INTRODUCTION TO BIOLOGY: The cell: the basic unit of life, Structure and functions

of a cell. The Plant Cell and animal cell, Prokaryotic and Eukaryotic cell, Stem cells and
their application. Biomolecules: Properties and functions of Carbohydrates, Nucleic
acids, proteins, lipids. Importance of special biomolecules; Enzymes (Classification (with
one example each),Properties and functions), vitamins and hormones.

MODULE-1
Cells are the basic, fundamental unit of life. So, if we were to break apart an organism to
the cellular level, the smallest independent component that we would find would be the cell.
Explore the cell notes to know what is a cell, cell definition, cell structure, types and functions
of cells. These notes have an in-depth description of all the concepts related to cells.

Cell Definition

“A cell is defined as the smallest, basic unit of life that is responsible for all of life’s
processes.”

Types of Cells
Cells are similar to factories with different laborers and departments that work towards a
common objective. Various types of cells perform different functions. Based on cellular
structure, there are two types of cells:

● Prokaryotes
● Eukaryotes

Prokaryotic Cells: Prokaryotic cells have no nucleus. Instead, some prokaryotes such as
bacteria have a region within the cell where the genetic material is freely suspended. This
region is called the nucleoid. They all are single-celled microorganisms. Examples include
archaea, bacteria, and cyanobacteria. The cell size ranges from 0.1 to 0.5 µm in diameter. The
hereditary material can either be DNA or RNA. Prokaryotes generally reproduce by binary
fission, a form of asexual reproduction. They are also known to use conjugation – which is
often seen as the prokaryotic equivalent to sexual reproduction (however, it is NOT sexual
reproduction).

Eukaryotic Cells: Eukaryotic cells are characterized by a true nucleus. The size of the cells
ranges between 10–100 µm in diameter. This broad category involves plants, fungi, protozoans,
and animals. The plasma membrane is responsible for monitoring the transport of nutrients and
electrolytes in and out of the cells. It is also responsible for cell to cell communication. They
reproduce sexually as well as asexually. There are some contrasting features between plant and
animal cells. For eg., the plant cell contains chloroplast, central vacuoles, and other plastids,
whereas the animal cells do not.
Cell Structure
The cell structure comprises individual components with specific functions essential to carry
out life’s processes. These components include- cell wall, cell membrane, cytoplasm, nucleus,
and cell organelles.

Plant Cell Animal cell

● Cell Membrane
⮚ The cell membrane supports and protects the cell. It controls the movement of
substances in and out of the cells. It separates the cell from the external environment.
The cell membrane is present in all the cells.
⮚ The cell membrane is the outer covering of a cell within which all other organelles,
such as the cytoplasm and nucleus, are enclosed. It is also referred to as the plasma
membrane.
⮚ By structure, it is a porous membrane (with pores) which permits the movement of
selective substances in and out of the cell. Besides this, the cell membrane also protects
the cellular component from damage and leakage.
⮚ It forms the wall-like structure between two cells as well as between the cell and its
surroundings.
⮚ Plants are immobile, so their cell structures are well-adapted to protect them from
external factors. The cell wall helps to reinforce this function.

● Cell Wall
⮚ The cell wall is the most prominent part of the plant’s cell structure. It is made up of
cellulose, hemicellulose and pectin.
⮚ The cell wall is present exclusively in plant cells. It protects the plasma membrane and
other cellular components. The cell wall is also the outermost layer of plant cells.
 ⮚ It is a rigid and stiff structure surrounding the cell membrane.
⮚ It provides shape and support to the cells and protects them from mechanical shocks
and injuries.

● Cytoplasm
⮚ The cytoplasm is a thick, clear, jelly-like substance present inside the cell membrane.
⮚ Most of the chemical reactions within a cell take place in this cytoplasm.
⮚ The cell organelles such as endoplasmic reticulum, vacuoles, mitochondria, ribosomes,
are suspended in this cytoplasm.

● Nucleus
⮚ The nucleus contains the hereditary material of the cell, the DNA.
⮚ It sends signals to the cells to grow, mature, divide and die.
⮚ The nucleus is surrounded by the nuclear envelope that separates the DNA from the
rest of the cell.
⮚ The nucleus protects the DNA and is an integral component of a plant’s cell structure.

● Cell Organelles

Cells are composed of various cell organelles that perform certain specific functions to carry
out life’s processes. The different cell organelles, along with its principal functions, are as
follows:

Cell Organelles and their Functions

⮚ Nucleolus

The nucleolus is the site of ribosome synthesis. Also, it is involved in controlling cellular
activities and cellular reproduction.

⮚ Nuclear membrane

The nuclear membrane protects the nucleus by forming a boundary between the nucleus and
other cell organelles.

⮚ Chromosomes

Chromosomes play a crucial role in determining the sex of an individual. Each human cells
contain 23 pairs of chromosomes.

⮚ Endoplasmic reticulum

The endoplasmic reticulum is involved in the transportation of substances throughout the cell.
It plays a primary role in the metabolism of carbohydrates, synthesis of lipids, steroids and
proteins.
 ⮚ Golgi Bodies

Golgi bodies are called the cell’s post office as it is involved in the transportation of materials
within the cell.

⮚ Ribosome

Ribosomes are the protein synthesizers of the cell.

