Biology on Arachidonic Acid Functions

Questions and Answers

What is the primary physiological role of prostaglandins in the body?

Smooth muscle contraction during menstruation and labor (correct)

Maintenance of calcium levels in bones

Storage of fatty acids

Regulation of blood glucose levels

Which pathway is NOT involved in the synthesis of eicosanoids?

Cyclooxygenase pathway

Peptide synthesis pathway (correct)

Lipoxygenase pathway

Cytochrome P450 system

What is the structure characteristic of thromboxanes?

Three interconnected five-membered rings

A six-membered ring that includes an oxygen atom (correct)

No structural rings, linear configuration

Five-membered carbon ring without oxygen

How are eicosanoids produced within the body?

Only synthesized when needed Signup and view all the answers

Which cellular response is specifically attributed to the action of leukotrienes?

Contraction of smooth muscle in airways Signup and view all the answers

What function do eicosanoids NOT have in the body?

Increasing red blood cell production Signup and view all the answers

Which of the following best describes the relationship between eicosanoids and G-protein coupled receptors?

Eicosanoids bind to G-protein coupled receptors to mediate their effects Signup and view all the answers

Which of the following is a primary function of thromboxanes?

Enhancing platelet aggregation Signup and view all the answers

What property of eicosanoids allows them to have diverse tissue functions?

Plausibility of being continuously synthesized Signup and view all the answers

What is the primary effect of thromboxane A2 in relation to platelet function?

Encourages thrombus formation Signup and view all the answers

Which of the following statements regarding prostacyclin (PGI2) is correct?

It inhibits platelet aggregation. Signup and view all the answers

What is the mechanism of action of low-dose aspirin therapy?

Irreversibly acetylates a serine residue in COX-1 Signup and view all the answers

How does the inhibition of COX-1 by NSAIDs affect platelet function?

It prevents thromboxane A2 synthesis. Signup and view all the answers

What is the significance of platelet renewal in relation to aspirin treatment?

It reverses acetylation of COX-1 in platelets. Signup and view all the answers

What role does cortisol play in platelet homeostasis?

It inhibits phospholipase A2 activity. Signup and view all the answers

What is the primary function of COX-1 in the body?

Maintains healthy gastric tissue and platelet aggregation Signup and view all the answers

What type of inhibitor is celecoxib categorized as?

Selective COX-2 inhibitor Signup and view all the answers

Which fatty acid serves as a dietary precursor for the synthesis of prostaglandins?

Linoleic acid Signup and view all the answers

How does ibuprofen primarily act on PGH synthase?

By blocking the active site of PGH synthase Signup and view all the answers

What is the primary role of 5-lipoxygenase in the lipoxygenase pathway?

Converts arachidonic acid to leukotrienes Signup and view all the answers

Why does acetaminophen have poor ability to inhibit COX in high concentrations of peroxides?

It acts as a reversible inhibitor at low doses Signup and view all the answers

What pathway does the lipoxygenase family affect primarily?

Conversion of arachidonic acid to leukotrienes Signup and view all the answers

What influences the activity of COX-2 in tissues?

Activated immune and inflammatory cells Signup and view all the answers

Which of the following statements best describes leukotrienes?

They play a crucial role in allergic responses and inflammation Signup and view all the answers

What determines the rate of product formation from arachidonic acid?

The amount of free arachidonic acid released Signup and view all the answers

Which enzyme is responsible for hydrolyzing arachidonate?

Phospholipase A2 Signup and view all the answers

How is arachidonic acid stored in cell membranes?

As an ester of the 2 position of glycerol Signup and view all the answers

What is a primary precursor to thromboxanes and prostaglandins?

Arachidonic acid Signup and view all the answers

Which of the following stimulates arachidonic acid release in specific cell types?

Thrombin Signup and view all the answers

What is the role of phospholipase C regarding phosphatidylinositol?

It cleaves inositol from phosphatidylinositol Signup and view all the answers

Which type of cell would bradykinin specifically stimulate for arachidonic acid release?

Renal tubular cells Signup and view all the answers

Which of the following is NOT a product derived from arachidonic acid metabolism?

Fatty acids Signup and view all the answers

Which phospholipase is primarily involved in the release of arachidonic acid?

Phospholipase A2 Signup and view all the answers

What role does thrombin play regarding arachidonic acid?

Stimulator of arachidonate release in certain cells Signup and view all the answers

What is indicated by a subscript in nomenclature?

Number of unsaturated bonds Signup and view all the answers

Which of the following NSAIDs is specifically associated with increased leukotriene levels?

