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)
Most natural fats contains a complex mixture of triacylglycerols what happens to the melting point due to this
they can melt over a broad range of temps
eg. Cocoa butter is unusual in that it is mostly a single triacylglycerol (composed of palmitic, oleic and stearic acids) and has a fairly sharp melting point (so chocolate melts in the mouth without feeling greasy and melts quick).
where is the majour storage site of triacylglycerols in mammals
the cytoplasm of adipose cells (fat cells)
adipose cells are huge compared to normal cells
phat are phocpholipids structure
Are polar, ionic compounds composed of an alcohol, attached by a phosphodiester bridge to either diacylglycerol or sphingosine.
what does it mean that phospholipids are amphipathic
Polar head = phosphate group plus whatever is attached to it
Hydrophobic = hydrocarbon tail
The hydrophobic portion of phospholipids associates with what other non-polar components of membranes,
Glycolipids
Sphingosine
Protein
Cholesterol
what 2 categories can phospholipids be sub divided into
Phosphoglycerides
Sphingolipids
what are Phosphoglyceride and its structure
Are the major class of phospholipids which make up a large proportion of the membrane in mammals, bacteria and plants
Phosphoglycerides contain a glycerol backbone with 2 fatty acids bound, 1 at top and one at middle of the glycerol
and they have a phosphate group bound to end of glycerol with an alcohol group attached to it
what are the names of Phosphoglycerides based off of
the alcohol group attached
what are sphingolipids and their structure
Are not derived from glycerol
Backbone of sphingolipids is sphingosine, an amino alcohol that contains a long, unsaturated hydrocarbon tail
how is ceramide obtained from sphingolipids
If a fatty acid is linked via an amide bond to the amino group of sphingosine
what does further additions of the hydroxyl group lead to on sphingolipids
and give and ex and explain its structure
a variety of other membrane lipids
One important example is sphingomyelin, which is highly concentrated in the brain and nervous tissue.
In sphingomyelin one hydroxyl group is phosphorylated and a choline group attached
explain Glycosphingolipids structure
In glycosphingolipids, the alcohol group of sphingosine is attached to one or more sugar molecules, usually glucose or galactose.
Note that they do no contain phosphate and therefore are not classed as phospholipids.
what are the simplest glycosphingolipids and explain their structure and where theyre found
cerebrosides – in which there is usually only one sugar molecule attached
These are usually found in brain and neural tissue.
name a complex glycosphingolipid and its structure and where its found
gangliosides, contain a branched chain of up to 7 sugar residues.
These are normally found in nerve tissue
what group is cholesterol a member of
steroids
what does a steroidal compound (cholesterol) contain
a fused ring system, labelled A, B, C and D.
why is cholesterol incorporated into cell membranes
as it gives them rigidity
what other biological important molecules are derived from cholesterol
- steroid hormones: sex hormones - testosterone , progesterone
- corticosteroids, such as cortisol
- mineralocorticoids - such as aldosterone
- bile salts
what are bile salts structure
Polar derivatives of cholesterol
what do bile salts act as in the small intestine and why
Act as detergents in the small intestine to aid digestion of fats
what is the major mammalian bile salt called
glycoholate
