CHARACTERISTICS OF PROCARYOTIC CELLS

STD-11     UNIT-3     CHA-8

CELL : STRUCTURE AND FUNCTIONS

CHARACTERISTICS OF PROCARYOTIC CELLS

CHARACTERISTICS

• Nuclear Material . 
• DNA is naked and lies variously coiled in the cytoplasm . 
• It is often called genophore , nuclear body or nucleoid . 
• It is equivalent to a single naked chromosome and is , therefore , also called prochromosome .
• Many procaryotes also have additional small circular DNA entities called plasmids . 
• Plasmids carry additional specific factors like nitrogen fixation , resistance, fertility , etc.

Cell Wall . 

• It is present in bacteria and cyanobacteira . 
• A cell wall is absent in mycoplasma or PPLO .

Flagella and Fimbriae.  

• Flagella are present in some bacteria only.  
• The bacterial flagella are single - stranded as compared to 11 - stranded flagella of eukaryotes.  
• In bacteria, nonmotile appendages called pili or fimbriae also occur.  
• They take part in attachment (e.g. Neisseria gonorrhoeae) and conjugation (e.g. Escherichia coli).  

Photosynthetic Thylakoids.  

• Blue green algae and some bacteria are photo autotrophic.
• Their photosynthetic thylakoids lie freely in the cytoplasm.  
• They are not organized into chloroplasts.  

Membrane 

• lined Cell Organelles The prokaryotic (= prokaryotic) cells lack mitochondria, endoplasmic reticulum, golgi apparatus, lysosomes, microtubules, microfilaments and centrioles.  

Vacuoles.  

• Typical vacuoles are doubtful.  
• Instead complex gas vacuoles are found.  

Ribosomes.  

• Ribosomes are 70S as compared to 80S.  
• Similar 70S ribosomes occur inside chloroplasts and mitochondria of eukaryotes.  
• One - Envelope System.  
• In prokaryotic cells, membrane bound cell organelles are absent so that there is a single membrane that surrounds the cell.  
• Hence, prokaryotes have a single membrane or one - envelope system.  
• In eukaryotes many organelles are surrounded by their own covering membranes in addition to the cell membrane that covers the whole cell.  
• Therefore, eukaryotes have a double membrane or two - envelope system of organization.

DNA Content.  

• It is low.  

Transcription and Translation.  

• Both occur in the cytoplasm.  

Respiratory Enzymes.  

• They usually lie in contact with cell membrane.

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