Biochem Lipids Lecture 1 Flashcards by michael perna

Lipids are a chemically diverse group of compounds.

Are they soluble in water?

What about in organic solvents?

yes

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____ have the simplest structure of all lipids. Other types of lipids contain them or are derived from them

Fatty acids

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What lipids are not derived from fatty acids?

Steroids

Lipid Vitamins (A,D,E,K)

Terpenes

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What are terpenes derived from?

Isoprene

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What are the functions of lipids?

Storage (fats and oils)

Structural elements of biological membranes (phospholipids)

Signals (hormones), enzyme cofactors, and pigments

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Describe the structure of fatty acids

Carboxylic acids with long hydrocarbon chains (4 to 36 carbons)

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Are all fatty acid chains unbranched and saturated?

No, some are unbranched and saturated

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Stearic acid has 18 carbons in its chain with no double bonds, so its designated as

Other fatty acids contain one or more double bonds

18:0

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Oleic acid has 18 carbons in its chain with one double bond between the 9th and 10th carbon. It is described as…

18:1(Δ9)

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Linoleic acid is a polyunsaturated fatty acid containing 18 carbons and 2 double bonds, between the 9th and 10th and 12th and 13th carbons. it is abbreviated as

18:2 (Δ9,12)

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The double bonds are in the ___ conformation for nearly all naturally occurring unsaturated fatty acids

Cis

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____ fatty acids are obtained from dairy products and meat

Trans

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trans fatty acids are associated with _____ LDL and decreased _____

LDL (bad cholesterol)

HDL (good cholesterol)

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Do most fatty acids have an even or odd number of carbohydrates? Why?

Even because the are synthesized by condensation of two carbon units

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The melting points of saturated fatty acids INCREASES/DECREASES as the number of carbon atoms increases

Why?

Increases

The increased number of van der Waals interactions increases with each C

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The melting point INCREASES/DECREASES as the number of double bonds increases for 18 carbon chain fatty acids

Decreases

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______ fatty acids can pack tightly while ___ fatty acids have kinks in their hydrocarbon chains due to the cis double bonds. Their interactions with each other are weaker

Saturated

Unsaturated

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Triglycerols are composed of:

Three fatty acids

Each fa is an ester linkage with a single glycerol

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Simple triacylglycerols contain the samy fatty acids in all three positions and are named after that fatty acid

For 18:0 (stearic acid) the triacyl glycerol is

Stearin

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Most naturally occuring triacylglycerols are UNIFORM/MIXED

Mixed, they contain a mixture of saturated and unsaturated fatty acids of different chain length

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triacylglycerols are CHARGED/UNCHARGED, POLAR/NONPOLAR, HYDROPHILIC/HYDROPHOBIC

uncharged, nonpolar, hydrophobic

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The polar ____ of glycerol and the ___ of the fatty acids are bound in ester linkages

Hydroxyls

Carboxylates

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Depending on their melting point, triacylglycerols may be liquids or solids at RT. The melting point depends upon the type of ___ present

Unsaturated —>

Saturated—->

Fatty acids

Liquid

Solid

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Vegetable oils are mainly triacylglycerols with SATURATED/UNSATURATED

Thus, they are liquid/solid at RT

Unsaturated FAs

Liquid

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High lipid containing food spol "rancid" when exposed to Why?

Oxygen Double bonds in unsaturated fatty acids may undergo oxidative cleavage yielding aldehydes and carboxylic acids of shorter chain length and higher volatility (odor)

Commercial vegetable oils undergo _______ to improve shelf-life and high temperature stability What two things result?

hydrogenation Catalytic hydrogenation reduces some double bonds to single bonds “saturated” Catalytic hydrogenation converts others to trans double bonds (french fries, donuts and cookies have historically contained trans fatty acids).

