Unit

Unit III:
III: Cell
Cell biology
biology and
and Biomolecules
Biomolecules
CELL : THE UNIT OF LIFE
Chapter Outline
6.1. Discovery
6.2. Microscopy
6.3. Cell theory
6.4. Cell types
6.5. Plant cell and Animal cell
6.6. Cell organelles
6.7. Nucleus
6.8. Flagella
6.9. Cytological techniques
 The word ‘cell’ comes from the
Latin word ‘Celle” which
means ‘a small compartment’.
The word cell was first used
by Robert Hooke (1662)
therefore the term ‘cell’ is as
old as 300 years.
Robert Hooke
6.1. Discovery

Aristotle (384-322BC), was

the one who first
recognised that animals and
plants consists of organised
structural units but unable
to explain what it was.
6.1. Discovery

Robert
Robert Hooke
Hooke observed
observed something
something
which
which looks
looks like
like ‘honeycomb
‘honeycomb withwith aa
great
great little
little boxes’
boxes’ which
which was
was later
later
called
called as
as ‘cell’
‘cell’ from
from the
the cork
cork tissue
tissue in
in
1665.
1665.
He compiled his work as Micrographia. Later,
Antonie von Leeuwenhoek observed
unicellular particles which he named as
‘animacules’.
Robert Brown (1831-39) described the spherical body in the
plant cells as nucleus. H. J. Dutrochet (1824), a French scientist,
was the first to give idea on cell theory.
Later,
Later, Matthias
Matthias Schleiden
Schleiden (German
(German Botanist)
Botanist) and
and Theodor
Theodor
Schwann
Schwann (German
(German Zoologist)
Zoologist) (1833)
(1833) outlined
outlined the
the basic
basic features
features
of
ofthe
thecell
celltheory
theory..
Rudolf
Rudolf Virchow
Virchow (1858)
(1858) explained
explained the the cell
cell theory
theory byby
adding
adding aa feature
feature stating
stating that
that all
all living
living cells
cells arise
arise from
from
pre-existing
pre-existingliving
livingcells
cellsby
by‘cell
‘celldivision’.
division’.
 6.2. Microscopy

Microscope
Microscope is is an
an inevitable
inevitable instrument
instrument in
in studying
studying
the
the cell
cell and
and subcellular
subcellular structures.
structures.
 Resolution

Resolution: The term resolving power or resolution refers to the

ability of the lenses to show the details of object lying between
two points. It is the finest detail available from an object. It can be
calculated using the following formula
Resolution =
0.61λ
NA
Where, λ= wavelength of the light and NA is the numerical
aperture.
Numerical Aperture

Numerical Aperture: It is an important optical constant

associated with the optical lens denoting the ability to
resolve. Higher the NA value greater will be the resolving
power of the microscope.
 Magnification:

Magnification: The optical increase in the size of an image is

called magnification. It is calculated by the following formula

Magnification = size of image seen with the microscope

size of the image seen with normal eye
 6.2. Microscopy

It offers scope in studying microscopic organisms

therefore it is named as microscope (mikros – small; skipein
– to see) in Greek terminology. Compound microscope was
invented by Z. Jansen.
Microscope
Microscope works
works on on the
the lens
lens system
system which
which basically
basically relies
relies on
on
properties
properties of
of light
light and
and lens
lens such
such as
as reflection,
reflection, magnification
magnification andand
numerical
numericalaperture.
aperture.
The common light
microscope which has many
lenses are called as
compound microscope.
The microscope transmits visible light from sources to eye
or camera through sample, where interaction takes place.
The
The microscope
microscope transmits
transmits visible
visible light
light
from sources to eye or camera through
from sources to eye or camera through
sample,
sample,where
whereinteraction
interactiontakes
takesplace.
place.
 6.2.1 Bright field
Microscope

Bright field microscope is routinely used

microscope in studying various aspects of cells.
6.2.1 Bright field Microscope

It allows light to pass directly through specimen and shows a well

distinguished image from different portions of the specimen
depending upon the contrast from absorption of visible light.
6.2.1 Bright field Microscope

The contrast can be increased by staining the specimen

with reagent that reacts with cells and tissue components
of the object.
6.2.1 Bright field Microscope

The light rays are focused by condenser on to the specimen

on a micro slide placed upon the adjustable platform called
as stage.
6.2.1 Bright field Microscope

The light comes from the Compact Flourescent Lamp (CFL)

or Light Emitting Diode (LED) light system. Then it passes
through two lens systems namely objective lens (closer to the
object) and the eye piece (closer to eye).
 6.2.1 Bright field Microscope

There are four objective lenses (5X, 10X, 45X and 100X)
which can be rotated and fixed at certain point to get
required magnification.
6.2.1 Bright field Microscope

The first magnification of the microscope is done by the

objective lens which is called primary magnification
and it is real, inverted image.
6.2.1 Bright field Microscope

The second magnification of the microscope is obtained

through eye piece lens called as secondary magnification
and it is virtual and inverted image
 6.2.2 Dark Field Microscope

The dark field microscope was

discovered by Z. Sigmondy (1905).
Here the field will be dark but
object will be glistening so the
appearance will be bright.
6.2.2 Dark Field Microscope

A special effect in an
ordinary microscope
is brought about by
means of a special
component called
‘Patch Stop Carrier’.
 6.2.2 Dark Field Microscope

It is fixed in metal ring of the condenser component. Patch stop is a

small glass device which has a dark patch at centre of the disc
leaving a small area along the margin through which the light
passes.
6.2.2 Dark Field Microscope

The light passing through the margin will travel oblique like a
hollow cone and strikes the object in the periphery, therefore the
specimen appears glistening in a dark background.
 6.2.2 Dark Field Microscope

