Chpt 12 Lipids Flashcards
Lipids Definition
Defined on the basis of chemical properties, not chemical structure
-Heterogenous groups of water insoluble (hydrophobic)organic molecules that can be extracted from tissues by non polar solvents (Chloroform)
Fatty Acids
Long hydrocarbon chain of various lengths (C12-C24) and degree of saturation terminated with carboxylic acid group
Saturated-no double bonds
Unsaturated- contains double bonds (cis or trans)Fat
Alpha carbon-carbon 2
Beta Carbon- Carbon 3
Omega Carbon-Terminal Carbon
Fatty Acid Solubility
The longer the chain the less solube (solubility decreases)
-was less solube than carbohydrates
Nomenclature: Simplified System
of C: # of double bonds cis or trans Delta, Delta
Fatty Acids to Know
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Formic Acid- 1 carbon Acetic Acid-2 Carbons Propionic acid- 3 Carbons Butyric acid-4 carbons Capric Acid- 10 C's Lauric Acid- 12 C's
Palmitic acid 16:0
Palmit(ole)ic acid 16:1 cis 9
Stearic acid 18:0 Oleic Acid 18:1 cis 9 Linole(ic) 18:2 cisx2 9,12 Linole(nic) 18:3 cisx3 9,12,15 Arachidonic Acid 20:4 cisx4 5, 8, 11 ,14 Lignoceric acid 24:0 Nervonic Acid 24:1
Two essential Fatty Acids in humans
Linoleic Acid (Omega 6 FA)
- 18:2 cis, cis (delta 9,12)
- cis, cis-9,12 octadecadienoic acid
- Precursor of arachidonic acid
- Deficiency lead to making arachidonic acid essential
Linolenic Acid (Omega 3 FA)
- 18:3 cis, cis (Detal 9, 12, 15)
- cis, cis, cis-9,12,15-octandecatrienoic acid
- Precursor for other omega 3 fatty acids
- Deficiency leads to decreased vision, altered learning behavior
Functions of lipids
Cellmembranes:
Phospholipids, glycolipids, sterols
Energy Storage:
- Triacylglycerol or fat
- stores 2.5 x more energy than equal weight of carbohydrates
Cell Signaling:
steroid hormones
Phospholipids
or Phosphoglycerides
Amphipathic
contain a:
- Glycerol
- polar head group (phosphate)
- two non polar tails (fatty acids)
Amphipathic
molecule with both hydrophobic and hydrophilic regions
Common Phospholipids
Head groups: Serine, ethanolamine, choline, inositol
Sphingoymylin
Sphingomylin
- a non glycerol containing phospholipid
- contains sphigosine (modified serine)
Glycolipids
contain
- substituted Serine (like sphingosine)
- 2 fatty acids
- Carbohydrate (ex glucose)
Triacylglycerol (fats)
Glycerol
-three fatty acids-> accumulates as fat droplets in cytoplasm
Cholesterol
Multi ring, non polar structure with a hydroxyl
- component of cell membrane
- precursor of steroid hormones
- 27 carbons
- four Rings A, B, C ,D called steroid nucleus
Substituted with
- Hydroxyl group- may be substituted by addition of ester
- two methyl groups
- a branched 8 carbon side chain
- one double bond
Micelle
Formed by ionized fatty acids
-steric constants prevent formation of micelle by phospholipids and glycolipids, which usually form vesicles
Phospholipid bilayer
(or vesicle)
Liposome (lipid vesicle) aqueous compartment surround by a phospholipid bilayer
-contains phospholipids, glycolipids, cholesterol
Formation of Phospholipid bilayer
(or vesicles)
Phospholipids spontaneously form bilayers in aqueous environment
-Energy consideration-> hydrophobic interactions between fatty acid tails. Electrostate and hydrogen bonding between head group and water molecules.
1) Suspend liquid in aqueous solution
2) Sonicate
- agitating with high freq sound waves
3) Vesicles form
4) gel filtration- to seperate particles on size
Phospholipid bilayer: Membrane proteins
Vary in percentage of proteins
Two types of proteins:
Trasmembrane (integral) proteins
-protein passes through both layers of the bilayer
-extraction requires detergent or organic solvent
-cross the membrane by hydrophobic alpha helixes
-some cross the membrane by hydrophobic beta sheets (BETA BARRELL)
Peripheral proteins
- attached to one side of the membrane. Associations with polar head groups or membrane proteins
- extraction requires increase in ionic strength or change in pH
Bacteriorhodopsin
Aracheal protein
- uses light energy to transport protons out of cell to create a proton gradient
- seven alpha helixes span membrane
Hydropathy Index
- Hydrophobic alpha helixes can be identified by plotting the hydrophthy index
- Plot sliding 20 amin acid average of free energy change
- once it meets a critical/criterion level is transmembrane protein
Plotting hydropathy index is not able to detect BETA BARRELS
Glycophorin
Red blood cell membrane protein
-single alpha helix spans membrane
Porin
E. coli and Rhodobacter capuslatus
-allows movement of material across the membrane
Peripheral proteins
Peripheral proteins are anchored to the membrane by:
- lipid anchors
- GPI anchors
- sometimes Hydrophobic alpha helixes
Solubility of membranes
Continium not all or non process
Fluid Mosaic model of membrane
Membrane are 2D solutions oriented lipids and globular proteins (transmembrane and peripheral)
-“rigid” Fluid that separates two fluid filled compartments
Movement of phospholipids within bilayer:
- Lateral is rapid
- Transverse (flip flop) is VERY slow
Movements of proteins varies greatly:
- Lateral movements: some proteins move as fast as lipids, others do not due to being anchored to cytoskeleton
- transverse (flip flop)-does not happen for proteins- orientation of proteins is established at time of protein synthesis
Membrane Fluidity: Solid like vs fluid like
controlled by fatty acid composition and cholesterol content.
-fatty acids exist in rigid state or fluid state.
-changes of state changes abruptly at Tm: degrees of unsaturation and length of Fatty acid
Shorter fatty acids=Lower Tm
More double bonds=Lower Tm
Cholesterol-membrane antifreeze and coolant
Membranes are asymmetric
-membranes contain different lipids and protein components on the different surfaces (faces) of the membrane