Two advantages to using triacylglycerols as energy stores rather than polysaccharides

1. Carbon atoms of fatty acids are more reduced then those of sugars. Oxidation of triacylglycerols yield twice as much energy as carbohydrates. 2. Triacylglycerols are hydrophobic and unhydrated. No extra water needs to be stored in contrast to polysaccharides

These are esters of long chain (C14 to C36) saturated and unsaturated fatty acids with long chain (C16 to C30) alcohols Their melting points are HIGHER/LOWER than triacylglycerols

Waxes Higher

Are waxes water repellant? Are they firm?

Yes Yes Lanolin, beeswax, carnauba wax and wax extracted from spermaceti oil (whales) are used to make lotions, ointments and polishes.

What are the two major components of biological membranes

Glycerophospholipids and Sphingolipids

These are membrane lipids with two fatty acids esterified to the first and second carbons of glycerol, and a highly polar or charged group attached through a phosphodiester bond to the third carbon.

Glycerophospholipid

Glycerophospholipids are named as derivatives of their parent compound _____, according to the nonpolar/polar alcohol in the heat group One example is

Phosphatidic acid Polar Phosphatidylserine

T/F: the polar alcohol in glycerophospholipids may be negatively charged, positively charged, or neutral

True

What three glycerophospholipids are the most common? Do the fatty acids on them vary?

Choline, ethanolamine, and serine Yes widely

Sphingolipids are composed of

sphingosine (a long chain amino alcohol) a long chain fatty acid a polar head group joined by either a glycosidic or phosphodiester linkage

Draw the structure of a glycerophospolipid How many total bonds are on phosphate?

! 5

C1, C2, and C3 of sphingosine are structurally analagous to the three carbons of

Glycerol

When a fatty acid of sphingolipids is attached in amide linkage to NH2 on C2, the resulting compound is a

Ceramide

What are the three classes of sphingolipids? All are derivatives of ____ but have different head groups

sphingomyelins, glycosphingolipids and gangliosides Ceramides

This subclass of sphingolipids there is a phosphodiester linkage to the OH of C1 of sphingosine

Sphingomyelin

This subclass of sphingolipids one or more sugar molecules are connected in a glycosidic bond to the OH of C1 of sphingosine.

Glycosphingolipids

This subclass of sphingolipids have oligosaccharides as their polar head groups and one or more residues of N-acetylneuraminic acid

Gangliosides

Know phosphatidylchoine, phosphatidylethanolamine and phosphatidylserine structures.

This is the major sterol in animal tissues

Cholesterol

How many fused rings does cholesterol have? What else are they composed of?

4 (the steroid nucleus) Alkyl Side chain Polar head group (OH and C3)

The steroid nucleus of cholesterol is nearly ___ and ____, with no rotation about C-C bonds

Planar and rigid

What type of phospholipids are predominate in biological membrane?

Double chain phospholipids

Synthetic membranes, made from pure phospholipids, possess many of the same basic characteristics of natural membranes

Glycerophospholipids and sphingolipids are “polar lipids” which can be represented as follows:...

Glycerophospholipids and sphingolipids are “polar lipids” that form ___ in aqueous dispersions

Bilayers

The hydrocarbon chains of the lipids are ____. They aggregate together and minimize their contact with water (hydrophobic effect)

nonpolar

The hydrophilic, polar head groups aggregate together towards the surface where they maximize their contain with water through ___ and ___

H bonding Dipole-dipole interactions

The planar bilayers of glycerophospholipids and sphingolipids form a vesicle aka.. The __ regions at the edges of the bilayer are in contact with water The bilayer folds back on itself to form a hollow ____

Liposome Hydrophobic Sphere (vesicle)

Maximum stability of liposomes is present when there is a ______ inside the spherical bilayer

Water cavity

Precursors to the first living cells may have resembled ____

Vesicles

Biological membranes are composed of polar lipids and

Proteins

The ____ for membrane structure was developed to more fully describe the fundamental properties of membranes

Fluid Mosaic Model

In the fluid mosaic model, the ____ form a bilayer ____ are embedded in the bilayer sheet

