erythrocyte metabolsim

a

What is the average lifespan of a mature red blood cell in human circulation?

A. 120 days

B. 90 days

C. 60 days

D. 30 days

E. 150 days

b

Which process represents a passive metabolic function of the RBC requiring no energy expenditure?
A. Maintenance of skeletal protein deformability
B. Transport of O2 and CO2 gases
C. Glutathione synthesis
D. Intracellular cationic gradient maintenance
E. Nucleotide salvage reactions

c

What transmembrane protein is responsible for facilitating glucose entry into the RBC cytosol without energy consumption?

A. Band 3

B. Aquaporin 1

C. Glut-1

D. Glycophorin A

E. RhAG

d

How many net ATP molecules are generated from one molecule of glucose via the Embden-Meyerhof pathway?

A. 4 ATP

B. 1 ATP

C. 3 ATP

D. 2 ATP

E. 0 ATP

e

What percentage of RBC glucose catabolism normally enters the Hexose Monophosphate (HMP) pathway during steady-state conditions?

A. 1% to 2%

B. 20% to 30%

C. 50% to 60%

D. 80% to 90%

E. 5% to 10%

a

Which rate-limiting enzyme regulates the first step of the Hexose Monophosphate shunt?

A. Glucose-6-phosphate dehydrogenase (G6PD)

B. Hexokinase

C. Pyruvate kinase

D. Phosphofructokinase

E. Methemoglobin reductase

b

What key reduced cofactor is generated by the HMP pathway to protect RBC proteins from oxidative degradation?

A. NADH

B. NADPH

C. FADH2

D. ATP

E. 2,3-BPG

c

What state of iron (Fe) is required for hemoglobin to successfully bind oxygen?
A. Ferric state (Fe^3+)
B. Elemental state (Fe^0)
C. Ferrous state (Fe^2+)
D. Ferrate state (Fe^4+)
E. Hydroxide complex

d

Which enzyme provides more than 65% of the capacity to convert ferric iron back to ferrous iron in RBCs?
A. Glutathione peroxidase
B. Glucose-6-phosphate dehydrogenase
C. Bisphosphoglycerate mutase
D. Cytochrome b_5 methemoglobin reductase
E. Triosephosphate isomerase

e

What is the primary functional consequence of 2,3-BPG binding to hemoglobin?

A. Increases hemoglobin affinity for oxygen

B. Prevents oxidation of membrane lipids

C. Drives glucose uptake by Glut-1

D. Inhibits anaerobic glycolysis

E. Enhances oxygen delivery to peripheral tissues

a

What enzyme diverts 1,3-BPG to generate 2,3-BPG in the Rapoport-Luebering pathway?

A. Bisphosphoglycerate mutase

B. Phosphoglycerate kinase

C. Enolase

D. Pyruvate kinase

E. Aldolase

b

Approximately what proportion of the RBC membrane composition by weight is composed of proteins?

A. 40%

B. 52%

C. 8%

D. 25%

E. 70%

c

Which two phospholipids predominate in the outer layer of the RBC membrane lipid bilayer?

A. Phosphatidylserine and Phosphatidylethanolamine

B. Phosphatidylinositol and Phosphatidylglycerol

C. Phosphatidylcholine and Sphingomyelin

D. Cholesterol and Glycolipids

E. Cardiolipin and Glycophorin

d

Exposure of which membrane phospholipid on the outer RBC surface signals splenic macrophages to destroy senescent red blood cells?

A. Phosphatidylcholine

B. Sphingomyelin

C. Glycolipid

D. Phosphatidylserine

E. Phosphatidylethanolamine

e

What type of membrane lipid comprises approximately 5% of the total membrane lipid weight and anchors carbohydrate chains extending into the extracellular space?

A. Phosphatidylcholine

B. Unesterified cholesterol

C. Sphingomyelin

D. Phosphatidylserine

E. Glycolipids

a

Which transmembrane protein serves as the primary anion transporter in the RBC membrane, exchanging \text{HCO}_3^- for \text{Cl}^-?
A. Band 3
B. Glycophorin A
C. Aquaporin 1
D. RhAG
E. Glut-1

b

Which sialic acid-rich transmembrane protein provides the RBC surface with a negative charge and carries MN blood group antigens?

