Lecture 22: The Pentose Phosphate Pathway Of Hate

Question 1

What is the pentose phosphate pathway?

Answer 1

• Alternate pathway for the oxidation of glucose
• Synthesizes pentoses, e.g., ribose and deoxyribose
• Produces NADPH needed for reductive biosynthesis, e.g., cholesterol synthesis
• Initial step is rate limiting –Glucose 6-phophate dehydrogenate

Question 2

What is favism?

Answer 2

• There is An X-linked recessive disorder – enzyme deficiency
• Also called favism
• Affects hundreds of millions of people
• Causes hemolytic anemia because of deficient levels of NADPH in red cells
• Altered G6PD produces low levels of NADPH, leading to low levels of reduced glutathione in red cells
• Reduced glutathione is needed to maintain healthy red cell membranes

Question 3

Stare the shit outta slide 5

Answer 3

Yeah. What up?

Question 4

What is the significance of a G6PD deficiency

Answer 4

• Coincides with prevalence of Malaria

* May impart some degree of malaria resistance –E.g. sickle cell anemia

Question 5

Need to memorize step 1 of the PPP

Answer 5

• Initial step is rate limiting
  – Glucose 6-phophate dehydrogenate
  – Oxidative phase
• Wouldn’t hurt to know the next 3 steps afterwards either.

Question 6

Know the final product of oxidative and nonoxidative PPP

Answer 6

See slide 9

Question 7

Describe Mode 1 of the PPP

Answer 7

• Much more ribose 5-phosphate than NADPH is required

- And also should study in deeper detail. (Slide 10)

Question 8

When does Mode 2 of the PPP occur?

Answer 8

• Mode 2. The needs for NADPH and for ribose 5-phosphate are balanced.
• And also, draw dat shit.

Question 9

Describe Mode 3 of the PPP

Answer 9

• Much more NADPH than ribose 5-phosphate is required

- And as usual, blah, blah, know that too.

Question 10

Describe Mode 4 of the PPP

Answer 10

Both NADPH and ATP are required
- Don’t they mean produced? Cuz according to that picture, that’s what’s produced, not required.

• See Slide 14

Question 11

Describe the male to female ration of G6PD deficiencies

Answer 11

• Male cases are over represented compared with female cases
• Males are hemizygous for the G6PD gene; therefore the expression is either normal or deficient
• In contrast, in females who have two copies of the gene on each chromosome, the gene expression can be normal, or heterozygous.
• Homozygous inheritance in females can occur; whereas heterozygous females have genetic mosaicism secondary to X-chromosome inactivation and can have a similar manifestation as male neonates.

Question 12

What happens in a G6PD deficiency

Answer 12

• Glucose 6 Phosphate dehydrogenase deficiency impairs the ability of an erythrocyte to form NADPH, resulting in hemolysis.
• See Slide 16
• Also see Slide 17 for information about the disproportion between men and female prevalence of this deficiency.

Question 13

Which PPP path occurs when there is a cellular need for NADPH only?

Answer 13

• Oxidative Reaction –> NADPH
• Nonoxidative reactions generate: Fructose 6-P, which is converted to G6P, which can be used to produce more NADPH if needed.

Question 14

Which PPP path occurs when there is a cellular need for both NADPH and ribose 5-P

Answer 14

• Oxidative Reaction –> NADPH

* Nonoxidative Reaction –> Ribose 5-P

Question 15

What PPP pathway occurs when there is a cellular need for only Ribose 5-P?

Answer 15

Oxidative Reactions: Don’t really occur, or aren’t operating

Nonoxidative Reactions: Produce glycolysis intermediates that are converted into ribose 5-P

Question 16

What PPP path occurs when there is a cellular need for NADPH and pyruvate (energy)

Answer 16

Oxidative Reaction –> NADPH

Nonoxidative Reaction: Produces glycolysis intermediates that are converted into energy.