Pentose Phosphate Pathway and Related Metabolism

These flashcards cover key concepts, enzymes, and regulatory mechanisms related to the Pentose Phosphate Pathway, fatty acid metabolism, lipid structure, and nitrogen metabolism.

What are the two phases of the Pentose Phosphate Pathway (PPP)?

Oxidative Phase (Irreversible) and Non-oxidative Phase (Reversible).

What is the primary purpose of the Oxidative Phase of PPP?

To generate NADPH and convert Glucose-6-Phosphate (G6P) to Ribulose-5-Phosphate.

Which enzyme is the major regulated step in the Oxidative Phase of PPP?

Glucose-6-phosphate dehydrogenase (G6PD).

What are the main products of the Non-oxidative Phase of the PPP?

Ribose-5-Phosphate, Glyceraldehyde-3-Phosphate, and Fructose-6-Phosphate.

How does the Non-oxidative Phase of PPP differ from the Calvin Cycle?

PPP is catabolic and produces NADPH, while the Calvin Cycle is anabolic and consumes ATP and NADPH.

What regulates the PPP and how?

NADP⁺ availability regulates the PPP; high NADP⁺ activates the oxidative phase, low NADP⁺ (high NADPH) inhibits G6PD.

What is the primary role of G6PD in reducing oxidative stress?

It produces NADPH which keeps glutathione in its reduced state to detoxify reactive oxygen species.

What are the key lipases involved in the mobilization of fatty acids?

ATGL, HSL, and MGL.

What triggers the mobilization of fatty acids from adipose tissue?

Glucagon and epinephrine activate PKA which in turn stimulates lipases.

What is the role of Carnitine in fatty acid oxidation?

It facilitates the transport of long-chain fatty acids into the mitochondrial matrix.

What are the four repeated steps of β-Oxidation?

Oxidation, Hydration, Oxidation, and Thiolysis.

What is the final product of one cycle of β-Oxidation?

1 FADH₂, 1 NADH, and 1 Acetyl-CoA, with the fatty acid chain shortened by 2 carbons.

What is the committed step in fatty acid synthesis?

The conversion of Acetyl-CoA to Malonyl-CoA by the enzyme Acetyl-CoA Carboxylase (ACC).

What are the key sources of NADPH needed in fatty acid synthesis?

Pentose Phosphate Pathway (PPP) and the malic enzyme.

What triggers the regulation of ACC in fatty acid metabolism?

ACC is activated when dephosphorylated; AMPK phosphorylates it to inactivate.

What is the structure of lipids such as phosphatidate?

Phosphatidate consists of a glycerol backbone connected to two fatty acids and a phosphate head group.

What enzymes participate in the urea cycle?

CPS-I, ASS, ASL, and Arginase.

What are the three sources of backbone atoms in the urea cycle?

NH₃, Aspartate, and CO₂.

What is the significance of nitrogen fixation?

It converts atmospheric N₂ into NH₃, which is usable by most organisms.

What is the significance of the committed step in purine synthesis?

The first product is IMP, built on PRPP; it is crucial for the synthesis of purines.