Prokaryotic cell structure

The basic definition of cell can be stated as, “The structural and functional unit of life.”

It can also be defined as a complete expression of the fundamental structure and function of all living organisms.

The cells are able to replicate themselves. A new cell can only come from pre-existing ones. It was derived from the Greek word, ‘Kytos’, which

stands for ‘hollow space’.

The cell was first observed and described by a British scientist named Robert Hooke in 1665.

He published the original images of cells in a paper, ‘The texture of cork by means of magnifying lenses’, in Micrographic.

Tiny comb-cavities were observed by him in the cork. The term ‘cell’ was specifically used by him because of their

likeness to the cells in a honeycomb. The substances found inside the cell were termed ‘sarcode’

by Felix Dujardin. (Later named protoplasm by Jan Evangelista)

Nucleus of the cell was discovered by Robert Brown.

ABOUT The prokaryotic cells are single cellular ,primitive as well as

relatively simple cells. ‘Pro’ means ‘pre’ i.e initial or undeveloped nucleus. They had appeared 3.5 billion years ago at the time when life was

first originated. The prokaryotic cell lacks the membrane-bound organelles such as ER , Golgi, lysosomes, mitochondria and chloroplast.

A Prokaryotic cell lacks nuclear membrane therefore it’s nucleus is known as nucleoid.

Some examples: E coli , cyanobacteria , proteobacteria.

CHARACTERISTICS : CELL WALL -

The cell wall is made up of peptidoglycan and glucose units . The wall protects the cell, maintains the shape of the cell and provides anchorage to it.

NUCLEOID –This contains the genetic material of the cell

known as genophore (lacks nuclear membrane).

FLAGELLUM–A whip like structure which is responsible for the

locomotion of the cell.

PILI-It forms a bridge between two cells and helps in

conjugation.

ABOUT The name Eukaryote comes from a Greek word ,’well’ or ‘true’. Unlike prokaryotes, Eukaryotes have a nucleusEnclosed within membranes. They contain membrane bound organelles such as ER ,Golgi, mitochondria etc. The major role in evolutionof eukaryotic cell is played by Endosymbiosis. Examples: FUNGAL CELL,ANIMAL AND PLANT CELL.

CHARACTERISTIC STRUCTURE- NUCLEUS –

It contains the entire genetic material (DNA) of the cell .

MITOCHONDRIA-Generally known as the ‘power house of the cell’ because it

releases energy in the form of ATP. It contains it’s own DNA.

CHLOROPLAST-It’s main role is to conduct photosynthesis.

(only present in plant cell).

RIBOSOMES-Plays a role in protein synthesis.

GOLGI COMPLEX-Responsible for manufacturing, warehousing

and shipping certain cellular products.

ENDOPLASMIC RETICULUM-The region with ribosomes(rough ER)

or without(smooth ER) is responsible formanufacturing membranes, proteins , carbs , etc.

LYSOSOMES-It recycles a cell’s organic material by

digesting it’s cellular macromolecules such as nucleic acid ,proteins , fats.

ANIMAL CELL Contains cell wall. Chloroplast present which

helps in photosynthesis. One large vacuole present. Ex: xylem and phloem.

PLANT CELL

Cell wall is absent. Chloroplast (green

pigment) is absent. Small vacuoles present which are large in number. Ex: Muscle cell,white blood cells.

EUKARYOTE Contains circular DNA Contains no organelles Contains nucleoid without a nuclear

membrane Usually unicellular. Produced by binary fission. Absence of plasma membr-Ane.

PROKARYOTE It contains a linear DNA. Contains all the organelles. Contains nucleus with nuclear membrane. Usually multicellular. Produced by meiosis. Plasma membrane present.

A cell is basic unit of life. It consists of Eukaryote(multicellular)

and Prokaryote(single-cellular) Pro(initial)karyotes lack organelles and nucleus. Eukaryotes(true cell) contains all organelles and nucleus. Two important eukaryotic cells are-Animal cells and plant cells .