THE CELL AND ITS

GENERALIZED STRUCTUTES

BY : MUNEEB UR REHMAN
 INTRODUCTION TO CELL :

 Cells is the basic building block of all the

living things.
 The human body is composed of trillions of
cells.
 They provide structure for the body, take in
nutrients from food, convert those
nutrients into energy, and carry out
specialized functions.
 Cells also contain the body’s hereditary
material and can make copies of
themselves.
DISCOVERY OF CELL :

The term “cells” was first coined in 1665

by a British scientist Robert Hooke. He
was the first person to study living
things under a microscope and
examined a thin slice of cork under a
microscope and observed honeycomb-
like structures. Robert Hooke called
these structures as cells.
TYPES OF CELL :
 CELL STRUCTURES :

1. CELL MEMBRANE:
• The cell membrane, also called the
plasma membrane, is found in all cells
and separates the interior of the cell
from the outside environment.
• The cell membrane consists of a lipid
bilayer that is semipermeable. The cell
membrane regulates the transport of
materials entering and exiting the cell.
2. CYTOPLASM :
• Cytoplasm is the gelatinous liquid that fills the inside of a cell.
• It is composed of water, salts, and various organic molecules.
Some intracellular organelles, such the nucleus and
mitochondria, are enclosed by membranes that separate them
from the cytoplasm.
• The cytoplasm is the gel-like fluid inside the cell. It is the medium
for chemical reaction. It provides a platform upon which other
organelles can operate within the cell. All of the functions for cell
expansion, growth and replication are carried out in the
cytoplasm of a cell. Within the cytoplasm, materials move
by diffusion, a physical process that can work only for short
distances.
 CELL ORGANELLES :

 An organelle is a subcellular 1. Nucleus

structure that has one or more
specific jobs to perform in the 2. Mitochondrion
cell, much like an organ does in 3. Golgi Complex
the body. Among the more
4. Endoplasmic reticulum
important cell organelles are the
nuclei, which store genetic 5. Lysosomes
information; mitochondria, which 6. Ribosomes
produce chemical energy; and
ribosomes, which assemble 7. Cytoskeletons
proteins. 8. Peroxisomes
 NUCLEUS :

• A nucleus is the membrane-enclosed organelle

within a cell that contains the chromosomes
and darker than cytoplasm. Discovered in
1831 by Robert Brown.
• The nucleus is one of the most obvious parts
of the cell when you look at a picture of the
cell.
• It's in the middle of the cell In Animals and at
the peripheral position In Plant cells .
• Nucleus contains all of the cell's
chromosomes, which encode the genetic
material. So this is really an important part of
the cell to protect.
Types of Cells on the basis of no nucleus…..
• The nucleus has a membrane around it that keeps all the chromosomes inside
and makes the distinction between the chromosomes being inside the nucleus
and the other organelles and components of the cell staying outside.
• Sometimes things like RNA need to traffic between the nucleus and the
cytoplasm, and so there are pores in this nuclear membrane that allow
molecules to go in and out of the nucleus.
• Inbound Traffic includes Nuclear proteins and Ribosomal proteins
• Outbound Traffic includes mRNA And Ribosomal Subunits.
Components Of Nucleus:
Nucleolus:
This is the Largest nuclear organelle and is a specialized region in a cell nucleus. Here RNA is
synthesized and assembled and later transported out of the nucleus through the nuclear pores
for protein synthesis in the cytoplasm.
Chromatin:
Humans and nearly all other species carry their genetic information in DNA. This DNA is
packaged as chromatin. Chromatin fibers are coiled and condensed to form chromosomes
within the nucleus of eukaryotic cells.
Nuclear Membrane (Envelope):
The inner and outer nuclear membranes are two membranes that enclose the nucleus and
protect the cell's DNA from the chemical reactions occurring elsewhere in the cell. The outer
membrane is continuous with the endoplasmic reticulum.
Nuclear pore:
The nuclear membrane has a variety of protein-lined channels (called the nuclear pore
complex) that enable the selective passage of specific molecules, such as proteins and nucleic
acids, into and out of the nucleus.
Nucleoplasm:
The nucleoplasm is a gel-like substance in the central area of the cell whose main function is
to store DNA and enable DNA-dependent processes such as transcription, gene expression,
and DNA repair to occur in a controlled environment.
 Functions of Nucleus:

1. It contains the cell’s heredity material Information and control the cell growth and Reproduction.
2. First and foremost, it is possible to duplicate one’s DNA in the nucleus. This process has been named
DNA Replication and produces an identical copy of the DNA.
3. Producing two identical copies of the body or host is the first step in cell division, where every new
cell will get its own set of instructions
4. Secondly, the nucleus is the site of Transcription. Transcription creates different types of RNA from
DNA.
5. Transcription would be a lot like creating copies of individual pages of the human body’s
instructions which may be moved out and read by the rest of the cell.
6. The central rule of biology states that DNA is copied into RNA, and then proteins
 MITOCHONDRIA :

• Mitochondria is the Power House

of cell and is double membrane
bounded organelle found in
eukaryotic organisms

• Chemical energy produced by

the mitochondria is stored in a
small molecule called adenosine
triphosphate (ATP).
 RIBOSOMES :

• A ribosome is an intercellular
structure made of both RNA and
protein, and it is the site of protein
synthesis in the cell.

• The ribosome reads the

messenger RNA (mRNA) sequence
and translates that genetic code
into a specified string of amino
acids, which grow into long chains
that fold to form proteins.
 ENDOPLASMIC RETICULUM :

• The endoplasmic reticulum (ER) is a

continuous membrane system that forms a
series of flattened sacs within
the cytoplasm of eukaryotic cells.
• All eukaryotic cells contain an ER.
• In animal cells, the ER usually constitutes
more than half of the membranous content
of the cell.
• The ER can be classified in two functionally
distinct forms: the smooth endoplasmic
reticulum (SER) and the rough endoplasmic
reticulum (RER).
 Smooth ER:
• The smooth endoplasmic
reticulum functions in many
metabolic processes. It
synthesizes lipids,
phospholipids as in plasma
membranes, and steroids.
• Cells that secrete these
products, such as cells of the
testes, ovaries, and skin oil
glands, have an excess of
smooth endoplasmic reticulum.
Rough Endoplasmic Reticulum (RER) :
• Series of connected flattened sacs, part of
a continuous membrane organelle within
the cytoplasm of eukaryotic cells, that
plays a central role in the synthesis
of proteins.
• The rough endoplasmic reticulum (RER) is
so named for the appearance of its outer
surface, which is studded with protein-
synthesizing particles known
as ribosomes.
• This feature distinguishes it superficially
and functionally from the other major type
of endoplasmic reticulum (ER), the smooth
endoplasmic reticulum (SER), which lacks
ribosomes and is involved in the synthesis
and storage of lipids.
 LYSOSOMES :

• Lysosomes are membrane-enclosed

organelles that contain an array of
enzymes capable of breaking down all
types of biological polymers—proteins,
nucleic acids, carbohydrates, and
lipids.
• Lysosomes function as the digestive
system of the cell, serving both to
degrade material taken up from
outside the cell and to digest obsolete
components of the cell itself.
 GOLGI APPARATUS :

• A Golgi body, also known as a Golgi apparatus, is a

cell organelle that helps process and package
proteins and lipid molecules, especially proteins
destined to be exported from the cell.
• Named after its discoverer, Camillo Golgi, the Golgi
body appears as a series of stacked membranes.
• Functions as a factory in which proteins received
from the ER are further processed and sorted for
transport to their eventual destinations: lysosomes,
the plasma membrane, or secretion. In addition, as
noted earlier, glycolipids and sphingomyelin are
synthesized within the Golgi.
 CYTOSKELETONS :

