Pentose Phosphate Pathway

Question 1

Pentose Phosphate Pathway

Answer 1

• part of carbohydrate metabolism
• occurs in cytoplasm of all cells
• no ATP is consumed or produced
• as glucose begins to go through glycolysis, some is shunted away and goes to this pathway

Question 2

What are the two functions of this pathway?

Answer 2

• production of NADPH (functions in donating electrons which is important in anabolic reactions)
• production of pentose sugar (ribose 5-phosphate) which is a substrate involved in nucleotide synthesis

Question 3

What are the two big phases of this pathway?

Answer 3

1. oxidative phase

2. nonoxidative phase

Question 4

Oxidative Phase

Answer 4

• begins with glucose 6-phosphate and ends with ribulose 5-phosphate
• irreversible
• major product is NADPH
• rate-limiting enzyme: glucose 6-phosphate dehydrogenase

Question 5

Glucose 6-Phopshate Dehydrogenase

Answer 5

• enzyme that converts glucose 6-phosphate to 6-phosphogluconate while reducing NADP+ to NADPH
• activated by insulin and NADP+
• inhibited by NADPH

Question 6

Non-Oxidative Phase

Answer 6

• begins with ribulose 5-phosphate which can be broken down by an isomerase into ribose 5-phosphate
• allows for interconversion of various sugars that can be used in biosynthesis
• intermediates of this phase can feed into glycolysis (ex. fructose 6-phosphate, glyceraldehyde 3-phosphate)
• reversible

Question 7

NAD+

Answer 7

• much more of this form in the body compared to the reduced form (NADH)
• high energy electron acceptor
• potent oxidizing agent because it helps another molecule get oxidized while being reduced in the process

Question 8

NADPH

Answer 8

• much more of this form in the body compared to the oxidized form (NADP+)
• acts as an electron donor
• potent reducing agent because it helps other molecules get reduced while being oxidized in the process
• 3 primary functions: involvement in biosynthesis of lipids and cholesterol (precursor to steroid hormones), assist in cellular bleach production in white blood cells (contributes to bactericidal activity), maintains supply of reduced glutathione

Question 9

Glutathione

Answer 9

• reducing agent
• can help reverse free radical formation which prevents these free radicals from damaging DNA or lipids in the cell membrane