Lipids Flashcards
How are lipids defined
by chemical property of hydrophobicity - dissolved in organic solvents
What are the biological functions of lipids
- Energy storage: triaclyglycerols
- strucutral elements of biological membranes: phospholipids and sterols
- signal transduction (cell-cell communication): steriod hormones, prostaglandins
- enzyme cofactors: Coenzyme q, mitochondrial electron transport chain
- Vitamins: A,D,E,K
Light absorbing pigments: caratene
What are glycolipids
contain both sugar and lipid portions. important constituents of cell membranes
ex: human blood group are defined by glycolipids displayed on the outer surface of blood cells
ex: sphingolipids, gangliosides
what are lipoproteins
- plasma lipoproteins that are associated with cardiovasicular health and disease
- help to transport hydrophobic lipids in body
ex: VLDL, LDL, HDL
What are triacylglycerols
- fat storage
What are phosphoglycerides
- major lipids in membranes
What are fatty acids
- smallest lipid (least complex)
- building blocks of many complex lipids
- central intermediates in metabolism, free fatty acid present in trance quantities
What is the strucutre of a fatty acid?
- carboxylic acids with hydrocarbon chains ranging from 4-36 carbons
- if no double bonds: saturated fatty acid
- fatty acid with one (monounsaturated) or more (polyunsaturated) double bond in chain called : unsaturated fatty acid
How are fatty acids named
- when labelling number 1 assignmed to carboxyl carbon, and alpha is the carbon next to it
- name format A:B Δ^c,d
- A= number of carbons, B= number of double bonds, C= location of first double bond, d= location of second double bond
- alternative convention in naming PUFA is to specify the position of the double bonds relative to the methyl carbon (ω) count from methyl carbon
What are the common features of fatty acids
- have an even number of carbon atoms (usually)
- are unbranched
- double bonds found in cis configuartion
- double bonds in polyunsaturated fatty acids (PUFA) are **Methylene bridged /=\/=\/=**
- separated by a methlene carbon and therefore bond pattern is double, single, single, double
What are common occuring saturated fatty acids
Laurate: 12 (bay, laurel)
Myristate: 14 (myrtle nutmeg)
Palmitate: 16 (palm)
Stearate: 18 (tallow)
Arachidate: 20 (peanut
*Let Me Pick Some Apples
What are the typical unsaturated
*dont memroize structures just know how to name
What are transfatty acids
- partial dehydrogenation of unsaturated fatty aicds
- has transdouble bond
- manufactured this way, not naturally in nature
- want to partially hydrogenate to make solid at room temperature
how does solubilty and melting point differ from saturated fatty acids and unsaturated
- saturated chains adopt extended conformation, pack in fairly orderly way
- extensive favourable interactions, makes it more difficult to separate, as side chain length increases the melting point increases and solubility decreases
- unsaturated pack less regularly, less thermal energy required thus multing temp much lower
* due to extended nature, trans fatty pack more regualrly and show higher melting temp than cis formation
**double bonds melt easier**
What are derivatives of fatty acids
Carboxylic acids can combine with alcohols to form Esters
Carboxylic acids can combine with acids to form acid Anhydrides
What are Triacylglycerols?
TAGS (Fats and oils)
- “acyl” acid derivative
- majority of fatty acids in biological systems are found in the form of triacylglycerols
- Triacylglycerols are formed by linking three fatty acids to a glyercol molecule thorugh ester lnkages
- -* TAGs are the major constituaent of bulk fats and oils, inc human body fat
- highly hydrophobic as the polar carboxylic acids of fatty acids are tied up as (less polar) esters
- melting points of TAGs depend on length and degree of saturation of fatty acid constituents
What are most natural fats comprised of
complex mixtures of simple and mixed TAGs
- Simple: all fatty acid in all 3 positions
- Mixed: 2 or 3 different fatty acids
*Higher amount of long chain (C16 and C18) saturated fatty acids, higher the melting temperature of a natural fat
What are phosphate derivatives? why are they important?
Phosphoric acid (H3PO4) is a triprotic acid
- at neutral pH exists as an equilibrium mixture of H2PO4- and HPO42-
- mixture is represented by notation Pi
- phosphorylation adds negative charges to molecules, leading to an increase in water solubility
When phosphoric acids reacts with alcohols:
phosphate ester is formed
When phosphoric acid reacts with acids:
phosphoanhydrides are formed
What are glycerophospholipids
- phosphoglycerides
- primary constituents of Biological membranes
- carbon atoms 1 and 2 of glycerol are esterfied to two fatty acids (tail) while a highly polar or charged group is attached thorugh a phosphodiester linkage to the third “head”
- Glycerophospholipids are amphipathic, combine both hydrophilic (head portion) and hydrophobic (tail)
- property differentiates them from TAG and allows them to form lipid bilayer
What are the Major classes of Glycerophospholipids
What is Phosphatidycholine
- lecithin
- phosphatidylcholine (like all other glycerophospholipids) represents a class of lipids rather than a single moleule
- different combinations of fatty acids at position R1 anf R2 correspond to different phosphatidylcholine molecules
What happens to lipids in water
- aggregate to form roughly spherical micelles (smallest and simplest lipid aggregate; diameters of approz 3- a few hundred nm)
- hydrophobic tails are too bulky to pack into michelles, they aggregate into bilayers: which spontaneously fold back on themselves to form liposomes or vesicles with diameters as large as 1 micron or more
How are lipids analysed?
two phase extraction
- separated based on polarity on a column of silica gel or thorugh TLC
- progressively polar lipids elute from the column as solvents of increasing polarity are passed through it
- on thin layer plate less polar lipids move further
* separated fatty acids can be definitively identified through mass spectrometry
