Lipids Flashcards
Lipids
Lipids (fats)—are diverse class of biological molecules,
containing hydrogen, carbon and oxygen atoms.
They are insoluble in water because they are hydrophobic
Lipids typically form
aggregates not
polymers– (Because
individual lipid
molecules are not
covalently bonded.)
Lipid Function
Fats and oils store energy. They are used as energy source and for energy storage.
Phospholipids play
important structural
roles in cell membranes.
Continued
Carotenoid and chlorophyll help plants capture light
energy.
Steroids and modified fatty acids play regulatory roles as
hormones and vitamins
Fat in animal bodies serves as thermal insulation.
A lipid coating around nerves provides electrical insulation.
Oil or wax on the surfaces of skin, fur, feathers, and
leaves repels water and prevents excessive evaporation of
water from terrestrial animals and plants.
Fatty Acids
Fatty acids are carboxylic acids with a long
hydrocarbon chain
Fatty acids differ from one another in:
* Length of the hydrocarbon tails.
* Degree of unsaturation (double bonds).
* Position of the double bonds in the chain.
Most chains have an even number of carbons.
Most fatty acids have 12 to 22 carbons.
IUPAC Rules
IUPAC (International Union of Pure and Applied Chemistry)
nomenclature: carboxyl carbon is C-1 and is named as ‘a’.
Then comes, carbon 2, C2, b.
After that comes carbon 3, C3, g.
(Common nomenclature: α, β, γ, δ, ε etc. from C-1.)
Carbon which is the most further away from carboxyl is the ω
(omega) carbon.
Saturated
No double bonds in
the carbon chain
The molecule
contains the
maximum number
of H atoms it can
possibly have
Unsaturated
The molecule does
NOT contain the
maximum number of H
atoms it can possibly
have
At least 1
double bond in
the carbon
chain.
1 double bond
monounsaturated
> 1 double bonds
polyunsaturated
Naming Unsaturated FAs
Position of double bonds are indicated by Δn, where n indicates
the carbon after which there is a double bond.
Example: 20:4 Δ5,8,11,14
Total # carbons= 20
# double bonds= 4
Δdouble bond positions= after carbons 5, 8, 11, 14
Saturated FA MPT
Melting point
HIGH
they are packed in an orderly
way
it takes lots of energy to
break the interactions
between fatty acids
Mixture of saturated and
unsaturated fatty acids
Melting point
LOW
they are packed in a less orderly
way, because of the kink.
How do double-bonds affect melting temperature?
it takes less energy to break the
interactions between fatty acids
Essential FAs
Essential fatty acids,
which your body can’t
make.
They needed to be
supplemented through
diet.
Dietary fat and health
Monounsaturated and polyunsaturated fats are an essential part of a
healthy diet.
There is a link between high consumption of saturated fat and
coronary heart disease
Trans-fatty acids (trans-fats) are a by-product of the industrial
process called hydrogenation (adding hydrogen) and are used in the
manufacture of highly processed foods.
Increased intake of trans-fats is associated with an increased risk in
mortality and cardiovascular diseases
Cis fats
All naturally occurring
unsaturated fatty acids are in cis
conformation.
Triglycerides
Fatty acids are rarely found in the body in a free form. Most
exist as triglycerides.
Triglycerides provide a
useful energy reserve
because fats produce much
more energy than
carbohydrates when they
are metabolised.
An ester bond is
formed between
glycerol and the fatty
acid.
For each fatty acid,
one H2O molecule is
produced.
In total, 3 H2O
molecules are
produced
Trends
- As number of double bonds increase → melting point decreases
- As number of carbons in the fatty acid chain increases →
melting point increases
Lipid Modification
Often one of the fatty acid chains in a triglyceride is replaced
with a polar molecule.
This creates a molecule that is both hydrophobic and hydrophilic
– called amphipathic.
A common example of a modified lipid is a phospholipid, where a
phosphate group is attached to the glycerol molecule.
Other molecules are commonly added to the phosphate group –
such as choline (a nutrient) or serine (amino acid).
Phospholipids
One of the fatty acid chains in a triglyceride is replaced with a phosphate
group molecule.
This creates a molecule that is both hydrophobic and hydrophilic – called
amphipathic.
What holds the phospholipid molecules together?
The membrane is held together
by hydrogen bonds on the
outside and hydrophobic
interactions + van der Waals on
the inside.
NOT by covalent bonds
Phosphatidyl Choline
It is type phospholipid present in cell membrane
Sphingomyelin
The glycerol group is replaced
by sphingosine (an 18-carbon
amino alcohol).
The head group is typically
phosphocholine
Importance of S
Sphingomyelin is abundant in nerve tissue.
Sphingomyelin provides insulation for nerve cells (myelin
sheath), which increases the speed of electrical conduction
If the myelin sheath is damaged, then the nerve impulses are not transmitted properly.
This leads to serious conditions like multiple sclerosis with symptoms, such as:
Muscle stiffness and paralysis.
Difficulties with balance, dizziness.
Fatigue.
This is an auto-immune disorder.
Cholesterol function 1: Precursor of steroid hormones
- A hormone is a type of signalling molecule that is
produced by one organ in the body and has effects on
another organ or cell type. - Cholesterol is the precursor to many hormones, including
testosterone, oestrogen, progesterone and cortisol
Cholesterol function 2: Precursor of Vitamins
Vitamins are small molecules not synthesised in the human
body (or only synthesised in inadequate quantities), so the
remainder must be acquired from diet.
They are needed in only trace amounts.
Vitamins A, E and K are lipids with structures containing chains
and rings (but not the 4 rings like cholesterol).