Ibuprofen Signup and view all the answers

How does the structure of Hydroperoxy-eicosatetraenoic acid differ from other eicosanoids?

It is a hydroxyl fatty acid derivative Signup and view all the answers

What effect do NSAIDs such as aspirin have on the blood flow at a clot site?

Reduce blood flow to hinder clotting Signup and view all the answers

Substitutions at which positions are indicated for Hydroperoxy in nomenclature?

5, 12, 15 Signup and view all the answers

Which of the following is NOT a recognized nonsteroidal anti-inflammatory drug (NSAID)?

Prednisone Signup and view all the answers

What is the primary biological activity associated with Hydroperoxy-eicosatetraenoic acid?

No clear biologic activity Signup and view all the answers

Which NSAID is known for potentially triggering asthma attacks?

Aspirin Signup and view all the answers

What is a common use of eicosanoids in the body?

Regulating immune responses Signup and view all the answers

What does the additional capital letter signify in the nomenclature of compounds?

Ring substitutions Signup and view all the answers

Study Notes

Eicosanoids Function

Derived from arachidonic acid, a 20-carbon polyunsaturated fatty acid.
Not stored but synthesized on demand, responding to cellular signaling.
Mediated by G-protein coupled receptors, influencing various physiological functions.

Functions of Eicosanoids

Reproductive functions including smooth muscle contraction during menstruation and labor.
Modulation of inflammation, resulting in fever and pain responses.
Involvement in blood clot formation and regulation of blood flow to specific organs.
Influence on wake-sleep cycles and responsiveness to hormones like epinephrine and glucagon.
Regulation of gastric acid secretion and blood pressure.

Pathways for Eicosanoid Synthesis

Cyclooxygenase Pathway: Produces prostaglandins and thromboxanes.
Lipoxygenase Pathway: Generates leukotrienes, HETE (Hydroxyeicosatetraenoic acid), and lipoxins.
Cytochrome P450 System: Synthesizes epoxides, HETE, and diHETE.

Prostaglandins

Composed of a 20-carbon fatty acid structure with a 5-membered internal carbon ring and a hydroxyl group at carbon 15.
Nomenclature begins with "PG" followed by capital letters indicating specific substitutions.

Thromboxanes

Feature a 6-membered ring including an oxygen atom.
Nomenclature uses "TX" with capital letters for ring substitutions and subscripts indicating unsaturated bonds.
Function primarily in blood clot formation and reduction of blood flow to injury sites.

Hydroperoxy-eicosatetraenoic Acid (HETE)

Hydroxyl fatty acid derivative of arachidonic acid, lacking a ring structure.
Nomenclature includes hydroperoxy substitutions at positions 5, 12, and 15.

Metabolism of Eicosanoids

Arachidonic acid is a precursor for major eicosanoids, stored as phospholipid esters in cell membranes.
Released by phospholipase A2 when stimulated, influencing the rate of eicosanoid synthesis.
Specific agonists like thrombin and bradykinin stimulate arachidonic acid production.

Synthesis of Eicosanoids

Linoleic acid, an omega-6 fatty acid, is essential for prostaglandin production.
Arachidonic acid is derived from dietary intake of linoleic acid.
Prostaglandin H2 (PGH2) synthesized through oxidative cyclization of arachidonic acid, requiring oxygen and reducing agents.

Inhibition of Eicosanoid Synthesis

Nonsteroidal anti-inflammatory drugs (NSAIDs) including aspirin, ibuprofen inhibit cyclooxygenase (COX) enzymes, shifting production to lipoxygenase pathways.
NSAIDs can potentially induce asthma attacks through increased leukotriene synthesis.

Roles of Prostaglandins in Platelet Homeostasis

Thromboxane A2 (TXA2): Promotes platelet aggregation and vasoconstriction; synthesized by COX-1 in activated platelets.
Prostacyclin (PGI2): Inhibits platelet aggregation and promotes vasodilation; produced by COX-2 in vascular endothelium.

Aspirin and Its Effects

Provides antithrombogenic effects by irreversibly acetylating COX enzymes, reducing TXA2 synthesis in platelets while affecting PGI2 synthesis in endothelial cells.
Low-dose aspirin therapy lowers the risk of stroke and heart attacks by decreasing thrombus formation.

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Description

This quiz focuses on the functions of arachidonic acid, a polyunsaturated fatty acid derived from 20-carbon chains. We explore its production, action at low concentrations, and its role in smooth muscle contraction during menstruation and labor. Test your knowledge on cellular and tissue functions mediated by G-protein coupled receptors.