EUNICE LING LI XUAN H3T02A

Molecules of life
&

Cell structures and Functions

Name : EUNICE LING LI XUAN

Matrix Number : MS2213201314

Practicum : H3T02A

Main types of molecules

Water :

• It is a universal solvent

due to its polarity.

• It has high specific heat

capacity

• It has high latent heat of

vaporisation

• It has maximum density

of 4°C

• It has cohesion force

between water

molecules

Carbohydrates :

• There are 3 classes of

carbohydrates which are

monosaccharides,

disaccharides and

polysaccharides.

• It is composed of carbon

(C), hydrogen (H) and

oxygen (O) with the

proportion 1:2:1

Main types of molecules

Lipids:
• It is made up or C,H,O
• It is a large and non-polar
• There are 3 types of lipids:
= Triglycerides, Phospholipids, Steroids

Protein :
• Protein = Polypeptides
= (Monomer = amino acid)
• It is made up of C,H,O,N (sometimes S)
• There are 4 levels of protein structure :
= Primary, Secondary, Tertiary & Quaternary

Nucleic Acid :
• There are two types of

nucleic acid :
1. Deoxyribonucleic acid

(DNA)
2. Ribonucleic acid (RNA)
• Monomer = nucleotide

Classify lipid into three main
types based on their structures

and characteristics

Structures :

A triglyceride or triacylglycerol is formed when 3
hydroxyls (OH-) groups of a single glycerol
molecule react with the carboxyl group (COOH-)
of 3 fatty acids by ester bond.

In the presence of acid and heat, or under
biological conditions, triglycerides (fats) can be
hydrolyzed to produce glycerol and three fatty
acids.

Characteristics :

Triglycerides are completely hydrophobic = they
cannot integrate into membranes. Thus,
triglycerides bind to lipoproteins to enable them
to travel through the blood.

Phospholipids is a compound lipid consist of two
hydrophobic “tails” which are fatty acid chains,
and one hydrophilic “head” which is phosphate
group.

Phospholipid form lipid bilayers and are a key
component of all the cell membranes.

Phospholipids are amphipathic molecules.
Phospholipids are water-soluble due to polar head.
Phospholipid is charged molecules.

Steroid is a molecular structure that contained
17 carbon atoms arranged in four fused
hydrocarbon rings.

Steroid hormones - Can easily diffuse across both
cell and nuclear membrane.

E.g : Testosterone, Progesterone, Aldosterone ++
Steroids vary by the functional groups attached to

this four-ring core and by the oxidation state of
the rings.

The structure of
plasma membrane.

According to the fluid mosaic model, protein molecules
float within the phospholipid bilayer, forming a mosaic
pattern that changes frequently.

Figure above is the labelled diagram of plasma membrane
• 1. The head of phospholipid molecule in outer

layer face the extracellular fluid
2. Phospholipid heads in the inner layer face the

cytoplasm.
3. The tails of the phospholipid molecule of two

layers face each other.

• There are few type of protein molecules embedded
partially or fully within the membrane :

1. The protein molecules with channels or canals are
known as channel protein .

2. The protein molecules that function as carrier are
known as carrier protein

*** Some protein & lipid have carbohydrate chain
attached to them which known as glycoprotein or
glycolipid.

There are also cholesterol molecules in the plasma
membrane which make the phospholipid bilayer stronger,
more flexible and less permeable to water-soluble
substances such as ions.

Channel Protein Carrier Protein

All in all, the phospholipid bilayer, protein &
cholesterol are not static but form a dynamic
and flexible structure which make plasma
membrane more flexible & have fluid
characteristics.

Explain how certain type of cells
consists type of lipids ensures the
fluidity of the plasma membrane

while some other type of lipids
may reduce its fluidity.

1. Cholesterol

o It can keep the membrane fluid as it lies alongside of
phospholipid in plasma membrane that tends to dampen
the effects of temperature on the membrane.

o It functions as a buffer, preventing lower temperatures
from inhibiting fluidity and preventing higher
temperatures from increasing fluidity too much.

2. Saturated fatty acid

o It has no double bonds in the hydrocarbon chain, and the
maximum amount of hydrogen.

o The absence of double bonds decreases fluidity, making
the membrane very strong and stacked tightly.

3. Unsaturated fatty acid

o It has at least one double bond, creating a "kink" in the
chain.

o The double bond increases fluidity.