USMLE Questions Flashcards
Hospital testing reveals that the infant can increase her blood glucose after breast feeding but that it is not maintained at normal levels 3-4 hours after feeding. What’s the most likely diagnosis?
a) intestinal malabsorption of lactose
b) galactosemia with inability to convert lactose to glucose
c) fructosemia with inability to liberate sucrose from glucose
d) glycogen storage disease
e) growth hormone deficiency with inability to maintain glucose
Glycogen storage disease
Which glycoside contains fructose and therefore should be avoided when feeding or treating this infant?
a) sucrose
b) oaubain
c) lactose
d) maltose
e) streptomycin
Sucrose
Which of the following carbohydrates would be most abundant in the diet of strict vegetarians?
a) amylase
b) lactose
c) cellulose
d) maltose
e) glycogen
Cellulose
Which of the following results after exercise would support a diagnosis of glycogen storage disease in this teenager?
a) increase oxaloacetate, decreased glucose
b) increased glycerol and glucose
c) increased lactate and glucose
d) increased pyruvate and stable glucose
e) stable lactate and glucose
Increased lactate and glucose
Independent of specific enzyme levels, the availability of what other substance is rate-limiting in the clearance of ethanol?
a) NADH
b) NAD+
c) FADH
d) FAD+
e) NADPH
NAD+
Poorly perfused areas exposed to chronic hypoxia have decreased metabolic energy for tissue maintenance and repair. What is an important reason for this?
a) increase hexokinase activity owing to increased oxidative phosphorylation
b) increased ethanol formation from pyruvate on changing from anaerobic to aerobic metabolism
c) increased glucose utilization via the pentose phosphate pathway on changing from anaerobic metabolism
d) decreased ATP generation and increased glucose utilization on changing from aerobic to anaerobic metabolism
e) decreased respiratory quotient on changing from carbohydrate to fat as the major metabolic fuel
Decreased ATP generation and increased glucose utilization on changing from aerobic to anaerobic metabolism
Following a fad diet meal of skim milk and yogurt, patient experiences abdominal distention, nausea, cramping, and pain followed by watery diarrhea. This set of symptoms is observed each time the meal is consumed. What is the most likely diagnosis?
a) steatorrhea
b) lactase deficiency
c) maltose deficiency
d) sialidase deficiency
e) lipoprotein lipase deficiency
Lactase deficiency
Genetic variation in an enzyme that metabolizes the liver metabolite of alcohol, which is which of the following?
a) methanol
b) acetone
c) acetylaldehyde
d) hydrogen peroxide
e) glycerol
Acetaldehyde
Glycogen storage disease exhibits symptoms due to altered liver or muscle metabolism. Which conversions explains the difference in these presentations?
a) conversion of glycogen to lactate in liver
b) conversion of glycogen and lactase to glucose in liver
c) conversion of glycogen to glucose in muscle
d) conversion of glycogen to alanine in muscle
e) conversion of glycogen to glucose-6-phosphate in liver
Conversion of glycogen and lactate to glucose in liver
The child’s anemia is explained by the fact that ATP is produced by which of the following pathways?
a) glycogen breakdown
b) glycolysis
c) oxidative phosphorylation
d) pentose phosphate cycle
e) lactate conversion to glucose (Cori cycle)
Glycolysis
The physician suspects G6PD deficiency, implying defective synthesis of which of the following compounds?
a) deoxyribose and NADP
b) glucose and lactate
c) lactose and NADPH
d) Ribose and NADPH
e) sucrose and NAD
Ribose and NADPH
A blood screen for galactosemia is positive, and lactose-containing substances are removed from the diet. Lactose is toxic in this case because of what?
a) excess glucose accumulates in the blood
b) galactose is converted to the toxic substance galacitol (dulcitol)
c) galactose competes for glucose during hepatic glycogen synthesis
d) galactose is itself toxic in even small amounts
e) glucose metabolism is shut down by excess galactose
Galactose is converted to the toxic substance galacitol (dulcitol)
Which of the following best explains why fructose is often used as a carbohydrate substitute in special foods for patients with diabetes mellitus?
a) fructose is a better substrate for hexokinase
b) fructose stimulates residual insulin release
c) fructose has a specific kinase in liver that allows bypass of phosphofructokinase
d) fructose is phosphorylated and cleaned to triose phosphates, which cannot be used for gluconeogenesis
e) hexokinase phosphorylates fructose in extra hepatic tissues, and its activist will not be affected by high glucose concentrations in diabetes
Fructose has a specific kinase in liver the allows bypass of phosphofructokinase
Her physician suspects hereditary fructose intolerance, which is a deficiency of the enzyme aldolase B. The symptoms and serum abnormalities of this disease are due to what?
a) accumulation of hexose phosphates, phosphate and ATP depletion, defective electron transport, and glycogen phosphorylase inhibition
b) accumulation of triose phosphates, phosphate and ATP excess, defective glycolysis, and glycogen synthase inhibition
c) accumulation of triose phosphates, phosphate and ATP depletion, defective electron transport, and glycogen synthase inhibition
d) accumulation of hexose phosphates, phosphate and ATP depletion, defective electron transport, and glycogen phosphorylate stimulation
e) accumulation of hexose phosphates, phosphate and ATP excess, defective electron transport, and glycogen phosphorylase stimulation
Accumulation of hexose phosphates, phosphate and ATP depletion, defective electron transport, and glycogen phosphorylase inhibition.
