Rapoport- Leubering Cycle

Rapoport Leubering cycle

Q. 1

The phenomenon of cancer cells switching to glycolysis even in the presence of adequate oxygen for oxidative phosphorylation is known as:

 A

Tyndall effect

 B

Warburg effect

 C

Hawthorne effect

 D

None of the above

Q. 1

The phenomenon of cancer cells switching to glycolysis even in the presence of adequate oxygen for oxidative phosphorylation is known as:

 A

Tyndall effect

 B

Warburg effect

 C

Hawthorne effect

 D

None of the above

Ans. B

Explanation:

Even in the presence of ample oxygen, cancer cells shift their glucose metabolism away from the oxygen hungry, but efficient, mitochondria to glycolysis.
This phenomenon, called the Warburg effect and also known as aerobic glycolysis, has been recognized for many years (indeed, Otto Warburg received the Nobel Prize for discovery of the effect that bears his name in 1931), but was largely neglected until recently.

This metabolic alteration is so common to tumors that some would call it the eighth hallmark of cancer.
             
Ref:
Robbins 8th edition Chapter 2.

Q. 2

Within the RBC, hypoxia stimulates glycolysis by which of the following regulating pathways?

 A

Hypoxia stimulates pyruvate dehydrogenase by increased 2,3 DPG

 B

Hypoxia inhibits hexokinase

 C

Hypoxia stimulates release of all glycolytic enzymes from band 3 on RBC membrane

 D

Activation of the regulatory enzymes by high PH

Q. 2

Within the RBC, hypoxia stimulates glycolysis by which of the following regulating pathways?

 A

Hypoxia stimulates pyruvate dehydrogenase by increased 2,3 DPG

 B

Hypoxia inhibits hexokinase

 C

Hypoxia stimulates release of all glycolytic enzymes from band 3 on RBC membrane

 D

Activation of the regulatory enzymes by high PH

Ans. C

Explanation:

During Hypoxia, the glycolytic enzymes that bind in the same region of band 3 of Hb are released from the membrane resulting in an increased rate of glycolysis. Increased glycolysis increases ATP production and the hypoxic release of ATP.
 
Ref: Oxygen Transport to Tissue, Xxxiii, edited by Martin Wolf, David K Harrison, 2012, Page 188.

Q. 3

Within the RBC, hypoxia stimulates glycolysis by which of the following regulating pathways?

 A

Hypoxia Stimulates pyruvate dehydrogenase by increased 2,3 DPG

 B

Hypoxia inhibits hexokinase

 C

Hypoxia stimulates release of all Glycolytic enzymes from Band 3 on RBC membrane

 D

Activation of the regulatory enzymes by high PH

Q. 3

Within the RBC, hypoxia stimulates glycolysis by which of the following regulating pathways?

 A

Hypoxia Stimulates pyruvate dehydrogenase by increased 2,3 DPG

 B

Hypoxia inhibits hexokinase

 C

Hypoxia stimulates release of all Glycolytic enzymes from Band 3 on RBC membrane

 D

Activation of the regulatory enzymes by high PH

Ans. C

Explanation:

C i.e. Hypoxia stimulates release of all glycolytic enzymes from Band 3 on RBC membrane

RBC membrane cytoskeletal protein spectrin is anchored to transmembrane anion exchanger protein Band 3 by protein ankyrin & protein 4.2. Another cytoskeletal protein actin is attached to transmembrane glycophorin C by protein 4.1. Tropomyosin, tropomodulin, adducin and 4.9 are other proteins.

  • Band 3, is a multifunction RBC transmembrane protein, which is important for its cytoskeletal structure, cell shape, anion exchange activity and glycolysisQ. Band 3 is responsible for chloride shift in RBCQ. Hypoxic deoxygenation of hemoglobin causes Band 3 tyrosine phosphorylation and thereby stimulates glycolysis by releasing glycolytic enzymes from band 3 on RBC membraneQ.
  • In kidney, I cells contain Band 3, an anion exchange protein in their basolateral cell membrane, which may function as a

Cl- – HCO3 exchanger for the transport of HCO3 to interstitial fluid.

  • In animal cells, principal regulators of intracellular pH are HCO3 transporters such as Band 3 CI – Hog; exchanger, 3Na+ – Hcq cotransporters and a le – HCO3 cotransporter.

Q. 4

Number of ATP produced by RBC when Glycolysis occurs through Rapoport Leubering pathway

 A

1

 B

2

 C

3

 D

4

Q. 4

Number of ATP produced by RBC when Glycolysis occurs through Rapoport Leubering pathway

 A

1

 B

2

 C

3

 D

4

Ans. A

Explanation:

 

Usually 2 ATP molecules are formed in glycolysis by substrate level phosphorylation.

Quiz In Between



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