This document provides an introduction to cell biology, including the history of cell discovery and the cell theory. It describes the key differences between prokaryotic and eukaryotic cells, including that eukaryotes have membrane-bound organelles like the nucleus, endoplasmic reticulum, Golgi apparatus and ribosomes, while prokaryotes do not. It also provides an overview of several important cell organelles and their functions.

1. Introduction to Molecular Cell
Biology - 1
Introduction to Cell, Prokaryotes and Eukaryotes, Cell
Organelles.

2. Cell and it’s History
The Cell can be defined as Structural and functional unit of life. Smallest unit
that can carry out all activities of life.
 Robert Hooke (1665) :) First reported cells as Micrographia from the cork
(of dead plant material.
 Lorenz Oken (1805) : German Scientist believed that all living beings
originate from or consist of vesicles.
 Jean Baptist de-Lamarck (1809) : Said that nobody can have life if its
constituents parts are not cellular tissues or are not formed of cellular
tissues.
 Robert Brown (1809) : Reported the presence of nucleus in the cell.
 Theodor Schwann (1839) & Schleiden (1838) : came out with a theory
called cell theory.
 Rudolph Virchow (1855) : Hypothesized that new cells can only were
formed only by the division of previously existing cells, “Omnis cellula e
cellula”.
 Louis Pasteur (1862) : Supplied experimental proof of virchow’s hypothesis.
 August Weismann (1880) : Said all living cells have same origin because
they have basic similarities in structure and molecules etc.

3. Cell Theory
 All organisms are composed of one or more cells.
 All cells arise from pre existing cells.
 Cell is basic structural as well as functional unit for
all organisms.

4. Prokaryotic vs. Eukaryotic Cells
Prokaryotic cells Eukaryotic Cells
Prokaryotes do not have a nuclear
membrane . Their circular shaped
genetic material dispersed throughout
cytoplasm.
Nuclear membrane surrounds linear
genetic material (DNA)
Prokaryotes do not have membrane-
bound organelles . Ribosomes are the
only organelles.
Eukaryotes do have membrane-bound
organelles .
Prokaryotes have a simple internal
structure.
Eukaryotes have a complex internal
structure.
Prokaryotes are smaller in size when
compared to Eukaryotes.
Eukaryotes are larger than
prokaryotes in size
Circular DNA Linear DNA
Unicellular Unicellular as well as Multicellular
Appeared 4 billion years ago Appeared 1 billion years ago

5. Prokaryotic vs. Eukaryotic Cells

6. Cell Organelles
 Plasma Membrane
 Outer Boundary of cell, covered with Cell wall in plant
cells. Composed of lipids and proteins.
 60-80% are proteins while 20-40% are lipids. Small
quantity of carbohydrates.
 The protein layers are not confined to the surface of
membrane but are embedded in lipid bi layers in a mosaic
manner (Fluid Mosaic Model).
 It contain charged pores through which movement of
materials take place, both by active and passive
transport.

7.  Cell Wall
 The cell wall is different in plant cell from that of prokaryotes,
both in structure and chemical composition.
 It is secreted by protoplasm of cell.
 Its thickness varies in different cells of the plant.
 Composed of three main layers; primary wall, secondary wall,
and middle lamella.
 Middle lamella is first to be formed in between primary walls of
neighbouring cells.
 Primary wall is composed of cellulose and some deposition of
pectin and hemicellulose (in plants).
 Secondary wall is thick and composed of inorganic salts, silica,
waxes, cutin, lignin.
 Prokaryotic cell wall lacks cellulose, its strengthening material
is peptidoglycan or murein.
 Fungal cell wall contains chitin.

8.  Cytoplasm
 Living contents of eukaryotic cells are divided into
cytoplasm and nucleus, collectively called Protoplasm.
 Soluble part of cytoplasm is Cytosol.
 Most important function of the cytoplasm is to act as store
house and a site for glycolysis.

9.  Endoplasmic Reticulum
 Network of channels seen extending throughout
cytoplasm and often appear to be in contact with nuclear
membrane.
 Material present in these channels is Cisternae.
 Smooth ER is without ribosome while Rough ER is with
ribosomes and is involved in synthesis of proteins.
 SER helps in metabolism of number of different type of
molecules particularly lipids.. Helps in detoxification of
harmful drugs. Responsible for transmission of impulses
e.g. Muscle cell, nerve cell.
 In addition SER plays an important role in transport and
provide mechanical support to the cell.

10.  Ribosomes
 Tiny granular structure composed of RNA and protein.
 Either freely dispersed or attached to RER.
 Two subunits; in eukaryotes 60S (larger subunit
sediments at 60 Svedberg, unit used in
ultracentrifugation), while smaller subunit sediments at
40S. Attached to each other and make 80S Particle,
while in prokaryotes its 70S (50S and 30S).
 Attachment is controlled by Mg+2 ions.
 A group of ribosomes attached to mRNA is known as
Polysome.

11.  Golgi Apparatus
 Discovered by Golgi in 1898.
 Consist of sac of flattened, membrane bound sacs, called
cisternae.
 It is concerned with cell secretions formed within the cell
on ribosome and then passed to the outside through ER
and Golgi Apparatus.
 Most important function is to modify proteins and lipids by
adding carbohydrates and converting them into
Glycolipids or glycoproteins.