A Phase ring and light source

The Phase ring stops part of the light so that it cannot reach the
detector anymore
 SAMPLE

When sample is inserted ,it screen part of the light even if its
transparent .This scattered light is focused on the detection
6.2.3 Phase contrast microscope

This was invented by Zernike (1935). It is a

modification of light microscope with all its basic
principle.
6.2.3 Phase contrast microscope

The objects observed by increasing the

contrast by bringing about change in
amplitude of the light waves. The
contrast can be increased by introducing
the ‘Phase Plate’ in the condenser lens.
 6.2.3 Phase contrast microscope

Phase plate is a circular component with circular annular

etching.
Light passes with different velocity after coming out of the
thinnest and thickest areas of the phase plate thereby
increasing the contrast of the specimen
6.2.3 Phase contrast microscope

A hollow cone of light passes through the condenser. Direct light

pass through thin area of phase plate, whereas light passing from
the specimen reaches thick area of phase plate
6.2.3 Phase contrast microscope

The light passing through thicker area travel at low speed, on the
other hand the light passing through thin area reach fast therefore
contrast is increased in the specimen.
6.2.3 Phase contrast microscope

Phase contrast microscope is used to observe living cells,

tissues and the cells cultured invitro during mitosis.
6.2.4 Electron Microscope

Electron Microscope was first introduced by Ernest Ruska (1931)

and developed by G Binning and H Roher (1981). It is used to
analyse the fine details of the cell and organelles called
ultrastructure.
6.2.4 Electron Microscope

It uses beam of accelerated electrons as source of illumination and

therefore the resolving power is 1,00,000 times than that of light
microscope.
6.2.4 Electron Microscope

The specimen to be viewed under electron microscope is

dehydrated and impregnated with electron opaque chemicals like
gold or palladium. This is essential for withstanding electrons
and also for contrast of the image.
6.2.4 Electron Microscope Transmission Electron Microscope (TEM)

There are two kinds of

electron microscopes namely
Transmission Electron
Microscope (TEM)
Scanning Electron
Microscope (SEM)
Scanning Electron Microscope (SEM)
1. Transmission electron microscope:

Figure 6.4: a. Transmission electron microscope; b. Image of TEM

Scanning electron microscope
 Scanning electron microscope

A beam of electron passes through the specimen to form

an image on fluorescent screen. The magnification is 1–3
lakhs times and resolving power is 2–10 AÅ .
Scanning electron microscope

It electron microscope which

provides two dimensional image.
The components of the microscope
are as follows:
a. Electron Generating System
b. Electron Condensor
c. Specimen Objective
d. Tube Lens
e. Projector
Comparison of
Microscopes
2. Scanning Electron Microscope:

This is used to obtain three dimensional image and has a lower

resolving power than TEM. In this, electrons are focused by
means of lenses into a very fine point.
2. Scanning Electron Microscope:

The interaction of electrons with the specimen results in the

release of different forms of radiation (such as auger electrons,
secondary electrons, back scattered electrons) from the surface of
the specimen.
2. Scanning Electron Microscope:

These radiations are then captured by an appropriate detector,

amplified and then imaged on fluorescent screen. The
magnification is 2,00,000 times and resolution is 5–20 nm (Figure
6.5 a and b).
6.3. Cell Theory

In 1833, German botanist Matthias Schleiden and German

zoologist Theodor Schwann proposed that all plants and animals
are composed of cells and that cells were the basic building blocks
of life.
 These
Theseobservations
observationsled
ledto
tothe
theformulation
formulationof
ofmodern
moderncell
celltheory.
theory.

All organisms are made up of cells.

New cells are formed by the division of pre-existing cells.
Cells contains genetic material, which is
passed on from parents to daughter
cells.
All metabolic reactions take place
inside the cells.
6.3.1 Exception to Cell Theory

Viruses are puzzle in biology. Viruses, viroids and

prions are the exception to cell theory.
6.3.1 Exception to Cell Theory

They lack protoplasm, the essential part of the cell and

exists as obligate parasites which are sub-cellular in nature.
 6.3.2 Cell Doctrine (Cell Principle)

The features of cell doctrine are as follows:

A cell contains hereditary information which is passed on

from cell to cell during cell division.
All the cells are basically the same in chemical composition
and metabolic activities.
•The structure and function of cell is controlled by DNA.
6.3.3 Protoplasm Theory

Corti first observed protoplasm. Felix Dujardin (1835)

observed a living juice in animal cell and called it “Sarcode”.
Purkinje (1839) coined the term protoplasm for sap inside a
plant cell. Hugo Van Mohl (1846) indicated importance of
protoplasm.
Protoplasm
6.3.3 Protoplasm Theory

Max Schultze (1861) established similarity between Protoplasm and

Sarcode and proposed a theory which later on called “Protoplasm
Theory” by O. Hertwig (1892). Huxley (1868) proposed Protoplasm
as a “physical basis of life”.
Protoplasm as a Colloidal System

Protoplasm is a complex colloidal system which was suggested by

Fisher in 1894 and Hardy in 1899. It is primarily made of water
contents and various other solutes of biological importance such
as glucose, fatty acids, amino acids, minerals, vitamins, hormones
and enzymes.
Protoplasm as a Colloidal System

These solutes may be homogeneous (soluble in water) or

heterogeneous mass (insoluble in water) which forms the
basis for its colloidal nature.
Physical Properties of Protoplasm

The protoplasm exist either in semisolid (jelly-like) state

called ‘gel᾿ due to suspended particles and various chemical
bonds or may be liquid state called ‘sol᾿.
Physical Properties of Protoplasm

The colloidal protoplasm which is in gel form can change

into sol form by solation and the sol can change into gel by
gelation. These gel-sol conditions of colloidal system are
prime basis for mechanical behaviour of cytoplasm.
Physical Properties of Protoplasm

Protoplasm is translucent, odourless and polyphasic fluid.

