Biochem Lipids Lecture 1 Flashcards
Lipids are a chemically diverse group of compounds.
Are they soluble in water?
What about in organic solvents?
No
yes
____ have the simplest structure of all lipids. Other types of lipids contain them or are derived from them
Fatty acids
What lipids are not derived from fatty acids?
Steroids
Lipid Vitamins (A,D,E,K)
Terpenes
What are terpenes derived from?
Isoprene
What are the functions of lipids?
Storage (fats and oils)
Structural elements of biological membranes (phospholipids)
Signals (hormones), enzyme cofactors, and pigments
Describe the structure of fatty acids
Carboxylic acids with long hydrocarbon chains (4 to 36 carbons)
Are all fatty acid chains unbranched and saturated?
No, some are unbranched and saturated
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
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)
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)
The double bonds are in the ___ conformation for nearly all naturally occurring unsaturated fatty acids
Cis
____ fatty acids are obtained from dairy products and meat
Trans
trans fatty acids are associated with _____ LDL and decreased _____
LDL (bad cholesterol)
HDL (good cholesterol)
Do most fatty acids have an even or odd number of carbohydrates? Why?
Even because the are synthesized by condensation of two carbon units
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
The melting point INCREASES/DECREASES as the number of double bonds increases for 18 carbon chain fatty acids
Decreases
______ 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
Triglycerols are composed of:
Three fatty acids
Each fa is an ester linkage with a single glycerol
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
Most naturally occuring triacylglycerols are UNIFORM/MIXED
Mixed, they contain a mixture of saturated and unsaturated fatty acids of different chain length
triacylglycerols are CHARGED/UNCHARGED, POLAR/NONPOLAR, HYDROPHILIC/HYDROPHOBIC
uncharged, nonpolar, hydrophobic
The polar ____ of glycerol and the ___ of the fatty acids are bound in ester linkages
Hydroxyls
Carboxylates
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
Vegetable oils are mainly triacylglycerols with SATURATED/UNSATURATED
Thus, they are liquid/solid at RT
Unsaturated FAs
Liquid
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
- Carbon atoms of fatty acids are more reduced
then those of sugars. Oxidation of triacylglycerols
yield twice as much energy as carbohydrates. - 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?
4
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
!