A. Band 3

B. Glycophorin A

C. ICAM-4

D. Glycophorin C

E. Kell

c

What method is standard for separating RBC membrane proteins according to their molecular weight?

A. High-Performance Liquid Chromatography (HPLC)

B. Agarose gel electrophoresis

C. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE)

D. Isoelectric focusing

E. Gas chromatography

d

What principal protein forms the backbone hexagonal lattice of the RBC membrane cytoskeleton?

A. Ankyrin

B. Actin

C. Protein 4.1

D. Spectrin

E. Adducin

e

Defects in vertical membrane protein linkages (such as mutations in ankyrin or Band 3) typically cause which RBC disorder?

A. Sickle cell anemia

B. Hereditary elliptocytosis

C. Acanthocytosis

D. Paroxysmal nocturnal hemoglobinuria

E. Hereditary spherocytosis

a

What structural defect is responsible for hereditary elliptocytosis?

A. Defect in horizontal cytoskeleton interactions (e.g., spectrin dimer self-association)

B. Complete absence of the Glut-1 transporter

C. Loss of total membrane cholesterol

D. Impaired G6PD enzymatic activity

E. Accumulation of intracellular calcium ions

b

A mutation in the gene PIGA causes a defect in the GPI anchor synthesis, leading to which acquired disorder?
A. Hereditary pyropoikilocytosis
B. Paroxysmal nocturnal hemoglobinuria
C. Glucose-6-phosphate dehydrogenase deficiency
D. Congenital dyserythropoietic anemia
E. Rh deficiency syndrome

c

What complement-inhibiting regulatory proteins are missing from the cell surface in Paroxysmal Nocturnal Hemoglobinuria?

A. Ankyrin and Protein 4.1

B. Glycophorin A and Glycophorin B

C. CD55 (DAF) and CD59 (MIRL)

D. Band 3 and Protein 4.2

E. Aquaporin 1 and Glut-1

d

What intracellular cation ratio (\text{Na}^+ to \text{K}^+) is maintained inside normal RBCs compared to plasma?
A. 1:1
B. 25:1
C. 10:1
D. 1:12
E. 1:50

e

What percentage of total RBC ATP production is consumed by cation active transport pumps (\text{Na}^+-\text{K}^+ ATPase and \text{Ca}^{2+}-ATPase)?
A. 5%
B. 50%
C. 30%
D. 25%
E. 15%

a

Accumulation of intracellular \text{Ca}^{2+} in RBCs due to ATPase pump failure leads to:
A. Cell swelling and membrane expansion
B. Loss of intracellular \text{K}^+ and water, causing cell dehydration and rigidity
C. Increased glucose consumption
D. Enhanced spectrin flexibility
E. Conversion of methemoglobin to oxyhemoglobin

b

What membrane protein complex bridges spectrin to Band 3 in the vertical linkage system?

A. Glycophorin A

B. Ankyrin complex (Ankyrin and Protein 4.2)

C. Actin junctional complex

D. Aquaporin 1

E. Stomatin

c

Which protein stabilizes the junctional complex connecting spectrin, actin, and tropomyosin?

A. Glut-1

B. RhAG

C. Protein 4.1

D. Aquaporin 1

E. Ankyrin

d

​An increase in membrane cholesterol relative to phospholipids leads to the formation of:

A. Spherocytes

B. Elliptocytes

C. Schistocytes

D. Acanthocytes or Target cells

E. Schizocytes

e

Glycophorin C carries the antigens for which blood group system?

A. MN

B. Ss

C. Kell

D. Duffy

E. Gerbich

a

How many times does the Rh protein span the lipid membrane?

A. 12 times

B. 1 time

C. 7 times

D. 2 times

E. 24 times

b

What component of the cytosolic red cell environment regulates the calcium pump via binding excess intracellular \text{Ca}^{2+}?
A. Calmodulin
B. Glutathione
C. Methemoglobin
D. Spectrin
E. Stomatin

c

Which enzyme converts 2-phosphoglycerate (2-PG) to phosphoenolpyruvate (PEP) in the glycolytic pathway?

