hemoglobin metabolism

d

What type of protein structure is hemoglobin, consisting of four polypeptide chains and four heme groups?

A. Monomer

B. Dimer

C. Trimer

D. Tetramer

E. Hexamer

a

Which form of iron is required in each of the four heme groups of a hemoglobin molecule to bind oxygen reversibly?
A. Ferrous (Fe^{2+})
B. Ferric (Fe^{3+})
C. Metallic (Fe^0)
D. Ferritin
E. Transferrin 

c

Where does the initial step of heme synthesis take place inside the developing red blood cell?

A. Cytosol

B. Ribosome

C. Mitochondrion

D. Endoplasmic reticulum

E. Golgi apparatus

b

Which two starting molecules condense together in the first step of heme biosynthesis?

A. Protoporphyrin IX and iron

B. Succinyl-CoA and glycine

C. Delta-aminolevulinic acid and iron

D. Porphobilinogen and uro'porphyrinogen

E. Coproporphyrinogen III and oxygen

c

Which rate-limiting enzyme catalyzes the condensation of succinyl-CoA and glycine in heme biosynthesis?

A. Ferrochelatase

B. Heme synthase

C. Aminolevulinic acid (ALA) synthase

D. Uroporphyrinogen decarboxylase

E. Coproporphyrinogen oxidase

b

In which cellular compartment do the intermediate steps of heme synthesis (from ALA to coproporphyrinogen III) take place?

A. Nucleus

B. Cytosol

C. Mitochondria

D. Cell membrane

E. Lysosome

c

Which enzyme catalyzes the insertion of ferrous iron (Fe^{2+}) into protoporphyrin IX to form heme as the final step?
A. ALA synthase
B. Biliverdin reductase
C. Ferrochelatase
D. Glucose-6-phosphate dehydrogenase
E. Methemoglobin reductase

c

On which chromosome is the alpha (\alpha) globin gene cluster located in human cells?
A. Chromosome 11
B. Chromosome 12
C. Chromosome 16
D. Chromosome 21
E. Chromosome X

a

On which chromosome is the beta (\beta) globin gene cluster located in human cells?
A. Chromosome 11
B. Chromosome 16
C. Chromosome 6
D. Chromosome 18
E. Chromosome 12 

d

How many total alpha (\alpha) globin genes are present in a normal diploid human genome (two per chromosome 16)?
A. 1
B. 2
C. 3
D. 4
E. 6 

a

Which major embryonic hemoglobin is composed of two zeta (\zeta) and two epsilon (\epsilon) chains?
A. Hb Gower-1
B. Hb Gower-2
C. Hb Portland
D. Hb F
E. Hb A 

b

Which embryonic hemoglobin consists of two alpha (\alpha) chains and two epsilon (\epsilon) chains?
A. Hb Gower-1
B. Hb Gower-2
C. Hb Portland-1
D. Hb Bart's
E. Hb A2 

c

What is the predominant hemoglobin present during intrauterine fetal development (fetal hemoglobin)?
A. Hb A (\alpha_2\beta_2)
B. Hb A2 (\alpha_2\delta_2)
C. Hb F (\alpha_2\gamma_2)
D. Hb Portland (\zeta_2\gamma_2)
E. Hb Gower-1 (\zeta_2\epsilon_2)

c

What globin chain composition defines adult Hemoglobin A (Hb A), which constitutes >95% of normal adult hemoglobin?
A. Two alpha (alpha) and two gamma (gamma) chains
B. Two alpha (alpha) and two delta (delta) chains
C. Two alpha (alpha) and two beta (beta) chains
D. Two beta (beta) and two gamma (gamma) chains
E. Two zeta (zeta) and two epsilon (epsilon) chains

c

What globin chain composition defines adult Hemoglobin A2 (Hb A2), which constitutes 1.5% to 3.7% of total adult hemoglobin?
A. alpha2 beta2
B. alpha2 gamma2
C. alpha2 delta2
D. zeta2 epsilon2
E. beta4 

b

What effect does excess intracellular heme have on the rate of heme synthesis in red blood cell precursors?

A. Stimulates ALA synthase activity

B. Inhibits ALA synthase activity via negative feedback

C. Increases iron uptake by transferrin

D. Accelerates globin mRNA translation

E. Has no regulatory effect

b

How does the oxygen affinity of fetal hemoglobin (Hb F) compare to that of adult hemoglobin (Hb A)?

A. Hb F has a lower affinity for oxygen than Hb A

B. Hb F has a higher affinity for oxygen than Hb A

C. Hb F has the exact same oxygen affinity as Hb A

D. Hb F cannot bind oxygen at all

E. Hb F binds oxygen only under high temperature conditions

c

What shape does the normal adult hemoglobin-oxygen dissociation curve demonstrate due to cooperative binding?

