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