Lipids

Why are lipids primarily nonpolar in nature?

They consist mostly of nonpolar carbon–carbon ($C-C$) or carbon–hydrogen ($C-H$) bonds.

How do cells primarily use fats for energy?

Cells store fats for long-term energy use.

How do lipids provide physical protection for aquatic birds and mammals?

They form a water-repellent hydrophobic layer over fur or feathers to keep them dry.

List the five main types of lipids mentioned in the text.

Fats, oils, waxes, phospholipids, and steroids.

What are the two main components of a fat molecule?

Glycerol and fatty acids.

Describe the chemical structure of glycerol.

It is an organic alcohol with three carbons, five hydrogens, and three hydroxyl ($-\text{OH}$) groups.

What is the typical range of carbon atoms in a fatty acid chain?

4 to 36 carbons (12-18 most common).

Which specific functional group is attached to the long hydrocarbon chain of a fatty acid?

A carboxyl group ($-\text{COOH}$).

How do fatty acids and glycerol molecules bond in fat?

A fatty acid attaches to each of the glycerol's carbons with an ester bond thorugh an oxygen atom.

How many water molecules are released during the formation of one triacylglycerol molecule?

Three water molecules.

Define a saturated fatty acid.

A fatty acid with only single bonds between neighboring carbons in the hydrocarbon chain.

Palmitic acid and stearic acid are ____.

saturated fatty acids.

What is an unsaturated fatty acid?

A fatty acid that contains at least one double bond in its hydrocarbon chain.

What is the difference between monounsaturated and polyunsaturated fats?

Monounsaturated fats have one double bond, while polyunsaturated fats have more than one.

Which physical state do saturated fats typically maintain at room temperature?

Solid

Oleic acid is an ___.

unsaturated fatty acid.

Why do saturated fats tend to be solid at room temperature?

Their long, straight fatty acid chains pack together tightly.

In which specialized cells do mammals store fat globules?

Adipocytes

What is the role of stored fats or oils in plant seeds?

They serve as an energy source during seedling development.

How does a $cis$ double bond affect the shape of a fatty acid chain?

It causes a bend or "kink" in the chain.

Trans fat

Hydrogen atoms are on two different planes around the double bond of an unsaturated fat.

Cis fat

Hydrogen atoms are present in the same plane around the double bond of an unsaturated fat.

Why are unsaturated fats typically liquid at room temperature?

$Cis$ double bond kinks prevent the fatty acids from packing tightly.

What is the primary health risk associated with saturated fat consumption mentioned in the text?

They might contribute to plaque formation in the arteries.

What is the purpose of the artificial hydrogenation of oils in the food industry?

To make the oils semi-solid and achieve a consistency desirable for processed foods.

Examples of unsaturated fats?

Olive oil, corn oil, canola oil, cod liver oil.

How are $trans$ fats chemically created from oils?

Hydrogen gas is bubbled through oils, converting $cis$-conformation double bonds to $trans$-conformation.

What is the physiological impact of consuming high levels of $trans$ fats?

They increase low-density lipoproteins (LDL or "bad" cholesterol), leading to plaque deposition and heart disease.

What defines an "essential" fatty acid?

A fatty acid that the human body requires but cannot synthesize, meaning it must be ingested through the diet.

Why is an omega-3 fatty acid specifically named "$\omega-3$"?

A double bond connects the third carbon from the end of the hydrocarbon chain to its neighbor.

Which carbon in a fatty acid chain is designated as the "omega" ($\omega$) carbon?

The carbon farthest away from the carboxyl group.

List three nutritionally important polyunsaturated omega-3 fatty acids.

Alpha-linolenic acid (ALA), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA).

According to research, how do omega-3 fatty acids benefit heart health?

They reduce sudden death from heart attacks, lower triglycerides, decrease blood pressure, and prevent thrombosis.

What are the chemical constituents of waxes?

Long fatty acid chains esterified to long-chain alcohols.

What is the primary function of waxes on leaf surfaces and bird feathers?

Their hydrophobic nature prevents water from sticking to the surface.

Which type of lipid is the major constituent of the plasma membrane?

Phospholipids

What is the structural difference between a triacylglycerol and a phospholipid?

A phospholipid has two fatty acids and a modified phosphate group occupying the glycerol's third carbon instead of three fatty acids.

What is phosphatidate?

A diacylglycerol 3-phosphate molecule that serves as the precursor to phospholipids.

Concept: Amphipathic

Definition: A molecule possessing both a hydrophobic region and a hydrophilic region.

Which part of a phospholipid molecule is hydrophilic?

The phosphate-containing head.

Which part of a phospholipid molecule is hydrophobic?

The fatty acid tails.

How do phospholipids orient themselves in a plasma membrane bilayer?

Hydrophobic tails face inward toward each other, and hydrophilic heads face the outward aqueous sides.

What spherical structure do phospholipids spontaneously form when placed in water?

A micelle.

What is the defining structural characteristic of steroids?

A fused ring structure consisting of four linked carbon rings.

Why are steroids classified as lipids despite their unique ring structure?

They are hydrophobic and insoluble in water.

Which steroid is the most common and serves as a precursor to many hormones?

Cholesterol

Which organ is responsible for synthesizing cholesterol in the human body?

The liver.

List two steroid hormones for which cholesterol is a precursor.

Testosterone and estradiol.

Provide an example of a saturated fatty acid commonly found in meat.

Stearic acid

Which vitamin can be synthesized from cholesterol as a precursor?

Vitamin D

Many steroids have what functional group?

-OH (giving them alcohol classification).