⮚ Mitochondria

The mitochondrion is called “the powerhouse of the cell.” It is called so because it produces
ATP – the cell’s energy currency.

⮚ Lysosomes

Lysosomes protect the cell by engulfing the foreign bodies entering the cell and help in cell
renewal. Therefore, they are known as the cell’s suicide bags.

⮚ Chloroplast

Chloroplasts are the primary organelles for photosynthesis. It contains the pigment called
chlorophyll.

⮚ Vacuoles

Vacuoles store food, water, and other waste materials in the cell.

Characteristics of Cells
Following are the various essential characteristics of cells:

⮚ Cells provide structure and support to the body of an organism.

⮚ The cell interior is organized into different individual organelles surrounded by a
separate membrane.
⮚ The nucleus (major organelle) holds genetic information necessary for reproduction and
cell growth.
⮚ Every cell has one nucleus and membrane-bound organelles in the cytoplasm.
⮚ Mitochondria, a double membrane-bound organelle is mainly responsible for the
energy transactions vital for the survival of the cell.
⮚ Lysosomes digest unwanted materials in the cell.
⮚ Endoplasmic reticulum plays a significant role in the internal organization of the cell
by synthesising selective molecules and processing, directing and sorting them to their
appropriate locations.

Functions of Cell
A cell performs major functions essential for the growth and development of an organism.
Important functions of cell are as follows:
 ⮚ Provides Support and Structure

All the organisms are made up of cells. They form the structural basis of all the organisms. The
cell wall and the cell membrane are the main components that function to provide support and
structure to the organism. For eg., the skin is made up of a large number of cells. Xylem present
in the vascular plants is made of cells that provide structural support to the plants.

⮚ Facilitate Growth Mitosis

In the process of mitosis, the parent cell divides into the daughter cells. Thus, the cells multiply
and facilitate the growth in an organism.

⮚ Allows Transport of Substances

Various nutrients are imported by the cells to carry out various chemical processes going on
inside the cells. The waste produced by the chemical processes is eliminated from the cells by
active and passive transport. Small molecules such as oxygen, carbon dioxide, and ethanol
diffuse across the cell membrane along the concentration gradient. This is known as passive
transport. The larger molecules diffuse across the cell membrane through active transport
where the cells require a lot of energy to transport the substances.

⮚ Energy Production

Cells require energy to carry out various chemical processes. This energy is produced by the
cells through a process called photosynthesis in plants and respiration in animals.

⮚ Aids in Reproduction

A cell aids in reproduction through the processes called mitosis and meiosis. Mitosis is termed
as the asexual reproduction where the parent cell divides to form daughter cells. Meiosis causes
the daughter cells to be genetically different from the parent cells.

Thus, we can understand why cells are known as the structural and functional unit of life. This
is because they are responsible for providing structure to the organisms and perform several
functions necessary for carrying out life’s processes

Stem cells
Stem cells are special human cells that can develop into many different types of cells, from
muscle cells to brain cells.

What are Stem Cells?

“Stem cells also have the ability to repair damaged cells. These cells have strong healing
power. They can evolve into any type of cell”.

Types of cells
Stem cells are of the following different types:
 ⮚ Embryonic Stem Cells
⮚ Adult Stem Cells
⮚ Induced stem cells

● Embryonic Stem Cells

The fertilized egg begins to divide immediately. All the cells in the young embryo are totipotent
cells. These cells form a hollow structure within a few days. Cells in one region group together
to form the inner cell mass. This contains pluripotent cells that make up the developing foetus.

The embryonic stem cells can be further classified as:

⮚ Totipotent Stem Cells: These can differentiate into all possible types of stem cells.
⮚ Pluripotent Stem Cells: These are the cells from an early embryo and can differentiate
into any cell type.
⮚ Multipotent Stem Cells: These differentiate into a closely related cell type. E.g., the
hematopoietic stem cells differentiate into red blood cells and white blood cells.
⮚ Unipotent Stem Cells: They can produce cells only of their own type. Since they have
the ability to renew themselves, they are known as unipotent stem cells. E.g., Muscle
stem cells.

● Adult Stem Cells

These stem cells are obtained from developed organs and tissues. They can repair and replace
the damaged tissues in the region where they are located. For eg., hematopoietic stem cells are
found in the bone marrow. These stem cells are used in bone marrow transplants to treat
specific types of cancers.

● Induced Stem Cells

These cells have been tested and arranged by converting tissue-specific cells into embryonic
cells in the lab. These cells are accepted as an important tool to learn about the normal
development, onset and progression of the disease and are also helpful in testing various drugs.
These stem cells share the same characteristics as embryonic cells do. They also have the
potential to give rise to all the different types of cells in the human body.

Applications of Stem Cells

Following are the important applications of stem cells:

● Tissue Regeneration

This is the most important application of stem cells. The stem cells can be used to grow a
specific type of tissue or organ. This can be helpful in kidney and liver transplants. The doctors
have already used the stem cells from beneath the epidermis to develop skin tissue that can
repair severe burns or other injuries by tissue grafting.
 ● Treatment of Cardiovascular Disease

A team of researchers have developed blood vessels in mice using human stem cells. Within
two weeks of implantation, the blood vessels formed their network and were as efficient as the
natural vessels.