It is a crystal colloid solution which is a mixture of chemical
substances forming crystalloid i.e. true solution (sugars, salts,
acids, bases) and others forming colloidal solution (Proteins
and lipids)
Physical Properties of Protoplasm

It is the most important property of the protoplasm by which it

exhibits three main phenomena namely Brownian movement,
amoeboid movement and cytoplasmic streaming or cyclosis.
Viscosity of protoplasm is 2–20 centipoises. The Refractive index of
the protoplasm is 1.4.
Physical Properties of Protoplasm

4.The pH of the protoplasm is around 6.8, contain 90% water

(10% in dormant seeds)
5.Approximately 34 elements are present in protoplasm but
only 13 elements are main or universal elements i.e. C, H, O, N,
Cl, Ca, P, Na, K, S, Mg, I and Fe. Carbon, Hydrogen, Oxygen and
Nitrogen form the 96% of protoplasm.
Physical Properties of Protoplasm

Protoplasm is neither a good nor a bad conductor of

electricity. It forms a delimiting membrane on coming in
contact with water and solidifies when heated.
Physical Properties of Protoplasm

Cohesiveness: Particles or molecules of protoplasm are

adhered with each other by forces, such as Van der Waal’s
bonds, that hold long chains of molecules together. This
property varies with the strength of these forces.
Physical Properties of Protoplasm

Contractility: The contractility of protoplasm is important for

the absorption and removal of water especially stomatal
operations.
Physical Properties of Protoplasm

Surface tension: The proteins and lipids of the protoplasm

have less surface tension, hence they are found at the surface
forming the membrane. On the other hand the chemical
substances (NaCl) have high surface tension, so they occur in
deeper parts of the cell protoplasm.
6.3.4 Cell sizes and
shapes

Cell
Cellgreatly
greatlyvary
varyin
insize,
size,shape
shapeand
andalso
alsoin
infunction.
function.
Physical Properties of Protoplasm

Group of cells with similar structures are called tissue they integrate
together to perform similar function, group of tissue join together to
perform similar function called organ, group of organs with related
function called organ system, organ system coordinating together to
form an organism.
 Shape

The shape of cell vary greatly from organism to organism

and within the organism itself.
In bacteria cell shape vary from round (cocci) to rectangular
(rod).
 Shape

In virus, shape of the envelope varies from round to

hexagonal or ‘T’ shaped. In fungi, globular to elongated
cylindrical cells and the spores of fungi vary greatly in
shape.
 Shape

In plants and animals cells vary in shape according to cell types

such as parenchyma, mesophyll, palisade, tracheid, fiber,
epithelium and others
parenchyma
Mesophyll
 Shape

 In bacteria cell shape vary from round (cocci) to rectangular

(rod). In virus, shape of the envelope varies from round to
hexagonal or ‘T’ shaped.
 In fungi, globular to elongated cylindrical cells and the spores of
fungi vary greatly in shape.
Size:
6.4. Types of cells

On the basis of the cellular organization and the nuclear

characteristics, the cell can be divided into
 Prokaryotes
 Mesokaryotes and
 Eukaryotes
6.4.1 Prokaryotes

Those organisms with primitive

nucleus are called as prokaryotes
(pro – primitive; karyon – nucleus).
6.4.1 Prokaryotes The DNA lies in the ‘nucleoid’
which is not bound by the
nuclear membrane and
therefore it is not a true
nucleus and is also a
primitive type of nuclear
material
 6.4.1 Prokaryotes

The DNA is without histone proteins.

Example: Bacteria, blue green algae,
Mycoplasma, Rickettsiae and
Spirochaetae.
6.4.2 Mesokaryotes

In
In the
the year
year 1966,
1966, scientist
scientist Dodge
Dodge and
and his
his coworkers
coworkers
proposed another kind of organisms
proposed another kind of organisms called called
mesokaryotes.
mesokaryotes.
 6.4.2 Mesokaryotes

These organisms which shares some of the characters of both

prokaryotes and eukaryotes. In other words these are
 6.4.2 Mesokaryotes

These contains well organized nucleus with nuclear membrane and

the DNA is organized into chromosomes but without histone protein
components divides through amitosis similar with
prokaryotes.
6.4.2 Mesokaryotes

In other words these are organisms intermediate

between pro and eukaryotes. These contains well
organized nucleus with nuclear membrane and the
DNA is organized into chromosomes but without
histone protein components divides through
amitosis similar with prokaryotes
6.4.2 Mesokaryotes

Certain Protozoa like Noctiluca, some phytoplanktons like

Gymnodinium, Peridinium and Dinoflagellates are
representatives of mesokaryotes.
Noctiluca Gymnodinium

Peridinium Dinoflagellates

phytoplanktons
phytoplanktonslike
likeGymnodinium,
Gymnodinium,
Peridinium
Peridiniumand
andDinoflagellates
Dinoflagellatesare
are
representatives of mesokaryotes.
representatives of mesokaryotes.
6.4.3 Eukaryotes

Those organisms which have true nucleus are called

Eukaryotes (Eu – True; karyon – nucleus). The DNA is
associated with protein bound histones forming the
chromosomes.
Membrane bound organelles are present. Few organelles may be
arisen by endosymbiosis which is a cell living inside another cell.
The organelles like mitochondria and chloroplast well support
this theory.
Comparison between types of cellular organisation
 A model of endosymbiotic theory

