Chapter 11: Lipids

methylene group

-CH2-

Fatty acids are

-a main source of fuel -chains of hydrogen-bearing carbon atoms that have a carboxylic acid at one end and a methyl group at the other end.

What are sterols

-also known as steroid alcohols, are a subgroup of the steroids and an important class of organic molecules. They occur naturally in plants, animals, and fungi, and can be also produced by some bacteria (however likely with different functions). The most familiar type of animal sterol is cholesterol, which is vital to cell membrane structure, and functions as a precursor to fat-soluble vitamins and steroid hormones. -any of a group of naturally occurring unsaturated steroid alcohols, typically waxy solids.

Cholesterol

-the most common steroid and plays a role in maintaining membrane fluidity. -Cholesterol is also a precursor to steroid hormones.

We will examine five classes of lipids:

1. Free Fatty Acids 2. Triacylglycerols 3. Phospholipids 4. Glycolipids 5. Steroids

The three common types of membrane lipids are:

1. Phospholipids 2. Glycolipids 3. Cholesterol (all components of membrane)

Three examples of omega-3 fatty acids

1. a-Linolenate 2. Eicosapentaenoate (EPA) 3. Docosahexaenoate (DHA)

1. Fatty acid carbon atoms are usually numbered beginning with the (look at slide 7 after answering this) 2. Carbon atoms 2 and 3 are also referred to as

1. carboxyl terminal carbon atom. 2. α and β, respectively.

1. For fatty acids: The positions of double bonds are indicated with 2. Give an example of this

1. the symbol Δ, with the first atom of the double bond indicated by superscript number. 2. Δ9 indicates a double bond between carbon atoms 9 and 10.

Fatty acids in biological systems usually contain an even number of carbon atoms, with the ____ and ___ carbon atom chains the most common.

16, 18

Free fatty acids:

A common fuel.

Describe the electron micrograph of an adipocyte:

A small band of cytoplasm surrounds the large deposit of triacylglycerols.

Explain how triacylglycerols are energy rich?

Because they are hydrophobic and reduced, a gram of anhydrous fat stores more than six times the energy of a gram of hydrated glycogen.

What are the simplest glycolipids and how are they simple?

Cerebrosides; they contain a single sugar residue, either glucose or galactose.

What factors determine the melting point of fatty acids?

First chain length (the long the chain, the higher the melting point) (kinks lower the melting point). Then the intermolecular interactions in unsaturated molecules are much weaker than saturated molecules. As a result, the melting points are much lower for unsaturated fatty acids.

Explain Hutchinson-Gilford progeria syndrome (HGPS)

Inappropriate farnesylation is a cause of Hutchinson-Gilford progeria syndrome, a disease of premature aging. Failure to remove a farnesyl group from the nuclear protein lamin results in a deformed nuclear membrane and impaired nuclear function.

What is Niemann-Pick disease?

It can result from the accumulation of sphingomyelin owing to the lack of sphingomyelinase, an enzyme that degrades sphingomyelin. Symptoms of this disease include mental retardation, seizures, eye paralysis, ataxia (the loss of full control of bodily movements), and retarded growth

Glycolipids:

Membrane lipids composed in part of carbohydrates.

Phospholipids:

Membrane lipids.

Compare the structures of the two fatty acids, palmitate and oleate (look at these structures on slide 6)

Palmitate is a 16-carbon, saturated fatty acid, and oleate is an 18-carbon fatty acid with a single cis double bond (this means oleate is monosaturated) Palmitate is more flexible

Steroids:

Polycyclic hydrocarbons with a variety of functions/roles

Saturated vs unsaturated fatty acids

Saturated fatty acids lack double bonds between the individual carbon atoms, while in unsaturated fatty acids there is at least one double bond in the fatty acid chain.

What enhances the fluidity of fatty acids?

Short chain length and the presence of cis double bonds enhances the fluidity of fatty acids.

Triacylglycerols:

Storage form of fatty acids.

For membrane lipids, what provide the hydrophobic properties and what provide the hydrophilic properties?

The fatty acid components provide the hydrophobic properties, while the the alcohol and phosphate components, called the polar head group, provide the hydrophilic properties.

