Chapter 11: Lipids

Is it found in eukaryotes?

-yes, it is found to varying degrees in virtually all animal membranes

They are important ___________ consitituents.

They are important MEMBRANE consitituents.

This creates a macromolecule with a _________ head and a _________ tail.

This creates a macromolecule with a POLAR head and a NONPOLAR tail.

What is the most common chain length?

-16 and 18 carbons long

The amino group of the sphingosine backbone is acylated by...?

-a fatty acid (as in sphingomyelin)

In adipose cells, droplets of triacylglycerol coalesce to form...?

-a large globule in the cytoplasm -->this may occupy most of the cell volume

What does it contain?

-a single sugar residue, either glucose or galactose

The glycogen and glucose stores provide enough energy to sustain biological function for how long?

-about 18 to 24 hours

What are unsaturated fatty acids?

-acids with on eor mor edouble or triple bonds

What is the major site of accumulation of triacylglycerols in mammals?

-adipose tissue

Glycolipids are ubiquitous in...?

-all cell membranes

What are carbon atoms 2 and 3 often referred to as?

-alpha and beta, respectively

In sphingomyelin, the amino group of the sphingosine backbond is linked to a fatty acid by...?

-an amide bond

What is sphingosine?

-an amino alcohol that contains a long, unsaturated hydrocarbon chain

The major phosphoglycerides are derived from phosphatidate through the formation of...?

-an ester linkage between the phosphoryl group of phosphatidate and the hydroxyl group of one of several alcohols

The double bonds in polyunsaturated fatty acids are always separated by...?

-at least one methylene group

Why are these acids considered to be saturated?

-because every carbon atom is attached to four other atoms

Why is the concentration of free fatty acids in cells or the blood so low?

-because free fatty acids are strong acids -high concentrations would disrupt the pH balance of the cells

Why are fats good fuels?

-because they are more reduced than carbohydrates

In contrast, certain cis-polyunsaturated fatty acids are essential in our diets. Why are they essential?

-because we cannot synthesize them

Fatty acids in biological systems are usually how long?

-between 14 and 24 carbon atoms -->they usually contain an even number of carbon atoms

In phosphoglycerides, where are esther bonds formed between glycerol and the fatty acids?

-between the hydroxyl groups at C-1 and C-2 of glycerol and the carboxyl groups of the two fatty acid chains

How are traicylglycerols formed?

-by the attachement of three fatty acid chains to a glycerol molecule

What are glycolipids bound to?

-carbohydrates

Fatty acids always terminate in...?

-carboxylic acid groups

Where they play a role in...?

-cell-cell interactions

What is the simplest glycolipid?

-cerebroside

What is the most common steroid?

-cholesterol

Is the configuration of most double bonds in fatty acids cis or trans?

-cis

What is this process known as?

-esterification

What do they consist of?

-fatty acids attached to a scaffold that bears a charged phosphoryl group

What are saturated fatty acids?

-fatty acids composed of single bonds

What are free fatty acids used for?

-fuel

What are two key roles for fatty acids?

-fuels -building blocks for membrane lipids

Too much saturated and trans-unsaturated fats in the diet are correlated with...?

-hypercholesterolemia -cardiovascular disease

Describe how glycolipids are oriented within cell membranes.

-in an asymmetric fasion

What role does cholesterol have in cell membranes?

-it helps to maintain proper membrane fluidity

What, then, does it exist as outside of membranes?

-it is esterified to a fatty acid for storage and transport

What are triacylglycerols used for?

-it is the storage from of fatty acids

The repertoire of membrane lipids is extensive. However, these lipids possess a critical common structural theme. What is this?

-membrane lipids are amphipathic molecules containing both a hydrophilic and a hydrophobic moiety

Therefore, can a gram of anhydrous fat store more or less energy than a gram glycogen?

-much more (x6 times)

Do lipids form polymers?

-no

Is cholesterol found in prokaryotes?

-no

What are sphingolipids?

-phospholipids built on a sphingosine backbone

What are phosphoglycerides?

-phospholipids derived from glycerol

What is the C-3 hydroxyl group of the glycerol esterified to...?

-phosphoric acid

What is the reason for this trend.

-presence of a double bond introduces a kink in the fatty acids and makes tight packing between chains impossible

Where is adipose tissue found?

