, due to its conversion to glucose.
Bicarbonate  (choice C)  levels drop  as the  bicarbonate  buffers the  hydrogen ions  produced by  the ketone bodies.
Chylomicrons  (choice D)  are the  lipid form  seen after  absorption of  dietary fat,  and would  drop because the person is not feeding.
Glucose (choice E) is maintained in the blood at a much lower than normal level during starvation.

zhangheng1020UID：2130513

A  15-year-old girl is  seen by a dermatologist for removal of multiple squamous cell carcinomas of the skin.  The patient has nearly  white hair, pink irises, very pale skin, and a history of burning easily when  exposed  to the  sun. This  patient's condition  is caused by  a disorder  involving which of the following substances?
A. Aromatic amino acids
B. Branched chain amino acids
C. Glycolipids
D. Glycoproteins
E. Sulfur-containing amino acids

zhangheng1020UID：2130513

Explanation:
The  correct  answer is A.  The disease is  albinism. The most  common form of  albinism is caused by a deficiency  of  copper-dependent tyrosinase (tyrosine  hydroxylase), blocking the production of melanin from  the  aromatic amino acid tyrosine.  Affected individuals lack  melanin pigment in skin, hair, and eyes,  and are  prone to develop sun-induced  skin cancers, including both squamous cell carcinomas and melanomas.
Maple  syrup urine  disease is  an example  of  a disorder  of branched  chain amino  acids (choice  B) causing motor abnormalities and seizures.
Tay-Sachs  disease is  an  example  of a  disorder  of  glycolipids (choice  C).  In  this disorder,  a deficiency of hexosaminidase A leads to accumulation of ganglioside GM2.
Hunter's  disease is  an example of a  disorder of glycoproteins (choice D). This mucopolysaccharidosis is inherited as an autosomal recessive trait.
Homocystinuria disease is an example of a disorder of sulfur-containing amino acids (choice E).

zhangheng1020UID：2130513

A  7-year-old boy is referred to a specialty clinic because of digestive problems. He often experiences severe  abdominal  cramps after eating a  high fat meal.  He is worked  up and diagnosed with a genetic defect  resulting in  a deficiency of lipoprotein  lipase. Which of the following substances would most likely be elevated in this patient's plasma following a fatty meal?
A. Albumin-bound free fatty acids
B. Chylomicrons
C. HDL
D. LDL
E. Unesterified fatty acids

zhangheng1020UID：2130513

Explanation:
The  correct answer  is B. After eating a  high fat meal, triglycerides are processed by the intestinal mucosal  cells. They  are  assembled in  chylomicrons  and  eventually sent  into  the circulation  for delivery  to  adipocytes and other cells.  Chylomicrons are too large  to enter cells, but are degraded while  in  the circulation  by  lipoprotein  lipase.  A defect  in  this  enzyme  would result  in  the accumulation of chylomicrons in the plasma.
Albumin-bound  free fatty  acids  (choice A)  is  incorrect  because fatty  acids  leave the  intestine esterified as triglycerides in chylomicrons.
HDL (choice C) is not a carrier of dietary fat from the intestine.
LDL  (choice  D) would be not  be elevated in  this patient after a  high fat meal. However, VLDL would be  elevated  if the patient  ate a high  carbohydrate meal. In  this situation, the carbohydrate would be  converted into fat  in the liver and sent out  into circulation as VLDL. VLDL would be unable to be degraded to LDL and, therefore, would accumulate.
A  defect  in lipoprotein lipase would  cause a decrease, not  an elevation of unesterified fatty acids (choice E), since the chylomicrons contain esterified fatty acids.

zhangheng1020UID：2130513

A 38-year-old man in a rural area presents to a physician for an employment physical. Ocular examination reveals  small opaque  rings on the lower edge of  the iris in the anterior chamber of the eye. Nodular lesions  are  found on his Achilles  tendon. Successful therapy should  be aimed at increasing which of the following gene products in hepatocyte cell membranes?
A. Apo B-100
B. Apo B-100 receptor
C. Apo E
D. Apo E receptor
E. Lecithin cholesterol acyltransferase

