Iron, folate, and vitamin B12 Metabolism Practice Questions Flashcards
Which is a true statement regarding iron metabolism in the human body?
A) Iron is highly toxic and can generate damaging free radicals
B) Iron is necessary as an essential ligand for the proper function of Vitamin B12
C) Iron is important in human biochemical functions only in the blood
D) Iron is captured from the blood by binding to Ferritin receptors on cells
E) Iron is present in the ferric (Fe+3) state in erythrocytes, but not the ferrous (Fe+2) state
A
A patient presents with signs and symptoms of Iron Deficiency Anemia. Which is the most commonly used biochemical clinical test of marrow iron status, indicating iron stores levels for erythrocyte formation?
A) Analysis of free iron concentration in skin biopsy
B) Hemosiderin concentration in liver biopsy
C) Ferritin concentration in blood
D) Transferrin concentration in blood
E) Oral iron absorption analysis
C
Iron transport across the brush border is enhanced by ascorbic acid, and inhibited by tannins (constituents of tea and other plants). What is the explanation for the enhancement by ascorbic acid?
A) Ascorbate transfers its bound iron to heme
B) Ascorbate maintains iron in the reduced state
C) Ascorbate is recognized by the DMT1 receptor
D) Ascorbate maintains iron in its oxidized state
E) Ascorbate activates iron binding enzymes, which transport iron in the blood
B
The major iron carrier of blood, transferrin, is associated with iron by chelation to acidic side-chains of amino acids in the iron binding site. What is the name of the amino-acid residues which chelate the iron?
A) Glutamate and Aspartate
B) Tyrosine and Phenylalanine
C) Glycine and Alanine
D) Cysteine and Methionine
E) Serine and Threonine
A
The Total Iron Binding Capacity (TIBC), is a measure of the capacity for blood to associate with iron introduced in the ‘free’ form. TIBC is estimated by adding ‘free’ iron up to the capacity of iron binding by the sample. In a patient with a very high TIBC, what is the primary iron binding protein which captures and binds to the iron introduced into the sample?
A) Ferritin
B) DMT transport protein
C) Cytochrome c
D) Hemoglobin
E) Transferrin
E
Which clinical presentation is expected to result in the greatest loss of bodily iron stores?
A) Ingestion of large quantities of vitamin C
B) Normal menstruation
C) Vitamin B12 deficiency
D) Liver cirrhosis
E) Ferrous sulfate ingestion
B
While normal iron homeostasis requires mobilization of very limited amounts of iron from iron stores, patients with Iron Deficiency Anemia (IDA) may require up to 40 mg per day from reticulocyte storage. In what form is the iron mobilized stored within reticulocytes iron depots?
A) Hemoglobin iron
B) Ferritin iron
C) Free intracellular iron pools
D) Enzyme-bound iron
E) Sulfur-cluster enzymes
B
A 20-year-old woman is involved in a car accident and has lost blood. She has observed inflammation surrounding the areas of wounds sustained. When being discharged from the hospital the woman is given nutritional guidance to augment iron nutrition with meats and spinach. What is the name of the hormone most closely associated with regulation of iron absorption and mobilization through the blood?
A) Erythropoietin
B) Insulin
C) Thyroxine
D) Prostaglandin
E) Hepcidin
E
A 45-year-old woman presents complaining of fatigue, and occasional dizzyness. She is a vegetarian, and does not drink. Her co-workers complain that she hasn’t shown enough spontaneity in her interactions with her customers, and it is affecting her company’s sales.
Blood analysis is as follows:
Measurement First Visit Low normal
Hemoglobin (g/dL) 11.1 (normal: >12.0)
Hemocrit (cell/mL) x 100 34% (normal: >36%)
Mean corpuscular Volume (fL/cell) 82 (normal: >85)
Transferrin Saturation (%) 11 (normal: >16)
Ferritin (ng/L) 4 (normal: >12)
Based on the patient’s presentation, and the initial lab values – What is the likely diagnosis?
A) Folate deficiency
B) B12 deficiency
C) Homocysteinemia
D) Hyperbilirubinemia
E) Iron deficiency
E
What is the most informative and specific evidence above which supports the diagnosis you would assign for the previous question?
A) Low Hemoglobin
B) Low Hematocrit
C) Low Transferrin Saturation
D) Low Ferritin
E) Occasional Dizziness
F) Fatigue
G) Vegetarian Diet
D (but also C)
A 50-year-old male patient presents complaining of lethargy, pain in the second and third metacarpo-phalangeal joints, and a loss of libido. A physical examination indicates hepatomegaly, hypogonadism and slate gray skin pigmentation on the lower forearms and lower legs. The patient is mildly obese, and seems at risk for diabetes mellitus based on C-protein levels in blood. What is the most likely special feature of liver cells following cellular microscopy of a liver biopsy sample of the patient?
A) Presence of hemosiderin
B) Presence of mitotic cells
C) Absence of mitochondria
D) Absence of nuclei
E) Absence of glycogen granules
A
In the previous question, what is the best treatment for the patient?
A) Blood transfusion
B) Infusion of packed red cells
C) Avoidance of iron intake and iron supplements
D) Repeated phlebotomy
E) Supplementation with vitamin B12
D
The rate of transport of iron across the brush border of the duodenum is increased in patients with inherited hemochromatosis. What is the typical age and gender of patients who present with this condition?
