Lecture 12 Flashcards
are lipids water soluble?
no because of the increase in hydrocarbons
they do not form covalent polymers –> there are noncovalent interactions
structure of lipids
polar, hydrophilic head
&
larger, nonpolor hydrophobic tail
tail driven by entropy effect
2nd stabilizing force: van der waals @ HC
amphiapatic
causes formation of micelles and membrane bilayers.
fatty acids
carboxylic acid with a long HC chain– usually 12-24 carbons
- weak acid with pka of ~4.5
saturated
all carbons saturated with hydrogens (no double bonds)
unsaturated
1+ double bonds, naturally occurring, (cis)
as bonds insert and bend into HC, still have freedom of rotation–> many conformations
there are even # of C’s b/c of 2C precursor
monolayers in air
water interface with carboxylate group immersed in water and HC tail out of water
micelles
if shaken with water, HC tail cluster together
Triacylglycerols: Fats
long HC= ^ energy storage b/c carbon is in reduced form so it yields a large amount of energy on oxidation.
this is why it’s used for storage of metabolic energy.
Triacylglycerols structure
triester of fatty acids and glycerols; major long term energy storage molecules in many organisms.
simple fats
same fatty acid esterified, mixed= more common
fats rich in unsat EA = liquid at room temp
fat storage functions
E production: most fat in animals is oxidized for the generation og ATP, to drive metabolic processes
heat prod: some specialized cells oxidized triglycs for heat prod rather than to make ATP
insulation: layers of fat cells under the skin serve as thermal insulation
membrane lipids
amphipathic- form surface monolayers, bilayers or vesicles when in contact with h2o
Boundary – defines cells and organelles
But - must be selectively permeable & allow for transmission of molecules and information
Membranes can be used to store and utilize energy
Must maintain concentration gradients
(eg. H+, Na+, K+, Ca+2, small molecules)
(used for transport and signaling)
membrane must be
flexible- adopt various shapes and be self sealing
- Must accommodate proteins of various types and shapes
- Must allow for diffusion (both Lipids and Proteins)
- Must allow for vesicle formation and membrane fusion
• Must be adaptable to varying cellular conditions and functions
Glycerophospholipids :
Important building blocks of biological membranes
ion gradient
way to store energy
- transport molecules
- signaling
Fatty Acids:
Important building blocks of glycerophospholipids and many other lipids like sphingolipids, and fats
Fatty Acids- four key biological roles
- Essential components of biological
membranes
2.Post-translational modifications –
localization of proteins to membranes
3.Intra- and Inter-cellular signaling molecules
4.Energy storage: Main component of
Fats
Fatty Acids - starting point for understanding Cellular Membranes and Lipid Metabolism
Carboxylic Acids with long hydrocarbon chains
Most commonly have 12-24 carbons
Typically linear
Can have one or more double bonds
(cis-double bonds: 30° kink in the hydrocarbon chain)
n-Octadecanoate
18:0
Oleate cis-9-Octadecanoate
18:1(Δ9)
9,12,15- Octadecanoate
Linolenate
18:3(Δ9,12,15)
18:3 n-3
ω3 fatty acid
Double bonds in Fatty Acids are not conjugated
Laurate
12:0 44.2
Myristate
14:0 53.9
Palimitate
16:0 63.1
Stearate
18:0 69.6
Arachidate
20:0 76.5
Palmitoleate
16:1Δ9 -0.5
Oleate
18:1Δ9 16.0
Linoleneate
18:3Δ9,12,15 -11.0
Arachidonate
20:4Δ5,8,11,14 -50.0
diff between 18 carbon fatty acids
stearate
oleate
elaidate
stearate 18:0 69.6°C
oleate 18:1Δ9 12.0 °C
elaidate 18:1Δ9 45.0 °C
(oleate= cis, elaidate= trans)
Note: Elaidate is the major trans fat found in hydrogenated vegetable oils. Some is found naturally in cow milk.
Lipid
A Lipid is: “any of various substances that are soluble in nonpolar organic solvents (such as chloroform and ether), that are usually insoluble in water, that with proteins and carbohydrates constitute the principal structural components of living cells”
Triacylglycerols (Fats or Triglycerides)
Stored in Lipid Droplets in Adipocytes (below) and other cell types
Fats are very hydrophobic
Fats pack closely together excluding water
Efficient form of stored energy.
Membrane Lipids – Cardiolipins
- Cardiolipin - “double” phospholipid that has four fatty acid tails
- Important component of the inner mitochondrial membrane. Constitutes about 20% of the total lipid.
- Serves as an insulator and stabilizes the activity of protein complexes important to the electron transport chain
Ceramides
the parent compounds of more abundant sphingolipids
Sphingomyelins
Conformationally similar to phosphoglycerides.
Found in Myelin sheath that surrounds neuronal cells
Cerebrosides
Head group is a single
sugar (non-ionic)
Gangliosides
Complex oligosaccharide head group with at least one sialic acid
Complex carbohydrate head group:
- Can specifically bind proteins
- Certain pituitary hormones
- Attachment site for Cholera Toxin
- Cell-cell recognition
- Growth and Differentiation
• Altered metabolism can lead to severe neurological disorders
• Tay-Sachs disease
• Defect in a lysosomal
enzyme needed to degrade Gangliosides
Membrane Lipids - Cholesterol
Steroids have four fused, non-planar rings
(Sterols are a subgroup of steroid alcohols)
Parent compound to other steroids
Lipids self-associate into larger complexes in aqueous solutions
Lipid self-association is driven by the Hydrophobic Effect
• Minimize contact of hydrocarbon chains with water
– maximize entropy (ΔS) (ΔG=ΔH-TΔS)
• Favorable van der Waals Interactions
Amphipathic Lipids like Glycerophospholipids & Sphingolipids
- Hydrophilic head group is highly hydrated
- Spontaneously form a bilayer
- No exposed edges – self-sealing
- Self-assembly is a highly cooperative process
Amphipathic properties of phospholipids
promote self-assembly of lipid bilayers
Shape matters – Phosphoglycerides spontaneously form bilayers.
Single Fatty-Acyl chains, like detergents, tend to form micelles.
What would you expect from the self-assembly of fats in aqueous solutions?
Amphipathic properties of phospholipids promote self-assembly of lipid bilayers
Shape matters – Phosphoglycerides spontaneously form bilayers.
Single Fatty-Acyl chains, like detergents, tend to form micelles.
Biological Membranes
The Fluid Mosaic Model of membrane organization
- The Lipid Bilayer – a thin two-dimensional fluid
- Membrane is assembled by non-covalent interactions
- Membrane is Asymmetric
- Lipids, Peripheral and Integral Proteins, Glycosylation
Summary
- Structures, nomenclature, and properties of fatty acids
- Fatty acids are an important component of many biological lipids
- Properties of many lipids are determined by their component fatty acids
• Types of Membrane Lipids
• Triacylglycerols (fats) - energy storage
• Glycerophospholipids, sphigolipids, sterols –
Membrane lipids (amphipathic molecules)
- Self-Assembly into larger structures
- Globules, micelles, bilayers