zhangheng1020UID：2130513

Explanation:
The  correct answer  is B.  This  man has  characteristic  signs of  familial hypercholesterolemia,  an autosomal  dominant  disorder affecting about  1 in  500 persons. The  xanthomas on the Achilles tendon and  the  arcus lipoides  (the opaque  rings in the  eye) are  pathognomonic. Affected individuals have very  high  LDL cholesterol because of  deficient endocytosis of  LDL particles by LDL receptors. These receptors  recognize  the apo  B-100 protein  cotransported with cholesterol  esters in LDL. Treatments aim  at  increasing  genetic expression  of  LDL  receptors  (i.e.,  apo B-100  receptors)  to  enhance clearance  of LDL  particles. Dietary changes, a  resin drug, niacin, or an HMG-CoA reductase inhibitor could be tried.
Apo  B-100  (choice A) is the  apoprotein of liver-produced lipoproteins  such as VLDL, IDL and LDL. It is  therefore not  in the hepatic cell membranes,  and it might be expected to decrease with decreasing concentrations of circulating LDL.
Apo  E (choice  C) is an apoprotein found  on VLDL, IDL, and chylomicrons, allowing "scavenging" by the liver of remnants or of the lipoprotein itself. It is not found in the hepatocyte membrane.
Apo  E receptor  (choice D)  would  actually be  increased  by the  treatment with  hypocholesterolemic agents. However, the apo E receptor is not involved in the scavenging of LDL particles. Lecithin  cholesterol acyl  transferase (choice  E) or  LCAT, is  activated by  apo AI,  and esterifies free  cholesterol in  plasma. Plasma levels of HDL  cholesterol and apo AI are inversely related to the risk of coronary heart disease.

zhangheng1020UID：2130513

Which of the following structures is common to all sphingolipids?
A. Carnitine
B. Ceramide
C. Diacylglycerol
D. Sphingomyelin
E. Squalene

zhangheng1020UID：2130513

Explanation:
The  correct answer  is B.  Sphingolipids  are a  class of  lipids  that are  structural components  of membranes.  Ceramide  is a  component of  sphingolipids. Ceramide  is composed  of sphingosine, a long-chain  amino alcohol  with a  saturated fatty  acid linked  to the  amino group.  Sphingolipids can  be differentiated  on  the basis  of the "X"  group that is  esterified to  the terminal hydroxyl group of ceramide.
Carnitine  (choice  A)  is involved  in  the  oxidation  of  fatty  acids. Carnitine  is  important  in transferring fatty acids from the cytoplasm into the mitochondria (the carnitine shuttle).
Diacylglycerol  (choice C)  is the  alcohol  common to  all  phospholipids. The  second alcohol  (e.g., choline,  ethanolamine,  serine) contributes  the polar  head that  distinguishes the different classes of phospholipids. Like sphingolipids, phospholipids are found in membranes.
Sphingomyelin  (choice  D) is a  sphingolipid with phosphocholine  as its "X"  group. It is a component of the myelin sheath.
Squalene (choice E) is a 30-carbon intermediate in the synthesis of cholesterol.

zhangheng1020UID：2130513

A  47-year-old  male patient presents with  painful arthritis in the  right big toe and uric acid renal stones.  He  has been  taking allopurinol  for his condition.  What biochemical  defect would likely be found in this patient?
A. A defect in urea synthesis
B. An abnormality of the purine degradation pathway
C. An inability to synthesize non-essential amino acids
D. Defective topoisomerases
E. Increased levels of leukotrienes

zhangheng1020UID：2130513

Explanation:
The  correct  answer  is B.  This  patient  has  gout,  characterized  by  painful joints  due  to  the precipitation  of uric  acid crystals caused by excessive  production of uric acid (a minority of cases are  associated with  underexcretion of uric acid). Kidney  disease is also seen due to accumulation of uric  acid  in  the  tubules.  The  disease  mostly affects  males,  and  is  frequently  treated  with allopurinol,  an  inhibitor of  xanthine oxidase.  Xanthine oxidase  catalyzes the sequential oxidation of hypoxanthine to xanthine to uric acid.
A defect in urea synthesis (choice A) would result in the accumulation of ammonia.
Phenylketonuria  is  a disease in which  tyrosine cannot be  produced from phenylalanine (choice C). It is characterized by a musty body odor and mental retardation.
Defective topoisomerases (choice D) would affect DNA unwinding, and therefore replication Leukotrienes  (choice E)  are  potent constrictors  of  smooth muscle  and would  more  likely lead  to bronchoconstriction.