Chapter 12: Lipids and Cell Membranes Copyright © 2007 by W. H. Freeman and Company Berg Tymoczko...
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Transcript of Chapter 12: Lipids and Cell Membranes Copyright © 2007 by W. H. Freeman and Company Berg Tymoczko...
Chapter 12:Lipids and Cell Membranes
Copyright © 2007 by W. H. Freeman and Company
Berg • Tymoczko • Stryer
BiochemistrySixth Edition
Lipids
• Classified by solubility, not structure.
• Lipids are any molecules that can be extracted from cells using nonpolar organic solvents.
• Lipids are non-polar molecules and are not water soluble although some are amphipathic.
Lipid Classes
Triglycerides (triacylglycerols)
Glycerol based phospholipids
Sphingosine derivatives: sphingomyelins and gangliosides
Steroids/sterols: cholesterol (C27), bile acids (C24), adrenocortical hormones (C21), and sex hormones (C19 & C18)
Eicosinoids: prostaglandins, thromboxanes, leucotrienes and prostacyclins
Fat-soluble vitamins (pg 424)
Triacylglycerol (triglyceride)
Triglyceride (as shown below) is derived from glycerol plus one molecule each of palmitic acid, oleic acid, and stearic acid, the three most abundant fatty acids.
CH2OC(CH2)14CH3
CH2OC(CH2)16CH3
CH3(CH2)7CH=CH(CH2)7COCH
O
O
O
oleate (18:1)
stearate (18:0)
palmitate (16:0)
A very non-polar molecule (storage fat)
Triacylglycerol
• Physical properties of triglycerides depend on the fatty acid components.– the melting point increases as the number of
carbons in the hydrocarbon chain increases and as the number of double bonds decrease.
– triglycerides rich in unsaturated (cis double bonds) fatty acids are generally liquid at room temperature and are called oilsoils.
– triglycerides rich in saturated fatty acids are generally semisolids or solids at room temperature and are called fatsfats.
Fatty AcidsNaturally occuring components of triacylglycerols and phospholipids
Naming Fatty Acids
omega end () carboxyl end (1)
Table of Fatty Acids
Phospholipids
• Phospholipids are the second most abundant group of naturally occuring lipids.– they are found almost exclusively in plant and
animal membranes. Membranes vary in the lipid vs protein content depending upon function.
– the most abundant phospholipids are derived from phosphatidic acid, a molecule in which glycerol is esterified with two molecules of fatty acid and one of phosphoric acid.
– a second class of phospholipids are the sphingomyelins derived from N-acylsphingosine (ceramide) and a phosphate.
Phosphatidic Acid
Glycerol residue
phosphate
Glycerophospholipid cartoon
Head-polar
Tail – nonpolar
An amphipathic structure
Head Pieces
Glycerophospholipids
Sphingophospholipids
PalmitoylSCoA + Serine Sphingosine
Trans db
Trans db
Ceramide phosphate
CH
CH
CH2-O-P-O-
OH
N
O
from serine
from palmitic acid
stearic acid O
O-
• N-acylsphingosine-P (ceramide phosphate)
– the N-acyl fatty acid is usually unsaturated. – the alcohol normally attached to the phosphate is
choline.
Trans db
Glycolipids (no phosphate)
(Ceramide + glucose or galactose)
Glycolipids
A complexcarbohydrate
Gangioside
(Ceramide + a complex carbohydrate)
Isoprenoids & the Sterol Family
Isoprenoids are derived from isopentenyl-PP (related to 5-carbon isoprene). Compounds include the terpenes, sterols and fat soluble vitamins.
Sterol Family:
Cholesterol: (C27) Parent molecule and a membrane component
Bile acid salts: (C24) Emulisfy fats for digestion
Adrenocortical Hormones & Progesterone: (C21) Communication
Sex Hormones: Male (C19) and Female (C18)
Cholesterol, C27
Bile acids, C24
C21, C19 and C18
AdrenocorticalHormone
Sex Hormones
Male Female
Eicosanoids
ProstaglandinsProstacyclins, Thromboxanes,Leucotrienes,
Cis - - eicosatetraenoic acid
Eicosanoids
Eicosanoids
Lipid Aggregation
Lipids aggregate to form large non-covalent assemblies.
Micelles are spontaneously formed by fatty acids to provide stabilization in aqueous media.
Phospholipids spontaneously for lipid bilayers. The non-polar tails associate with each other and the polar heads interact with water.
Singer & Nicolson proposed the fluid-mosaic membrane model to incorporate proteins and provide functionality.
Tail (nonpolar) Head (Polar)
Similar structures
Soap Micelle (cross section)
Fatty acid salts
Non-polar inside; Polar outside
Lipid Biayer Cartoon
Phospho lipids
Non-polar inside; Polar surface
Space Filling Model
Close pack with saturated sidechains (less fluid)
Space Filling ModelPacking disrupted by unsaturated sidechains
(more fluid)
Liposome (Lipid vesicle)
Spontaneous formation of liposomes
Trapping Glycine inside of liposomes
Membrane Permeability
Low permeability for ions. Small non-polar molecules (O2, CO2, HOH) pass more easily.
Integral (a,b,c) and peripheral (d,e) Proteins
Bacteriorhodopsin ( strands)
Porin ( strands)
Permits free transport of small molecules.
Diagonal lines show hydrogen bonding between anti-parallel strands.
Non-polar residues are in yellow.
Protein Domain Anchor
Membrane Anchors
Mannose
NAcGlc
Glycophorin in red cells
Hydropathy Plot
Fluid Mosaic Model
Fluid Mosaic Model
Membrane Composition
Inner and Outer Leaflets
Membrane Diffusion
Membrane components are fluid.
The two sides are assymetric.
Phase Transition Temperature
Transition Temperatures
Fat Soluble Vitamins
Saturated
Unsaturated (cis)
Lipoproteins
Endocytosis
End of Chapter 12
Copyright © 2007 by W. H. Freeman and Company
Berg • Tymoczko • Stryer
BiochemistrySixth Edition