The
The first
first cell
cell might
might have
have evolved
evolved approximately
approximately 3.8
3.8 billion
billion years
years
ago.
ago. The
The primitive
primitive cell
cell would
would have
have been
been similar
similar to
to present
present day
day
protists
protists
 6.5. Plant and Animal cell
6.5.1 Ultra Structure of Eukaryotic Cell

The eukaryotic cell is highly

distinct in its organisation.
It shows several variations
in different organisms.
For instance, the eukaryotic
cells in plants and animals
vary greatly
Animal Cell

Animal cells are surrounded by cell membrane or plasma

membrane. Inside this membrane the gelatinous matrix called
protoplasm is seen to contain nucleus and other organelles
which include the endoplasmic reticulum, mitochondria, golgi
bodies, centrioles, lysosomes, ribosomes and cytoskeleton.
 Plant cell

A typical plant cell has prominent cell wall, a large central vacuole and
plastids in addition to other organelles present in animal cell
Animal cell
6.5.2 Protoplasm

Protoplasm is the living content of the cell that is surrounded

by plasma membrane. It is a colourless material that exists
throughout the cell together with the cytoplasm, nucleus and
other organelles.
 6.5.2 Protoplasm

Protoplasm is composed of a mixture of small particles, such as

ions, amino acids, monosaccharides, water, macromolecules like
nucleic acids, proteins, lipids and polysaccharides.
6.5.2 Protoplasm

It appears colourless, jelly like gelatinous, viscous elastic and

granular. It appears foamy due to the presence of large number of
vacuoles. It responds to the stimuli like heat, electric shock,
chemicals and so on.
 6.5.3 Cell Wall

Cell wall is the outermost protective cover of cell. It is present

in bacteria, fungi and plants whereas it is absent in animal cell.
6.5.3 Cell Wall

It was first observed by Robert Hooke. It is an actively growing

portion. It is made up of different complex material in various
organism.
6.5.3 Cell Wall

In bacteria it is composed of peptidoglycan, in fungi chitin and

fungal cellulose, in algae cellulose, galactans and mannans. In
plants it is made up of cellulose, hemicellulose, pectin, lignin,
cutin, suberin and silica.
 6.5.3 Cell Wall

In plant, cell wall shows three distinct regions (a) Primary

wall (b) Secondary wall (c) Middle lamellae (Figure 6.11).
 a. Primary wall

It is the first layer inner to middle lamellae, primarily consisting of

loose network of cellulose microfibrils in a gel matrix. It is thin,
elastic and extensible. In most plants the microfibrils are made up of
cellulose oriented differently based on shape and thickness of the
wall.
a. Primary wall

The matrix of the primary wall is composed of hemicellulose,

pectin, glycoprotein and water. Hemicellulose binds the
microfibrils with matrix and glycoproteins control the
orientation of microfibrils while pectin serves as filling
material of the matrix. Cells such as parenchyma and
meristems have only primary wall.
b. Secondary wall

Secondary wall is laid during maturation. It plays a key role in

determining the shape of a cell. It is thick, inelastic and is
made up of cellulose and lignin.
b. Secondary wall

The secondary wall is divided into three sublayers

termed as S1, S2 and S3 where the cellulose microfibrils are
compactly arranged with different orientation forming a
laminated structure and the cell wall strength is increased.
c. Middle lamellae

It is the outermost layer made up of calcium and magnesium

pectate, deposited at the time of cytokinesis. It is a thin
amorphous layer which cements two adjacent cells. It is
optically inactive (isotropic).
Plasmodesmata and Pits

Plasmodesmata act as a channel between the protoplasm of

adjacent cells through which many substances pass through.
Moreover, at few regions the secondary wall layer is laid unevenly
whereas the primary wall and middle lamellae are laid
continuously such regions are called pits.
Plasmodesmata and Pits

The pits of adjacent cells are

opposite to each other. Each pit
has a pit chamber and a pit
 Plasmodesmata and Pits

The pit membrane has many minute pores and thus they
are permeable. The pits are of two types namely simple
and bordered pit.
Functions of cell wall

The cell wall plays a vital role in holding several

important functions given below
1.Offers definite shape and rigidity to the cell.
2. Serves as barrier for several molecules to
enter the cells.
Functions of cell wall

Provides protection to the internal protoplasm against

mechanical injury.
4. Prevents the bursting of cells by maintaining the osmotic
pressure.
5. Plays a major role by acting as a mechanism of defense for the
cells.
 6.5.4 Cell Membrane

The cell membrane is also called cell surface (or) plasma

membrane. It is a thin structure which holds the cytoplasmic
content called ‘cytosol’.
6.5.4 Cell Membrane
 6.5.4 Cell Membrane

It is made up of lipids and proteins together with a little amount

of carbohydrate. The lipid membrane is made up of
phospholipid.
6.5.4 Cell Membrane

The phospholipid molecule has a hydrophobic tail and

hydrophilic head. The hydrophobic tail repels water and
hydrophilic head attracts water.
The proteins of the membrane are globular proteins which are
found intermingled between the lipid bilayer most of which are
projecting beyond the lipid bilayer. These proteins are called as
integral proteins.
 6.5.4 Cell Membrane

Few are superficially attached on either surface of the lipid bilayer

which are called as peripheral proteins. The proteins are
involved in transport of molecules across the membranes and also
act as enzymes, receptors (or) antigens.
 6.5.4 Cell Membrane

The movement of membrane lipids from one side of the

membrane to the other side by vertical movement is
called flip flopping or flip flop movement.
6.5.4 Cell Membrane

This movement takes place more slowly than lateral

diffusion of lipid molecule. The phospholipids can have flip
flop movement because the phospholipids have smaller
polar regions, whereas the proteins cannot flip flop
because the polar region is extensive.
6.5.4 Cell Membrane
 Function of Cell Membrane

The functions of the cell membrane is enormous which

includes cell signalling, transporting nutrients and
water, preventing unwanted substances entering into
the cell, and so on.
Cell Transport Cell
Cell membrane
membrane act
act as
as aa channel
channel of
of transport
transport
for molecules.
for molecules.