A. Linear

B. Hyperbolic

C. Sigmoidal (S-shaped)

D. Parabolic

E. Exponential

b

What term describes the process where the binding of one oxygen molecule to hemoglobin increases the affinity for binding subsequent oxygen molecules?

A. Allosteric inhibition

B. Cooperative interaction (cooperativity)

C. Bohr effect

D. Haldane effect

E. Competitive inhibition

b

What is the definition of P_{50} on an oxygen dissociation curve?
A. The partial pressure of oxygen at which hemoglobin is 100% saturated
B. The partial pressure of oxygen at which hemoglobin is 50% saturated
C. The percentage saturation of hemoglobin at 50 mmHg PO_2
D. The pH at which hemoglobin gives up 50% of its oxygen
E. The concentration of 2,3-BPG needed to release 50% oxygen 

c

What is the normal P_{50} value of normal human adult hemoglobin under physiological conditions (\text{pH } 7.40, 37^\circ\text{C})?
A. 12 mmHg
B. 20 mmHg
C. 27 mmHg
D. 40 mmHg
E. 50 mmHg 

b

​A shift of the oxygen dissociation curve to the RIGHT indicates which of the following?
A. Increased affinity of hemoglobin for oxygen (holds oxygen tightly)
B. Decreased affinity of hemoglobin for oxygen (releases oxygen more readily)
C. Decreased P_{50} value
D. Inhibited delivery of oxygen to peripheral tissues
E. Complete absence of 2,3-BPG binding

b

​A shift of the oxygen dissociation curve to the LEFT indicates which of the following?
A. Decreased affinity of hemoglobin for oxygen
B. Increased affinity of hemoglobin for oxygen (holds oxygen tightly)
C. Increased P_{50} value
D. Enhanced oxygen release to active muscles
E. High concentration of hydrogen ions (H^+) 

c

Which of the following conditions causes a RIGHT shift in the hemoglobin-oxygen dissociation curve?
A. Decreased body temperature
B. Increased pH (alkalosis)
C. Increased 2,3-BPG level, decreased pH (acidosis), or increased temperature
D. Decreased PCO_2
E. Presence of fetal hemoglobin (Hb F) 

d

Which of the following conditions causes a LEFT shift in the hemoglobin-oxygen dissociation curve?
A. Increased 2,3-BPG concentration
B. Decreased pH (acidosis)
C. Increased body temperature
D. Decreased body temperature, increased pH (alkalosis), or decreased 2,3-BPG
E. Increased partial pressure of carbon dioxide (PCO_2) 

b

What organic phosphate compound produced in red blood cells stabilizes the deoxygenated T-structure of hemoglobin to promote oxygen delivery?

A. 1,3-bisphosphoglycerate

B. 2,3-bisphosphoglycerate (2,3-BPG)

C. Adenosine triphosphate (ATP)

D. Glucose-6-phosphate

E. Nicotinamide adenine dinucleotide (NADH)

b

What is the "Bohr effect"?
A. The effect of oxygen tension on carbon dioxide carriage
B. The influence of pH and H^+ concentration on hemoglobin's affinity for oxygen
C. The effect of temperature on methemoglobin reduction
D. The binding of carbon monoxide to iron in heme
E. The shift in 2,3-BPG synthesis during hypoxia 

b

Which conformational state describes deoxygenated hemoglobin, which has low oxygen affinity?

A. Relaxed (R) state

B. Tense (T) state

C. Dissociated state

D. Met-state

E. Glycated state

b

Which conformational state describes fully oxygenated hemoglobin, which has high oxygen affinity?

A. Tense (T) state

B. Relaxed (R) state

C. Unstable state

D. Sulf-state

E. Glycated state

c

In what form is the majority of carbon dioxide (CO2) transported from peripheral tissues to the lungs?
A. Dissolved directly in blood plasma
B. Bound directly to heme iron
C. Bicarbonate ion (HCO3^-) in plasma
D. Carbaminohemoglobin
E. Carbonic acid (H2CO3) crystals

a

Which enzyme inside red blood cells rapidly converts CO_2 and H_2O into carbonic acid (H_2CO_3)?
A. Carbonic anhydrase
B. Methemoglobin reductase
C. Biliverdin reductase
D. Ferrochelatase
E. Lactate dehydrogenase

c

What term describes hemoglobin bound to carbon dioxide via its terminal amino groups?

A. Oxyhemoglobin

B. Deoxyhemoglobin

C. Carbaminohemoglobin

D. Carboxyhemoglobin

E. Methemoglobin

c

What derivative form of hemoglobin contains iron in the oxidized ferric state (Fe^3+) and cannot reversibly bind oxygen?
A. Oxyhemoglobin
B. Sulfhemoglobin
C. Methemoglobin
D. Carboxyhemoglobin
E. Glycated hemoglobin 

b

Which enzyme system is primarily responsible for reducing methemoglobin (Fe^3+) back to functional hemoglobin (Fe^2+) in normal red cells?
A. NADPH-dependent methemoglobin reductase
B. NADH-dependent cytochrome b5 methemoglobin reductase
C. Glutathione peroxidase
D. Superoxide dismutase
E. Catalase 

b

What classic clinical symptom is characteristically observed when methemoglobin levels exceed 10% to 15% in circulation?