In mammals, the major site for triacylglycerol storage is

adipose tissue. Each adipocyte (adipose cell or fat cell) contains a large lipid droplet, in which the triacylglycerols are housed.

Membrane lipids are __________ molecules, containing hydrophobic and hydrophilic properties.

amphipathic

Glycolipids are oriented in

an asymmetric fashion in membranes with the sugar residues always on the extracellular side of the membrane.

Lipids are defined as molecules that

are not soluble in water, but are soluble in organic solvents.

Soaps

are the sodium or potassium salts of fatty acids generated by the treatment of triacylglycerides with a strong base, a process called saponification.

In polyunsaturated fatty acids, the double bonds are separated by

at least one methylene group.

Glycolipids are _____-containing lipids.

carbohydrate

Fatty acids vary in

chain length and degree of unsaturation

The properties of fatty acids are dependent on

chain length and degree of unsaturation.

Hopaniods and various sterols play the role of ________ in

cholesterol; prokaryotes and plants

When double bonds are present, the fatty acid are commonly in the ____ configuration.

cis

Membrane of extremophiles are built from

ether lipids with branched chains

fatty acids usually have a(n) ______ number of carbons

even

The carbohydrate components of glycolipids are on the

extracellular surface of the cell membrane, where they play a role in cell-cell recognition.

Phospholipids are composed of four components:

fatty acids (2 or more), a platform (on which phospholipids are built), and a phosphorylated-OH group

More complex glycolipids, such as __________, contain

gangliosides; a branched chain of as many as seven sugar residues.

Two common platforms are

glycerol (a three-carbon alcohol) or sphingosine (a more complex alcohol)

Diplopterol is a

hopanoid (nonsterol)

Cis polyunsaturated fatty acids are essential components of our diets because

humans cannot synthesize them. These fatty acids are precursors to a variety of hormones and appear to offer some protection from coronary heart disease.

The ether linkages and branching structure of membrane lipids of extremophiles prevent

hydrolysis and oxidation of membranes in harsh environments.

Membrane lipids contain a _________ and a _________ moiety

hydrophilic, hydrophobic

Membrane anchors are

hydrophobic groups that are covalently attached to proteins and tether the proteins to the membrane.

Because fatty acids are ______ at physiological pH, they are usually referred to as

ionized; their carboxylate form, rather than the unionized acid.

What is sphingomylein

it is a common membrane sphingolipid and is especially common in the myelin sheath of nerve cells

What are hopanoids

natural pentacyclic compounds (containing five rings) based on the chemical structure of hopane.

Fatty acids can also be numbered from the methyl carbon atom, which is called the

omega (ω) carbon.

The major phospholipids are derived from

phosphatidate.

Phospholipids with a glycerol platform are called

phosphoglycerides or phosphoglycerols.

The major class of membrane lipids

phospholipids

Sitosterol is a

plant sterol

Migratory birds use fat stores to

power long flights without the opportunity to feed.

Steroids function as

powerful hormones such as estradiol and testosterone, facilitate the digestion of lipids in the diet, and are key membrane constituents.

Fatty acids may be ________ or ________

saturated, unsaturated

Phospholipids built on a sphingosine platform are called

sphingolipids.

Glycolipids in animals are derived from

sphingosine

All steroids have a tetracyclic ring structure called the

steroid nucleus. The steroid nucleus consists of three cyclohexane rings and a cyclopentane ring joined together.

Steroids are built on a _________ platform, consisting of

tetracyclic; three cyclohexane rings and a cyclopentane ring fused together. (Unlike the other classes of lipids, steroids exhibit a cyclical rather than linear structure.)

Common sources of triacylglycerides are

the animal lipids lard (from hogs) or tallow (from beef or sheep)

Some proteins are modified by

the covalent attachment of hydrophobic groups. Proteins are sometimes covalently bound to lipids to localize the protein to the cell membrane.

Premature aging can result from

the improper attachment of a hydrophobic group to a protein

Fatty acids are stored as _________ in which

triacylglycerols; three fatty acids are esterified to one molecule of glycerol. (Whats in membranes basically; Head groups (polar); chains-very hydrophobic; Chains can vary in length)