Lipids and Waxes Overview (Moni Quiz 3)

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Questions and Answers

Which type of lipids can be converted into smaller molecules by hydrolysis?

Hydrolyzable lipids (correct)

Saturated lipids

Nonhydrolyzable lipids

Trans fats

What characteristic defines fatty acids?

They are nonpolar molecules.

They always have an even number of carbon atoms.

They are cyclic structures.

They are carboxylic acids with long carbon chains. (correct)

Which type of fatty acid contains only one double bond?

Monounsaturated fatty acid (correct)

Saturated fatty acid

Polyunsaturated fatty acid

Hydrolyzable fatty acid

How does the melting point of fatty acids change with the number of double bonds?

It decreases as the number of double bonds increases. Signup and view all the answers

What distinguishes linoleic acid as an omega-6 acid?

It has its first double bond on the sixth carbon from the end. Signup and view all the answers

What are waxes formed from?

High molecular weight alcohols and fatty acids Signup and view all the answers

What products are formed when wax is hydrolyzed in the presence of acid or base?

Fatty acid and alcohol Signup and view all the answers

Which fatty acid has multiple double bonds and is known as omega-3?

Linolenic acid Signup and view all the answers

What are triglycerides primarily composed of?

Three fatty acids and glycerol Signup and view all the answers

Which type of triglyceride has three identical fatty acid side chains?

Simple triacylglycerols Signup and view all the answers

What is the primary function of lipase in relation to triacylglycerols?

To hydrolyze triacylglycerols Signup and view all the answers

Which type of phospholipid resembles a triacylglycerol but has an alcohol replacing the third fatty acid?

Phosphoacylglycerol Signup and view all the answers

What distinguishes sphingomyelins from phosphoacylglycerols?

Sphingomyelins do not have a glycerol backbone Signup and view all the answers

Which of the following is a common type of phosphoacylglycerol?

Cephalin Signup and view all the answers

What part of a phosphoacylglycerol is charged or polar?

The phosphodiester end Signup and view all the answers

What is a key structural difference between phosphoacylglycerols and triglycerides?

Phosphoacylglycerols contain a phosphate group Signup and view all the answers

What triggers the increase of LDL levels in the plasma?

High concentration of cholesterol inside cells Signup and view all the answers

Which vitamin is synthesized from cholesterol?

Vitamin D Signup and view all the answers

What is the primary function of HDL cholesterol?

Transport excess cholesterol to the liver Signup and view all the answers

What condition is caused by a deficiency of Vitamin D?

Rickets Signup and view all the answers

Which vitamin regulates the synthesis of clotting proteins such as prothrombin?

Vitamin K Signup and view all the answers

Which antioxidant vitamin prevents the oxidation of unsaturated fatty acids?

Vitamin E Signup and view all the answers

What is a common outcome of high LDL cholesterol in the blood?

Formation of arterial plaque Signup and view all the answers

What happens to cholesterol synthesis in the liver when serum cholesterol levels are low?

It increases dramatically Signup and view all the answers

What are sphingomyelins primarily categorized as?

Lipids Signup and view all the answers

Which of the following components is NOT a part of the cell membrane structure?

Nucleotides Signup and view all the answers

What type of transport is required for larger polar molecules to efficiently cross the cell membrane?

Facilitated transport Signup and view all the answers

Which lipoprotein is often referred to as 'good cholesterol'?

High-density lipoprotein (HDL) Signup and view all the answers

What is the main function of low-density lipoproteins (LDLs)?

Transport cholesterol to the tissues Signup and view all the answers

What mechanism controls the number of LDL receptors on the surface of cells?

Feedback mechanism Signup and view all the answers

Which statement about cholesterol is true?

Cholesterol has a carbon skeleton made of multiple fused rings. Signup and view all the answers

Which of the following statements about the cell membrane is accurate?

The cell membrane allows nutrients in and waste out. Signup and view all the answers

What fatty acid is primarily used in the synthesis of prostaglandins?

Arachidonic acid Signup and view all the answers

What physiological effect does Prostaglandin E2 (PGE2) have on blood vessels?

Relaxes muscle cells Signup and view all the answers

Which enzyme is responsible for synthesizing prostaglandins from arachidonic acid?

Cyclooxygenase Signup and view all the answers

Which COX enzyme is mainly involved in inflammation-induced prostaglandin production?

COX-2 Signup and view all the answers

What is a common effect of leukotrienes on the body?

Inducing muscle contraction Signup and view all the answers

Which of the following statements about NSAIDs is true?

They inhibit both COX-1 and COX-2 enzymes. Signup and view all the answers

What role does Prostaglandin F2α (PGF2α) play in childbirth?

Stimulates uterine contractions Signup and view all the answers

Leukotrienes mainly occur in which type of cells?

Leukocytes (white blood cells) Signup and view all the answers

Study Notes

Lipids

Lipids are a diverse group of naturally occurring organic compounds that are generally insoluble in water, but soluble in organic solvents like chloroform and ether.
They can be categorized into hydrolyzable and non-hydrolyzable lipids.
Hydrolyzable lipids can be broken down into smaller molecules by hydrolysis, while non-hydrolyzable lipids cannot.
Hydrolyzable lipids are derived from fatty acids.
Fatty acids are carboxylic acids with long carbon chains of 12 to 20 carbon atoms.
Fatty acids contain an even number of carbon atoms.
Saturated fatty acids have only single bonds between carbon atoms, while unsaturated fatty acids have at least one double bond.
Naturally occurring unsaturated fatty acids contain cis double bonds.
Monounsaturated fatty acids have one double bond, and polyunsaturated fatty acids (PUFA) have multiple double bonds.
As the number of double bonds in a fatty acid increases, its melting point decreases.

