Prokaryotic Cells
Scientist Dougherty first classified the cells in 1957. Cells are classified on the basis of structural organisation of their nucleus into two main types that are prokaryotic cells and eukaryotic cell. The term “pro” means premitive and “karyoplasms” means nucleus.
Examples of prokaryotic cells are - different types of bacteria (cocci, bacillus, spirilum) etc.
Definition of prokaryotic cell - Prokaryotic cells are the organisms that do not have membrane bound organelles and well defined nucleus, nucleoid is present instead of nucleus.
Definition of eukaryotic cell - Eukaryotic cells are the organism in which membrane bound organelles, well defined nucleus is present in it. Their genetic material is well placed and proper DNA is present.
Prokaryotic cells - prokaryotic cells are premitive plant cells that having the simplest organisation. Prokaryotic cells include bacteria, blue green algae, mycoplasma or PPLO that is pkeuro pneumonia like organisms, rickettsiae and spirochaete. Prokaryotic cells are smaller than eukaryotic cells in size. Cells of prokaryotes contain mass of protoplasm and is covered by cell covering. Each cell is bounded by a complex cell wall beneath which the plasma membrane lies. Plasma membrane surrounds the protoplasm of the cell. In some places plasma membrane invaginated to form internal membranous structure. Protoplasm of prokaryotic cells are not well defined like eukaryotic cell. Means protoplasm is not divided into nucleus and cytoplasm. In eukaryotic cells nucleus contains genetic material which is membrane bound but in prokaryotic cells genetic material is localised in a discrete region called nucleoid or genophore or chromatin body. It is made up of DNA threads. Here DNA is not complexed with his tone proteins and it does not form chromosome. That means true chromosome are not formed. The nucleoid is not separated by the delimiting membrane. Thus the genetic material of the prokaryotic cells called nucleoid. Here in prokaryotic cell DNA threads are divided by binary fission.
Organelles
of prokaryotic cell - Prokaryotic cells do not have any membrane bound
organelles like mitochondria, plastids, endoplasmic reticulum, Golgi body etc.
In the prokaryotic cell plasma membranes are folded in different regions to
form mesosome or are called desmosome which may contain respiratory enzymes and
it may function as mitochondria.
Pigments - Photosynthetic pigments are present in vesicles like chromatophores, disc like thylakoids, tubules like lamellae. These together are considering as plastids. As true plastids are not present in the prokaryotic cells.
Ribosome in prokaryotic cells - Ribosome are 70S in prokaryotic cells. The bigger subunit is 50s and the smaller subunit is 30s. Ribosomes and inclusion bodies are freely scattered on the cytoplasm. Ribosomes are not associated with a membranous organelles as they are not present.
Cell wall – Prokaryotic cell wall is made up of nitrogen containing complex of compound that is made up of mucopeptide in nature.
Microtubules - Microtubules are not present in the prokaryotic cells.
Flagellum of prokaryotic cell - flagella is simple and 9+2 organisation is absent. It is a whip like structure associated with locomotion of prokaryotes.
Pilli of prokaryotic cell - Different types of Pilli are present in prokaryotic cell .
In some cases glycoprotein’s are present.
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Explain Microbodies | Definition | Glyoxisomes|Glycosome|Hydrogenosome
This in 1954 first was the first to observed microbodies. Microbodies are spherical or oval in shape with the diameter of 0.2 to 1.5 micrometer. It has outer covering with lipid and lipoprotein membrane. It contains different enzymes for catalase but do not contain any
Centrosome and Centrioles | Distribution of the Centrosome | Structure
Definition of Centrosome - Centrosomeis a more or less spherical mass of dense cytoplasm situated close to the nucleus and contains a pair of cylindrical bodies which are concerned with spindle formation during cell division. In 1888 Boveri first discovered these organelles
Cilia and Flagella | Definition | Location | Origin |Types of Flagella
Definition – Cilia and flagella are hair like micro tubular organelles projecting from the cell surface into the extra cellular medium and are concerned with cell motility.
Explain about Nucleus | Nuclear Envelope | Nucleoplasm |Nuclear matrix
Robert Brown in 1831 first discovered a double membrane covered protoplasmic body that contains hereditary information. A cell usually contains a single nucleus (uninucleate, monokaryote).
Explain about Ribosomes | Distribution and Origin of Ribosomes
Ribosomes are small ,granular, non- membranous structure which is mafe up of RNA and protein and concerned with protein synthesis. In 1943 presence of ribosomes are first observed by Claude and later in 1955 Palade described a detailed description of it by define the name.
Cytoskeletal Structure | Functions and Types of Cytoskeleton Structure
Cytoskeletal structures are fibrous or fine tubular structures that consists of supportive structure of cell. The term cytoskeletal is coined by Koltzoff in 1928.
Define the Plastids | Structure of Plastids | Types of Plastids
Plastids are semi-autonomous cell organelles which are surrounded by double membrane envelope, take part in storage and synthesis of organic compounds which occurred in some plant and protistans.Plastidome consists of all the whole plastids complex of cell.
Explain about Mitochondria | Functions of Mitochondria | Distribution
The term mitochondria can be broken into mito and chondrion. The term “mito “ means fibril and” chondrion “means granule. Definition of mitochondria - The rod like filamentous, spherical or oval, double membrane bound cytoplasmic organelles of eukaryotic cells ,which are
Endomembrane System | Endoplasmic Reticulum | Golgi Apparatus
Endoplasmic reticulum-It is discovered by Porter et al and Thompson in 1945. The name was given by Porter in 1953.It is a system of membrane lines channels found in all eukaryotic cells except mature erythrocytes.
Cell Wall | Definition of Cell Wall |Middle Lamella|Primary, Secondary
Definition of cell wall- The thick and rigid , nonliving covering present just outside the plasma membrane of plant cells is called cell wall. It is discovered by Robert Hooke in 1665 while observing cell in the section of cork.
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