The
The membrane
membrane is
is selectively
selectively permeable
permeable to
to
molecules.
molecules.
Cell Transport

It transports molecules through energy dependant

process and energy independent process.

The membrane proteins (channel and carrier) are

involved in movement of ions and molecules across
the membrane
Endocytosis and Exocytosis

Cell surface membrane are able to transport individual

molecules and ions. Through this special process Large quantity
of solids and liquids are taken into cell (endocytosis) or out of
cell (exocytosis)
Endocytosis and Exocytosis

Cell surface membrane are able to transport individual molecules

and ions. Through this special process Large quantity of solids
and liquids are taken into cell (endocytosis) or out of cell
(exocytosis )
endocytosis
Endocytosis

Endocytosis: During endocytosis the cell membrane in folds around

the material to form a vacuole and brings it into cytoplasm. There are
two types of endocytosis:
Phagocytosis

Phagocytosis – Solid Particles are engulfed by membrane,

which folds around it and forms a vesicle. The enzymes digest
the material and products are absorbed by cytoplasm.
Phagocytosis
Pinocytosis – Fluid droplets are engulfed by membrane, by
forming vesicles around them.
Exocytosis:

Exocytosis: Vesicles fuse with plasma membrane and

eject contents. This passage of material out of the cell is
known as exocytosis. This material may be a secretion
in the case of digestive enzymes, hormones or mucus.
Signal Transduction

The process by which the cell

receive information from outside
and respond is called signal
Signal Transduction

Plants, fungi and animal cell use nitric oxide as one

of the many signalling molecules. The cell
membrane is the site of chemical interactions of
signal transduction.
Signal Transduction

Receptors receives the information from first

messenger and transmit the message through series of
membrane proteins.
Signal Transduction

It activates second messenger which stimulates the cell to

carry out specific function.
Cytoplasm

Cytoplasm is the main arena of various activities of a cell.

It is the semifluid gelatinous substance that fills the cell.
It is made up of eighty percent water and is usually clear
and colourless.
Cytoplasm

The cytoplasm is sometimes described as non nuclear

content of protoplasm.
The
Thecytoplasm
cytoplasmserves
servesas
asaamolecular
molecularsoup
soupwhere
whereall
allthe
the
cellular
cellularorganelles
organellesare
aresuspended
suspendedand
andbound
boundtogether
togetherbybyaa
lipid
lipidbilayer
bilayerplasma
plasmamembrane.
membrane.
Cytoplasm

It constitutes dissolved nutrients, numerous salts and

acids to dissolve waste products. It is a very good
conductor of electricity. It gives support and protection
to the cell organelles.
It helps movement of the cellular materials around the cell
through a process called cytoplasmic streaming. Further, most
cellular activities such as many metabolic pathways including
glycolysis and cell division occur in cytoplasm.
The system of membranes in a eukaryotic cell, comprising the
plasma membrane,
6.6 Cell Organellesnuclear membrane, endoplasmic reticulum,
golgi apparatus, lysosomes
6.6.1 Endomembrane System and vacuolar membranes (tonoplast).

6.6 Cell Organelles

6.6.1 Endomembrane System

6.6 Cell Organelles
6.6.1 Endomembrane System

Endomembranes are made up of phospholipids with embedded

proteins that are similar to cell membrane which occur within the
cytoplasm. The endomembrane system is evolved from the inward
growth of cell membrane in the ancestors of the first eukaryotes
6.6.2 Endoplasmic Reticulum
6.6.2 Endoplasmic Reticulum

The largest of the internal membranes is called the

endoplasmic reticulum (ER). The name endoplasmic
reticulum was given by K.R. Porter (1948). It consists
of double membrane.
Morphologically the structure of endoplasmic reticulum
consists of:

Cisternae are long, broad, flat, sac like structures

arranged in parallel bundles or stacks to form
lamella. The space between membranes of cisternae
is filled with fluid.
Vesicles are oval membrane bound vacuolar structure.
Tubules are irregular shape, branched, smooth
walled, enclosing a space
Tubules

Endoplasmic reticulum is associated with nuclear membrane

and cell surface membrane. It forms a network in cytoplasm
and gives mechanical support to the cell. Its chemical
environment enables protein folding and undergo
modification necessary for their function.
Tubules

Misfolded proteins are pulled out and are degraded in

endoplasmic reticulum. When ribosomes are present in the
outer surface of the membrane it is called as rough
endoplasmic reticulum(RER), when the ribosomes are absent
in the endoplasmic reticulum it is called as smooth
Endoplasmic reticulum(SER)
Tubules

Rough endoplasmic reticulum is involved in protein

synthesis and smooth endoplasmic reticulum are the
sites of lipid synthesis. The smooth endoplasmic
reticulum contains enzymes that detoxify lipid soluble
drugs, certain chemicals and other harmful compounds.
6.6.3 Golgi Body (Dictyosomes)

In 1898, Camillo Golgi

visualized a netlike
reticulum of fibrils near the
nucleus, were named as
Golgi bodies.
In plant cells they are found as smaller vesicles termed as
dictyosomes.
Golgi apparatus is a stack of flat membrane enclosed sacs.
It consist of cisternae, tubules, vesicles and golgi vacuoles.
6.6.3 Golgi Body (Dictyosomes)

In plants the cisternae are 10-20 in number placed in piles

separated from the cytoplasm of the cell. Peripheral edge of
cisternae forms a network of tubules and vesicles.
6.6.3 Golgi Body (Dictyosomes)

