THE CELL
INTRODUCTION
v
The cell is the
smallest structural and functional unit of the body.
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The human body
is made up of millions of cells of different types, each with its own form and
functions.
v
Human body is
made up of 75 trillion cells.
v
The cells are
organized in tissues, tissues combine to form organs, and organs work together
in organ systems.
v
Cell biology is the study of cellular structure and function.
DEFINITION :
v
A cell is the
structural and functional unit of living organism.
v
A cell is a
minute (jelly like) mass of protoplasm containing a nucleus held together by a
cell membrane.
STRUCTURE
OF CELL
The cell
is made up of the following structures.
1.
Cell membrane
(or) Plasma membrane. 2. Nucleus. 3.Cytoplasm:
THE
SIMPLE CELL
1.
CELL MEMBRANE OR PLASMA MEMBRANE.
v The cell membrane is a protective sheath of the cell
body
v The cell membrane is the semi permeable membrane. So
there is free exchange of certain substances between the extracellular and
intracellular fluids.
v The structure of cell wall is fluid mosaic model.
v The cell membrane is made up of proteins, lipids and
a little amount of carbohydrates.
Function of Cell Membrane:
v It forms outermost boundary of the organelles.
v It takes in food materials.
v It excretes waste products.
v Some are involved in transport across the membrane.
Cilia and flagella
v Cilia and flagella are mobile thread-like
projections through the cell membrane.
v Cilia are usually shorter than flagella,
v The flagellum provides motility, or movement
2. NUCLEUS:
v It is the largest organelle.
v It is spherical structure surrounded by a permeable
membrane called Nuclear membrane & is similar to the plasma membrane.
v It has tiny pores through which some substances can
pass between it and the cytoplasm.
v It contains the genetic material which directs all
the metobolic activities of the cell.
v This is built from DNA and proteins called histones
coiled together forming a fine network of threads called chromatin.
v Chromatin resembles tiny strings of beads.
v During cell division the chromatin replicates and
becomes more tightly coiled forming chromosomes.
v Nucleus consists of 46 chromosomes, which are made
from deoxyribonucleic acid (DNA).
v The functional subunits of chromosomes are called genes.
v Nucleoli are the staining spherical bodies found
within the nucleus.
Functions of Nucleus
v Controls cellular structure.
v Directs cellular activities.
v Produce ribosome in nuclei.
3. CYTOPLASM
Cytoplasm
(cell forming material) is the cellular material between the plasma membrane
and nucleus.
The cytoplasm
contains the following cell organelles:
a)
Endoplasmic
Reticulum
b)
Mitochondria
c)
Ribosomes
d)
Golgi apparatus
e)
Lysosomes
f)
Peroxysomes
g) Centrosomes
h) Cytoskeleton
a) Endoplasmic Reticulum (ER)
v Endoplasmic reticulum is a series of interconnecting
membranous canals in the cytoplasm.
v The endoplasmic reticulum is of two types:
1. Rough endoplasmic reticulum
2. Smooth endoplasmic reticulum
1.
Rough endoplasmic reticulum:
v Endoplasmic reticulum with granular structure
(ribosome) on its outer surface called rough endoplasmic reticulum.
Functions:
v It helps in synthesis of protein.
2. Smooth
endoplasmic reticulum:
v The Smooth endoplasmic reticulum does not have
ribosomes on its surface.
Functions:
v Synthesis of lipids and steroid hormones.
v Detoxification of drugs & certain pesticide
b) Mitochondria:
v They are power houses of the cell.
v They are sausage shaped structure in the cytoplasm.
v The mitochondia is composed of two layers of
membranes:
Ø An outer layer which is smooth
Ø An inner layer folded into sheets of tubles called christae.
v Both these layers enclose a central cavity called
matrix.
v The mitochondria are made up of proteins,
phospholipids and RNA.
Functions:
v It helps in oxidation of glucose.
v Mitochondria are power generating units of cells
(synthesis of ATP)
v It also contains DNA and can synthesis proteins.
a) Ribosome:
v Ribosomes are tiny granules composed of RNA and
proteins.
v Some ribosomes are attached to rough endoplasmic
reticulum.
v The remaining are present as free ribosomes in the
cytoplasm.
Function:
v Synthesis of protein.
b) Golgi
Apparatus:
v A canal like structure lying next to the nucleus.
Functions:
v It involved in the secretary activities of the cell.
c) Lysosome:
v They are formed by golgi apparatus.
v They present throughout the cytoplasm.
v Lysosomes are filled with variety of hydrolytic
enzymes are called lysozymes.
Functions:
v It is capable of digesting proteins and fats.
v Removal of unwanted damaged substances and foreign
bodies like bacteria.
v Removal of excessive secretory products in the cells
of the glands.
d) Peroxisome::
v It’s structure is similar to that of lysosomes.
v They contain oxidase.
v Peroxisome catalyze reaction generating hydrogen
peroxide.
e) Centrosomes
v Centrosomes are structures present near the nucleus
v They are made up of structures called centioles
v Centrioles are two short cylinders arranged at right
angles to each other.
v It is visible only during cell division.
f) Cytoskeleton
v Cytoskeleton is a system of fibres that maintains
structure of cell.
v It permits cell to change its shape
v It helps in movement of cell.
v Cytoskeleton is made up of
ü Microfilaments
ü Intermediate filaments
ü Microtubules.
- Irritability: The cell has the ability to detect and responds to changes in its environment.
- Nutrition: The cell is capable of absorbing fluids and dissolved substances directly through cell membrane and these can be used by the cell growth and repair, to provide.
- Respiration: The cell has the ability to use oxygen combined with food substances to form carbon dioxide and water, while releasing energy for intra cellular activity.
- Excretion: The cell is able to discharge unused and waste membrane through cell membrane.
- Growth and Reproduction: The cell has the ability to increase in size and when it reaches the limit of its growth it reproduces by dividing into 2 smaller cells.
- Movement: Some cells have power of movement.
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