Tag: Rapoport- Leubering Cycle

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



Rapoport- Leubering Cycle

Rapoport- Leubering Cycle


  • Rapoport- Leubering Cycle occurs in RBCs (erythrocytes).

  • In this cycle, 1,3 – BPG is converted into 2, 3 –BPG by an enzyme biphosphoglycerate  mutase.
  • 2,3- BPG is then converted into 3- phosphoglycerate by enzyme 2,3- biphosphoglycerate phosphatase. 

Significance of Rapaport- Leubering Cycle-

  • The 2, 3 – BPG combines with haemoglobin and reduces the affinity towards oxygen. So, its presence has oxyhemoglobin unloads more oxygen to the tissues.
  • 2,3BPG shifts the oxygen Dissociation curve to right.
  • If the glycolysis of RBCs is impaired there will be impaired synthesis of 2, 3 – BPG  which causes left shift of O2  dissociation curve and increase oxygen affinity of haemoglobin.
  • Under hypoxic, high altitude, fetal tissues, anaemic condition the 2, 3- BPG concentration in the RBC increases.

Exam Important

  • Rapoport Leubering cycle occurs in erythrocytes
  • 2, 3 –bisphosphoglycerate combines with hemoglobin & reduces affinity towards oxygen.
  • 2,3 BPG shifts the oxygen Dissociation curve to right due to reduced affinity towards oxygen
  • No ATP is generated (only one molecule generated through glycolysis in RBC utilized)
  • Under hypoxic conditions, 2, 3- BPG increases in RBCs
  • Cancer cells switching to glycolysis even in the presence of adequate O2 for oxidative phosphorylation c/d Warburg effect
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