Chapter 26: The Pentose Phosphate Pathway Flashcards
Pentose Phosphate Pathway consists of two phases:
- ) Oxidative generation of NADPH
2. ) Non-oxidative interconversion of sugars
The Pentose Phosphate Pathway yields…
NADPH and 5-Carbon Sugars
NADPH is the source of _____ in all organisms.
Biosynthetic reducing power (Delivers electrons for biosynthetic pathways)
Pentose Phosphate Pathway takes place in the _____.
Cytoplasm
Second step of Pentose Phosphate Pathway. Give:
- Enzymes
- Catalyst
- If any product is generated
6-Phosphoglucono-delta-lactone –> 6-Phosphogluconate
-Converted by Lactonase
Third step of Pentose Phosphate Pathway. Give:
- Enzymes
- Catalyst
- If any product is generated
6-Phosphogluconate –> Ribulose 5-Phosphate
- Converted by 6-Phosphogluconate Dehydrogenase
- Generates NADPH and CO2 (6C–>5C)
Fourth step of Pentose Phosphate Pathway. Give:
- Enzymes
- Catalyst
- If any product is generated
Ribulose 5-Phosphate –> Ribose 5-Phosphate
-Isomerized by Phosphopentose Isomerase
Pentose Phosphate Pathway and Glycolysis are linked by _____ and _____.
Transketolase and Transaldolase
The non-oxidative phase consists of 3 reactions: Reaction 1?
C5 + C5 C3 + C7
By transketolase
The non-oxidative phase consists of 3 reactions: Reaction 2?
C3 + C7 C6 + C4
By transaldolase
The non-oxidative phase consists of 3 reactions: Reaction 3?
C4 + C5 C6 + C3
By transketolase
Fifth step of Pentose Phosphate Pathway. Give:
- Enzymes
- Catalyst
- If any product is generated
Ribulose 5-Phosphate –> Xylulose 5-Phosphate
-Converted by Phosphopentose epimerase (Rearrangement)
The net result of the non-oxidative reactions is the conversion of _____ into _____ and _____.
3 Pentoses –> Two Hexoses and One Triose
3C5 2C6 + C3
Reaction 1 of the non-oxidative phase
Xylulose 5-Phosphate + Ribose 5-Phosphate –> Glyceraldehyde 3-Phosphate + Sedoheptulose 7-Phosphate
-By transketolose
Reaction 2 of non-oxidative phase
Glyceraldehyde 3-phosphate + Sedoheptulose 7-Phosphate –> Fructose 6-Phosphate + Erythrose 4-Phosphate
-By transaldolase
Reaction 3 of non-oxidative phase
Erythrose 4-phosphate + Xylulose 5-phosphate –> Fructose 6-phosphate + Glyceraldehyde 3-phosphate
-By transketolase
The sum of the reactions catalyzed by the epimerase…
3 Ribose 5-phosphate –> 2 fructose 6-phosphate + Glyceraldehyde 3-phosphate
The rate of the pentose phosphate pathway is controlled by _____.
NADP+ Levels
Which reaction is the rate-limiting step of the Pentose Phosphate Pathway?
The first reaction: Glucose 6-phosphate –> 6 Phosphoglucono-delta-lactone
-By glucose 6-phosphate dehydrogenase
The most important regulatory factor is the concentration of _____.
NADP+
The fate of glucose 6-phosphate depends on the need for _____, _____ and _____.
NADPH, Ribose 5-phosphate and ATP
The Pentose Phosphate Pathway can operate in 4 distinct modes that result from various combos of the oxidative phase, nonoxidative phase, glycolysis, and gluconeogenesis. What is #1?
Ribose 5-phosphate needs exceed the needs for NADPH
The Pentose Phosphate Pathway can operate in 4 distinct modes that result from various combos of the oxidative phase, nonoxidative phase, glycolysis, and gluconeogenesis. What is #2?
The NADPH and ribose 5-phosphate needs are balanced
The Pentose Phosphate Pathway can operate in 4 distinct modes that result from various combos of the oxidative phase, nonoxidative phase, glycolysis, and gluconeogenesis. What is #3?
More NADPH is needed than ribose 5-phosphate
The Pentose Phosphate Pathway can operate in 4 distinct modes that result from various combos of the oxidative phase, nonoxidative phase, glycolysis, and gluconeogenesis. What is #4?
NADPH and ATP are both required
**Mode 1. Ribose 5-phosphate needs exceed the needs for NADPH
Non-oxidative phase of PPP converts 2 Fructose 6-phosphate and 1 Glyceraldehyde 3-phosphate into 3 Ribose 5-phosphate
Mode 2. The NADPH and ribose 5-phosphate needs are balanced
*Oxidative
Glucose 6-phosphate –> 2 NADPH and 1 Ribose 5-phosphate
Intermediate: Ribulose 5-phosphate
Mode 3. More NADPH is needed than ribose 5-phosphate.
3 steps:
- Oxidative phase forms 2 NADPH and 1 Ribose 5-phosphate
- Non-oxidative phase converts ribose 5-phosphate to fructose 6-phosphate and glyceraldehyde 3-phosphate
- Glycolysis converts fructose 6-phosphate and glyceraldehyde 3-phosphate to pyruvate, which can be oxidized to generate ATP
First Step of Pentose Phosphate Pathway. Give:
- Enzymes
- Catalyst
- Any products generated
Glucose 6 Phosphate –> 6-phosphoglucono-delta-lactone
- Converted by Glucose 6-phosphate dehydrogenase
- Reduces NADP+ to NADPH
The pentose phosphate pathway is very important for preventing damage from reactive oxygen species (ROS) and a deficiency in glucose 6-phosphate dehydrogenase leads to:
- hyperglycemia.
- hemolytic anemia.
- type 1 diabetes.
- Beriberi.
- vitamin deficiency.
Hemolytic anemia
T or F: The non-oxidative phase requires the enzymes transaldolase and transketolase.
True
T or F: PPP produces 5 GTP per glucose entering the pathway.
False
T or F: The non-oxidative phase involves the interconversion of sugars.
True
T or F: PPP contains two ATP-consuming steps.
False
T or F: PPP takes place in the mitochondrial matrix.
False
The pentose phosphate pathway operates in four distinct modes. Mode 2 is active when the need for NADPH and ribose 5-phosphate are balanced. Which pathway(s) operate during Mode 2?
- Oxidative phase only.
- Non-oxidative phase only.
- Oxidative phase → non-oxidative phase → gluconeogenesis.
- Oxidative phase → non-oxidative phase → glycolysis.
- Non-oxidative phase → citric acid cycle.
Oxidative Phase only
