Cholesterol and Omega-3 Fatty Acids Quiz

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Questions and Answers

What is the primary health threat associated with cholesterol deposition in blood vessels?

Increased blood circulation

Decreased blood pressure

Plaque formation (correct)

Enhanced nutrient delivery

Which of the following conditions is a result of atherosclerosis?

Pulmonary embolism

Deep vein thrombosis

Hypertension

Coronary artery disease (CAD) (correct)

What is one consequence of the narrowing of blood vessels due to plaque formation?

Improved blood flow

Lower cholesterol levels

Increased risk of heart attack (correct)

Easier oxygen transport

Cholesterol deposition in blood vessels primarily leads to which of the following processes?

Atherosclerosis (B) Signup and view all the answers

The presence of plaque in blood vessels is most directly associated with which type of disease?

Coronary artery disease (CAD) (D) Signup and view all the answers

What are the three main omega-3 fatty acids?

Alpha-linolenic acid, eicosapentaenoic acid, and docosahexaenoic acid (D) Signup and view all the answers

Which fatty acid has the designation C20:5?

Eicosapentaenoic acid (EPA) (B) Signup and view all the answers

What is the role of docosa-hexaenoic acid in the body?

It contributes to the synthesis of the retina and cerebral cortex. (B) Signup and view all the answers

Which fatty acid is a precursor for docosa-hexaenoic acid?

Linolenic acid (B) Signup and view all the answers

What is one of the main functions of omega-3 fatty acids?

Production of prostaglandins and leukotrienes (A) Signup and view all the answers

Which of the following fatty acids is known to be beneficial for heart health?

Docosahexaenoic acid (DHA) (C) Signup and view all the answers

What is NOT a function associated with docosa-hexaenoic acid?

Building structural integrity of mitochondrial membranes (D) Signup and view all the answers

Which omega-3 fatty acid is primarily found in plant sources?

Alpha-linolenic acid (ALA) (C) Signup and view all the answers

In which areas of the body is docosa-hexaenoic acid especially important?

Retina and cerebral cortex (A) Signup and view all the answers

What type of fatty acid is docosa-hexaenoic acid classified as?

Omega-3 fatty acid (D) Signup and view all the answers

Which fatty acid is the dietary precursor of prostaglandins?

Linoleic acid (C) Signup and view all the answers

What is the final product formed from the elongation and desaturation of linoleic acid?

Arachidonic acid (B) Signup and view all the answers

What is the structure designation of arachidonic acid?

20:4(5,8,11,14) (A) Signup and view all the answers

Which of the following statements about linoleic acid is true?

It is essential for the production of prostaglandins. (B) Signup and view all the answers

What role does arachidonic acid play in the body?

It is a precursor for the synthesis of prostaglandins. (B) Signup and view all the answers

What are the sources of cholesterol entering the liver's cholesterol pool?

Both dietary cholesterol and cholesterol from extrahepatic tissues (C) Signup and view all the answers

Which statement accurately describes the sources of cholesterol in the liver?

The liver synthesizes cholesterol in addition to receiving it from dietary sources. (D) Signup and view all the answers

What role do extrahepatic tissues play in cholesterol metabolism?

They synthesize cholesterol which can then enter the liver's pool. (B) Signup and view all the answers

Which option best describes the relationship between dietary cholesterol and liver cholesterol?

The liver utilizes both dietary and synthesized cholesterol. (A) Signup and view all the answers

Which of the following is NOT a source of cholesterol for the liver?

Cholesterol removed from circulation by kidneys (C) Signup and view all the answers

What is the role of HMG CoA reductase in cholesterol synthesis?

It is the rate-limiting enzyme in cholesterol biosynthesis. (D) Signup and view all the answers

How does insulin affect cholesterol synthesis?

Insulin activates HMG CoA reductase, leading to increased cholesterol synthesis. (C) Signup and view all the answers

What effect does cholesterol have on HMG CoA reductase activity?

Cholesterol acts as a feedback inhibitor of HMG CoA reductase. (D) Signup and view all the answers

Which of the following drugs is a structural analog of HMG CoA that inhibits cholesterol synthesis?

Simvastatin (B), Atorvastatin (D) Signup and view all the answers

What regulates the activity of HMG CoA reductase through phosphorylation?

The actions of a protein kinase and a phospho-protein phosphatase. (A) Signup and view all the answers

Study Notes

Unsaturated Fatty Acids

Eicosanoids are compounds derived from eicosanoic acid (20 carbon atoms), which is formed from essential fatty acids.
Long-chain unsaturated fatty acids (C20, C22, C24) are derived from oleic, linoleic, and linolenic acids.
Examples of unsaturated fatty acids include palmitoleic acid, oleic acid, linoleic acid, linolenic acid, and arachidonic acid, and nervonic acid.
Essential fatty acids (linoleic acid and linolenic acid) cannot be synthesized by the body and must be obtained through diet.
Omega-3 fatty acids, such as alpha-linolenic acid (ALA), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA), are important.
These fatty acids are precursors of prostaglandins.
Eicosanoids have various functions, including prostaglandin and leukotriene synthesis, structural integrity of mitochondrial membranes, and synthesis of retina, cerebral cortex, and sperm.