● Treatment of Brain Diseases

Stem cells can also treat diseases such as Parkinson’s disease and Alzheimer’s. These can help
to replenish the damaged brain cells. Researchers have tried to differentiate embryonic stem
cells into these types of cells and make it possible to treat diseases.

● Blood Disease Treatment

The adult hematopoietic stem cells are used to treat cancers, sickle cell anaemia, and other
immunodeficiency diseases. These stem cells can be used to produce red blood cells and white
blood cells in the body.

Biomolecules:
Biomolecules are the most essential organic molecules, which are involved in the
maintenance and metabolic processes of living organisms. These non-living molecules are the
actual foot-soldiers of the battle of sustenance of life. They range from small molecules such
as primary and secondary metabolites and hormones to large macromolecules like proteins,
nucleic acids, carbohydrates, lipids etc.

Types of Biomolecules
Carbohydrates
Carbohydrates are macronutrients and are one of the three main ways by which our body
obtains its energy. They are called carbohydrates as they comprise carbon, hydrogen and
oxygen at their chemical level. Carbohydrates are essential nutrients which include sugars,
fibers and starches. They are found in grains, vegetables, fruits and in milk and other dairy
products. They are the basic food groups which play an important role in a healthy life.

The food containing carbohydrates are converted into glucose or blood sugar during the
process of digestion by the digestive system. Our body utilizes this sugar as a source of energy
for the cells, organs and tissues. The extra amount of energy or sugar is stored in our muscles
and liver for further requirement. The term ‘carbohydrate’ is derived from a French term
‘hydrate de carbone‘ meaning ‘hydrate of carbon‘. The general formula of this class of organic
compounds is Cn(H2O)n.

Classification of Carbohydrates
The carbohydrates are further classified into simple and complex which is mainly based on
their chemical structure and degree of polymerization.

● Simple Carbohydrates (Monosaccharides, Disaccharides and Oligosaccharides)

Simple carbohydrates have one or two sugar molecules. In simple carbohydrates,

molecules are digested and converted quickly resulting in a rise in the blood sugar levels. They
are abundantly found in milk products, beer, fruits, refined sugars, candies, etc. These
carbohydrates are called empty calories, as they do not possess fiber, vitamins and
minerals.Plants, being producers, synthesize glucose (C6H12O6) using raw materials like carbon
dioxide and water in the presence of sunlight. This process of photosynthesis converts solar
energy to chemical energy. Consumers feed on plants and harvest energy stored in the bonds
of the compounds synthesized by plants.

1. Monosaccharides
Glucose is an example of a carbohydrate monomer or monosaccharide. Other examples of
monosaccharides include mannose, galactose, fructose, etc. The structural organization of
monosaccharides is as follows:
Monosaccharides may be further classified depending on the number of carbon atoms:

(i)Trioses (C3H6O3): These have three carbon atoms per molecule. Example: Glyceraldehyde

(ii)Tetroses (C4H6O4): These monosaccharides have four carbon atoms per molecule.
Example: Erythrose.

Similarly, we have-

(iii) Pentoses,

(iv) Hexoses, and

(v) Heptoses

2. Disaccharides
Two monosaccharides combine to form a disaccharide. Examples of carbohydrates having two
monomers include- Sucrose, Lactose, Maltose, etc.

3. Oligosaccharides

Carbohydrates formed by the condensation of 2-9 monomers are called oligosaccharides. By

this convention, trioses, pentoses, hexoses are all oligosaccharides.

● Complex Carbohydrates (Polysaccharides)

Complex carbohydrates have two or more sugar molecules, hence they are referred to as starchy
foods. In complex carbohydrates, molecules are digested and converted slowly compared to
simple carbohydrates. They are abundantly found in lentils, beans, peanuts, potatoes, peas,
corn, whole-grain bread, cereals, etc.

Polysaccharides are complex carbohydrates formed by the polymerization of a large number

of monomers. Examples of polysaccharides include starch, glycogen, cellulose, etc. which
exhibit extensive branching and are homopolymers – made up of only glucose units.
 ⮚ Starch is composed of two components- amylose and amylopectin. Amylose forms the
linear chain and amylopectin is a much-branched chain.
⮚ Glycogen is called animal starch. It has a structure similar to starch, but has more
extensive branching.
⮚ Cellulose is a structural carbohydrate and is the main structural component of the plant
cell wall. It is a fibrous polysaccharide with high tensile strength. In contrast to starch
and glycogen, cellulose forms a linear polymer.
Sources of Carbohydrates

⮚ Simple sugars are found in the form of fructose in many fruits.

⮚ Galactose is present in all dairy products.
⮚ Lactose is abundantly found in milk and other dairy products.
⮚ Maltose is present in cereal, beer, potatoes, processed cheese, pasta, etc.
⮚ Sucrose is naturally obtained from sugar and honey containing small amounts of
vitamins and minerals.

These simple sugars that consist of minerals and vitamins exist commonly in milk,
fruits, and vegetables. Many refined and other processed foods like white flour, white rice, and
sugar, lack important nutrients and hence, they are labelled “enriched.” It is quite healthy to
use vitamins, carbohydrates and all other organic nutrients in their normal forms.

