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Midterm 4
Lecture 26: Pentose Phosphate Pathway
Questions:
What is the pentose phosphate pathway?
Catalyzes the exchange of 3C and 6C intermediates from glycolysis with 5C
sugars
What does the PPP generate?
NADPH
What is essential for DNA and RNA and how does that relate to PPP?
5C sugars and this pathway allows cells to utilize 5C sugars in food
What is the PPP also called?
Phosphogluconate pathway
Hexone monophosphate shunt
Pentose phosphate shunt
What are pathways with NADPH?
Fatty acid
Cholesterol
Neurotransmitter
Nucleotide
Cytochrome P450
Reduction of oxidized glutathione
What are the 2 phases of the pentose phosphate pathway?
Midterm 4 1
, Oxidative and nonoxidative
What is the oxidative phase?
3 reactions
G6P → R5P (generates NADPH and CO2)
What is the nonoxidative phase?
4 reactions
Interconverts ribulose to ribose, 3C, 4C, 6C, and 7C
Where does the PPP take place?
Cytoplasm
What is G6P dehydrogenase?
Oxidation of G6P to 6PL
Generates NADPH
Committed step
What does lactonase do?
Hydrolyzes 6PL into 6PG
What does 6 Phosphogluconate dehydrogenase do?
Generates R5P and generates NADPH and CO2
What is phosphopentose isomerase?
Nonoxidative
Ribulose5P to Ribose5P(precursor for nucleotides)
What do you do when cells need more NADPH than ribose?
Ribose converted to G3P and F6P
What is transketolase and transaldolase?
Moves 2C units
Moves 3C units
How is xylulose5P made?
Midterm 4 2
, From Ribulose5P by phosphopentose epimerase
What steps are irreversible in PPP?
Only first step in oxidative phase
How is G6P DH regulated?
Amounts of NADP+(high) and NADPH(low)
What does the nonoxidative phase do?
In equilibrium and flux determined by cell needs
What is mode 1?
Rapid growth
Need R5P > NADPH
Glycolysis predominates and nonoxidative used to make R5P
5 G6P + ATP → R5P + ADP + H+
What is mode 2?
Oxidative phase used to make NADPH and R5P
G6P + 2 NADP+ + H2O → R5P + 2 NADPH + H+ + CO2
What is mode 3?
Need NADPH > R5P
Synthesis of FA in liver
Oxidative makes NADPH
Nonoxidative makes F6P and G3P → G6P
G6P → CO2 + NADPH
Complete oxidation of glucose to NADPH
G6P + 12 NADP+ + 7 H2O → 6 CO2 + 12 NADPH + 12 H+ + Pi
When do cells operate in mode 3?
When they need high levels of NADPH
What is mode 4?
Midterm 4 3
Midterm 4
Lecture 26: Pentose Phosphate Pathway
Questions:
What is the pentose phosphate pathway?
Catalyzes the exchange of 3C and 6C intermediates from glycolysis with 5C
sugars
What does the PPP generate?
NADPH
What is essential for DNA and RNA and how does that relate to PPP?
5C sugars and this pathway allows cells to utilize 5C sugars in food
What is the PPP also called?
Phosphogluconate pathway
Hexone monophosphate shunt
Pentose phosphate shunt
What are pathways with NADPH?
Fatty acid
Cholesterol
Neurotransmitter
Nucleotide
Cytochrome P450
Reduction of oxidized glutathione
What are the 2 phases of the pentose phosphate pathway?
Midterm 4 1
, Oxidative and nonoxidative
What is the oxidative phase?
3 reactions
G6P → R5P (generates NADPH and CO2)
What is the nonoxidative phase?
4 reactions
Interconverts ribulose to ribose, 3C, 4C, 6C, and 7C
Where does the PPP take place?
Cytoplasm
What is G6P dehydrogenase?
Oxidation of G6P to 6PL
Generates NADPH
Committed step
What does lactonase do?
Hydrolyzes 6PL into 6PG
What does 6 Phosphogluconate dehydrogenase do?
Generates R5P and generates NADPH and CO2
What is phosphopentose isomerase?
Nonoxidative
Ribulose5P to Ribose5P(precursor for nucleotides)
What do you do when cells need more NADPH than ribose?
Ribose converted to G3P and F6P
What is transketolase and transaldolase?
Moves 2C units
Moves 3C units
How is xylulose5P made?
Midterm 4 2
, From Ribulose5P by phosphopentose epimerase
What steps are irreversible in PPP?
Only first step in oxidative phase
How is G6P DH regulated?
Amounts of NADP+(high) and NADPH(low)
What does the nonoxidative phase do?
In equilibrium and flux determined by cell needs
What is mode 1?
Rapid growth
Need R5P > NADPH
Glycolysis predominates and nonoxidative used to make R5P
5 G6P + ATP → R5P + ADP + H+
What is mode 2?
Oxidative phase used to make NADPH and R5P
G6P + 2 NADP+ + H2O → R5P + 2 NADPH + H+ + CO2
What is mode 3?
Need NADPH > R5P
Synthesis of FA in liver
Oxidative makes NADPH
Nonoxidative makes F6P and G3P → G6P
G6P → CO2 + NADPH
Complete oxidation of glucose to NADPH
G6P + 12 NADP+ + 7 H2O → 6 CO2 + 12 NADPH + 12 H+ + Pi
When do cells operate in mode 3?
When they need high levels of NADPH
What is mode 4?
Midterm 4 3