Other Functions

Regulate inflammation and allergies.
Some elevate body temperature (producing fever).
Affect immune responses.
Some prostaglandins stimulate smooth muscle contraction during menstruation and labor, regulating pregnancy and birth.
Contribute to the perception of pain.
Affect blood flow to tissues, controlling blood pressure.

Dietary Precursor of Prostaglandins

The dietary precursor of prostaglandins is linoleic acid.
It is elongated and desaturated to form arachidonic acid (20:4(5,8,11,14)), the immediate precursor.
Different subfamilies of eicosanoids exist, prominently including prostaglandins, thromboxanes, leukotrienes, lipoxins, resolvins, and eoxins (further study required).

Inhibition of Prostaglandin Synthesis

Prostaglandin synthesis can be inhibited by various compounds.
Cortisol inhibits phospholipase A2 and COX-2 activity.
Aspirin, indomethacin, and phenylbutazone (NSAIDs) inhibit both COX-1 and COX-2, preventing PGH2 synthesis.
Celecoxib and similar inhibitors are specific for COX-2, reducing inflammation.

Synthesis of Leukotrienes

Arachidonic acid is converted to various hydroperoxy acids by lipoxygenase enzymes.
Neutrophils contain 5-lipoxygenase, converting arachidonic acid to 5-hydroxy-6,8,11,14 eicosatetraenoic acid (5-HPETE).
5-HPETE is converted into leukotrienes which mediate allergic response and inflammation.
Inhibitors of 5-lipoxygenase and leukotriene synthesis are used to treat asthma.

Role of Prostaglandins in Platelet Homeostasis

Thromboxane A2 (TXA2) is produced by activated platelets.
It promotes platelet adherence, aggregation, and vascular smooth muscle contraction, thus facilitating blood clot formation.
Leukotriene D4 induces contraction of the airway smooth muscle, causing asthma attacks.

Cholesterol

Cholesterol is synthesized by all human tissues from LDL and HDL, and diet.
Synthesis begins from acetyl-CoA in the cytoplasm and requires NADPH from the PPP.
Cholesterol is vital for cell membranes, bile acid synthesis, steroid hormone production, and vitamin D synthesis.
Cholesterol enters the liver's cholesterol pool from dietary cholesterol and extrahepatic and liver synthesis.
Cholesterol is eliminated from the liver as free cholesterol in bile or converted to bile salts, secreted into the intestinal lumen.
Gradual accumulation of cholesterol in blood vessels leads to plaque formation, causing atherosclerosis, and increased risk of coronary artery disease.

Cholesterol Structure

Cholesterol is a very hydrophobic compound.
It consists of four hydrocarbon rings (A, B, C, and D), plus an eight-carbon branched hydrocarbon chain attached to C-17 of the D ring.
Ring A has a hydroxyl group at C-3, and ring B has a double bond.

Cholesterol Esters (CE)

Most cholesterol exists in an esterified form (with a fatty acid at C-3), making it more hydrophobic than free cholesterol.
Due to hydrophobicity, cholesterol and its esters need protein association as lipoproteins to be transported.

Cholesterol Synthesis

Cholesterol is synthesized in the cytoplasm with acetyl CoA as the starting material and NADPH assistance.
The first two steps produce 3-hydroxy-3-methylglutaryl CoA (HMG CoA).
A third acetyl CoA joins, leading to HMG CoA, which is a six-carbon compound.

Mevalonic Acid Synthesis

The reduction of HMG CoA to mevalonic acid is catalyzed by HMG CoA reductase.
This is the rate-limiting step in cholesterol synthesis.
The process happens in the cytosol, uses two molecules of NADPH, and releases CoA.

Cholesterol Synthesis Pathway

The next steps in cholesterol synthesis involve farnesyl PP, squalene, and lanosterol, ultimately resulting in cholesterol production.
Cholesterol then leads to steriod hormones, vitamin D, and bile acids production.

Regulation of Cholesterol in Hepatocytes

HMG CoA reductase, the rate-limiting enzyme, is the major point of control in cholesterol biosynthesis.
Cholesterol itself inhibits HMG CoA reductase.
Insulin activates HMG CoA reductase, increasing cholesterol synthesis; glucagon inhibits it, decreasing synthesis.
LDL and chylomicron cholesterol in cells reduce HMG CoA reductase transcription, lowering synthesis.
Drugs like simvastatin, lovastatin, and mevastatin are HMG CoA reductase inhibitors, lowering cholesterol.

HMG CoA Reductase Regulation

HMG CoA reductase activity is controlled by phosphorylation/dephosphorylation.
Protein kinases deactivate the enzyme, decreasing cholesterol synthesis; phosphoprotein phosphatases activate it, increasing synthesis.
ATP reduces cholesterol synthesis by converting the active form of HMG CoA reductase to inactive.

Additional Home Work

Resolvins and eoxins: function.
Calcium's role in thrombus formation.
Comparison of PG E2 and PGF2 actions on uterine smooth muscles.
Insulin and glucagon in cholesterol and palmitate synthesis.
Protein kinase and phosphoprotein phosphatase in cholesterol synthesis and palmitate.

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Description

Test your knowledge on the health impacts of cholesterol deposition in blood vessels and the roles of various omega-3 fatty acids. This quiz covers topics such as atherosclerosis, the consequences of plaque formation, and the importance of specific fatty acids in the body. Challenge yourself to see how well you understand these essential concepts in cardiovascular health.