Properties of Carbohydrates:

⮚ Most of the mono, disaccharides and lower poly saccharides are sweet in taste, where
as starch and cellulose are tasteless.
⮚ They exhibit stereoisomerism
Eg: Glucose exhibit D & L isomerism
⮚ The sugars which having free aldehydes and ketones are called reducing sugar, the
sugar which not having aldehyde and ketones are no reducing sugars.
⮚ They exhibit optical activity i.e levo and dextro rotator.
Functions of Carbohydrates

The main function of carbohydrates is to provide energy and food to the body and to the
nervous system.

⮚ Carbohydrates are known as one of the basic components of food, including sugars,
starch, and fibre which are abundantly found in grains, fruits and milk products.
⮚ Carbohydrates are also known as starch, simple sugars, complex carbohydrates and so
on.
⮚ It is also involved in fat metabolism and prevents ketosis.
⮚ Inhibits the breakdown of proteins for energy as they are the primary source of energy.

An enzyme by name amylase assists in the breakdown of starch into glucose, finally to
produce energy for metabolism.

Nucleic Acid
“Nucleic acids are long-chain polymeric molecules, the monomer (the repeating unit) is
known as the nucleotides and hence sometimes nucleic acids are referred to as
polynucleotides.”

Deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) are two major types of nucleic
acids. DNA and RNA are responsible for the inheritance and transmission of specific
characteristics from one generation to the other. There are prominently two types of nucleic
acids known to us.

Deoxyribonucleic Acid (DNA)

Chemically, DNA is composed of a pentose sugar, phosphoric acid and some cyclic bases
containing nitrogen. The sugar moiety present in DNA molecules is β-D-2-deoxyribose. The
cyclic bases that have nitrogen in them are adenine (A), guanine (G), cytosine(C) and thymine
(T). These bases and their arrangement in the molecules of DNA play an important role in the
storage of information from one generation to the next one. DNA has a double-strand helical
structure in which the strands are complementary to each other.

The RNA molecule is also composed of phosphoric acid, a pentose sugar and some cyclic bases
containing nitrogen. RNA has β-D-ribose in it as the sugar moiety. The heterocyclic bases
present in RNA are adenine (A), guanine (G), cytosine(C) and uracil (U). In RNA the fourth
base is different from that of DNA. The RNA generally consists of a single strand which
sometimes folds back; that results in a double helix structure. There are three types of RNA
molecules, each having a specific function:

⮚ messenger RNA (m-RNA)

⮚ ribosomal RNA (r-RNA)
⮚ transfer RNA (t-RNA)
Properties of Nucleic acid

⮚ Under strong acids and temperature nucleic acid is completely hydrolysed in to bases.
⮚ When pH value increases physiological range it will have a more subtle (Ultra fine)
effect on the DNA structure.
⮚ Some chemical substances can denatured the DNA/RNA under neutral pH.
⮚ DNA high axial ratio and other properties make its aqueous solution highly viscous.
Long DNA molecule easily damaged by mechanical force or ultrasound.
⮚ The structure of nucleic acid is quite stable due to
❖ Hydrogen bond between base pairs
❖ Accumulation of bases
❖ Cation in the environment

The Functions of Nucleic Acids

⮚ Nucleic acids are responsible for the transmission of inherent characters from parent to
offspring.
⮚ They are responsible for the synthesis of protein in our body
⮚ DNA fingerprinting is a method used by forensic experts to determine paternity. It is
also used for the identification of criminals. It has also played a major role in studies
regarding biological evolution and genetics.
Proteins
Proteins are biopolymeric structures composed of amino acids, of which there are 20 commons
found in biological chemistry. Proteins serve as structural support, biochemical catalysts,
hormones, enzymes, building blocks, and initiators of cellular death.

We often see bodybuilders and physical trainer drinking whey protein along with milk to build-
up metabolism and strength. When it comes to our body, our hair and nails are mostly made of
proteins. Basically, proteins are the fundamental building blocks of our body. They are large
and complex macromolecules or bio-molecules which perform a major role in the functioning
and regulating of our body cells, tissues and other organs in the human body. They are also
used in providing strength to our body in producing hormones, enzymes, and other metabolic
chemicals. They are also involved in functioning and regulating of our body cells, tissues and
organs.

Proteins are composed of amino acids, arranged into different groups. These
fundamental amino acids sequences are specific and its arrangements are controlled by the
DNA. Since our body cannot synthesize these essential amino acids by its own, we should have
plenty of protein foods in our everyday diet to keep our body metabolisms stable.

Protein Structure

In general, they are two types of protein molecules fibrous proteins and globular proteins.
Fibrous proteins are insoluble and elongated. Globular proteins are soluble and compact.
Fibrous and Globular proteins may comprise one or four types of protein structures and they
include primary, secondary, tertiary and quaternary structure.

Primary Structure: It is a specific sequence of amino acids. The order of amino acids bonded
together is detected by information stored in genes.

Secondary Structure: It is a three-dimensional form of a local segment of proteins. They are

formed by hydrogen bonds between the atoms along the backbone of the polypeptide chain.
Tertiary Structure: It is determined by R-groups. It is a three-dimensional shape of a protein.
Many numbers of tertiary structure fold to form Quaternary Structure.

Quaternary Structure: It is the arrangement of multiple folded protein subunits in a multi-

subunit complex.