-primarily, underneath the skin

What is the biochemical basis for this correlation?

-remains to be determined

What are the five most common alcohol moieties of phosphoglycerides?

-serine -ethanolamine -choline -glycerol -inositol

Triacylglycerol stores allow survival for how long?

-several weeks

Compare the melting points of short chains vs. long chains.

-short chains have lower melting temperatures than long chains

What is a common sphingolipid found in membranes?

-sphingomyelin

What are the glycolipids in animal cells derived from?

-sphingosine

How are fatty acid carbons usually numbered?

-starting at the carboxyl terminus

What are glycolipids?

-sugar-containing lipids

What does this mean?

-the carbon atoms are bonded to hydrogen atoms and other carbon atoms rather than to oxygen atoms

What does this mean in terms of their carboxylic acid groups?

-the carboxylic acid groups are deprotonated

When energy is required during a fast, what happens to triacylglycerol molecules?

-the fatty acids are cleaved from the triacylglycerol and carried to the cells

How do glycolipids differ from sphigomyelin?

-the identity of the unit that is linked to the primary hydroxyl group of the sphingosine backbone -->in glycolipids, one or more sugars, rather than phosphorylcholine) are attache dto this group

Sphingomyelin is especially rich in...?

-the myelin sheath of nerve cells

What is a fatty acid's systematic name derived from?

-the name of its parent hydrocarbon with the substitution of "oic" for the final e

What part of glycolipids sit on the EC side of the membrane?

-the side with the sugar residues

All steroids have a tetracyclic ring structure called...?

-the steroid nucleus

What is the position of a double bond represented by?

-the symbol Δ followed by a superscript number

What is the last carbon atom in the chain called?

-the ω-carbon atom

How do steroids differ from other classes?

-they are polycyclic hydrocarbons

What role do they play in the body?

-they are precursors to important hormones

How are steroids different from other classes of lipids?

-they take a cyclical rather than a linear structure

How does this impact the van der waals interactions?

-this limits van der waals interactions

How many carbons does glycerol have?

-three

What does the steroid nucleus consist of?

-three cyclohexane rings and a cyclopentane ring joined together

How are the fatty acids attached to glycerol?

-through ester linkages

What is are phospholipids use for?

-to construct membranes

Why are lipids often attached to proteins?

-to provide them with additional biochemical properties -often, such attachments are necessary for a protein to associate with a hydrophobic environment such as a membrane

Fatty acids required for energy generation are stored as...?

-triacylglycerols

When...?

-undergoing combustion to carbon dioxide and water

Compare the melting points of unsaturated vs. saturated fatty acids.

-unsaturated fatty acids have lower melting points than those of saturated fatty acids of the same length

What is the definition of lipids?

-water-insoluble molecules that are highly soluble in organic solvents

Are fatty acids ionized at physiological pH?

-yes

The properties of fatty acids and lipids are markedly dependent upon what two factors?

1. chain length 2. degree of saturation

List some of the biochemical roles of lipids.

1. energy storage 2. components of membranes 3. play a variety of roles in signal transduction pathways

List the five major classes of lipids.

1. free fatty acids 2. triacylglycerols 3. phospholipids 4. glycolipids 5. steroids

What two different molecules can be used as the platform on which phospholipids are built?

1. glycerol 2. sphingosine, a more complex alcohol

List the three major components of phosphoglycerides.

1. glycerol backbone 2. two fatty acids 3. phosphorylated alcohol

A phospholipid is constructed from what four components?

1. one or more fatty acids 2. platform to which the fatty acids are attached 3. a phosphate 4. an alcohol attached to the phosphate

List the three major types of membrane lipids.

1. phospholipids 2. glycolipids 3. cholesterol

List four functions of adipose tissue.

1. synthesis of triacylglycerols 2. storage of triacylglycerols 3. mobilization of triacylglycerols into fuel molecules 4. thermal insulation

Because if this greater reduction, fats yield more _______ than carbohydrates.

Because if this greater reduction, fats yield more ENERGY than carbohydrates.

Is much phosphatidate present in membranes?

-no

When no further additions are made, what is the resulting compound known as?

-phosphatidate

Fatty acids are hydrophobic and so are stored in a nearly _________ form.

Fatty acids are hydrophobic and so are stored in a nearly ANHYDROUS form.

Does free cholesterol exist outside of membranes?

-no