TOPIC 2

BIOLOGICAL
MOLECULES
 Topic 2:
THE CHEMICAL BASIS OF LIFE
What is this Reading Material all about?

The study of biology is a point of convergence for the information and tools from all of the
natural sciences. Biological systems are the most complex chemical systems on Earth, and their
many functions are both determined and constrained by the principles of other sciences. In
another way, no new laws of nature can be gleaned from the study of biology—but that study
does illuminate and illustrate the workings of those natural laws. But taking into a glimpse, any
biological system apart is made up of cell that is considered the structural and functional unit of
all living and eventually these are made of chemicals combining at the molecular level. In this
course, we closely study cells, the basic concepts of cell, the working of major and subcellular
structures/organelles, the structures and functions of organic compounds that comprises the
chemistry and molecules of the cell.

What are you expected to do?

After completing this module, you are expected to be able to:
• Examine the different macromolecules; and
• Analyzed the importance of macromolecules to life.
 What do you know about this topic? (pre-test)

Before you proceed to our lesson in this module, let us check first what you know about
this topic. Write the phrase or sentence that answer the question or completes the statement.

1. Which of the following is not considered to be an emergent property of water?

A. cohesion C. transpiration
B. moderation of temperature D. insulation of bodies of water by floating ice
2. A covalent bond is formed as the result of?
A. transferring electrons C. transferring protons
B. sharing an electron pair D. sharing a proton pair
3. Which three particles that makes up an atom?
A. protons, neutrons, and isotopes C. neutrons, isotopes, and electrons
B. positives, negatives, and electrons D. protons, neutrons, and electrons
4. A solution with a high concentration of hydrogen ions ______________________.
A. is called a base B. has a high pH. C. is called an acid D. both b and c
5. An atom with a net positive charge must have more
A. protons than neutrons C. electrons than neutrons
B. electrons than protons D. protons than electrons
6. DNA and RNA are examples of _________.
A. lipids B. proteins C. carbohydrates D. nucleic acid
7. What is the monomer of proteins?
A. amino acids B. polypeptides C. nucleotides D. monosaccharides
8. Which macromolecule stores energy, insulates us, and makes up the cell membrane?
A. lipids B. proteins C. carbohydrates D. nucleic acid
9. Macromolecule used for energy that shows a 1 to 2 to 1 ratio of carbon, hydrogen, and
oxygen.
A. lipids B. proteins C. carbohydrates D. nucleic acid
10. Which of the following nitrogenous bases is found in DNA but is not found in RNA?
A. adenine B. guanine C. thymine D. uracil
 Let’s explore

LESSON 1
THE MOLECULES OF LIFE

Think about everything that surrounds you—chairs, books, clothing, other students, and
air. What are all these things made up of? If you answer “matter and energy”, You are right. But
what is matter?
Matter is anything that has mass and takes up space. This includes the solids, liquids and
gases in our surroundings as well as in our bodies. All matter is composed of fundamental
substance called Elements. An element can’t be broken down into a simpler form by chemical
reactions. Think of it this way: When you burn wood, you are left with ash. But when you burn
ash, you only get more ash. That is because wood is a complex mixture of elements, while ash
is a pure element (carbon) that cannot be further broken. As of 2022, there are about 118
elements that have been discovered. Of these, 90 elements occur in nature in substantial
amounts and there are another 8 elements that occur in nature as a result of radioactive decay
of heavier elements for a total of 98 natural element.
There are about 25 elements that are considered as essential to life. Four of these
elements make up about 96% of the weight of the human
body as well as other living matter. These elements
include, oxygen (O), carbon (C), hydrogen (H) and
nitrogen (N). The remaining 4% is accounted for by 7
elements that includes Calcium (Ca), Phosphorous (P),
Potassium (K), Sulfur (S), Sodium (Na), Chlorine (Cl)
and Magnesium (Mg). Less that 0.01% of the body
weight is made up of trace elements. Trace elements
are required in only very small amounts, but one cannot
live without them. Ex. An Average human individual only
needs a tiny bit of iodine, about 0.15 mg per day. If this
will not be consumed, it will lead to iodine deficiency that
will prevent the normal functioning of the thyroid gland
resulting to goiter. Chemical composition of a human body weight
 WHY IS SALT IODIZED?
Iodine (in the form of iodide)
is added to table salt to help
prevent iodine deficiency that
causes goiter. Since the 1980s
there have been efforts to have
universal salt iodization. This
has been an affordable and
effective way to combat iodine
deficiency around the world.

ORGANIC SUBSTANCES

Important groups of organic substances in cells include carbohydrates, lipids, proteins,

and nucleic acids. These four are also regarded as “macromolecules”.