Tubules interconnect cisternae and are 30-50nm in

dimension. Vesicles are large round or concave sac. They
are pinched off from the tubules.They are
smooth/secretary or coated type.
 6.6.3 Golgi Body (Dictyosomes)

Golgi vacuoles are large spherical filled with granular or

amorphous substance, some function like lysosomes.
The Golgi apparatus compartmentalises a series of steps
leading to the production of functional protein.
6.6.3 Golgi Body (Dictyosomes)
6.6.3 Golgi Body (Dictyosomes)

Small pieces of rough endoplasmic reticulum are

pinched off at the ends to form small vesicles. A
number of these vesicles then join up and fuse
together to make a Golgi body.
Golgi complex plays a major role in post translational
modification of proteins and glycosidation of lipids
 Functions:

Glycoproteins and glycolipids are produced

Transporting and storing lipids.
Functions:

Formation of lysosomes.
• Production of digestive enzymes.
• Cell plate and cell wall formation
Secretion of Carbohydrates for the formation
of plant cell walls and insect cuticles.
6.6.4 Mitochondria

It was first observed by A. Kolliker (1880). Altmann (1894)

named it as Bioplasts. Later Benda (1897, 1898), named as
mitochondria. They are ovoid, rounded, rod shape and
pleomorphic structures. Mitochondrion consists of double
membrane, the outer and inner membrane.
6.6.4 Mitochondria

The outer
membrane is
smooth, highly
permeable to
small molecules
and it contains
proteins called
Porins
6.6.4 Mitochondria

which form channels that allows free diffusion of molecules

smaller than about 1000 daltons and the inner membrane divides
the mitochondrion into two compartments, outer chamber
between two membranes and the inner chamber filled with
matrix.
The inner membrane is convoluted (infoldings), called crista
(plural: cristae). Cristae contain most of the enzymes for
electron transport system.
6.6.4 Mitochondria

Inner
Inner chamber
chamber ofof the
themitochondrion
mitochondrion
is
isfilled
filledwith
withproteinaceous
proteinaceous material
material
called mitochondrial matrix.
6.6.4 Mitochondria

The inner membrane consists of stalked particles called

elementary particles or Fernandez Moran particles, F1
particles or Oxysomes. Each particle consists of a base, stem
and a round head. In the head ATP synthase is present for
oxidative phosphorylation.
 6.6.4 Mitochondria

Inner membrane is impermeable to most ions, small

molecules and maintains the proton gradient that drives
oxidative phosphorylation
Mitochondria contain 73%
of proteins, 25-30% of
lipids, 5-7 % of RNA, DNA
(in traces) and enzymes
(about 60 types).
Mitochondria are called
Power house of a cell, as
they produce energy rich
ATP.
6.6.4 Mitochondria

All the enzymes of Kreb’s cycle are found in the matrix

except succinate dehydrogenase. Mitochondria consist of
circular DNA and 70S ribosome.
They multiply
by fission and
replicates by
strand
displacement
model.
Because of
the presence
of DNA it is
semi-
autonomous
organelle.
6.6.4 Mitochondria

Unique characteristic of mitochondria is that they are

inherited from female parent only. Mitochondrial
DNA comparisons are used to trace human origins.
6.6.4 Mitochondria

Mitochondrial DNA is used to track and date recent

evolutionary time because it mutates 5 to 10 time faster
than DNA in the nucleus.
6.6.5 Plastids

The term plastid is derived from the Greek word Platikas

(formed/moulded) and used by A.F.U. Schimper in 1885. He
classified plastids into following types according to their
structure, pigments and function. Plastids multiply by
fission.
6.6.5 Plastids
 Chloroplasts are vital
6.6.6 Chloroplast organelle found in
green plants.
Chloroplast has a
double membrane the
outer membrane and
the inner membrane
separated by a space
called periplastidial
space.
6.6.6 Chloroplast

The space enclosed by the inner membrane of chloroplast is filled

with gelatinous matrix, lipo-proteinaceous fluid called stroma.
Inside the stroma there is flat interconnected sacs called
thylakoid. The membrane of thylakoid enclose a space called
thylakoid lumen.
6.6.6 Chloroplast
Grana (singular: Granum) are formed when many of these
thylakoids are stacked together like pile of coins. Light is absorbed
and converted into chemical energy in the granum, which is used
in stroma to prepare carbohydrates.
6.6.6 Chloroplast

Thylakoid contain chlorophyll pigments. The chloroplast

contains osmophilic granules, 70s ribosomes, DNA
(circular and non histone) and RNA.
6.6.6 Chloroplast

These chloroplast genome encodes approximately 30

proteins involved in photosynthesis including the
components of photosystem I & II, cytochrome bf complex
and ATP synthase. One of the subunits of Rubisco is
encoded by chloroplast DNA.
6.6.6 Chloroplast

It is the major protein component of

chloroplast stroma, single most
abundant protein on earth. The
thylakoid contain small, rounded
photosynthetic units called
quantosomes. It is a semi-
autonomous organelle and divides
by fission (Figure 6.19).
 Photosynthesis
Functions: Light reactions takes place in granum
Dark reactions take place in stroma,
Chloroplast is involved respiration
6.6.7 Ribosome

Ribosomes were first

observed by George
Palade (1953) as dense
particles or granules in
the electron microscope.
6.6.7 Ribosome

Electron microscopic observation

reveals that ribosomes are
composed of two rounded sub
units, united together to form a
complete unit.
Mg is required for structural cohesion of
2+

ribosomes. Biogenesis of ribosome are denova

formation, auto replication and nucleolar origin.
Ribosome consists of RNA and
protein: RNA 60 % and Protein
40%. During protein synthesis
many ribosomes are attached
to the single mRNA is called
polysomes or polyribosomes.
Ribosome

Each ribosome is made up of one small and one large sub-unit

Ribosomes are the sites of protein synthesis in the cell.
Ribosome is not a membrane bound organelle (Figure 6.20).
ribosome
 Ribosome

Ribosome consists of RNA and protein: RNA 60 % and Protein 40%.

