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Cell structure and function
Cell:
Meaning:
Cell is derived from Latin word“ cellus” which means chamber
...

Definition:
“It is the basics unit of all living organisms on the basis of structure and function”
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Cell theory:
History of emergence of cell theory:
Various scientists play role in the formulation of cell theory
...
Robert hook:
1
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2
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3
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4
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2
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He was a Dutch scientist
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He made much powerful microscope
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Through his microscope he studies a drop of water and saw tiny unicellular creature
in it
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He called these creature as “animalcules” swimming around
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Jean Baptist de Lamarck:
1
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2
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3
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4
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He was British botanist
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He describe nucleus in a cell and made a new concept that the center of the cell
is not empty
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schleiden (1838) and schwann(1839):
Two German biologists, schleiden (1838) a botanist and schwann (1839) a
zoologist, formulated the cell theory
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1
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3
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5
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All living organisms are composed of one or more cells
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New cells are formed from pre-existing cells
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e
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All the metabolic processes take place within cells
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Different methods to study structure or component of cell:
The following technique is used for isolating and examining various cell components
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Staining: (staining means colorization/dye)
Definition: staining is the process in which cell or tissue is colorized with particular
stains (chemical solution or dye) for identification or study
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Types of staining
a
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c
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2
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3
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Definition:
“it is a method in which a tissue fragment of an organism is treated in a medium
(enzyme, control environment) to produce a whole organism”
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Chromatography: (chromo=color, graphing= to write)
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”
Types:
a
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Column chromatography
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Electrophoresis: (means = being carried/ separate)
Definition:
“Electrophoresis is a method of separation of charge molecules applying an
electric filed”
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Spectrophotometry:
Definition:
“the process in which the change in percentage transmission of light (absorption
of light) is measured suspension materials”
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Micro dissection: (dissection means= to cut into small pieces)
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Cell organelles structure and function
Cell wall:
Definition:
“it is rigid, hard, permeable and non- living outmost b boundary of plant
cell”
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❖ Cell wall is made up of living protoplasm of cell
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➢ The plant cell wall is composed of cellulose, cemented by pectin and lignin
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➢ The prokaryotic cell wall (bacteria)is made up of murine
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1
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“it is the first formed layer between the two primary walls of the two adjacent cells”
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Composition:
Middle lamella is mainly composed of pectin in the form of calcium or
magnesium pectate
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Primary wall: (1—3 micro meter thick)
Introduction:
“It is a true wall develops in newly growing cell”
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➢ Cellulose molecule are arranged into cress cross arrangement
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Secondary wall: (5—10 mm)
Introduction:
“it is formed in the inner surface of primary wall and is comparatively thick and
rigid
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Composition:
Chemically it is composed of cellulose, lignin, inorganic salt, silica and waxes etc
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➢
➢
➢
➢
➢

Cell wall provides a definite shape to the cell
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It is a permeable membrane and many materials can pass through it
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It is hydrophilic (water loving)and imbibe(absorb) in water thus in the
movement of water and nutrient
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Definition:
“it is thin, delicate, elastic and semi—permeable, the outer most layer of animal cell but
in plant cell it is located below the cell wall
...
g – phospholipid and cholesterol)
➢ Carbohydrate (2 – 10%)
Structure of plasma membrane:
Different models were presented by many biologists to explain the structure of cell
membrane, but the most widely accepted model is the “Fluid Mosaic Model
...
”

Development of Fluid mosaic model:
This model was presented by S
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singer and G
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Nicholson in 1972
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2) Proteins:
In lipid bilayer the protein molecules are embedded here and there just like a mosaic
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b) Intrinsic protein:
While some protein are partially or wholly embedded within the lipid bilayer is
known as intrinsic proteins
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3) Glycolipids:
When carbohydrates are attached with lipids in plasma membrane, it makes a
structure called Glycolipid
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Glycolipids and Glycoproteins provide receptor sites that receive different types of
stimuli and inform the cell for response
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It serves as an envelope that gives mechanical strength, support , protection and
external form to protoplasm of cell(cytoplasm)
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It controls the entry and exit of polar molecules and ions
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5- Sugar and amino-acids (polar molecules) are carried through plasma membrane by
special protein called permeases
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Q: what is cytoplasm, structure and functions of cytoplasmic organelles
...
”
➢ It us the part of protoplasm which consists of
1) Cytosol:
The soluble part of cytoplasmic bodies called organelles, such as – Mitochondria,
ribosomes etc
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2 True solution:
True solution contains all small sized fundamental biochemical molecules of life
which dissolve in water of cytoplasm forming homogenous system (solution)
...
g
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3 Colloidal system(solution)
In colloidal solution large sized molecules form a heterogeneous system
(solution)
...
g
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➢ The colloidal solution may be
1
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Gel – jelly like or viscous solution
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Cytoplasm acts as a store house of biochemical molecules, e
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–Amino –acid, sugar,
nucleotides etc
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It also acts as a site for certain metabolic processes, e
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–glycolysis
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Many substances such as amino –acids, fatyacids, and nucleic –acids are also
synthesized here
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The cytoskeleton presents in the cytoplasm maintaining the shape and helps the
movement of cell organelles
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It provides suitable environment for organelle functions
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1) Endoplasmic reticulum:(ER)
Meaning:
Endo –inside
Plasma –cytoplasm or cell
Reticulum –network
...
”
Discovery:
Endoplasmic reticulum was second reported by porter in 1945
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Structure:
➢ The ER (also called channels) is often continuous to plasma –membrane and also
appears to be in contact with the nuclear membrane
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➢ Cisternae:
The material present in these channels is separated from cytoplasmic materials
by the spherical or tubular membrane called cisternae
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I
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R to which ribosomes are attached and appears granular and
rough on form
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Smooth endoplasmic reticulum(SER)
“It is the type of E
...
”

