Lipids

Question 1

How are lipids defined

Answer 1

by chemical property of hydrophobicity - dissolved in organic solvents

Question 2

What are the biological functions of lipids

Answer 2

• 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

Question 3

What are glycolipids

Answer 3

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

Question 4

what are lipoproteins

Answer 4

• plasma lipoproteins that are associated with cardiovasicular health and disease
• help to transport hydrophobic lipids in body
  ex: VLDL, LDL, HDL

Question 5

What are triacylglycerols

Answer 5

• fat storage

Question 6

What are phosphoglycerides

Answer 6

• major lipids in membranes

Question 7

What are fatty acids

Answer 7

• smallest lipid (least complex)
• building blocks of many complex lipids
• central intermediates in metabolism, free fatty acid present in trance quantities

Question 8

What is the strucutre of a fatty acid?

Answer 8

• 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

Question 9

How are fatty acids named

Answer 9

• 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

Question 10

What are the common features of fatty acids

Answer 10

• 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

Question 11

What are common occuring saturated fatty acids

Answer 11

Laurate: 12 (bay, laurel)

Myristate: 14 (myrtle nutmeg)

Palmitate: 16 (palm)

Stearate: 18 (tallow)

Arachidate: 20 (peanut

*Let Me Pick Some Apples

Question 12

What are the typical unsaturated

Answer 12

*dont memroize structures just know how to name

Question 13

What are transfatty acids

Answer 13

• 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

Question 14

how does solubilty and melting point differ from saturated fatty acids and unsaturated

Answer 14

• 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**

Question 15

What are derivatives of fatty acids

Answer 15

Carboxylic acids can combine with alcohols to form Esters

Carboxylic acids can combine with acids to form acid Anhydrides

Question 16

What are Triacylglycerols?

Answer 16

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

Question 17

What are most natural fats comprised of

Answer 17

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

Question 18

What are phosphate derivatives? why are they important?

Answer 18

Phosphoric acid (H₃PO₄) is a triprotic acid

• at neutral pH exists as an equilibrium mixture of H2PO4^- and HPO4^2-
• mixture is represented by notation P_i
• phosphorylation adds negative charges to molecules, leading to an increase in water solubility

Question 19

When phosphoric acids reacts with alcohols:

Answer 19

phosphate ester is formed

Question 20

When phosphoric acid reacts with acids:

Answer 20

phosphoanhydrides are formed

Question 21

What are glycerophospholipids

Answer 21

• 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

Question 22

What are the Major classes of Glycerophospholipids

Answer 22

Question 23

What is Phosphatidycholine

Answer 23

• 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

Question 24

What happens to lipids in water

Answer 24

• 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

Question 25

How are lipids analysed?

Answer 25

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*