During protein synthesis many ribosomes are attached to the single
mRNA is called polysomes or polyribosomes.
Ribosome

The function of polysomes is the formation of several copies

of a particular polypeptide during protein synthesis. They
are free in non-protein synthesising cells. In protein
synthesising cells they are linked together with the help of
Mg ions.
2+
6.6.8 Lysosomes
(Suicidal Bags of Cell)
Lysosomes were discovered by
Christian de Duve (1953),
these are known as suicidal
bags. They are spherical
bodies enclosed by a single
unit membrane.
 6.6.8 Lysosomes (Suicidal Bags of Cell)

They are found in eukaryotic cell. Lysosomes are small

vacuoles formed when small pieces of golgi body are
pinched off from its tubules.
6.6.8 Lysosomes (Suicidal Bags of Cell)

They contain a variety of hydrolytic enzymes, that can digest

material within the cell. The membrane around lysosome
prevent these enzymes from digesting the cell itself
6.6.8 Lysosomes (Suicidal Bags of Cell)
Functions:

Intracellular digestion: They

digest carbohydrates, proteins and
lipids present in cytoplasm.
Autophagy:
Autophagy: During
During adverse
adverse condition
condition they
they digest
digest their
their
own
own cell
cell organelles
organelles like
like mitochondria
mitochondria and
and endoplasmic
endoplasmic
reticulum
reticulum
Autolysis: Lysosome causes self destruction of cell on
Ageing: Lysosomes have
autolytic enzymes that
disrupts intracellular
molecules.
Phagocytosis: Large cells or contents are engulfed and
digested by macrophages, thus forming a phagosome in
cytoplasm.
These phagosome fuse with lysosome for further digestion.
Exocytosis:
Lysosomes release
their enzymes
outside the cell to
digest other cells
 6.6.9 Peroxisomes

Peroxisomes were identified as organelles by Christian

de Duve (1967). Peroxisomes are small spherical bodies
and single membrane bound organelle.
6.6.9 Peroxisomes

It takes part in photorespiration and associated with

glycolate metabolism. In plants, leaf cells have many
peroxisomes. It is also commonly found in liver and
kidney of mammals. These are also found in cells of
protozoa and yeast (Figure 6.23).
6.6.9 Peroxisomes
6.6.10 Glyoxysomes

Glyoxysome was discovered by Harry Beevers (1961).

Glyoxysome is a single membrane bound organelle.
6.6.10 Glyoxysomes
It is a sub cellular organelle and contains enzymes of
glyoxylate pathway. β-oxidation of fatty acid occurs in
glyoxysomes of germinating seeds Example: Castor seeds.
Castor
Castor seeds
seeds
6.6.11 Microbodies

Eukaryotic cells
contain many enzyme
bearing membrane
enclosed vesicles
called microbodies.
They are single unit membrane bound cell
organelles: Example: peroxisomes and glyoxysomes.
 6.6.12 Sphaerosomes

It is spherical in shape and enclosed by single unit

membrane. Example: Storage of fat in the endosperm
cells of oil seeds.
6.6.13 Centrioles

Centriole consist of nine triplet peripheral fibrils made up

of tubulin. The central part of the centriole is called hub,
is connected to the tubules of the peripheral triplets by
radial spokes (9+0 pattern).
 6.6.13 Centrioles

The centriole form the basal body of cilia or flagella and

spindle fibers which forms the spindle apparatus in animal
The membrane is absent in
centriole (non membranous organelle)
 6.6.14 Vacuoles

In plant cells vacuoles are large, bounded by a single

unit membrane called Tonoplast.
6.6.14 Vacuoles

The vacuoles contain cell

sap, which is a solution of
sugars, amino acids, mineral
salts, waste chemical and
anthocyanin pigments.
 6.6.14 Vacuoles

Beetroot cells contains anthocyanin pigments in their

vacuoles. Vacuoles accumulate products like tannins.
The osmotic expansion of a cell kept in water is chiefly
regulated by vacuole and the water enters the vacuoles by
osmosis.
The major function of plant
vacuole is to maintain water
pressure known as turgor
pressure, which maintains the
plant structure.
Vacuoles organises itself into a storage/sequestration
compartment. Example: Vacuoles store, most of the
sucrose of the cell.
6.6.14 Vacuoles

i . Sugar in Sugar beet and Sugar cane.

ii. Malic acid in Apple.
iii. Acids in Citrus fruits.
iv. Flavonoid pigment Cyanidin 3 rutinoside in the
petals of Antirrhinum.
6.6.14 Vacuoles

v. Tannins in Mimosa pudica.

vi. Raphide crystals in Dieffenbachia.
vii. Heavy metals in Mustard
(Brassica).
viii. Latex in Rubber tree and
Dandelion stem.
Cell Inclusions

The cell inclusions are the non-living materials

present in the cytoplasm. They are organic and
inorganic compounds.
Inclusions in prokaryotes

In prokaryotes, reserve materials such as phosphate

granules, cyanophycean granules, glycogen granules,
poly β-hydroxy butyrate granules, sulphur granules,
carboxysomes and gas vacuoles are present.
Inclusions in prokaryotes

In prokaryotes, reserve materials such as phosphate granules,

cyanophycean granules, glycogen granules, poly β-hydroxy
butyrate granules, sulphur granules, carboxysomes and gas
vacuoles are present. Inorganic inclusions in bacteria are
polyphosphate granules (volutin granules) and sulphur granules.
These granules are also known as metachromatic granules.
Metachromatic granules.
Inclusions in Eukaryotes