Waxes

Waxes are esters formed from a fatty acid and a high molecular weight alcohol.
They are hydrolyzed in the presence of acid or base to reform the carboxylic acid and alcohol.

Triglycerides

Triglycerides (also known as triacylglycerols) are esters formed from glycerol and three molecules of fatty acids.
Simple triglycerides have three identical fatty acid side chains.
Mixed triglycerides have two or three different fatty acids.
Animal fats contain mainly saturated triglycerides, which are solid at room temperature.
Vegetable oils contain mainly unsaturated triglycerides, which are liquid at room temperature.
Triacylglycerols are hydrolyzed in the presence of acid, base, or enzymes (like lipase) to produce glycerol and fatty acids.

Phospholipids

Phospholipids are lipids containing a phosphorus atom.
They are the major components of cell membranes and are responsible for the selective permeability of the cell membrane.
Two common types of phospholipids are phosphoacylglycerols and sphingomyelins.
Phosphoacylglycerols structurally resemble a triacylglycerol with a phosphodiester bonded to an alcohol replacing the third fatty acid.
Cephalin (or phosphatidylethanolamine) and lecithin (or phosphatidylcholine) are two main types of phosphoacylglycerols.
Sphingomyelins do not contain a glycerol backbone; they have a sphingosine backbone instead.
The myelin sheath, which surrounds nerve cells, is rich in sphingomyelins.

Steroids

Steroids are lipids containing a carbon skeleton composed of several fused rings.
Cholesterol is the most prominent steroid and is synthesized in the liver.
Cholesterol is obtained in the diet from meat, cheese, butter, and eggs.
Lipoproteins are carriers (transporters) of cholesterol.
The four main types of lipoproteins are:
- High-density lipoprotein (HDL)
- Low-density lipoprotein (LDL)
- Very low-density lipoprotein (VLDL)
- Chylomicrons
HDL ("good cholesterol") consists of about 33% protein and 30% cholesterol, while LDL ("bad cholesterol") contains about 25% protein and 50% cholesterol.
LDL transports cholesterol from the liver to the tissues, while HDL transports cholesterol from tissues back to the liver.
When LDL receptors are sufficient, LDL is removed from circulation, decreasing its concentration in blood plasma.
The number of LDL receptors is controlled by a feedback mechanism.
High levels of cholesterol in the cell suppress the synthesis of LDL receptors, resulting in increased LDL levels in blood plasma.
Excess LDL cholesterol deposits on the walls of arteries, forming plaque that restricts blood flow.
HDL reduces LDL levels in the bloodstream by transporting excess cholesterol back to the liver.
HDL levels can be increased by exercise and weight loss.
The synthesis of cholesterol in the liver is regulated by serum cholesterol levels.
Statin drugs inhibit the synthesis of cholesterol by blocking HMG-CoA reductase, a key enzyme in cholesterol synthesis.

Vitamins

Vitamins are organic compounds required in small quantities for normal metabolism.
They are obtained from the diet and are either water-soluble or fat-soluble.
The four fat-soluble vitamins (A, D, E, and K) are found in fruits, vegetables, fish, liver, and dairy products.
Fat-soluble vitamins are stored in adipose cells and used when needed.
Vitamin A is found in liver, fish, and dairy products.
Vitamin A deficiency causes night blindness and dry eyes and skin.
Vitamin D is synthesized from cholesterol and can be obtained in the diet from many foods.
Vitamin D deficiency causes rickets (bone malformation).
Vitamin E is an antioxidant that protects the unsaturated side chains in fatty acids from oxidation.
Vitamin E deficiency can cause neurological problems.
Vitamin K regulates the synthesis of clotting proteins.
Vitamin K deficiency leads to excessive or fatal bleeding.

Prostaglandins and Leukotrienes

Prostaglandins are fatty-acid-like substances with a 20-carbon skeleton of prostanoic acid.
They are not stored in tissues but are synthesized from membrane-bound 20-carbon polyunsaturated fatty acids (like arachidonic acid) in response to physiological triggers.
Prostaglandins are synthesized from arachidonic acid through ring closure at carbons 8 and 12 catalyzed by the enzyme cyclooxygenase (COX).
COX occurs in two forms:
- COX-1 catalyzes the normal production of prostaglandins.
- COX-2 is responsible for the production of prostaglandins in response to inflammation.
Nonsteroidal anti-inflammatory drugs (NSAIDs) like aspirin and ibuprofen inhibit both COX enzymes.
Drugs like Vioxx, Bextra, and Celebrex specifically block the COX-2 enzyme.

Leukotrienes

Leukotrienes are synthesized from arachidonic acid and are found mainly in white blood cells (leukocytes).
They cause inflammation, fever, and muscle contractions, especially in the lungs, and can contribute to asthma-like attacks.
Zileuton is a drug that inhibits the enzyme 5-lipoxygenase, which is involved in the synthesis of leukotrienes.

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Description

This quiz covers the essential concepts of lipids, including their classification into hydrolyzable and non-hydrolyzable types, the structure of fatty acids, and the characteristics of saturated and unsaturated fatty acids. Additionally, it touches on the properties of waxes. Test your understanding of these crucial organic compounds!