Diagram:
Functions:
1
...

3
...

5
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7
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They help in the transport of material within the cell
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SER helps in lipid metabolism
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SER plays a role in muscle contraction
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It provides mechanical support to the cell, so that its shape can be maintained
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Ribosomes:(Ribonucleoprotein particles)
Meaning:
Ribo –ribose (a pentose sugar c5h10o5)
Soma –body
...
”

Discovery:

Ribosome is commonly known Engine
of the cell
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Chemical composition:
They ate composed of almost equal amount of RNA and protein; hence they are called
ribonucleoprotein particles
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i
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Subunits:
Each ribosome consists of two subunits i
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one is large and the other is smaller
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Polysome:
Many ribosomes get attached to the same strand of mRNA for protein synthesis
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Diagram:

Types:
On the basis of their size and sedimentation, the following types ribosomes have been
recognized
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➢ These ribosomes have small subunit 40s and larger subunit 60s
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b) 80 s- ribosome
➢ It is large and is present in eukaryotic cells
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Function:
The ribosome plays an important role in the synthesis of protein with the help of mRNA
and rRNA
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Golgi bodies:(Dictyosome)
Definition:

“It is double membrane bounded structure consists of stacks of flattened sacs
present in the eukaryotic cytoplasm
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Chemical composition:
Chemically Golgi bodies are composed of proteins, lipids Enzymes and law
concentration of DNA and RNA
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➢ Each cisternae having a cis face (concave) and a Trans face (convex)
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Function:
➢ Many molecule travels through Golgi bodies on their way to other
organelles or to plasma membrane
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➢ It modifies the protein and lipids of plasma membrane by adding
carbohydrates and converting them into glycoprotein or glycolipids
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➢ They are involved in the primary lysosome
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g
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➢ Secretory vesicles when fuse with plasma membrane, add more surface area
to it
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Lysosome: (suicide sacs)
Meaning:
Lyse—splitting/breakdown soma—body
Definition:

“It is rounded dense, single membrane bounded structure having
hydrolytic enzyme which help in the digestion of food particles
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Chemical composition:
The lysosomes are chemically composed of protein, lipids and enzyme
(hydrolase)
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➢ If the hydrolytic enzymes are release into the cell cytoplasm, they would quickly digest
the cell
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Formation:
The digestive enzyme present in the lysosome is synthesized by the ribosome on RER and is
transported to the Golgi apparatus
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Malfunctioning of lysosome: (mal means—bad)
...
g
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Examples:
(1) Glycogenesis type—ii disease:
“it occurs due to the accumulation of glycogen in the liver and muscle” due to
the absence of lysosome enzyme which convert glycogen into glucose
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e
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”
Function:
➢ They are involved in the digestion of material present inside or outside the cell
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➢ Lysosomes rupture and release their enzyme in aged cells which are not functioning
properly and thus destroy them
...
g
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➢ Lysosomes also digest unrequired material in the cell by a process called autophagy
(self-eating) and clean the cytoplasm
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Peroxisomes: (micro bodies)
...
g
...
”
Discovery:
De Duve and co-worker isolated in 1965 particles from liver and other
tissues, which were enriched with some oxidative enzyme
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Structure: (0
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➢ They are similar to lysosomes, containing some oxidative enzymes (e
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—
peroxidase, catalase)
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They protect cell from H2O2 corrosive effects
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They take part in the destruction of toxic effect of Alcohol
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”
➢ They are abundantly in plant seedling and lipid rich seeds for short period in the
germination
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g Glycolic acid, oxidase and
catalase
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Their main function is the conversion of fatty acids into carbohydrate through
Glyoxylate cycle
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Glyoxisomes provided site for the break down (metabolism) of lipid in lipid rich
endospermic seed
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”
Chemical composition:
They are mainly composed of protein i
...
tubulin, actin, myosin and Tropomyosin
etc
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➢ They are made up of a protein called tubulin and traces of RNA
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Functions:

1
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g chromosomes
movement during cell division
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They from the spindle fires of the dividing cells
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They play an important role in formation of centrioles, cilia and flagella etc
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They also provide support to maintain the shape of the cell
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➢ In skeletal muscle cells they lie parallel to each other
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Diagram:

Functions:
1
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3
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They provide support and strength to the cell
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They have a role in muscle contraction
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Intermediate filament: (10nm in diameter)
Structure:
➢ They are intermediate between microfilaments and microtubules
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➢ The fibers are made up of keratin protein found in hair, skin etc
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2
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4
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They provide mechanical support to the cell
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They help in locomotion process with the association to the microtubules
...
”
Structure: (0
...
5µ long, 0
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Microtubules:
➢ In cross section each centriole consists of a cylindrical array (set)
of nine microtubules
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➢ The two centrioles are usually placed at right angle to each other
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Functions:
1
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Then they move to the opposite
poles (sides) and organize microtubules and spindle fibers which help to separate
chromosomes during cell division
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They help in the formation of cilia and flagella
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(granules)
Definition:
“It is a double membrane bounded, colorless body, widely distributed in the cytoplasm
of eukaryotic cell
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Chemical composition:
Chemically the mitochondrion is composed up of proteins, lipids, RNA and small amount
of DNA
...

Structure:
i)

Membrane:
Mitochondria is oval structure encircled (surrounded) by double
membrane i
...
the outer membrane is smooth while the inner membrane is in
folded
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➢ The inner surface of cristae in the mitochondrial matrix has small knob like structure
known as elementary particles
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Diagram:

Function: (powerhouse of the cell)
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Cell use this energy for the
performance of various cellular functions, “that is why
mitochondria is known as the power house of the cell
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Plastid:
Definition:
“It is a large pigment containing bodies present in plant cells
...

1
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Meaning:
Chloro—chlorophyll (green) plast—plastid

Each plant cell contains 10—100
chloroplast
...
”
➢ Chloroplast is commonly known as kitchen of the cell
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Membrane:
Chloroplast is surrounded by double membrane
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e
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B
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c
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d
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The grana become green due to the presence chlorophyll
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Intergrana:
The grana are inter connected by thread like connection called Intergrana
2
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”
Pigments:
Chromoplast may be red, brown, yellow, blue, purple or of any other
color pigment
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Chlorophyll molecule resemble
hemoglobin the only and main
difference b/w the two molecules
is that chlorophyll has mg+2 while
hemoglobin has fe+2 as the central
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Leucoplasts:
Meaning:
Leukos—colorless plast—plastid
...
”
➢ They are mostly present in the underground portion of plants
...
g
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e
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➢ In chloroplast the stoma helps in dark reaction of photosynthesis
I
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—co2 is fixed (reduce) to sugar
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➢ Chromoplast is present in the fruits attacking animals and birds
for dispersal of seed
...
g
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10
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Discovery:
Nucleus was first reported by Robert brown in 1831
...

i)
Nuclear membrane:
Introduction:
“It is the outer most boundary of nucleus which separates the
Nuclear membrane is made up of proteins and lipids
...
e
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➢ The pores present in the nuclear membrane, allow the mRNA to escape the
cytoplasm for protein synthesis
...
g
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ii)
Nucleoplasm:
Introduction:
“It is a transparent, semisolid, present inside the nuclear
membrane (Nucleus)
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Composition:
The nucleoplasm consists of proteins, enzymes, Nucleic acids, lipids and
minerals
...
”
➢ They may be one or many in number in a single nucleus
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Composition:
Chemically nucleolus is composed of DNA, RNA and proteins
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iv)
Chromosomes: (chromo –colored, soma –body )
Introduction:
“They are dark staining (color) bodies which Transfer genetic
information from parent to offspring
...
After in 1908, Sutton identified
the function of chromosomes, that they take part in the transfer of heredity characters
...

Structure:
a) Chromatids:
Each chromosome is made up of arms called chromatids
...

Number:
Each species is having a constant number of chromosomes
Drosophila = 8
Garden pea = 14
Onion
= 16
Maize
= 20

Tomato
= 24
Grass hopper = 24
Frog
= 26
Rhesus monkey = 42

Wheat
= 42
Man
= 46
Chimpanzee = 48
Potato
= 48
Pigeon
= 80

Function of nucleus:
1
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2
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e
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3
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4
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5
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6
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g
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