lipids Flashcards
what is a fat
Any molecule which is solid at room temperature and soluble in an organic solvent
what is an oil
Any molecule which is liquid at room temperature and soluble in an organic solvent
what are lipids
Lipids are biological molecules which are soluble in organic solvents (e.g. acetone, ethanol, hexane).
Generally proteins and carbohydrates are insoluble in organic solvents.
At room temperature some lipids may be fats, others may be oils
The term ‘lipid’ encompasses a large and diverse range of compounds.
what are the 4 major functions of lipids in the body
Structural elements of biological membranes
Some (e.g. triacylglycerols) serve as highly efficient energy reserves and also provide insulation.
Many vitamins and hormones are lipids or derivatives of lipids.
Some (e.g. bile acids) help to solubilise other lipids during digestion.
explain the generalised lipid structure
NON-POLAR TAIL, Hydrophobic (water hating)
POLAR HEAD GROUP, Hydrophilic (water loving)
what is amphipathic
when Compounds which exhibit both hydrophilic (water loving) and hydrophobic (water hating) properties
what can amphipathic substances form in water
peculiar substances
what forms when we put lipids in water
a monolayer
how does a monolayer form
from the hydrophobic tails sticking away from the water
how are micelles formed
when the lipid / water mixture is vigorously stirred:
they are circular and look like the structure of a ‘smartie’ ( w outer chocolate layer being the heads and then the middle chocolate being the tails)
explain the biological membranes bilayer
this is structure of cell membrane
Hydrocarbon tails tend to lie in roughly parallel arrays.
Interaction is via Van der Waals forces
Polar head group is heavily hydrated
what are the 5 lipid categories
- Fatty acids
- Triacylglycerols
- Phospholipids
Phosphoglycerides
Sphingolipids - Glycosphingolipids
- Cholesterol
Steroid hormones
Bile acids
explain fatty acid structure
A fatty acid consists of a hydrocarbon chain with a terminal carboxylic acid group: CH3(CH2)nCOOH
Have carboxylic acid group with long polar tail
Because of the carboxylic acid group, fatty acids are weakly acidic and have a pKa of around 4.5
Because physiological pH is around 7.4, fatty acids therefore are ionised and amphipathic in behaviour
what are fatty acids in relation to lipids
they’re the building block of lipids
in biological systems are the fatty acid carbon numbers odd or even
even
how are fatty acids categorised
by chain length
explain fatty acids chain lengths
Short chain fatty acids C2 – C8 (volatile and smelly) ex; parmesan cheese
Medium chain fatty acids C10 - C14
ex; goats cheese
Long chain fatty acids C16 - C18 (most common) ex; palmitic acid found in palm oil (liquid), lard
Very long chain fatty acids C20 – C26
ex; cod liver oil
what do fatty acids vary in their degree of, and how
unsaturation
as;
- They may be saturated with no double bonds,
- Unsaturated with one double bond (monunsaturated),
- Or unsaturated with more than one double bond (polyunsaturated),
in most naturally occurring fatty acids the orientation around the double bond is in what conformation
cis rather than trans
why is the cis conformation important for structure
because each cis double bond inserts a bend into the hydrocarbon tail
With no double bonds theyre straight
With 1 double bond they have a slight bend
With 2 theyre more kinked
With 3 theyre even more kinked
And with 4 they basically fold
explain the physiological functions of fatty acids
Low levels of free fatty acids exist in all tissues
Poor solubility in water means they have to be transported in the blood by albumin (this likes hydrophobic molecules) – a plasma protein
Fatty acids are the precursors of many other lipids, see later
They provide about 9kcal/g compared to 4kcal/g for carbohydrates and proteins
In the form of triacylglycerols, they serve as the major energy reserves in the body and serve an insulatory function.
Essential fatty acids: linoleic & linolenic acid must be obtained from the diet, important in infant development and later life.
what are triacylglycerol’s sometimes called
triglycerides or fats
whats the structure of Triacylglycerols
Three fatty acids are covalently linked via an ester bond to a molecule of glycerol
The three fatty acids can all be different, all the same, or only two the same.
what can the Chain lengths of the fatty acids in triacylglycerols can be from
and whats the most common length of chain
4 - 22 carbon atoms
16 and 18 are the most common
Shorter chain lengths are found in butter and cheeses (characteristic smells)
