Lipids

Question 1

Lipids

Answer 1

 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.)

Question 2

Lipid Function

Answer 2

 Fats and oils store energy. They are used as energy source and for energy storage.
 Phospholipids play
important structural
roles in cell membranes.

Question 3

Continued

Answer 3

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.

Question 4

Fatty Acids

Answer 4

 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.

Question 5

IUPAC Rules

Answer 5

 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.

Question 6

Saturated

Answer 6

No double bonds in
the carbon chain
The molecule
contains the
maximum number
of H atoms it can
possibly have

Question 7

Unsaturated

Answer 7

The molecule does
NOT contain the
maximum number of H
atoms it can possibly
have
At least 1
double bond in
the carbon
chain.

Question 8

1 double bond

Answer 8

monounsaturated

Question 9

> 1 double bonds

Answer 9

polyunsaturated

Question 10

Naming Unsaturated FAs

Answer 10

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

Question 11

Saturated FA MPT
Melting point
HIGH

Answer 11

they are packed in an orderly
way

 it takes lots of energy to
break the interactions
between fatty acids

Question 12

Mixture of saturated and
unsaturated fatty acids
Melting point
LOW

Answer 12

 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

Question 13

Essential FAs

Answer 13

Essential fatty acids,
which your body can’t
make.
They needed to be
supplemented through
diet.

Question 14

Dietary fat and health

Answer 14

 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

Question 15

Cis fats

Answer 15

All naturally occurring
unsaturated fatty acids are in cis
conformation.

Question 16

Triglycerides

Answer 16

 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

Question 17

Trends

Answer 17

1. As number of double bonds increase → melting point decreases
2. As number of carbons in the fatty acid chain increases →
   melting point increases

Question 18

Lipid Modification

Answer 18

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).

Question 19

Phospholipids

Answer 19

 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

Question 20

Phosphatidyl Choline

Answer 20

It is type phospholipid present in cell membrane

Question 21

Sphingomyelin

Answer 21

 The glycerol group is replaced
by sphingosine (an 18-carbon
amino alcohol).
 The head group is typically
phosphocholine

Question 22

Importance of S

Answer 22

 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.

Question 23

Cholesterol function 1: Precursor of steroid hormones

Answer 23

• 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

Question 24

Cholesterol function 2: Precursor of Vitamins

Answer 24

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).

Question 25

Vit D

Answer 25

Most vitamin D is synthesised in the skin from cholesterol in a
reaction that is dependent on sunlight exposure. Few foods
contain vitamin D.
 Vitamin D
Vitamin D regulates calcium levels.
Vitamin D deficiency results in ‘rickets’ in children
Rickets is associated with
softening and weakening of the
bones

Question 26

Vitamin A

Answer 26

It is found in eggs, meat & dairy (retinol form), and plants (β-
carotene) and is used to make a molecule called retinal, the
aldehyde form of retinol, which is required for vision.
Vitamin A deficiency causes night blindness (poor vision in dim
light).

Question 27

Vitamin E

Answer 27

Vitamin E has antioxidant activity.
It protects against the process of oxidation, which damages
cell membrane lipids, proteins and DNA.
Deficiency is rare but causes anaemia.
Vitamin E is found in many foods, particularly vegetable and nut
oils.

Question 28

Vitamin K

Answer 28

Two natural forms:
- Vitamin K1 (made in plants)
- Vitamin K2 (made by bacteria in the gut)
Main function is to help in blood clotting. It activates proteins
called coagulation factors.
Deficiency can lead to excessive,
uncontrolled bleeding.
Vitamin K is found in green leafy vegetables,
oils and cereals

Question 29

Cholesterol function 3: Precursor of bile salts

Answer 29

 Bile is a complex mixture of bile acids, bile salts,
cholesterol, phospholipids and water.
 It is secreted by the liver and acts as a detergent to
emulsify fats in the digestive system so that they are
easier to digest and absorb.
(Note: Molecules functioning as detergents are amphipathic.)
 Bile salts have a similar structure to cholesterol.
 They are effective detergents because of 3 extra
hydrophilic groups

Question 30

Cholesterol function 4: Cell membrane component
Will be taught in other modules!

Question 31

How are lipids transported in blood?

Answer 31

by lipoproteins

Question 32

Types

Answer 32

transports
triglycerides
from gut to
tissues
Very Low Density
Lipoprotein
transports
triglycerides
from liver to
tissues
Intermediate Density
Lipoprotein
not
commonly
found
Low Density
Lipoproteintransports
cholesterol
from gut to
tissues
High Density
Lipoprotein
transports
cholesterol
from tissues
to liver for
breakdown
Types of lipoproteins

Question 33

Cholesterol and Disease

Answer 33

Too much cholesterol in the blood can lead to a
pathological accumulation of cholesterol in blood
vessels, called atherosclerosis.
 Cholesterol is not soluble in the blood so to move it around
the body it is carried by other molecules, called Low Density
lipoproteins (LDLs) and High Density Lipoproteins (HDLs).
 LDLs are called “bad fats” because they accumulate with
cholesterol to form plaques in arteries atherosclerosis.→
 HDLs are called “good fats” because they transport
cholesterol back to the liver to be broken down.
 Trans-fats increase the level of LDL and reduce HDL levels.