Pentose Phosphate Pathway (PPP) and Monosaccharides

Comprehensive vocabulary flashcards covering the Pentose Phosphate Pathway (PPP) stages, key enzymes, chemical intermediates, and monosaccharide classifications from the lecture notes.

Pentose Phosphate Pathway (PPP)

A metabolic pathway using $glucose-6-phosphate$ to produce $NADPH$ for biosynthesis and $ribose-5-phosphate$ for nucleotide synthesis; also known as the hexose monophosphate shunt.

Oxidative Phase

The irreversible first stage of the PPP that yields $NADPH$ and $ribose-5-phosphate$ ($Ru5P$) and includes the first committed step catalyzed by $glucose-6-phosphate$ dehydrogenase.

Non-oxidative Phase

The reversible second stage of the PPP that interconverts pentose phosphates and shuttles carbon sources back into glycolysis as $fructose-6-phosphate$ and $glyceraldehyde-3-phosphate$.

NADPH

A key product of the PPP used for fatty acid synthesis, cholesterol synthesis, and maintaining oxidative homeostasis via $glutathione$ reductase.

Ribose-5-phosphate

A five-carbon sugar produced in the PPP used for the synthesis of $DNA$, $RNA$, and cofactors such as $CoA$, $FAD$, $SAM$, and $NAD^+/NADP^+$.

Glucose-6-phosphate Dehydrogenase (G6PDH)

The enzyme that catalyzes the first committed step of the PPP, controlling the rate of $NADPH$ production.

Ring-Chain Tautomerism

The equilibrium state where sugars exist between their open-chain form and various closed-chain (cyclic) forms.

Pyranose

The six-membered cyclic form of a sugar, such as the form that constitutes 99% of $D-glucose$ in equilibrium.

Furanose

The five-membered cyclic form of a sugar, which constitutes less than 1% of $D-glucose$ in equilibrium.

Anomers

Diastereomers (designated as $\alpha$ and $\beta$ forms) created at the chiral center of $C-1$ during sugar ring closure.

Transketolase

An enzyme in the non-oxidative branch of the PPP that requires the coenzyme thiamine pyrophosphate ($TPP$ or $vitB_1$) to transfer two-carbon units.

Transaldolase

An enzyme in the non-oxidative phase of the PPP that transfers three-carbon units and does not require $TPP$.

Epimerase

An enzyme that inter-converts stereoisomers, specifically converting $ribulose-5-phosphate$ to $xylulose-5-phosphate$.

Isomerase

An enzyme that converts a ketose to an aldose, such as transforming $ribulose-5-phosphate$ into $ribose-5-phosphate$.

Thiamine Pyrophosphate (TPP)

The active form of vitamin $B_1$ required as a coenzyme by transketolase in the pentose phosphate pathway.

6-Phosphogluconate Dehydrogenase

An enzyme that converts $6-phosphogluconate$ to $ribulose-5-phosphate$, yielding $NADPH$ and releasing $CO_2$.

Gluconolactone-6P

An intermediate (also called $6-phosphogluconolactone$) formed from $glucose-6-phosphate$ by the action of $G6PDH$.

Aldopentose

A five-carbon monosaccharide with an aldehyde group, examples include $D-ribose$, $D-xylose$, and $D-arabinose$.

Ketopentose

A five-carbon monosaccharide with a ketone group, such as $L-xylulose$ or $ribulose-5-phosphate$.

Glutathione Reductase

An enzyme that uses $NADPH$ as a coenzyme to recycle glutathione, essential for maintaining reduced glutathione in Red Blood Cells.

Ketohexose

A six-carbon monosaccharide containing a ketone group, with fructose being a primary example.

Aldohexose

A six-carbon monosaccharide containing an aldehyde group, such as glucose, mannose, or galactose.