A. Pyruvate kinase

B. Phosphoglycerate mutase

C. Enolase

D. Hexokinase

E. Aldolase

d

What is the main function of reduced glutathione (GSH) in the RBC?
A. Transport anions across the membrane
B. Drive ATP production
C. Anchor spectrin to actin
D. Neutralize intracellular peroxides and cellular oxidants
E. Maintain intracellular \text{K}^+ levels

e

Which protein anchors the actin filaments at the junctional complex in the RBC membrane?

A. Band 3

B. Ankyrin

C. Glycophorin A

D. Aquaporin 1

E. Tropomodulin and Adducin

a

What happens to the mean corpuscular hemoglobin concentration (MCHC) when an RBC loses membrane area relative to its volume?
A. MCHC increases above normal limits (>36\%)
B. MCHC decreases significantly
C. MCHC remains unchanged at 10%
D. MCHC drops to zero
E. MCHC fluctuates randomly

b

What molecule is formed when 6-phosphogluconate is oxidized by 6-phosphogluconate dehydrogenase in the HMP pathway?

A. Glucose-6-phosphate

B. Ribulose 5-phosphate

C. Fructose 1,6-bisphosphate

D. Glyceraldehyde 3-phosphate

E. Lactic acid

c

The Duffy blood group antigen system is located on which functional protein?

A. Anion transporter Band 3

B. Glucose transporter Glut-1

C. A G-protein-coupled chemokine receptor

D. Sialic acid transport system

E. Urea transporter protein

d

What is the structural conformation of the spectrin heterodimer?
A. Parallel \alpha\alpha homodimer
B. Parallel \beta\beta homodimer
C. Circular tetramer
D. Antiparallel \alpha and \beta heterodimer
E. Globular monomer

e

What clinical term describes red blood cells with irregular membrane projections resulting from altered cholesterol-to-phospholipid ratios?

A. Spherocytes

B. Elliptocytes

C. Schistocytes

D. Stomatocytes

E. Acanthocytes

a

Which enzyme catalyzes the initial ATP-consuming reaction of the Embden-Meyerhof pathway converting glucose to G6P?

A. Hexokinase

B. Phosphofructokinase

C. Pyruvate kinase

D. Phosphoglycerate kinase

E. Triosephosphate isomerase

b

What enzyme converts oxidized glutathione (GSSG) back to reduced glutathione (GSH)?

A. Glutathione peroxidase

B. Glutathione reductase

C. Methemoglobin reductase

D. Glucose-6-phosphate dehydrogenase

E. Lactate dehydrogenase

c

Which of the following proteins is classified as a skeletal (peripheral) protein rather than a transmembrane (integral) protein?

A. Band 3

B. Glycophorin A

C. Ankyrin

D. Aquaporin 1

E. Glut-1

d

What organ's microenvironment tests red cell deformability and traps rigid, senescent RBCs?

A. Liver

B. Kidney

C. Bone marrow

D. Spleen

E. Thymus

e

What protein mediates water transport across the erythrocyte membrane?

A. Band 3

B. Glut-1

C. RhAG

D. ICAM-4

E. Aquaporin 1

a

What product is generated alongside NADPH in the reaction catalyzed by G6PD?

A. 6-Phosphogluconolactone (6-PG)

B. Fructose 6-phosphate

C. Pyruvate

D. Glyceraldehyde 3-phosphate

E. 2,3-Bisphosphoglycerate

b

In the second phase of glycolysis, what enzyme converts G3P into 1,3-BPG?

A. Aldolase

B. Glyceraldehyde-3-phosphate dehydrogenase (G3PD)

C. Phosphoglycerate kinase

D. Pyruvate kinase

E. Enolase

c

What structural feature of spectrin repeat domains provides the elastic recoil ability to the RBC membrane?

A. Beta-pleated sheets

B. Triple-helical repeat units unfolding and refolding

C. Triple-stranded collagen fibers

D. Random coil disulfides

E. Lipid hydrophobic anchors

d

Which skeletal membrane protein binds \beta-spectrin to regulate actin filament length?
A. Band 3
B. Protein 4.2
C. Ankyrin
D. Tropomyosin
E. Aquaporin 1

e

What is the fate of excess intracellular pyruvate under anaerobic conditions in human erythrocytes?

A. Oxidation in the citric acid cycle

B. Transamination to alanine

C. Conversion to acetyl-CoA

D. Phosphorylation to PEP

E. Reduction to lactate by lactate dehydrogenase