A. Jaundice

B. Cyanosis

C. Splenomegaly

D. Hemoglobinuria

E. Petechiae

b

What irreversible hemoglobin derivative is formed by the incorporation of a sulfur atom into the heme ring, giving blood a greenish color?

A. Methemoglobin

B. Sulfhemoglobin

C. Carboxyhemoglobin

D. Hb A1c

E. Oxyhemoglobin

d

Which dyshemoglobin forms when hemoglobin binds carbon monoxide (CO), presenting an affinity for CO that is ~200 times higher than for oxygen?
A. Methemoglobin
B. Sulfhemoglobin
C. Carbaminohemoglobin
D. Carboxyhemoglobin
E. Hb F 

b

What color appearance does the skin and blood typically display in severe carbon monoxide poisoning (carboxyhemoglobinemia)?

A. Chocolate brown

B. Bright cherry red

C. Bluish purple

D. Pale yellow

E. Dark green

c

What type of modified hemoglobin is Hb A1c, used clinically to monitor long-term blood glucose control in diabetic patients?

A. Oxidation product of ferric iron

B. Sulfated hemoglobin derivative

C. Glycated hemoglobin formed by non-enzymatic attachment of glucose

D. Embryonic precursor of adult hemoglobin

E. Mutant hemoglobin with single amino acid substitution

a

What reference method is recommended by the International Council for Standardization in Haematology (ICSH) for measuring total hemoglobin concentration?

A. Drabkin's cyanmethemoglobin method

B. Oxyhemoglobin spectrophotometry

C. Iron content titration

D. Specific gravity measurement

E. Electrophoresis

c

In the cyanmethemoglobin reagent (Drabkin's reagent), potassium ferricyanide converts hemoglobin iron from Fe^2+ to Fe^3+ to form:
A. Sulfhemoglobin
B. Cyanmethemoglobin
C. Methemoglobin
D. Carboxyhemoglobin
E. Hematin 

c

In the cyanmethemoglobin reaction, potassium cyanide reacts with methemoglobin to convert it into which stable compound measured at 540 nm?

A. Oxyhemoglobin

B. Deoxyhemoglobin

C. Cyanmethemoglobin

D. Hemochromogen

E. Biliverdin

d

Which abnormal form of hemoglobin is NOT converted to cyanmethemoglobin and thus cannot be measured by Drabkin's method?

A. Oxyhemoglobin

B. Methemoglobin

C. Carboxyhemoglobin

D. Sulfhemoglobin

E. Hb F

c

​At what wavelength in nanometers (nm) is cyanmethemoglobin absorbance measured in a spectrophotometer?

A. 410 nm

B. 500 nm

C. 540 nm

D. 630 nm

E. 650 nm

b

Which embryonic globin chain is the early developmental equivalent/analogue of the alpha (\alpha) chain?
A. Epsilon (epsilon)
B. Zeta (zeta)
C. Gamma (gamma)
D. Delta (delta)
E. Beta (beta)

s

Which embryonic globin chain is the early developmental equivalent/analogue of the beta (\beta) chain?
A. Epsilon (\epsilon)
B. Zeta (\zeta)
C. Alpha (\alpha)
D. Delta (\delta)
E. Gamma (\gamma)

b

​What happens to the hemoglobin concentration in plasma if a blood specimen exhibits severe lipemia during spectrophotometric analysis?

A. Falsely decreased due to light absorption

B. Falsely elevated due to increased turbidity

C. Unaffected because lipids do not absorb light

D. Completely unmeasurable due to hemolysis

E. Corrected automatically by cyanmethemoglobin reagent

b

Myoglobin exhibits what type of oxygen dissociation curve due to having a single heme monomer?

A. Sigmoidal curve

B. Hyperbolic curve

C. Linear curve

D. Parabolic curve

E. Bimodal curve

a

What is the primary function of hemoglobin in human red blood cells?

A. Transport oxygen from lungs to tissues and carbon dioxide from tissues to lungs

B. Synthesize iron for systemic utilization

C. Destroy senescent RBCs in spleen

D. Maintain osmotic balance across vessel walls

E. Transport glucose to brain cells

c

High altitude adaptation, chronic hypoxia, and anemia trigger an INCREASE in which intra-erythrocytic metabolite to promote oxygen delivery?

A. Methemoglobin

B. Glucose-6-phosphate

C. 2,3-BPG

D. Succinyl-CoA

E. Glutathione