Properties
⮚ Color and taste: All proteins are colorless, tasteless and homogeneous crystalline.
⮚ Shape and size: Simple crystalloid spherical to long fibrillar structure
Globular- Found in plants ex: Pepsin,edistin, and insulin etc..
Fibrillar- Thread like structure found in animals eg: Fabrinogen,myosin etc..
⮚ Molecular weight: Large molecular between 5000- 1000000
⮚ Colloidal nature: Because of their gaint size, they exhibit many colloidal properties
such as low diffusion rate, produces light scattering in solution, thus resulting in visible
turbidity.
⮚ Denaturation: DNA/RNA loss of biological activity which tend to form large arrogates
and to precipitate from solution
⮚ Amphoteric nature: They acts as both acids and alkaline. These migrate in an electric
field and direction of migration depends upon the net charged molecule.
⮚ Ion binding capacity:The proteins can form salts with both cation and anion based on
their netchange
⮚ Solubility: This is influenced by pH. Solubility is lowest at isoelectric point and
increases with increasing in acidity or alkanility.
⮚ Optical activity: All proteins solutions rotate the plain polarized light to the left i.e levo
rotatary.

Functions of Proteins

1. Enzymes: Enzymes mostly carry out all numerous chemical reactions which take place
within a cell. They also help in regenerating and creating DNA molecules and carry out
complex processes.
2. Hormones: Proteins are involved in the creation of various types of hormones which
help in balancing the components of the body. For example hormones like insulin,
which helps in regulating blood sugar and secretin. It is also involved in the digestion
process and formation of digestive juices.
3. Antibody: Antibody also known as an immunoglobulin. It is a type of protein which is
majorly used by the immune system to repair and heal the body from foreign bacteria.
They often work together with other immune cells to identify and separate the antigens
from increasing until the white blood cells destroy them completely.
4. Energy: Proteins are the major source of energy that helps in the movements of our
body. It is important to have the right amount of protein in order to convert it into
energy. Protein, when consumed in excess amounts, gets used to create fat and becomes
part of the fat cells.
 Listed below are few functions of Proteins.
Aspect Functions of Proteins in Human Body Examples

Storage Legume Storage, albumin, and proteins. Supplies food during the
early stage of the seedling or
embryo.

Hormone Counterpart activities of different body parts. Glucagon and Insulin.

Signalling

Transport It transport substances throughout the body through Hemoglobin.

lump or blood cells.

Contraction To carry out muscle contraction. Myosin.

Digestive Breaks down nutrients present in the food into smaller Pepsin, Amylase, and
Enzyme portions so that it can be easily absorbed Lipase

Lipids
Lipids are fatty compounds that perform a variety of functions in your body. They're part of
your cell membranes and help control what goes in and out of your cells. They help with
moving and storing energy, absorbing vitamins and making hormones. Having too much of
some lipids is harmful.

“Lipids are organic compounds that contain hydrogen, carbon, and oxygen atoms, which
form the framework for the structure and function of living cells.”

Classification of Lipids

Lipids can be classified into two main classes:

⮚ Nonsaponifiable lipids
⮚ Saponifiable lipids
 ● Nonsaponifiable Lipids

A nonsaponifiable lipid cannot be disintegrated into smaller molecules through hydrolysis.

Nonsaponifiable lipids include cholesterol, prostaglandins, etc

● Saponifiable Lipids

A saponifiable lipid comprises one or more ester groups, enabling it to undergo hydrolysis in
the presence of a base, acid, or enzymes, including waxes, triglycerides, sphingolipids and
phospholipids.

Further, these categories can be divided into non-polar and polar lipids.

● Nonpolar lipids, namely triglycerides, are utilized as fuel and to store energy.
● Polar lipids, that could form a barrier with an external water environment, are utilized
in membranes. Polar lipids comprise sphingolipids and glycerophospholipids.
● Fatty acids are pivotal components of all these lipids.

Types of Lipids

Within these two major classes of lipids, there are numerous specific types of lipids, which are
important to life, including fatty acids, triglycerides, glycerophospholipids, sphingolipids and
steroids. These are broadly classified as simple lipids and complex lipids.

Simple Lipids: Esters of fatty acids with various alcohols.

Fats: Esters of fatty acids with glycerol. Oils are fats in the liquid state

Waxes: Esters of fatty acids with higher molecular weight monohydric alcohols

Complex Lipids: Esters of fatty acids containing groups in addition to alcohol and fatty acid.

Phospholipids: These are lipids containing, in addition to fatty acids and alcohol, phosphate
group. They frequently have nitrogen-containing bases and other substituents, eg, in glycerol-
phospho-lipids the alcohol is glycerol and in sphingo-phospho-lipids the alcohol is
sphingosine.

Glycolipids (glycol-sphingo-lipids): Lipids containing a fatty acid, sphingosine and

carbohydrate.

Other complex lipids: Lipids such as sulfolipids and amino lipids. Lipoproteins may
also be placed in this category.

Waxes
⮚ Waxes are “esters” (an organic compound made by replacing the hydrogen with acid
by an alkyl or another organic group) formed from long-alcohols and long-chain
carboxylic acids.
 ⮚ Waxes are found almost everywhere. The fruits and leaves of many plants possess waxy
coatings, that can safeguard them from small predators and dehydration.
⮚ Fur of a few animals and the feathers of birds possess the same coatings serving as
water repellants.
⮚ Carnauba wax is known for its water resistance and toughness (significant for car wax).

Phospholipids

Membranes are primarily composed of phospholipids that are Phospho-acylglycerols.

