Hemoglobin and Heme Biosynthesis Quiz

Which of the following is the rate-limiting step in heme biosynthesis?

• Conversion of porphobilinogen to hydroxymethylbilane

• Incorporation of Fe²⁺ into protoporphyrin IX

• Formation of δ-aminolevulinic acid from glycine and succinyl-CoA

• Conversion of coproporphyrinogen III to protoporphyrinogen IX

The heme pocket in hemoglobin plays a crucial role by:

• Allowing reversible oxidation of Fe²⁺ to Fe³⁺

• Protecting Fe²⁺ from oxidation while permitting O₂ binding

• Binding 2,3-BPG directly to regulate O₂ affinity

• Forming covalent bonds with oxygen molecules

Which hemoglobin variant has the highest oxygen affinity due to weaker interaction with 2,3-BPG?

• Hb A

• Hb A₂

• Hb F

• Hb Portland

In adult blood, the expected percentage of Hb A₂ is normally up to 3.5%. An Hb A₂ level greater than 3.5% is most indicative of:

• α-thalassemia trait

• β-thalassemia trait

• Iron deficiency anemia

• Sickle cell disease

Which statement best describes myoglobin compared to hemoglobin?

• It binds O₂ with lower affinity than Hb A

• It has a sigmoidal O₂ dissociation curve

• It stores O₂ in muscle and has a hyperbolic curve

• It transports CO₂ in muscle tissue

Which laboratory method is considered the reference method for hemoglobin measurement?

• Oxyhemoglobin method

• Hb electrophoresis

• Cyanmethemoglobin method

• HPLC

What wavelength is used to measure cyanmethemoglobin in the spectrophotometer?

• 340 nm

• 420 nm

• 540 nm

• 620 nm

Which condition would most likely cause a left shift in the O₂ dissociation curve?

• Acidosis

• Hyperthermia

• Increased 2,3-BPG

• Alkalosis

Which hemoglobin type appears after birth and remains <3.5% of adult hemoglobin?

• Hb A

• Hb A₂

• Hb F

• Hb Portland

Which enzyme deficiency causes accumulation of ALA and PBG, leading to porphyria?

• ALA dehydratase

• Ferrochelatase

• PBG deaminase

• Coproporphyrinogen oxidase