Assay of usual glycogen enzyme deficiencies in the liver specimen is normal, so the metabolic consultant recommends assay of rarer enzyme deficiencies that influence glycogen metabolism. These enzymes would most likely include?
a) hexokinase
b) cAMP-dependent protein kinase
c) G6PD
d) phosphofructokinase
e) fructose-1,6-diphophatase
cAMP-dependent protein kinase
The parents have immigrated from Russia and report that the child’s older brother was diagnosed with a “deb rancher” enzyme deficiency with similar glycogen storage. This diagnosis would imply accumulation of glycogen with which type of glucose linkages?
a) linear alpha-1 → 4 linkages with branching alpha-1 → 6 linkages
b) linear alpha-1 → 6 linkages with branching beta-1 → 4 linkages
c) linear beta-1 → 4 linkages only
d) linear beta-1 → 6 linkages only
e) branching beta-1 → 6 linkages only
Linear alpha-1 → 4 linkages with branching alpha-1 → 6 linkages
Further analysis of the urine reveals a small amount of fructose and a large amount of an unidentified pentose that is most likely which of the following?
a) galactose
b) glucose
c) lactose
d) mannose
e) xylulose
Lactose
What is a ketone isomer of glucose?
a) fructose
b) galactose
c) glucofuranose
d) glucopyranose
e) mannose
Fructose
What best explains why Pompe disease is more severe and lethal compared to other glycogen storage diseases?
a) the deficiency is a degradative rather than synthetic enzyme
b) the deficiency involves liver enzyme
c) the deficiency involves a lysosomal enzyme
d) the deficiency causes associated neutropenia
e) the deficiency involves a serum enzyme
The deficiency involves a lysosomal enzyme
What explains why individuals with hyperlipidemia and/or gout should minimize their intake of sucrose and high fructose syrups?
a) fructose is initially phosphorylated by liver fructokinase
b) after initial modification, fructose is cleaved by a specific enolase
c) fructose is converted to UDP-frucrose
d) fructose is ultimately converted to galactose
e) fructose can be phosphorylated by hexokinase in adipose cells
Fructose is initially phosphorylated by liver fructokinase
Animals cannot metabolize cellulose, for which of the following reasons?
a) cellulose is insoluble
b) they do not commonly consume cellulose
c) they do not have an enzyme to hydrolyze the beta linkage
d) they do not have an enzyme to hydrolyze the branches
They do not have an enzyme to hydrolyze the beta linkage
How many ATP molecules are generated by glycolysis of one glucose molecule?
a) one
b) two
c) four
d) six
e) twelve
Two
Which enzyme plays an important role in regulating blood glucose levels after feeding?
a) glucokinase
b) glucose-6-phosphate
c) phosphofructokinase
d) pyruvate kinase
Glucokinase
Student develops hemolytic anemia after taking the oxidizing antimalarial drug primaquine. Which of the following is the most likely cause of this severe reaction?
a) G6PD deficiency
b) concomitant scurvy
c) vitamin C deficiency
d) diabetes
e) glycogen phosphorylate deficiency
G6PD deficiency
Which event occurs during formation of phosphoenolpyruvate from pyruvate during gluconeogenesis?
a) CO2 is consumed
b) inorganic phosphate is consumed
c) acetyl-CoA is utilized
d) ATP is generated
e) GTP is generated
CO2 is consumed
Among the many molecules of high-energy phosphate compounds formed as a result of the functioning of the citric acid cycle, one molecule is synthesized at the substrate level. In which of the following reactions does this occur?
a) citrate → alpha-ketoglutarate
b) alpha-ketoglutarate → succinate
c) succinate → fumarate
d) fumarate → malate
e) malate → oxaloacetate
alpha-ketoglutarate → succinate
Which statement correctly describes human glucose metabolism?
a) liver is impermeable to glucose in the absence of insulin
b) pancreatic beta-cells, liver and brain are freely permeable to glucose due to specific glucose transporters
c) liver glucokinase phosphorylates glucose at high rates under all conditions
d) extra hepatic tissues are permeable to glucose when glucagon is present
e) liver takes up glucose when serum glucose is normal but releases it when serum glucose is high
Pancreatic beta-cells, liver and brain are freely permeable to glucose due to specific glucose transporters
What are the primary products of the pentose phosphate pathway?
