CELL : THE UNIT OF LIFE PART 2

BY ASHNI..GULF ASIAN ENGLISH SCHOOL..

PROKARYOTIC CELLSThe word : Prokaryote

s• PRO means NOT WELL

DEFINEDKARYO means NUCLEUS

• These cells DO NOT have a well DEFINED NUCLEUS

EXAMPLES :

DIFFERENCE IN SHAPES

• The cell is filled with fluid matrix called

• CYTOPLASM• The genetic material is not

enveloped by any nuclear membrane, therefore it is said to be Naked.

• In addition to genomic DNA , bacteria contains small round DNA’s called

• PLASMIDS.

…THE CELL…

CELL ENVELOP

Cell envelop is very complex in bacterial cells.Glycocalyx (outermost)-Plasma membrane- Cell wallAlthough they perform different functions , they together are known e are mainly three layers - as SINGLE PROTECTIVE UNIT

Bacteria on the basis of response to staining procedure developed by Gram viz , can be divided into :- Gram positive Bacteria which take up the gram stain.- Gram negativeBacteria which do not take up the gram stain.

Different Layers

Mesosome

- Formation of cell wall- Replication of DBA- Distribution of Daughter cells- Respiration & Secretion- Increase surface Area of Plasma Membrane

What are the Advantages Of Mesosme ??

Prokaryotes such as Cyanobacteria has membranous extensions into cytoplasm called CHROMATOPHORES which contain pigments.Bacterias can be Motile or Non motile , depending on the presence of Flagella , Pili

Flagella

PILI

FLAGELLA

Flagella ?!- These are the filamentous extensions from cell wall and has mainly 3 parts :- Hook – Basal Body – Filament

Pili ?!- These are elongated tubular made of proteins

Fimbria ?!- Small bristle like fibres sprooting out of the cell

Ribosomes and Inclusion Bodies

In prokaryotes , ribosomes are associated with plasma membrane.The size ranges from 15nm to 20nm ,

and has two subunits – 50S and 30S units which together form 70S.

Ribosomes are the site for the synthesis of proteins.Several Ribosomes may attach to a single Mrna and form a chain calledPOLYRIBOSOMES or POLYSOME -- translate the Mrna into proteins.

Inclusion Bodies

Reserve material in prokaryotic cells are stored in the form of INCLUSION BODIES.These are not bounded by any membrane system and lie free in cytoplasm.Gas vacuoles are found in blue green and purple and green photosynthetic bacteria.

Eukaryotic Cells

These organisms have an organised nucleus with a nuclear envelop.It has organelles and is filled with fluid called CYTOPLASMIn addition, they hve a variety of complex locomotory & cytoskeleton structures.Genetic materials are organised intoCHROMOSOMES

EXAMPLES

PLANT CELL & ANIMAL CELL

CELL MEMBRANE

PROTIENSCARBOHYDRATE CHAINS

PHOSPHOLIPIDS

LIPID

BILAYER

Cell Membrane

It is composed of lipids that are arranged in a bilayer.The lipids are arranged within the membrane with the polar head towards the outer sides and the hydrophobic tails towards the inner part.This ensures that the nonpolar tail of saturated hydrocarbons is protected from the aqueous environment.The lipid component of the membrane mainly consist ofPHOSPHOGLYCERIDES

The cell membrane also consist of protein and carbohydrate.The ratio of protein and lipid varies considerably in different cell types.In human being, the membrane of erythrocyte has approximately 52% protein and 40% lipids.Depending on the ease of extraction, membrane proteins can be classified as integral or peripheral.Peripheral proteins lie on the surface of membrane while the integral proteins are partially or totally buried in the membrane.

Fluid Mosaic Model

According to this , the quasi fluid nature of lipid enables lateral movement of proteins within the overall bilayer.The fluid nature of the membrane is also important from the point of functions likeCellular growthFormation of intercellular junctionsSecretion, endocytosis , cell division etc.

Functions of Plasma Membrane

The membrane is selectively permeable to some molecules present on either side of it.Many molecules can move breifly across the membrane without any requirement of energy Passive transport.Neutral solutes may move across the membrane by the process of simple diffusion along the concentration gradient , i.e , from higher concentration to lower.Water may also move across this membrane from higher to lower concentration .

Movement of water by diffusion is calledOsmosisA few ions or molecules are transported across the membrane against the concentration gradient , i.e frm the lower to higher concentration , such a transport is an energy dependent process , in which ATP is utilised and is calledActive transport.