Triacylglycerols and phosphor-acyl-glycerols are the same, but, the terminal OH group of the
phosphor-acyl-glycerol is esterified with phosphoric acid in place of fatty acid which results in
the formation of phosphatidic acid.
The name phospholipid is derived from the fact that phosphoacylglycerols are lipids containing
a phosphate group.

Steroids
Our bodies possess chemical messengers known as hormones, which are basically organic
compounds synthesized in glands and transported by the bloodstream to various tissues in order
to trigger or hinder the desired process.
Steroids are a kind of hormone that is typically recognized by their tetracyclic skeleton,
composed of three fused six-membered and one five-membered ring. The four rings are
assigned as A, B, C & D.

Cholesterol

● Cholesterol is a wax-like substance, found only in animal source

foods. Triglycerides, LDL, HDL, VLDL are different types of cholesterol found in
the blood cells.
● Cholesterol is an important lipid found in the cell membrane. It is a sterol, which means
that cholesterol is a combination of steroid and alcohol. In the human body, cholesterol
is synthesized in the liver.
● These compounds are biosynthesized by all living cells and are essential for the
structural component of the cell membrane.
 ● In the cell membrane, the steroid ring structure of cholesterol provides a rigid
hydrophobic structure that helps boost the rigidity of the cell membrane. Without
cholesterol, the cell membrane would be too fluid.
● It is an important component of cell membranes and is also the basis for the synthesis
of other steroids, including the sex hormones estradiol and testosterone, as well as
other steroids such as cortisone and vitamin D.

Properties of Lipids
Lipids are a family of organic compounds, composed of fats and oils. These molecules yield
high energy and are responsible for different functions within the human body. Listed below
are some important characteristics of Lipids.

● Lipids are oily or greasy nonpolar molecules, stored in the adipose tissue of the body.
● Lipids are a heterogeneous group of compounds, mainly composed of hydrocarbon
chains.
● Lipids are energy-rich organic molecules, which provide energy for different life
processes.
● Lipids are a class of compounds characterised by their solubility in nonpolar solvents
and insolubility in water.
● Lipids are significant in biological systems as they form a mechanical barrier dividing
a cell from the external environment known as the cell membrane.

Lipids play diverse roles in the normal functioning of the body:

⮚ They serve as the structural building material of all membranes of cells and organelles
⮚ They provide energy for living organisms - providing more than twice the energy
content compared with carbohydrates and proteins on a weight basis
⮚ They function as molecular messengers and signaling molecules in the body
⮚ Lipids are also biomarkers of disease and are involved in several pathological
conditions. Lipids are also known to play a role in genetic modification and influence
risk of chronic disease.

Special Biomolecules
Enzymes
“Enzymes can be defined as biological polymers that catalyze biochemical reactions.”

The majority of enzymes are proteins with catalytic capabilities crucial to perform different
processes. Metabolic processes and other chemical reactions in the cell are carried out by a set
of enzymes that are necessary to sustain life.
 The initial stage of metabolic process depends upon the enzymes, which react with a
molecule and is called the substrate. Enzymes convert the substrates into other distinct
molecules, which are known as products. The regulation of enzymes has been a key element in
clinical diagnosis because of their role in maintaining life processes. The macromolecular
components of all enzymes consist of protein, except in the class of RNA catalysts called
ribozymes. The word ribozyme is derived from the ribonucleic acid enzyme. Many ribozymes
are molecules of ribonucleic acid, which catalyze reactions in one of their own bonds or among
other RNAs.

Enzymes are found in all tissues and fluids of the body. Catalysis of all reactions taking
place in metabolic pathways is carried out by intracellular enzymes. The enzymes in the plasma
membrane govern the catalysis in the cells as a response to cellular signals and enzymes in the
circulatory system regulate the clotting of blood. Most of the critical life processes are
established on the functions of enzymes.

Enzyme Structure

Enzymes are a linear chain of amino acids, which give rise to a three-dimensional structure.
The sequence of amino acids specifies the structure, which in turn identifies the catalytic
activity of the enzyme. Upon heating, the enzyme’s structure denatures, resulting in a loss of
enzyme activity, which typically is associated with temperature.

Compared to its substrates, enzymes are typically large with varying sizes, ranging from
62 amino acid residues to an average of 2500 residues found in fatty acid syntheses. Only a
small section of the structure is involved in catalysis and is situated next to the binding sites.
The catalytic site and binding site together constitute the enzyme’s active site. A small number
of ribozymes exist which serve as an RNA-based biological catalyst. It reacts in complex with
proteins.

Enzymes Classification

Types of Enzymes

⮚ Earlier, enzymes were assigned names based on the one who discovered them. With
further research, classification became more comprehensive.
⮚ According to the International Union of Biochemists (I U B), enzymes are divided into
six functional classes and are classified based on the type of reaction in which they are
used to catalyze. The six kinds of enzymes are hydrolases, oxidoreductases, lyases,
transferases, ligases and isomerases.
⮚ Listed below is the classification of enzymes discussed in detail:

Types Biochemical Property

⮚ Oxidoreductases: The enzyme Oxidoreductase catalyzes the oxidation reaction

where the electrons tend to travel from one form of a molecule to the other.
⮚ Transferases: The Transferases enzymes help in the transportation of the functional
group among acceptors and donor molecules.
 ⮚ Hydrolases: Hydrolases are hydrolytic enzymes, which catalyze the hydrolysis
reaction by adding water to cleave the bond and hydrolyze it.
⮚ Lyases: Adds water, carbon dioxide or ammonia across double bonds or eliminate these
to create double bonds.
⮚ Isomerases: The Isomerases enzymes catalyze the structural shifts present in a
molecule, thus causing the change in the shape of the molecule.
⮚ Ligases: The Ligases enzymes are known to charge the catalysis of a ligation process.