a) NAD+ and ribose
b) NADH and ribose
c) NADP+ and ribose
d) NADPH and ribose
e) NAD+ and glucose
f) NADH and glucose
g) NADP+ and glucose
h) NADPH and glucose
NADPH and ribose
What is an energy-requiring step of glycolysis?
a) glucokinase
b) lactate dehydrogenase
c) phosphoglycerate kinase
d) pyruvate kinase
Glucokinase
What is a primary substrate for gluconeogenesis?
a) galactose
b) glycerol
c) glycogen
d) sucrose
Glycerol
Child ingested cyanide, what component of the citric acid cycle will be depleted first in the child?
a) NAD+ cofactor
b) citrate synthase
c) aconitase
d) citrate production
e) acetyl-CoA production
NAD+ cofactor
The most likely diagnosis and the reasons for hypoglycemia and glycogen accumulation is which of the following?
a) hereditary fructose intolerance with inhibition of liver phosphylate
b) hereditary fructose intolerance with inhibition of glycogen synthase
c) essential fructosuria with inhibition of glycogen synthase
d) essential pentosuria with inhibition of liver phosphorylase
e) essential fructosuria with allosteric stimulation of glycogen synthase
Hereditary fructose intolerance with inhibition of liver phosphorylate
Patient has a mitochondrial electron transport disorders examines the ratio of pyruvate to that of its product under resting conditions. What is the ratio and how would it be affected by abnormal electron transport?
a) Pyruvate/Acetyl-CoA - increased
b) Pyruvate/Acetyl-CoA - decreased
c) Pyruvate/Glucose - decreased
d) Pyruvate/Lactate - increased
e) Pyruvate/Lactate - decreased
Pyruvate/Lactate - decreased
Which enzyme reaction of the citric acid cycle leads to production of ATP (or GTP) by substrate-level phosphorylation?
a) aconitase
b) citrate synthase
c) fumarase
d) isocitrate dehydrogenase
e) alpha-ketoglutirate dehydrogenase
f) malate dehydrogenase
g) succinate dehydrogenase
h) succinate thiokinase
succinate thiokinase
Which compound is recycled in the citric acid cycle and this serves a catalytic role?
a) acetyl-CoA
b) citrate
c) oxaloacetate
d) succinate
oxaloacetate
A liver biopsy reveals excess glycogen in hepatocytes. Deficiency of which of the following enzymes best explains this phenotype?
a) alpha-1,1-glucosidase
b) alpha-1,1-galactosidase
c) alpha-1,4-glucosidase
d) alpha-1,4-galactosidase
e) alpha-1,6-galactosidase
alpha-1,4-glucosidase
What is the role of glucagon?
a) stimulate citric acid cycle
b) stimulate gluconeogenesis
c) stimulate glycolysis
d) stimulate pentose phosphate pathway
stimulate gluconeogenesis
A man on a hunger strike and confines himself to a liquid diet with minimal calories. Which of the following would occur after 4-5 hours?
a) decreased cyclic AMP and increased liver glycogen synthesis
b) increased cyclic AMP and increased liver glucogenolysis
c) decreased epinephrine levels and increased liver glycogenolysis
d) increased Ca2+ in muscle and decreased glycogenolysis
e) decreased Ca2+ in muscle and decreased glycogenolysis
Increased cyclic AMP and increased liver glycogenolysis
Which of the following is the donor of new glucose molecules in glycogen?
a) UDP-glucose-1-phosphate
b) UDP-glucose
c) UDP-glucose-6-phosphate
d) Glucose-6-phosphate
e) Glucose-1-phosphate
UDP-glucose
Which statement about the structure of glycogen is true?
a) glycogen is a copolymer of glucose and galactose
b) there are more branch residues than residues in straight chains
c) branch points contain alpha-1,4-glycosidic linkages
d) new glucose molecules are added to the C1 aldehyde group of chain terminal, forming a hemiacetal
e) the monosaccharide residues alternate between D- and L-glucose
New glucose molecules are added to the Ca aldehyde group of chain terminal, forming a hemiacetal
The citric acid cycle occurs in which sub cellular compartment?
a) cytosol
b) endoplasmic reticulum
c) golgi
d) mitochondria
e) nucleus
mitochondria
McArdle’s disease - Which enzyme is deficient?
a) hepatic hexokinase
b) muscle glycogen synthetase
c) muscle phosphorylase
d) muscle hexokinase
e) muscle debranching enzyme
muscle phosphorylase
Which is an example of a ketone sugar?
a) fructose
b) galactose
c) glucose
d) ribose
e) xylose
fructose