Phospholipids Integral protein molecules

The integral proteins in the phospholipid bilayer are held by ______ interactions between membrane lipids and the hydrophobic domain of the protein

Hydrophobic

Some integral proteins protrude only from one side of the bilayer while others span the entire membrane thickness

The surfaces of integral membranes exposed to water are hydrophobic/hydrophilic The surfaces of integral proteins embedded in the bilayer are hydrophobic/hydrophilic

Hydrophilic Hydrophobic

The bilayer membrane also contains ______ which interact with polar head groups of lipids and proteins on both sides of the bilayer

Peripheral Proteins

The membrane bilayer is fluid because most of the interactions among its components are _____

Weak (non-covalent)

T/F: Lipid and protein molecules are NOT free to diffuse laterally into the bilayer

False, they are free to move laterally in the bilayer

Lipids and proteins can diffuse ____ in the bilayer

Laterally

Lateral diffusion is very slow/fast

Very fast

Experimentally, lateral diffusion can be shown by using a method called

fluorescence recovery after photobleaching (FRAP)

In FRAP, fluorescent probes are attached to the ______ groups of lipids, and fluorecence microscopy is used to monitor the probes over time

Head groups

In FRAP, an intense laser light pulse is focused on a small area of a cell surface containing fluorescence-tagged lipids, and the fluorescence groups are bleached (i.e. they no longer fluoresce when viewed in the dimmer light of the fluorescence microscope.

Within milliseconds of bleaching in FRAP, the fluorescence in the bleached area returns indicating that the bleached molecules moved out of the region while unbleached molecules diffused into the region. The rate of fluorescence recovery after photobleaching (FRAP) is a measure of the rate of lateral diffusion of the lipids

Membrane proteins also diffuse laterally in the plane of the bilayer

! Slide 24

Two sides of a membrane are different with respect to the lipids and proteins present in the inner and out layers, these layers are also called

Leaflets

Different integral proteins are embedded in each side of the membrane during synthesis, assymetric arrangement of membrane proteins results in

functional asymmetry

`What must be overcome to move the hydrophilic portion of a protein across the lipid bilayer?

A large energy barrier

A protein must give up its interactions with water and then diffuse through a solvent (lipid) in which it is poorly soluble This prevents proteins from distributing themselves equally on both sides of the membrane

For membrane lipids, even with a single leaflet, the lipid distribution is not Cholesterol and sphingolipids form ____ in the outer monolayer of the plasma membrane They can often be thought of as rafts within a sea of more liquid disordered phospholipids, certain integral membrane proteins are more associated with these rafts

Random Microdomains

This type of diffusion of lipid molecules across the bilayer is caled "flip flop"

Transverse Diffusion

Is flip flop a fast process?

No, its half life is in days

Membranes are also impermeable to these two things Specific proteins are needed to help diffusion across the nonpolar lipid bilayer, called

Ions and polar most substances Transporters

Membranes are, however, permeable to ___ molecules

Water Molecules

_____ transporters can move substrates across the membrane against a concentration gradient

Active Transporters

A family of integral proteins, called ___, provide channels for the rapid movement of water molecules across plasma membranes

Aquaporins

How many aquaporins with specialized roles are there in humans? What speed do water molecules flow through them?

10 10^9 (s^-1)

Do aquaporins allow the transport of protons?

No.

Selectivity of AQP-1 is based upon its

Structure

How many monomers, each forming a transmembrane pore large enough for water to move through, does AQP-1 have?

Each of the 4 monomers of AQP-1 has how many transmembrane helical segments and __ shorter helices with the sequence N P A

6 transmembrane helical segments, 2 shorter helices

Where do the 6 transmembrane proteins of AQP-1 form a pore?

Through the monomer

The NPA-containing helices extend to the middle of the bilayer from opposite sides. The NPA regions overlap in the middle to form a structure that only allows water to pass

Biochem Lipids Lecture 1 Flashcards

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