1. Carbohydrates
Carbohydrates provide much of the energy that cells require. They also supply
materials to build certain cell structures, and they often are stored as reserve energy
supplies. Carbohydrates are water-soluble molecules that include atoms of carbon,
hydrogen, and oxygen. These molecules usually have twice as many hydrogen as
oxygen atoms, the same ratio of hydrogen to oxygen as in water molecules. This ratio is
easy to see in the molecular formulas of the carbohydrates glucose and sucrose.
Carbohydrates can be classified as follows:
a. Monosacharide: The simplest carbohydrates with a general molecular formula
of CH2O in 1:2:1 ratio. Examples includes the following:
• Glucose - made by green plants
• Fructose - fruit sugar
• Galactose - found in milk

Fruits is rich in fructose;

Galactose are found in milk
b. Disaccharide: Sugar that are formed when two monosaccharides are joined
together by glycosidic linkage. The most important disaccharide includes the
following:
• Sucrose - consists of glucose and fructose linked together.
• Lactose - is found in milk & dairy products; consists of
galactose & glucose.
• Maltose - produced by
partial hydrolysis of starch;
consists of two glucose.

Sucrose is also known as

table sugar; Lactose is
found in milk and milk
products

c. Oligosacharide: A type of carbohydrate formed when three to 10 simple sugars

are linked together. They act as prebiotics, providing food for the good bacteria
in the gut. Few examples include the following:
• Raffinose – Galactose, Glucose and Fructose
• Stachyose – Glucose, Fructose and 2 galactose
• Galactooligosaccharide – 4 glucose and 5 galactose

d. Polysacharide: consist of long chains of

carbohydrate molecules, composed of several
smaller monosaccharides. These complex bio-
macromolecules functions as an important source of
energy in animal cell and form a structural
component of a plant cell. Examples includes
starches, glycogen, cellulose, and chitin.

The cuticle of this cicada is

composed of chitin
 LACTOSE INTOLERANCE
Lactose intolerance is a common digestive problem where the
body is unable to digest lactose. Symptoms of lactose intolerance
usually develop within a few hours of consuming food or drink that
contains lactose. They may include:
• farting
• diarrhoea
• a bloated stomach
• stomach cramps and pains
• stomach rumbling
• feeling sick

The severity of your symptoms and when they appear depends on

the amount of lactose you have consumed

There's no cure for lactose intolerance, but cutting down on food

and drink containing lactose usually helps to control the symptoms.

2. Lipids
Lipids are a group of organic chemicals that are insoluble in water but soluble in organic
solvents, such as ether and chloroform. Lipids include a number of compounds, such as fats,
wax, phospholipids, and steroids, that have vital functions in cells and are important
constituents of cell membranes.
a. Fats: The most common lipids that are
primarily used to supply energy for cellular
activities. Like carbohydrates, fat
molecules are composed of carbon,
hydrogen, and oxygen atoms. However,
fats have a much smaller proportion of
oxygen than do carbohydrates.
The building blocks of fat molecules
are fatty acids and glycerol. Fatty acids are
attached to each of the three carbons of
the glycerol molecule with an ester bond
through an oxygen atom. Fats are also
called triacylglycerols or triglycerides
because of their chemical structure.
The cuticle of this cicada is Composition of Fats

Fatty acids may be saturated or unsaturated.

a.1 Saturated fat: contain single carbon-to-carbon bonds and lots of hydrogen.
Saturated fatty acids are saturated with hydrogen; in other words, the number
of hydrogen atoms attached to
the carbon skeleton is
maximized. It is usually solid at
room temperature and are mostly
found in animal products. It is
advise to reduce Intake of these
kind of fats as it can clog blood
vessels.

Chemical structure of saturated fat and Example of

food rich in saturated fat
 a.2 Unsaturated fat: contain double or
triple carbon-to-carbon bonds &
fewer hydrogen atoms. Its
hydrocarbon chain contains a double bond, the
fatty acid is said to be unsaturated Liquid at room
temperature and are mostly acquired from
plant sources. Unsaturated fats is
better consumed than saturated fats.

Chemical structure on unsaturated fat and example

of food rich in unsaturated fat

a.3 Trans fat: a type of unsaturated fat that occur in small amounts in nature but
became widely produced industrially from vegetable fats.
In the food industry, oils are artificially hydrogenated
to make them semi-solid and of a consistency
desirable for many processed food products.
Recent studies have shown that an increase
in trans fats in the human diet may lead to an
increase in levels of low-density
lipoproteins (LDL), or “bad”
cholesterol, which in turn may lead
to plaque deposition in the arteries,
resulting in heart disease.
Food rich in trans fat

b. Wax: Waxes are part of water-repellent and lubricating secretions in plants and
animals. Water-repellent lipid with long fatty-acid tails bonded to long-chain alcohols or
carbon rings.
Wax covers the feathers of some aquatic birds and the leaf surfaces of some
plants. Because of the hydrophobic nature of waxes, they prevent water from sticking
on the surface.
c. Phospholipids: the main component of a plasma membrane, the outermost layer of
animal cells. It is composed of fatty acid chains attached to a glycerol, however, unlike
the triglycerides, there are only two fatty acids attached forming diacylglycerol, and
the third carbon of the glycerol is occupied
by a modified phosphate group.
Hydrophilic “water loving”
A phospholipid is an amphipathic ➢ Phosphate head
molecule, meaning it has a hydrophobic and
a hydrophilic part. The fatty acid chains are Hydrophobic “water fearing”
➢ Fatty acid tail
hydrophobic and cannot interact with water,
whereas the phosphate-containing group is
hydrophilic and interacts with water.
A Phospholipid

