Category: Biology Second Paper

1. Microfilaments provide cell shape and mechanical strength.
2. Microfilaments cause cellular movement.
3. Changes the position of the cell organelle.
4. Connects between cell membrane proteins and cytoplasmic proteins.
5. It causes cytokinesis (cell division).
6. Helps in opposite pole movement of chromosomes.
7. It regulates phagocytosis and pinocytosis.

Microfilaments are narrow, long, contractile and twisted biaxial. It is located under the cell membrane like a ribbon. Its diameter is 30-60Å. It is composed of actin protein and myosin protein.

Microfilaments are fine contractile fibers located in the cytoplasm of cells that aid in movement. They are also called actin filaments. It was first observed by scientist Paleviz in 1974.

1. Microtubules provide cell shape and mechanical strength.
2. It plays the role of cytoskeleton.
3. It forms the circulatory system or transport system of the cytoplasm.
4. Assists in cellular movement.
5. It acts as spindle fibers during cell division.
6. Helps in opposite pole movement of chromosomes.
7. Helps in cell wall formation.
8. Helps in the formation and movement of cilia and flagella.
9. Centrioles form in animal cells.
10. It binds to the cell membrane and nuclear membrane to maintain biological connections.
11. It helps in the secretion of essential substances.
12. It helps in the transmission of nerve impulses between nerve cells.
13. It indicates the arrangement of microfibrils.
14. It helps in communication and transportation.

Microtubules are long, cylindrical and hollow organelles. Its diameter is 10-20 mm and length is few microns. One end of them is marked as ‘+’ and the other end as ‘-‘. Each microtubule contains 13 prototubules. Each prototubule is composed of dimeric proteins. Each dimeric protein molecule consists of α and β ubulin.

Microtubules are the sub-structural components of flagella and cilia. It is attached to the centromere of the chromosome. Spindle fibers contain microtubules. It is present in centriole and basal body.

Long, cylindrical, hollow and unbranched organelles present in the cytoplasm of cells are called microtubules. In 1953, Robert and Franchi discovered it from animal nerve cells. In 1953, scientists Ledbetter and Porter first observed their location in plant cells.

In the cytoplasm, a number of cells meet in the space between cells to form a network called the cellular skeleton or cytoskeleton. The scientist Nikolay Koltzoff (1928) was the first to use the term cytoskeleton. The cytoskeleton is composed of three types of structures. These are microtubules, microfilaments and intermediate filaments.

1. Cell Division: Centriole helps in cell division. It plays a special role in cell division.
2. Mucous fibers production: During cell division, it produces mucous fibers. In the prometaphase state, the nucleus is formed. It acts as a carrier of chromosomes.
3. Aster-rays: It produces aster-rays during cell division. Aster rays are formed during prometaphase in animal cells.
4. Polar movement of chromosomes: It helps in the marginal movement of chromosomes. During anaphase, the cytoplasm contracts and the chromosomes move towards the poles.
5. Formation of microtubules: It produces microtubules. Microtubules form the cytoskeleton.
6. Sperm formation: It forms the tail of the sperm. As a result spermatozoa become motile.
7. Formation of flagella: Cilia and flagella form the basal body.

Physical structure of centriole
Centrioles are cylindrical and small organelles. It looks like a cylindrical barrel with two openings. It is 0.3-0.5 µm in length and about 0.15-0.25 µm in diameter. Each centriole consists of three main parts. These are-
1. Cylinder wall: At the center of the centriole there is a structure like a bullock cart wheel. It is called cart wheel model. The center of the cart wheel model is called the hub. The central rod is surrounded by walls or cylinder walls. Its wall is made up of 9 bundles or microtubules. Surrounding the centriole are 9 pericentriolar satellites above and below the microtubule.
2. Triplets: The centriole consists of 9 clusters of triplet molecules or triplets surrounding a cavity. Each tertiary microtubule has three equidistant subtubules. That is, each centriole (3×9) has 27 subtubules. Microtubules are attached to a central axis like the spokes of a wheel. Scientist Threadgold (1968) identified three subducts internally as A, B and C. The diameter of each subchannel is 250Å.
3. Linker: Linker is a type of protein fiber. The dense protein fibers that connect the tertiary tubules are called linkers. Channel A is connected to channel B and channel B is connected to channel C by connectors.
Centrioles are arranged in pairs. Each pair of centrioles is called diplosomes. The dark fluid surrounding the centriole is called the centrosphere.
Chemical structure of centriole
The main chemical component of centriole is protein. Also contains lipids and ATP.