Centrioles

 TOPIC # 10                     CENTRIOLES 

CENTRIOLES

     INTRODUCTION

               Small hollow cylinders, non membranic structure present in cytoplasm right angle to each other are called as centrioles.

They are only present in Animals cells,small microscopic organism cells and lower plants but absent in higher plants.(mcq point)

Higher plants contain phragmoplast instead of centrioles.

And phragmoplast is formed by golgi bodies.

SIZE

    Centrioles are about 0.3-0.5 micrometer in length and 0.2 micrometer in diameter.

LOCATION

    Each cell have two centrioles present in pair form located near to nucleus in cytoplasm of cell.

These two centrioles are usually placed right angle or orthognal to each other in cell and these two duplicate before cell division and one pair migrate to opposite side of the nucleus.

SYNTHESIS

   In previous blog we have studied that assembly and disassembly of spindle of fibers lead to formation of centrioles.

In cross section each centriole is consist of cyllindrical array of  9 microtubules and each microtubule is made up of 3 tubules.

IMPORTANT POINTS

                      1 cell = 2 centrioles

                       1 centrioles= 9 microtubule

                      1 microtubule=3 tubules

                      1 centriole = 27 tubules

                     2 centrioles( 1 cell)= 54 tubules

                    2 centrioles(1 cell)= 18 microtubules

FUNCTION OF CENTRIOLES:

Its have only one important function it help in finding location of furrowing during cell division and in the formation of cilia and flagella.

CILIA AND FLAGELLA

                    These are locomotary organs present in different cells  help in locomotion of cell.

Both are almost same but they are given different name because of thier locomotion and structure difference.

Cells have mostly more cilia than flagella like the mamalian spermatazoon have single flagella while the unicellular protozoan Paramecium have thousand of cilia.

And cilia is also smaller in structure than flagella.

Ciliary and flagellar beating is characterized by a series of bends,originating at the base of the structure and propagated toward the tip.

vitually, all eukaryotic cilia and flagella are remarkably similar in their organization and posesses a central bundle of microtubules called axoneme in which 9 outer duplet sorround a central pair of singlet microtubules.These bundles of microtubules and axoneme are covered by plasma membrane.

                       cilia and flagella= 9 pairs of microtubules=18 microtubules 

                                                   2 singlet microtubules  = 2 microtubules

                                                                                         = total of 20 microtubules and we know this one microtubules have 3 tubules so it concludes that cilia and flagella have 20 microtubules and 60 tubules.

IMPORTANT MCQS IN THIS TOPIC;

1-Hollow cylinders placed right angle to each other in cell called as:

Answer: CENTRIOLES

2-One cell have_ centrioles:

Answer: 2

3-Centrioles are absent in:

Answer: HIGHER PLANTS

4-centrioles have _ tubules:

Answer: 27

5-Centrioles have_microtubules:

Answer:  9 

6-One cell have _ microtubules:

Answer: 18

7-One cell have _tubules:

Answer:   54

8-Phragmoplast is formed by:

Answer: GOLGI BODIES

9-The length of centrioles is:

Answer:  0.3-0.5 MICROMETER

10-The diameter of centrioles is:

Answer: 0.2 micrometer

11-Cilia consist of_microtubules:

Answer: 20 

12-Which one is long cilia or flagella:

Answer: FLAGELLA

13-Flagella have_tubules:

Answer:  60

14- The diameter of flagella and cilia is:

Answer: 0.2 MICROMETER

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