A) male children
B) female adolescents
C) males aged 20 to 30
D) females aged 40 to 50
E) males aged 50-60
E
A 40 year-old female patient presents after complaining of fatigue, stomach cramps and nausea. Physical evaluation indicates pallor, and ataxia of gait is observed. A complete blood test is requested. The hematocrit is 35%. The blood smear indicates megaloblastic anemia. Homocysteine levels are ABOVE normal values. Further tests are requested, including serum vitamin B12 and serum folic acid.
What is the most likely reason for the patient’s high homocysteine levels?
A) Low DHFR (dihydrofolate reductase) activity
B) Low methionine synthase activity
C) Low TS (thymidylate synthase) activity
D) High dietary cysteine intake
E) High dietary folic acid intake
B
What is the most likely cause for confirmed Vitamin B12 deficiency in a 35-year-old woman?
A) Autoimmune destruction of gastric cells
B) Loss of function mutation in the intrinsic factor gene
C) Lack of sufficient dietary intake of Vitamin B12
D) Loss of function mutation of the Intrinsic Factor- B12 duodenal translocase
E) Cobalt deficiency
A
What is the most important downstream biochemical effect resulting from deficiency of folic acid and/or Vitamin B12 in pre-erythrocytes?
A) Lipid biosynthesis for cell membranes is impaired
B) Iron cannot enter enterocytes in the duodenum
C) Heme biosynthesis is inhibited by anapleurotic reactions
D) DNA and RNA biosynthesis is interrupted
E) Glycoprotein synthesis in the Golgi is restricted
D
A 22 y.o. college student of Asian ancestry has returned from a visit to her friend’s home in Sardinia on a summer break. She arrives at the airport complaining of fatigue, nausea, abdominal pain and fever. She has mild hemoglobinuria and jaundice. She ate a large dinner just prior to departure which included a local bean salad. ‘Bite cells’ and Heinz bodies are observed in blood smears. A Beutler fluorescent spot test is performed.
The most likely cause of this patient’s jaundice is due to which of the following?
A) Deficiency of albumin
B) Deficiency of liver enzymes which produce bilirubin-diglucoronides
C) Impaired liver-to-bile transport of conjugated bilirubin
D) Acute hemolysis due to an enzyme deficiency
E) Deficiency of spleen enzymes which produce bilirubin
D
The product of the Pentose Phosphate Pathway which is deficient in this woman is which of the following?
A) Ribose sugar (C5)
B) Sialic acid (C9)
C) NADPH (reduces nicotinamide adenine dinucleotide phosphate)
D) ATP (Adenosine triphosphate)
E) CO2 (Carbon dioxide)
C
Besides diet, what other restrictions will need to be explained to the patient prior to her release from the hospital?
A) Avoid dietary choices contributing to high caloric intake from carbohydrates
B) Inform her of drugs which could precipitate hemolytic anemia
C) Inform her of glucose 6-phosphatase deficiency drug restrictions
D) Inform her of the requirement for regular insulin injections
E) Inform her that she needs daily exercise
B
The first enzyme of the pentose phosphate pathway is controlled by which small molecule?
A) ATP
B) Ribose
C) Sialic acid
D) Lactic acid
E) NADP+ and NADPH
E
In addition to hemoglobin, which other protein listed below requires heme as a cofactor and/or coenzyme?
A) Cytochrome P450 (CYP450)
B) Hexokinase (HK)
C) Glucose-6-phosphate dehydrogenase (G6PDH)
D) Trypsin
E) Lactate Dehydrogenase
F) Aconitase
G) Phosphofructokinase-1 (PFK-1)
A
Nucleotides contain ribose or 2-deoxyribose. What is the initial carbon-based substrate for the metabolic pathway required to produce these 5-carbon sugars?
A) Glucose-6-phosphate
B) Alanine
C) Succinyl-CoA
D) NADPH
E) Fructose
F) 2,3-bisphosphoglycerate (2,3- BPG)
A
A 20 year-old woman with jaundice is given a series of liver enzyme tests which reveal low activity of enzymes required for glucuronidation (addition of glucose) to bilirubin. Such a condition is most likely to result in elevation of which substance in the woman’s blood?
A) Biliverdin, free form
B) Bilirubin, unconjugated, free form
C) Bilirubin, unconjugated, albumin bound
D) Bilirubin, conjugated, free form
E) Bilirubin, conjugated, albumin bound
C
A 2-day old neonate has moderately elevated levels of unconjugated bilirubin, resulting in jaundice. The neonate is treated effectively with phototherapy to assist elimination of bili-products accumulating in skin, and the jaundice resolves within two weeks. What is the most likely underlying cause of the neonate’s jaundice?
A) Overproduction of heme through accelerated hemolysis and consequent production of hemoglobin in spleen.
B) Immaturity of the liver, with low activity of bilirubin glucuronyl transferase enzymes.
C) Sequestration of all blood-borne bilirubin in skin as a result of low albumin carrying capacity.
D) Rapid intestinal reuptake of bilirubin diglucuronide into the blood through the gastrointestinal tract.
E) Blockage of the immature bile duct, which resolves after 2 weeks of development after birth.
B
