cell basics, classification of cell, prokaryotic cell with organelles

1. Introduction To Bio-Chemistry
Study The Cell
1 Submitted To : Prof. Abdullah Jan Sir (Gold-Medalist)
Assignment Content
#S.NO. TOPIC #PAGE NO.
1) Introduction To Cell 02
2) Classification Of Cell 02
 Prokaryotic Cell 02
 Eukaryotic Cell 02
3) Structure Of Prokaryotic Cell 03
 Cell Membrane 04
 Cytoplasm 04
 Ribosomes 04
 Genetic Material 05
 Plasmids 05
 Cell Wall 06
 Cell capsule or, Envelope 06
 Flagella 06
 Pili or, Fimbriae 06

2. Introduction To Bio-Chemistry
Study The Cell
2 Submitted To : Prof. Abdullah Jan Sir (Gold-Medalist)
1) Introduction To Cell :-
Meaning: The word cell comes from a Latin word called “cella” meaning a “small room”.
Definition No.1: Cell is the basic structural, functional and biological unit of all known
living organism.
Definition No.2: Cell is the unit of life which has the power to replicate independently
and is called the building block of life.
 Cell may consist of a semitransparent or, translucent matter called protoplasm enclosed within
membrane.
 The number of cell in plants & animals varies from species to species human contain about
100 trillion (1014
) cell.
 The human and plants cell are visible only under microscope having dimension between
1 - and 100 µm.
 All the organisms have been classified as:
 UNICELLULAR: An organism consists of only one piece cell is called unicellular.
e.g. Bacteria,Archaea
 MULTICELLULAR: An organism consist of more than one cell is called multicellular.
e.g. Plants, Animals
2) Classification Of Cell :-
A cell can be generally classified on the basis of unicellular or, multicellular organism.
 Prokaryotic Cell: (include unicellular organism such as bacteria, Archaea)
the simplest form of the cell having no membrane bound organelles.
 Eukaryotic Cell: (include multicellular organism such as Plants & Animals)
the most complex form of the cell having membrane bound organelles.
 Prokaryotic Cell:
 Prokaryotic cells were the first form of life on this planet (shown in figure a).
 They are smaller and simpler than eukaryotic cells.
 Prokaryotic cells lack a well-defined nucleus and membrane-bound organelles such as
the mitochondria.
 The DNA of a prokaryotic cell consists of a single chromosome which is in direct contact
with the cytoplasm.
 There are 20 – times more prokaryotic cell on earth than eukaryotic cell, this is only
minimum estimate about trillion of trillion are associated with eukaryotic cell and
archaea are also prokaryotes but there number is not sure.
 For example, bacteria and archaea.

3. Introduction To Bio-Chemistry
Study The Cell
3 Submitted To : Prof. Abdullah Jan Sir (Gold-Medalist)
Simple structure of prokaryotic cell (figure a)
3) Structure Of Prokaryotic Cell :- (Typically Study Bacteria )
A prokaryotic cell structure have the following component:
 Cell Membrane
 Cytoplasm
 Ribosomes
 Cytoplasm
 Genetic Material
 Plasmids
 Cell Wall
 Cell capsule or, Envelope
 Flagella
 Pili or, Fimbriae
ORGANALLES: (Little organ)
 Organelles are parts of the cell which are specialized for carrying out one or more vital functions.
 Both eukaryotic and prokaryotic cells have organelles, but prokaryotic organelles are generally
simpler and are not membrane-bound.
 There are severaltypes of organelles in a cell. , such as mitochondria, chloroplasts, peroxisomes and
lysosomes (hundreds to thousands).
 The cell is filled with a gelatinous fluid which surrounds the organelles. This fluid is known as
cytosol.

4. Introduction To Bio-Chemistry
Study The Cell
4 Submitted To : Prof. Abdullah Jan Sir (Gold-Medalist)
PLASMA MEMBRANE
Prokaryotic cells can have multiple plasma membranes (shown in figure b).
Plasma membrane in prokaryotic cells is responsible for exchange of materials between the cell and
its surrounding environment.
Plasma membranes also aids in sending and receiving chemical signals from other bacteria and
interacting with the cells of eukaryotic organisms during the process of infection.
Prokaryotes known as "gram-negative bacteria,"
For example, often have two plasma membranes with a space betweenthem known as the periplasm.
CYTOPLASM
The cytoplasm of the prokaryotic cells is a translucent or gel-like fluid substance in which all of the
other cellular components are suspended (shown in figure b).
It is very similar to the eukaryotic cytoplasm, except that it does not contain organelles.
Recently, biologists have discovered that prokaryotic cells have a complex and functional
cytoskeleton similar to that seen in eukaryotic cells.
The cytoskeleton helps prokaryotic cells maintaining its shape.
RIBOSOMES
Prokaryotic ribosomes are smaller and have a slightly different shape and composition than those
found in eukaryotic cells (shown in figure b).
Bacterial ribosomes, are about half of the amount of ribosomal RNA (rRNA) and one third fewer
ribosomal proteins (53 vs. ~ 83) than eukaryotic ribosomes.
Along these differences, the function of the prokaryotic ribosome is totally same to that of eukaryotic
cell.
Just like in eukaryotic cells, prokaryotic ribosome is involved in the synthesis of proteins by
translating messages sent from DNA in the shape of messenger RNA.
Figure b