Reserve food materials: Starch grains, glycogen granules,

aleurone grains, fat droplets
Secretions in plant cells are essential oil, resins, gums,
latex and tannins
Inclusions in Eukaryotes

Inorganic crystals – plant cell have calcium

carbonate, calcium oxalate and silica

Cystolith – hypodermal leaf cells of Ficus

bengalensis, calcium carbonate
Inclusions in Eukaryotes

Sphaeraphides – star shaped calcium oxalate, Colocasia

• Raphides – calcium oxalate, Eichhornia
• Prismatic crystals – calcium oxalate, dry scales of
Allium cepa
 6.7. Nucleus

Nucleus is an important unit of cell which control all activities

of the cell. Nucleus holds the hereditary information. It is the
largest among all cell organelles. It may be spherical, cuboidal,
ellipsoidal or discoidal.
6.7. Nucleus
It is surrounded by a double membrane structure called
nuclear envelope, which has the inner and outer membrane.
The inner membrane is smooth without ribosomes and the
outer membrane is rough by the presence of ribosomes and is
continues with irregular and infrequent intervals with the
endoplasmic reticulum.
6.7. Nucleus
6.7. Nucleus
6.7. Nucleus

The membrane is perforated by pores known as

nuclear pores which allows materials such as
mRNA, ribosomal units, proteins and other
macromolecules to pass in and out of the nucleus.
 6.7. Nucleus

The pores enclosed by circular structures called annuli.

The pore and annuli forms the pore complex. The space
between two membranes is called perinuclear space.
Nuclear space is filled with nucleoplasm, a gelatinous matrix has
uncondensed
DNA duplication and transcription takes place in the nucleus.
In nucleolus ribosomal biogenesis takes place.
 6.7.1 Chromosomes

Strasburger (1875) first reported its present in

eukaryotic cell and the term ‘chromosome’ was
introduced by Waldeyer in 1888.
Bridges (1916) first proved that chromosomes are the
physical carriers of genes. It is made up of DNA and
associated proteins.
Structure of chromosome
The chromosomes are
composed of thread like
strands called chromatin
which is made up of DNA,
protein and RNA. Each
chromosome consists of
two symmetrical
structures called
chromatids.

Structure of
chromosome
During cell division the chromatids forms
well organized chromosomes with
definite size and shape. They are identical
and are called sister chromatids.
A typical chromosome has narrow zones called constrictions.
There are two types of constrictions namely primary
constriction and secondary constriction.
Structure of chromosome

The primary constriction is made up of centromere and

kinetochore. Both the chromatids are united at centromere,
whose number varies.
The monocentric chromosome has one centromere and the
polycentric chromosome has many centromeres.
The centromere contains a complex system of protein fibres called
kinetochore.
Kinetochore is the region of
chromosome which is attached to
the spindle fibre during mitosis.
Structure of chromosome

Nucleoli develop from these secondary constrictions are called

nucleolar organizers. Secondary constrictions contains the
genes for ribosomal RNA which induce the formation of nucleoli
and are called nucleolar organizer regions
Figure 6.26: Structure of a
Chromosome
Structure of chromosome
A satellite or SAT Chromosome are short chromosomal
segment or rounded body separated from main
chromosome by a relatively elongated secondary
constriction.
Structure of chromosome

It is a morphological
entity in certain
chromosomes.
Structure of chromosome

Based on the position of centromere, chromosomes are

called telocentric (terminal centromere), Acrocentric
(terminal centromere capped by telomere), Sub
metacentric (centromere subterminal) and Metacentric
(centromere median).
 Telocentric
Chromosome

(terminal centromere)
 Acrocentric

(terminal centromere
capped by telomere)
Sub metacentric (centromere
subterminal)
Metacentric
(centromere median).
Structure of chromosome

The eukaryotic chromosomes may be rod shaped

(telocentric and acrocentric), L-shaped (sub-metacentric)
and V-shaped (metacentric)
Telomere is the
terminal part of
chromosome. It offers
stability to the
chromosome.
Telomere

DNA of the telomere has specific sequence of nucleotides.

Telomere in all eukaryotes are composed of many repeats of
short DNA sequences (5’TTAGGG3’ sequence in Neurospora
crassa and human beings).
Telomere

Maintenance of telomeres appears to be an important factor in

determining the life span and reproductive capacity of cells so
studies of telomeres and telomerase have the promise of
providing new insights into conditions such as ageing and
cancer.
Telomeres
prevents the
fusion of
chromosomal
ends with one
another.
Holocentric

Holocentric chromosomes hav

centromere activity distributed along
the whole surface of the chromosome
during mitosis.
Holocentric condition can be seen in Caenorhabditis elegans
(nematode) and many insects. There are three types of
centromere in eukaryotes.
Point centromere: the type of centromere in which the
kinetochore is assembled as a result of protein recognition
of specific DNA sequences.
Kinetochores assembled on
point centromere bind a
single microtubule. It is also
called as localized
centromere. It occurs in
budding yeasts
Regional centromere: In regional centromere where
the kinetochore is assembled on a variable array of
repeated DNA sequences.
Kinetochore assembled on regional centromeres
bind multiple microtubules. It occurs in fission
yeast cell, humans and so on.
Holocentromere- The microtubules bind all along the
mitotic chromosome. Example: Caenorhabditis elegans
(nematode) and many insects.
Based on the functions of chromosome it can be divided into
autosomes and sex chromosomes.
Autosomes are present in all cells controlling somatic
characteristics of an organism.
In human diploid cell, 44 chromosomes are autosomes
whereas two are sex chromosomes.