Pentose Phosphate Pathway (exam 3)

What is the first stage in the PPP?

In step 1, glucose-6-phosphate dehydrogenase transfers a hydride from c1 of G6P to NAPH+ to form 6-phosphoglucono-delta-lactone

What does the first step of the PPP produce?

NADPH

The enzyme Glucose-6-phosphate dehydrogenase is regulated by what in the PPP?

Regulated or inhibited by NADPH; if you have a bunch of NADPH, why make more?

What role does the enzyme 6-phosphogluconolactonase have in the oxidative stage of the PPP?

-It hydrolyzes 6 phosphoglucono-delta-lactone (opens the ring) to form 6-phosphogluconate

What role does the enzyme 6-phosphogluconate dehydrogenase have in the oxidative stage of the PPP?

-it oxidatively decarboxylates 6-phosphogluconate to Ribulose-5-phosphate (Ru5P)

How many NADPH molecules are generated in the oxidative reaction of the PPP, what else is produced?

2 NADPH molecules

-CO2

What is yield per glucose-6-phosphate in the PPP?

2 NADPH and 1 Ribulose-5-phosphate

Which amino acid is associated with the enzyme 6-phosphogluconolactonase?

Histidine. Acts as a general base catalysis to help deprotonate a water molecule. The OH- will act as the nucleophile that will attack the carbonyl carbon of the lactone ring

Which amino acids is associated with the enzyme 6-phosphogluconate dehydrogenase in the PPP?

-Lysine and Glutamate

After the phase 1, oxidative stage, of the PPP, what is involved in stage 2?

Ribulose-5-phosphate (Rub5P) is converted into Ribose-5phosphate (R5P) and Xylulose-5-phosphate (Xu5P)

Which enzyme is involved in the conversion of Ribuolse-5-phosphate to Ribose-5-phosphate?

Ribulose-5-phophate isomerase

Which enzyme is involved in the conversion of Ribulose-5-phosphate into Xylulose-5-phosphate?

Ribulose-5-phosphate epimerase

Is ribulose a ketone or aldose sugar?

ketone

Is ribose a ketone or aldose sugar?

aldose

Is xylulose a ketone or aldose sugar?

ketone sugar

Which intermediate does Ribulose-5-phosphate go through to become Xu5P or R5P?

Enediolate intermediate

What is stage 3 of the PPP?

carbon rearrangements; just moving stuff around

What role does the enzyme Transketolase have in the PPP?

Transketolase transfers C2 units using the cofactor TPP (lightsaber)

What is the role of Thiamine pyrophosphate (TPP) in the PPP?

TPP serves as a cofactor for transketolase. It stabilizes a reactive carbanion intermediate and carries a 2-carbon fragment from one sugar phosphate to another during carbon rearrangements in the nonoxidative phase of the pentose phosphate pathway.

What role does the Transaldose enzyme have in the PPP?

Transaldolase transfers a C3 unit from S7P to GAP, producing F6P and erythrose-4 phosphate (E4P)

What are the end products of the nonoxidative phase of the PPP?

fructose-6-phosphate and glyceraldehyde-3-phosphate for glycolysis

What is the purpose of NADPH generated from the PPP?

NADPH is used in anabolic (building) reactions and protection against oxidative damage.

What is the purpose of Ribose-5-phosphate that is generated from the PPP?

Ribose-5-phosphate provides the 5-carbon sugar backbone for nucleotides.

Why does the PPP exist?

it exists to produce:

1. NADPH → reducing power

2. Ribose-5-phosphate → nucleotide synthesis

Which enzyme regulates the PPP?

Glucose-6-phosphate dehydrogenase

What activates the PPP and what inhibits the PPP?

-High levels of NADP+ activate the PPP by binding to G6PD
-High levels of NADPH inhibit the PPP because the cell already has enough reducing power

What occurs when Ribose-5-phosphate is not needed?

It is converted to Fructose-6-phosphate and Glyceraldehyde-3-phosphate for glycolysis

What occurs when Ribose-5-phosphate is greater than the need for NADPH?

F6P and G3P are siphoned from glycolysis and used to make R5P by reversal of the transaldolase and transketolase reactions

What intermediates do transketolase and transaldolase go through?

carboanions

Which enzyme in the PPP is the rate limiting step and why?

enzyme Glucose-6-phosphate dehydrogenase

-inhibited when NADPH is abundant and activated when NADP+ is abundant

-high NADPH decreases PPP

-high NADP+ increases PPP

What occurs if ribose-5-phosphate is not need in the PPP?

Ribose-5-phosphate is redirected to glycolysis by converting into fructose-6-phosphate and glucose-3-phosphate