• The cytoskeleton is a structure that helps cells maintain their shape

and internal organization, and it also provides mechanical support
that enables cells to carry out essential functions like division and
movement.
• It is a complex, dynamic network of interlinking protein filaments
present in the cytoplasm of all cells, including those of bacteria and
archaea. In eukaryotes, it extends from the cell nucleus to the cell
membrane and is composed of similar proteins in the various
organisms
Three major types of filaments make
up the cytoskeleton:
Actin filaments, microtubules, and
intermediate filaments
EXOCYTOSIS AND ENDOCYSTOSIS :

EXOCYTOSIS: ENDOCYSTOSIS:
• Exocytosis is a form of active • ingestion of large particles
transport and bulk transport (such as bacteria) and the
in which a cell transports uptake of fluids or
molecules out of the cell. As macromolecules in small
an active transport vesicles. The former of these
mechanism, exocytosis activities is known as
requires the use of energy to phagocytosis (cell eating) and
transport material. the latter as pinocytosis (cell
drinking)
CELL JUNCTIONS :
1. TIGHT JUNCTIONS :

• Tight junctions act as a

barrier that prevents the
movements of unwanted
ions across the cell
• The cell of epithelial tissue
that found in stomach ,
intestine and urinary bladder
contain many tight junctions
that prevents leaking of
components into blood
stream .
 2. ADHESION JUNCTIONS :

• They are also called Belt

Desmosomes.
• They contain plaque of proteins
(dense layer).
• The glycol-protein present in these
junctions help to join the cell.
• Protein complexes that occur at cell
to cell junction in epithelial tissues.
They are basal than tight junctions
• Maintain physical integrity of
epithelium. Anchors to extracellular
matrix.
 3. DESMOSOMES :

• The cells keep neighbouring cells

together.
• They contain plaque and intermediate
filaments (made of keratin).
• The glycol-protein present in these
junctions help to join the cell.
• They are found in tissues that
experience intense mechanical stress.
• Cardiac , muscle and bladder tissues.
• In GIT mucosa and epithelia
 4. GAP JUNCTIONS :

• They are specialized

intracellular
connections between
cells which help in the
transfer of required
ions.
• Allows communication
of cells with each
other.
• Located in connective
tissue ,neural tissue
and muscular tissues .
 CELL CYCLE :

INTRODUCTION :
• The cell undergoes a sequence of changes, which involves
period of growth, replication of DNA, followed by cell division.
This sequence of changes is called cell cycle.
• It comprises two phases viz., interphase which is the period of
non-apparent division and the period of division also known as
mitotic phase. Each phase is further subdivided into different
sub-phases.
• Interphase is the longest part of the cell
cycle. This is when the cell grows and
copies its DNA before moving into
mitosis.
• It is the period of great biochemical
activity and can further be divided into:

I. G1-phase
II. S-phase
III. G2 -phase
MITOSIS :

“Mitosis is that step in the cell cycle where the newly formed DNA
is separated and two new cells are formed with the same number
and kind of chromosomes as the parent nucleus.”
• Mitosis helps in the development of an
organism. In single-celled organisms,
mitosis is the process of asexual
reproduction.

• Mitosis helps in the replacement of

damaged tissues.
 MIEOSIS :

• Meiosis is the special type of cell division in which the number of

chromosomes in daughter cells is reduced to half, as compared to the
parent cell.
• Each diploid cell after meiosis produces four haploid cells, because it
involves two consecutive divisions after single replication of DNA.
• Two divisions, are meiosis I and meiosis II. The first meiotic division is
the reduction division, whereas second meiotic division is just like the
mitosis. Both divisions can further be divided into substages like
prophase 1, metaphase 1, anaphase 1, telophase 1 and same names
are used for meiosis II also.
PROPHASE 1 :
NECROSIS AND APOPTOSIS :