d. Steroids: consists of carbon atoms arranged in four attached rings. All steroids have
four linked carbon rings and several of them, like cholesterol, have a short tail.
Cholesterol is the most common steroid. Cholesterol is mainly synthesized in the
liver and is the precursor to many steroid hormones such as testosterone and
estradiol. It is also the precursor to Vitamin D and the precursor of bile salts, which
help in the emulsification of fats and their subsequent absorption by cells.
Cholesterol is often spoken of in negative terms by lay people, as it is best-known
of its role in heart disease. It forms a large part of the fatty plaques that narrow arteries
and obstruct blood flow in atherosclerosis, however, Cholesterol is necessary for the
proper functioning of the body. It is a component of the plasma membrane of animal
cells and is found within the phospholipid bilayer.
3. Proteins
Proteins are large biomolecules and macromolecules that comprise one or more long
chains of amino acid residues (the monomers of proteins are amino acids). A linear chain of
amino acid residues is called a polypeptide and these amino acids are joined together by a
peptide bond. Proteins perform a vast array of functions within organisms that includes the
following:
a. Enzymatic proteins – function for selective acceleration of chemical reactions. Ex.
Digestive enzymes catalyze the hydrolysis of bonds in food molecules.
b. Defensive Proteins – function for protection against disease. Ex. Antibodies
inactivate and help destroy viruses and bacteria.
c. Contractile and Motor Proteins – functions for movement. Ex. Motor proteins are
responsible for the undulations of cilia and flagella. Actin and myosin are
responsible for the contruction of muscles.
d. Hormonal proteins – Functions for coordination of an organisms activities. Ex. The
hormone insulin causes other tissues to take up glucose, therby regulating the
blood sugar concentration.
e. Transport proteins – functions for the transport of substances within the body. Ex.
Hemoglobin, the iron-containing protein of vertebrate blood, transports oxygen from
the lungs to other parts of the body.
f. Receptor proteins – functions of cell to chemical stimuli. Ex. Receptors built into
the membrane of a nerve cell detect signaling molecules released by other nerve
cells.
g. Structural proteins – functions for support. Ex. Keratin is the protein of hair, horns,
feathers, and other skin appendages. Collagen and elstin proteins provide a fibrous
framework in animal connective tissues.
h. Storage proteins – storage of amino acids. Ex. Casein, the protein of milk, is the
major source of amino acids for baby mammals. Ovalbumin is the protein of egg
white, used as an amino acid source for the developing embryo.
4. Nucleic Acids
Nucleic acids carry the instructions that control a cell's activities by encoding the amino
acid sequences of proteins in its building blocks. Nucleic acids, and DNA in particular, are key
macromolecules for the continuity of life. DNA bears the hereditary information that’s passed on
from parents to children, providing instructions for how
(and when) to make the many proteins needed to build
and maintain functioning cells, tissues, and organisms. Nitrogenous
base
The very large and complex nucleic acids include
Phosphate
an atom of carbon, hydrogen, oxygen, nitrogen, and group sugar
phosphorus which form a building block called
A nucleotide
nucleotides. The nucleotide consists of a 5-carbon
sugar, a phosphate group and one of several nitrogen-containing, organic bases, called
nitrogenous bases.
There are two classes of nucleic acids are found in cells the 1) deoxyribonucleic acid and
2) ribonucleic acid.
1. Deoxyribonucleic Acid (DNA): the genetic blueprint of a living organism in which all
information is stored and from which all information can be passed on. It has a distinctive
double-helix form – two single strands which entwine around each other. The sugar in DNA
is deoxyribose, which contains one less hydroxyl group than RNA’s ribose. The bases in DNA
are Adenine (‘A’), Thymine (‘T’), Guanine (‘G’) and Cytosine (‘C’).
Deoxyribonucleic acid is found primarily in the nucleus. However, they can also be found
in mitochondria (mtDNA) where it supplies the genes necessary for adenosine triphosphate
production, the most important source of cellular energy.

2. Ribonucleic Acid (RNA) : converts the genetic information contained within DNA to a format
used to build proteins, and then moves it to ribosomal protein factories. RNA only has one
strand, but like DNA, is made up of nucleotides. RNA strands are shorter than DNA strands.
RNA contains ribose sugar molecules, without the hydroxyl modifications of deoxyribose.
RNA shares Adenine (‘A’), Guanine (‘G’) and Cytosine (‘C’) with DNA, but contains Uracil
(‘U’) rather than Thymine.
RNA forms in the nucleolus, and then moves to specialised regions of the cytoplasm
depending on the type of RNA formed.
 A comparison of the helix and base structure of RNA and DNA

References

1. Johnson, G.B. (2012). The Living World (2 nd ed.) New York, NY. The McGraw-Hill Companies,
Inc.
2. Solomon, E.P., Berg, L.R. & Martin, D.W. (2008). Biology (8 th ed.). California, USA. Thomson
Higher Education.
3. Seeley, R., Stephens, T., & Tate. P., (2001). Essentials of Anatomy & Physiology (4th Ed.) New
York, NY. The McGraw-Hill Companies, Inc.