5. Introduction To Bio-Chemistry
Study The Cell
5 Submitted To : Prof. Abdullah Jan Sir (Gold-Medalist)
GENETIC MATERIAL
All prokaryotic cells contain large quantities of genetic material in the form of DNA and RNA.
As prokaryotic cells do not have a well-defined nucleus, the single large circular strand of DNA
which contains most of the genes is found in the cytoplasm (shown in figure c).
These genes are required for the growth, survival, and reproduction of the cell.
The DNA looks like a mesh of string in the middle of the cell.
Generally, the DNA is spread throughout the entire cell, and is readily accessible for the transcription
into messenger RNA (mRNA) which is immediately translated by ribosomes into protein.
Sometimes, when biologist prepares prokaryotic cells for viewing under a microscope, the DNA will
condense in one part of the cell producing a darkened area known as nucleoid (shown in figure c).
PLASMIDS
Just eukaryotic cells,the prokaryotic chromosome is associated with special proteins involved in
maintaining the chromosomal structure and regulating gene expression (shown in fig c).
In addition to a single large piece of chromosomal DNA,many prokaryotic cells also contain small
pieces of DNA called plasmids.
These circular rings of DNA are replicated independently of the chromosome and can be transferred
from one prokaryotic cell to another through pili, which are small projections of the cell membrane
that can form physical channels with the pili of adjacent cells.
The transfer of plasmids between one cell and another is often referred to as "bacterial sex."
Plasmids encode additional genes, such as antibiotic resistance genes.
The genes for antibiotic resistance, or the gradual ineffectiveness of antibiotics in populations, are
often carried on plasmids (shown in fig c).
If these plasmids get transferred from resistant cells to nonresistant cells, bacterial infection in
populations can become much harder to control.
For example, it was recently learned that the multidrug-resistant Staphylococcus aureus, received
some of its drug-resistance genes on plasmids.
Transmission Electro Micrograph Image OfPlasmid (Small DNA) Fig – C

6. Introduction To Bio-Chemistry
Study The Cell
6 Submitted To : Prof. Abdullah Jan Sir (Gold-Medalist)
CELL WALL
The prokaryotic cells have a cell wall present outside the plasma membrane, with a few exceptions
such as Mycoplasma (bacteria) and Thermoplasma (archaea).
The cell wall consists of peptidoglycan in bacteria, and acts as an additional barrier against exterior
forces.
It also prevents the cell from expanding and bursting (cytolysis) from osmotic pressure due to a
hypotonic environment.
CELL ENVELOPE or CAPSULE
Some of the bacterial cells have an additional layer around the cell wall called a cell envelop or cell
capsule.
The envelope gives rigidity to the cell and separates the interior of the cell from its environment,
serving as a protective filter.
Inside the cell is the cytoplasmic region that contains the genome (DNA),ribosomes and various sorts
of inclusions.
The prokaryotic chromosome is usually a circular molecule (an exception is that of the bacterium
Borrelia burgdorferi).
Though not forming a nucleus,the DNA is condensed in a nucleoid.
Prokaryotes can carry extra chromosomal DNA elements called plasmids, which are usually circular.
FLAGELLA
The bacterial flagella are long and thick thread or whip-like structures,protein in nature which
stretches from cytoplasm through the cell membrane(s) and extrudes through the cell wall.
They are most commonly found in bacteria cells but are found in animal cells as well.
They are involved in the movements.
FIMBRIAE (PILI)
They are short and thin hair-like filaments, made up of protein called pilin (antigenic).
They are responsible for attachment of bacteria to specific receptors of human cell (adherence).
There are special types of pili called (sex pili) involved in conjunction.
Simple Structure Of Prokaryotic Cell
THE END!!!