● There are three kinds of cofactors present in enzymes:

⮚ Prosthetic groups: These are cofactors tightly bound to an enzyme at all times. FAD
(flavin adenine dinucleotide) is a prosthetic group present in many enzymes.
⮚ Coenzyme: A coenzyme binds to an enzyme only during catalysis. At all other times,
it is detached from the enzyme. NAD is a common coenzyme.
⮚ Metal ions: For the catalysis of certain enzymes, a metal ion is required at the active
site to form coordinate bonds. Zinc is a metal ion cofactor used by a number of enzymes.

Mechanism of Enzyme Reaction

Any two molecules have to collide for the reaction to occur along with the right
orientation and a sufficient amount of energy. The energy between these molecules needs to
overcome the barrier in the reaction. This energy is called activation energy.

Enzymes are said to possess an active site. The active site is a part of the molecule that
has a definite shape and the functional group for the binding of reactant molecules. The
molecule that binds to the enzyme is referred to as the substrate group. The substrate and the
enzyme form an intermediate reaction with low activation energy without any catalysts.

𝑟𝑒𝑎𝑐𝑡𝑎𝑛𝑡 (1 )+ 𝑟𝑒𝑎𝑐𝑡𝑎𝑛𝑡 (2) → 𝑝𝑟𝑜𝑑𝑢𝑐𝑡

𝑟𝑒𝑎𝑐𝑡𝑎𝑛𝑡 (1)+ 𝑒𝑛𝑧𝑦𝑚𝑒 → 𝑖𝑛𝑡𝑒𝑟𝑚𝑒𝑑𝑖𝑎𝑡𝑒
𝑖𝑛𝑡𝑒𝑟𝑚𝑒𝑑𝑖𝑎𝑡𝑒 + 𝑟𝑒𝑎𝑐𝑡𝑎𝑛𝑡 (2) → 𝑝𝑟𝑜𝑑𝑢𝑐𝑡 + 𝑒𝑛𝑧𝑦𝑚𝑒
Functions of Enzymes

The enzymes perform a number of functions in our bodies. These include:

⮚ Enzymes help in signal transduction. The most common enzyme used in the process
includes protein kinase that catalyzes the phosphor-rylation of proteins.
⮚ They break down large molecules into smaller substances that can be easily absorbed
by the body.
⮚ They help in generating energy in the body. ATP synthase is the enzyme involved in
the synthesis of energy.
⮚ Enzymes are responsible for the movement of ions across the plasma membrane.
⮚ Enzymes perform a number of biochemical reactions, including oxidation, reduction,
hydrolysis, etc. to eliminate the non-nutritive substances from the body.
⮚ They function to reorganize the internal structure of the cell to regulate cellular
activities.

Vitamins
The vitamins are natural and essential nutrients, required in small quantities and play a
major role in growth and development, repair and healing wounds, maintaining healthy bones
and tissues, for the proper functioning of an immune system, and other biological functions.
These essential organic compounds have diverse biochemical functions.There are thirteen
different types of vitamins and all are required for the metabolic processes. The discovery of
the vitamins was begun in the year 1912 by a Polish American biochemist Casimir Funk. Based
on his research and discoveries on vitamins, their sources, functions and deficiency disorders,
he is considered as the father of vitamins and vitamin therapy.

Similar to minerals, vitamins cannot be synthesized by our body. Therefore, we need to

get them from the food we consume or in extreme cases supplements to keep ourselves healthy.

Types of Vitamins

Based on the solubility, Vitamins have been classified into two different groups:

⮚ Fat-Soluble Vitamins.
⮚ Water-Soluble Vitamins.

● Fat-soluble vitamin
Fat-soluble vitamins are stored in the fat cells and as the name suggests, these vitamins
require fat in order to be absorbed. Vitamin A, D, E and K are fat-soluble vitamins.
 ● Water-soluble vitamin
Water-soluble vitamins are not stored in our body as its excess gets excrete through the
urine. Therefore, these vitamins need to be replenished constantly. Vitamin B and C are
water-soluble vitamins.

Sources of Vitamins

⮚ The human body is so designed that it takes what it needs from the food we eat and then
it passes out waste as excreta.
⮚ These organic substances are abundantly found in both plants and animals source and
play a vital role in both growth and development and optimal health.
⮚ Listed below are the different types of vitamins along with their sources.
⮚ The best sources of fat-soluble vitamins include:

Vitamin A: Found in potato, carrots, pumpkins, spinach, beef and eggs.

Vitamin D: Found in fortified milk and other dairy products.

Vitamin E: Found in fortified cereals, leafy green vegetables, seeds, and nuts.

Vitamin K: Found in dark green leafy vegetables and in turnip or beet green.

Vitamin B1 or Thiamin: Found in pork chops, ham, enriched grains and seeds.

Vitamin B2 or Riboflavin: Found in whole grains, enriched grains and dairy products.

