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Metabolism > Carbohydrates- Pentose Phosphate Pathway > Flashcards

Carbohydrates- Pentose Phosphate Pathway Flashcards

1
Q

What is the pentose phosphate pathway?

A
  • Alternative pathway of glucose metabolism
  • Distinct from glycolysis
  • Does not produce ATP
  • Does not oxidise glucose completely
  • Cytosolic pathway in all cells
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2
Q

What does the pentose phosphate pathway generate?

A
  • Pentose (5C) phosphates for the synthesis glucose-6-phosphate
  • NADPH (from NADP+)
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3
Q

At what point in glycolysis does the PPP branch from?

A
  • glucose-6-phosphate
  • Hexose monophosphate shunt
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4
Q

How can PPP intermediates be recycled into mainstream of glycolysis?

A
  • Conversion of intermediates into fructose-6-phosphate or glyceraldehyde-3-phosphate
  • Important for RBC and quiescent cells with little need for DNA and RNA
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5
Q

How much glucose within RBC is shunted through PPP and why?

A
  • About 10%
  • Generate NADPH for reduction of glutathione (GSH is an essential molecule for antioxidant defence)
  • Allows anabolic and catabolic reactions to occur simultaneously
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6
Q

What type of cells undergo PPP?

A
  • All types including RBC
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7
Q

What is the difference between NADPH and NADH?

A
  • Addition of phosphate group
  • No effect on electron carrier capability of either molecule
  • NAD- catabolic - NADP- anabolic
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8
Q

What is the purpose of the phosphate group on NADPH?

A
  • To distinguish the molecules and allow them to interact with different sets of enzymes
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9
Q

What is the purpose of having both NAD and NADP?

A
  • At any given time- single cell can have access to both oxidising and reducing agents for both anabolic and catabolic reactions
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10
Q

What is the first stage of PPP?

A
  • An irreversible redox stage
  • Yields NADPH and pentose phosphates
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11
Q

What is the second stage of PPP?

A
  • Reversible interconversion stage
  • Excess pentose phosphates converted to glycolytic intermediates
  • Only used when NADPH is needed but not pentose phosphate, e.g. RBC
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12
Q

What does the non-oxidative stage do?

A
  • Recycles excess pentose phosphates into glycolysis intermediates
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13
Q

What enzyme is used to divert glucose-6-phosphate molecule down oxidative stage of PPP?

A

Glucose-6-phosphate dehydrogenase

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14
Q

What does the final reaction of redox produce?

A

Ribulose-5-phosphate (5 carbon sugar)

  • In cells with active nucleic acid synthesis, ribulose-5-phosphate is isomerism to ribulose-5-phosphate
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15
Q

What is ribose-5-phosphate used for?

A
  • Used for synthesis ribo and deoxyribo- nucleotides for DNA and RNA
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16
Q

What is a transaldolase deficiency?

A
  • Abnormally low levels of transaldolase enzyme involved in interconversion stage of PPP
  • Autosomal recessive (very rare- consanguineous)
17
Q

How does a transaldolase deficiency present?

A
  • Growth retardation
  • Dysmorphic features
  • Cutis laxative’s
  • Congenital heart disease
  • Hepatosplenomegaly
  • Pancytopenia
  • Bleeding tendency
  • Non-specific features means often misdiagnosed
  • no treatment
18
Q

What is reduced glutathione?

A
  • Tripeptide composed of 3 different amino acids
  • Glutamate, cysteine and glycine
  • Acts as scavenger for dangerous oxidative metabolites within cell
19
Q

What does NADPH do in the red blood cell?

A
  • Reduces glutathione
  • Results in harmful peroxide converting to water
20
Q

What is Glucose-6-phosphate dehydrogenase deficiency?

A
  • Causes haemolytic anaemia
  • RBC destroyed faster than bone marrow produces them
  • X-linked recessive
  • More common in people living in malaria-prevalent areas
  • Changes G6PD shape making it not fully active
21
Q

What is the role of G6PD in the cell?

A
  • Maintains adequate levels of NADPH
  • In RBC, NADPH responsible for reducing GSSG to GSH
  • Without it RBC unable to neutralise peroxide (Strong oxidant) that will degrade RBC and cause haemolysis without reduction
  • Can be found in oxidative drugs, fava beans
22
Q

What is the clinical presentation of G6PD deficiency?

A
  • Neonatal jaundice- insufficient activity in liver
  • Haemolytic anaemia
  • Oxidative stress
  • Symptoms- fatigue, paleness, rapid heart rate, yellow skin, dark urine
23
Q

What is haemolytic anaemia?

A
  • Oxidative stress may result in denaturation of haemoglobin
  • Results in loss of function and inability of RBC to effectively transport oxygen around body
  • RBCs often prematurely destroyed
24
Q

What does treatment for G6PD deficiency depend on?

A
  • Discontinue oxidising drugs
  • Change diet
  • Blood transfusion

Metabolism (9 decks)

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