BIOC 503 - Pentose Phosphate Pathway

hexose monophosphate shunt

other name for pentose phosphate pathway

NADPH

the main product of the pentose phosphate pathway is the electron carrier ___

• using __ allows to save NADH for the electron transport chain and insure maximal amount of ATP

• __ is also used in other biosynthetic pathways and for detoxification

specificity

the NADPH ___ is due to the added esterified phosphate group making it bigger and more negative/charged

• does not fit with anything but its own enzyme

• allows for electron carriers ___ and differentiation

oxidative phase

produces NADPH

non-oxidative phase

produces ribose 5 phosphate & return glycolysis intermediates (F6P & G3P)

glucose 6 phosphate dehydrogenase

step 1: Glucose-6-phosphate made into 6-phosphoglucconate

• reaction carried by ___ enzyme

• 6-phosphogluconate is the acid form of glucose

• reduces NADP to NADPH

6-phosphogluconate dehydrogenase

step 2: 6-phosphogluconate made into ribulose-5-phosphate

• reaction carried by the ___ enzyme

• releases CO2

• reduces NADP into NADPH

• main regulatory point

isomerase

enzyme of pentose pathway turning ribulose-5-phosphate into ribose-5-phosphate

epimerase

step 3: ribulose-5-phosphate made into xylulose-5-phosphate

• reaction carried by ___ enzyme

glyceraldehyde-3-phosphate

The glycolysis intermediate ___ is returned as a product of the reaction between xylulose-5-phosphate and ribose-5-phosphate.

• other product of this reaction = sedoheptulose 7 phosphate

• via transketolase

fructose 6 phosphate

the glycolysis intermediate ___ is returned as a product from the reaction of sedoheptulose-7-phosphate and glyceraldehyde-3-phosphate

• other product = erythrose-4-phosphate

• via transaldolase

nucleic acid

ribose-5-phosphate is also used for ____ synthesis

3

pentose pathway starts with at least __ G6P from glycolysis

• leads to __ NADPH formed (2 per molecule of G6P)

• leads to 2 F6P and 1 G3P being returned to glycolysis

5, 6

Because the pentose pathway uses 3 glucose-6-phosphate molecules, but only returns 2 fructose-6-phosphate & 1 glyceraldehyde-3-phosphate, it only ends up making __ net ATPs for 3 glucose molecules

• on the other end, glycolysis alone makes __ net ATPs from 3 glucose molecules

glucose 6 phosphate dehydrogenase

because of the pentose pathway, the enzyme ___ is allosterically inhibited by excess NADPH

high/excess

No G6P is diverted from glycolysis unless there is ___ glucose 

insulin

glucose-6-phosphate dehydrogenate gene is regulated by ___

• __ stimulates ATP production and biosynthetic pathways that use ATP (which also require NADPH and thus stimulate pentose pathway)

glutathione

The reduced form of ___ (2GSH) is used to eliminate reactive oxygen species (ROS).

• reduced form is used as H donor to reduce hydrogen peroxide (H2O2) which is the precursor to ROS, thus reducing it prevents ROS formation

hydrogen peroxide

In order to reduce ___ (H2O2) to prevent ROS formation, reduced glutathione is used, which turns it into its oxidized form (GSSG).

• In order to recycle it, NADPH is used to turn it back into reduced form (2GSH) so it is functional again

Heinz bodies

ROS cause oxidation and cross-linking of hemoglobin, creating structures called ____ on red blood cells

• leads to hemolytic anemia under oxidative stress conditions

• can also be caused by a G6P dehydrogenase deficiency (no reducing NADP to NADPH needed to reform reduced glutathione)