Vitamin B3 or Niacin: Found in mushrooms, fish, poultry, and whole grains.

Vitamin B5 or Pantothenic Acid: Found in chicken, broccoli, legumes and whole grains.

Vitamin B6 or Pyridoxine: Found in fortified cereals and soy products.

Vitamin B7 or Biotin: Found in many fruits like fruits and meats.

Vitamin B9 or Folic Acid: Found in leafy vegetables.

Vitamin B12: Found in fish, poultry, meat and dairy products.

Vitamin C: Found in citrus fruits and juices, such as oranges and grapefruits.

Functions of Vitaminsof Vitamin A, B, C, D, E

Vitamins are essential micronutrients which the body requires for normal development,
functioning and growth. These nutrients can not be synthesised within the body and therefore
they are taken up by the body from the food that we consume. The deficiency of any vitamin
can have adverse effects on the body, therefore it is important to have a vitamin-rich balanced
diet. It is essential to know the functions of vitamins A, B, C, D, and E and the roles they play
in the human body.
Name of the
Function of the Vitamin
Vitamin

● Vitamin A helps in the development and maintenance of teeth and skeletal and
soft tissues.
● It is also important for the maintenance of skin and the mucous membrane
Vitamin A
● More importantly, the mucous membrane promotes good eyesight, specifically
in low light.
● Beta-carotene, a form of vitamin A, protects cells from free radicals. This may
reduce the risk of cancer.
● Promotes cell health
● Important for the development of RBCs
Vitamin B
● Vitamin B is required for healthy brain function
● It is also involved in the production of hormones and cholesterol
● Important for the growth and repair of body tissues
● Helps to heal wounds more effectively

Vitamin C ● Aids the absorption of iron

● Helpful for the maintenance of cartilage, teeth and bones
● Vitamin C is also an antioxidant, hence it aids in blocking some damage
caused by free radicals
● Required for the formation of bones
Vitamin D
● Required to maintain normal blood levels of phosphorus and calcium
● Functions as a powerful antioxidant.
● Protects the cells from the effects of free-radicals
Vitamin E
● Boosts immune system
● Required for fulfilling of various cellular functions

Hormones Definition
“Hormones are chemicals synthesized and produced by the specialized glands to control and
regulate the activity of certain cells and organs. These specialized glands are known as
endocrine glands.”

Types of Hormones
To regulate various functions, different types of hormones are produced in the body. They
are classified as follows:

⮚ Peptide Hormones
⮚ Steroid Hormones
Peptide Hormone

● Peptide hormones are composed of amino acids and are soluble in water.
● Peptide hormones are unable to pass through the cell membrane as it contains a
phospholipid bilayer that stops any fat-insoluble molecules from diffusing into the cell.
● Insulin is an important peptide hormone produced by the pancreas.

Steroid Hormones

Unlike peptide hormones, steroid hormones are fat-soluble and are able to pass through
a cell membrane. Sex hormones such as testosterone, estrogen and progesterone are
examples of steroid hormones.

Endocrine Glands and the Hormones Secreted

As stated before, hormones are released by the endocrine glands. These are different from
other glands of the human body as they are ductless.

● Hypothalamus: It controls the body temperature, regulates emotions, hunger, thirst,

sleep, moods and allow the production of hormones.
● Pineal: Pineal is also known as the thalamus. It produces serotonin derivatives of
melatonin, which affects sleep patterns.
● Parathyroid: This gland helps in controlling the amount of calcium present in the body.
 ● Thymus: It helps in the production of T-cells, functioning of the adaptive immune
system and maturity of the thymus.
● Thyroid: It produces hormones that affect the heart rate and how calories are burnt.
● Adrenal: This gland produces the hormones that control the sex drive, cortisol and
stress hormone.
● Pituitary: It is also termed as the “master control gland,”. This is because the pituitary
gland helps in controlling other glands. Moreover, it develops the hormones that trigger
growth and development.
● Pancreas: This gland is involved in the production of insulin hormones, which plays a
crucial role in maintaining blood sugar levels.
● Testes: In men, the testes secrete the male sex hormone, testosterone. It also produces
sperm.
● Ovaries: In the female reproductive system, the ovaries release estrogen,
progesterone, testosterone and other female sex hormones.
All these glands work together to produce and manage the hormones of the body.

List of Important Hormones

1. Cortisol – It has been named as the “stress hormone” as it helps the body in responding
to stress. This is done by increasing the heart rate, elevating blood sugar levels etc.
2. Estrogen-This is the main sex hormone present in women which bring about puberty,
prepares the uterus and body for pregnancy and even regulates the menstrual cycle.
Estrogen level changes during menopause because of which women experience many
uncomfortable symptoms.
3. Melatonin – It primarily controls the circadian rhythm or sleep cycles.
4. Progesterone – It is a female sex hormone also responsible for menstrual cycle,
pregnancy and embryogenesis.
5. Testosterone – This is the most important sex hormone synthesized in men, which
cause puberty, muscle mass growth, and strengthen the bones and muscles, increase
bone density and controls facial hair growth.

Functions of Hormones
Following are some important functions of hormones:

● Food metabolism.
● Growth and development.
● Controlling thirst and hunger.
● Maintaining body temperature.
● Regulating mood and cognitive functions.
● Initiating and maintaining sexual development and reproduction.